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1.  Hypothermia Blocks β-catenin Degradation after Focal Ischemia in Rats 
Brain research  2008;1198:182-187.
Dephosphorylated and activated glycogen synthase kinase (GSK) 3β hyperphophorylates β-catenin, leading to its ubiquitin-proteosome-mediated degradation. β-catenin-knockdown increases while β-catenin overexpression prevents neuronal death in vitro; in addition, protein levels of β-catenin are reduced in the brain of Alzheimer’s patients. However, whether β-catenin degradation is involved in stroke-induced brain injury is unknown. Here we studied activities of GSK3 β and β-catenin, and the protective effect of moderate hypothermia (30 °C) on these activities after focal ischemia in rats. The results of Western blot showed that GSK3 β was dephosphorylated at 5 and 24 hours after stroke in the normothermic (37 °C) brain; hypothermia augmented GSK3β dephosphorylation. Because hypothermia reduces infarction, these results contradict with previous studies showing that GSK3β dephosphorylation worsens neuronal death. Nevertheless, hypothermia blocked degradation of total GSK3β protein. Corresponding to GSK3β activity in normothermic rats, β-catenin phosphorylation transiently increased at 5 hours in both the ischemic penumbra and core, and the total protein level of β-catenin degraded after normothermic stroke. Hypothermia did not inhibit β-catenin phosphorylation, but it blocked β-catenin degradation in the ischemic penumbra. In conclusion, moderate hypothermia can stabilize β-catenin, which may contribute to the protective effect of moderate hypothermia.
PMCID: PMC2350209  PMID: 18241848
Focal ischemia; hypothermia; GSK-3β; β-catenin
2.  Lithium Treatment Reduces Brain Injury Induced by Focal Ischemia with Partial Reperfusion and the Protective Mechanisms Dispute the Importance of Akt Activity 
Aging and Disease  2012;3(3):226-233.
Lithium is a mood stabilizer shown to have neuroprotective effects against several chronic and acute neuronal injuries, including stroke. However, it is unknown whether lithium treatment protects against brain injury post-stroke in a rat model of permanent distal middle cerebral artery occlusion (MCAo) combined with transient bilateral common carotid artery occlusion (CCAo), a model that mimics human stroke with partial reperfusion. In addition, whether lithium treatment alters Akt activity as measured by the kinase activity assay has not been reported, although it is known to inhibit GSK3β activity. After stroke, Akt activity contributes to neuronal survival while GSK3β activity causes neuronal death. We report that a bolus of lithium injection at stroke onset robustly reduced infarct size measured by 2,3,5-triphenyltetrazolium chloride (TTC) staining at 48 h post-stroke and inhibited cell death in the ischemic penumbra, but not in the ischemic core, as shown by TUNEL staining performed 24 h post-stroke. However, lithium treatment did not alter the reduction in Akt activity as measured by Akt kinase assay. We further showed that lithium did not alter phosphorylated GSK3β protein levels, or the degradation of β-catenin, a substrate of GSK3β, which is consistent with previous findings that long-term treatment is required for lithium to alter GSK3β phosphorylation. In summary, we show innovative data that lithium protects against stroke in a focal ischemia model with partial reperfusion, however, our results dispute the importance of Akt activity in the protective effects of lithium.
PMCID: PMC3375079  PMID: 22724081
Lithium; Akt; Cerebral focal ischemia; GSK3β; β-catenin
3.  Targeting the oncogenic protein beta-catenin to enhance chemotherapy outcome against solid human cancers 
Molecular Cancer  2010;9:310.
Beta-catenin is a multifunctional oncogenic protein that contributes fundamentally to cell development and biology. Elevation in expression and activity of β-catenin has been implicated in many cancers and associated with poor prognosis. Beta-catenin is degraded in the cytoplasm by glycogen synthase kinase 3 beta (GSK-3β) through phosphorylation. Cell growth and proliferation is associated with β-catenin translocation from the cytoplasm into the nucleus.
This laboratory was the first to demonstrate that selenium-containing compounds can enhance the efficacy and cytotoxicity of anticancer drugs in several preclinical xenograft models. These data provided the basis to identify mechanism of selenium action focusing on β-catenin as a target. This study was designed to: (1) determine whether pharmacological doses of methylseleninic acid (MSeA) have inhibitory effects on the level and the oncogenic activity of β-catenin, (2) investigate the kinetics and the mechanism of β-catenin inhibition, and (3) confirm that inhibition of β-catenin would lead to enhanced cytotoxicity of standard chemotherapeutic drugs.
In six human cancer cell lines, the inhibition of total and nuclear expression of β-catenin by MSeA was dose and time dependent. The involvement of GSK-3β in the degradation of β-catenin was cell type dependent (GSK-3β-dependent in HT-29, whereas GSK-3β-independent in HCT-8). However, the pronounced inhibition of β-catenin by MSeA was independent of various drug treatments and was not reversed after combination therapy.
Knockout of β-catenin by ShRNA and its inhibition by MSeA yielded similar enhancement of cytotoxicity of anticancer drugs.
Collectively, the generated data demonstrate that β-catenin is a target of MSeA and its inhibition resulted in enhanced cytotoxicity of chemotherapeutic drugs.
This study demonstrates that β-catenin, a molecule associated with drug resistance, is a target of selenium and its inhibition is associated with increased multiple drugs cytotoxicity in various human cancers. Further, degradation of β-catenin by GSK-3β is not a general mechanism but is cell type dependent.
PMCID: PMC3014904  PMID: 21126356
4.  Lipoprotein Receptor–Related Protein-6 Protects the Brain From Ischemic Injury 
Background and Purpose
Loss-of-function mutations of the lipoprotein receptor–related protein-6 (LRP6), a coreceptor in the Wingless-related integration site-β–catenin prosurvival pathway, have been implicated in myocardial ischemia and neurodegeneration. However, it remains to be established whether LRP6 is also involved in ischemic brain injury. We used LRP6+/− mice to examine the role of this receptor in the mechanisms of focal cerebral ischemia.
Focal cerebral ischemia was induced by transient occlusion of the middle cerebral artery. Motor deficits and infarct volume were assessed 3 days later. Glycogen-synthase-kinase-3β (GSK-3β) phosphorylation was examined by Western blotting with phosphospecific antibodies, and the mitochondrial membrane potential changes induced by Ca2+ were also assessed.
LRP6+/− mice have larger stroke and more severe motor deficits, effects that were independent of intraischemic cerebral blood flow, vascular factors, or cytosolic β-catenin levels. Rather, LRP6 haploinsufficiency increased the activating phosphorylation and decreased the inhibitory phosphorylation of GSK-3β, a kinase involved in proinflammatory signaling and mitochondrial dysfunction. Accordingly, postischemic inflammatory gene expression was enhanced in LRP6+/− mice. Furthermore, the association of mitochondria with activated GSK-3β was increased in LRP6+/− mice, resulting in a reduction in the Ca2+ handling ability of mitochondria. The mitochondrial dysfunction was reversed by pharmacological inhibition of GSK-3β.
LRP6 activates an endogenous neuroprotective pathway that acts independently of β-catenin by controlling GSK-3β activity and preventing its deleterious mitochondrial and proinflammatory effects. The findings raise the possibility that emerging treatment strategies for diseases attributable to LRP6 loss-of-function mutations could also lead to new therapeutic avenues for ischemic stroke.
PMCID: PMC3933931  PMID: 23743975
cerebral ischemia; glycogen-synthase-kinase-3; mitochondria; stroke; Wnt signaling pathway
5.  δ-Catenin/NPRAP: A New Member of the Glycogen Synthase Kinase-3β Signaling Complex That Promotes β-catenin Turnover in Neurons 
Journal of neuroscience research  2010;88(11):10.1002/jnr.22414.
Through a multiprotein complex, glycogen synthase kinase-3β (GSK-3β) phosphorylates and destabilizes β-catenin, an important signaling event for neuronal growth and proper synaptic function. δ-Catenin, or NPRAP (CTNND2), is a neural specific member of the β-catenin superfamily, and is also known to modulate neurite outgrowth and synaptic activity. In this study, we investigated the possibility that δ-catenin expression is also affected by GSK-3β signaling, and it participates in the molecular complex regulating β-catenin turnover in neurons. Immunofluorescent light microscopy revealed co-localization of δ-catenin with members of the molecular destruction complex: GSK-3β, β-catenin, and APC in rat primary neurons. GSK-3β formed a complex with δ-catenin, and its inhibition resulted in increased δ-catenin and β-catenin expression levels. LY294002 and amyloid peptide, known activators of GSK-3β signaling, reduced δ-catenin expression levels. Furthermore, δ-catenin immunoreactivity increased and protein turnover decreased when neurons were treated with proteasome inhibitors, suggesting that the stability of δ-catenin, like that of β-catenin, is regulated by proteasome-mediated degradation. Co-immunoprecipitation experiments showed that δ-catenin overexpression promoted GSK-3β and β-catenin interactions. Primary cortical neurons and PC12 cells expressing δ-catenin treated with proteasome inhibitors showed increased ubiquitinated β-catenin forms. Consistent with the hypothesis that δ-catenin promotes the interaction of the destruction complex molecules, cycloheximide treatment of cells overexpressing δ-catenin showed enhanced β-catenin turnover. These studies identify δ-catenin as a new member of the GSK-3β signaling pathway and further suggest that δ-catenin is potentially involved in facilitating the interaction, ubiquitination, and subsequent turnover of β-catenin in neuronal cells.
PMCID: PMC3813950  PMID: 20623542
Glycogen synthase kinase-3β; δ-catenin/NPRAP; β-catenin; proteasome; ubiquitination
6.  Analysis of the Signaling Activities of Localization Mutants of β-Catenin during Axis Specification in Xenopus  
The Journal of Cell Biology  1997;139(1):229-243.
In Xenopus embryos, β-catenin has been shown to be both necessary and sufficient for the establishment of dorsal cell fates. This signaling activity is thought to depend on the binding of β-catenin to members of the Lef/Tcf family of transcription factors and the regulation of gene expression by this complex. To test whether β-catenin must accumulate in nuclei to establish dorsal cell fate, we constructed various localization mutants that restrict β-catenin to either the plasma membrane, the cytosol, or the nucleus. When overexpressed in Xenopus embryos, the proteins localize as predicted, but surprisingly all forms induce an ectopic axis, indicative of inducing dorsal cell fates. Given this unexpected result, we focused on the membrane-tethered form of β-catenin to resolve the apparent discrepancy between its membrane localization and the hypothesized role of nuclear β-catenin in establishing dorsal cell fate. We demonstrate that overexpression of membrane-tethered β-catenin elevates the level of free endogenous β-catenin, which subsequently accumulates in nuclei. Consistent with the hypothesis that it is this pool of non–membrane-associated β-catenin that signals in the presence of membrane-tethered β-catenin, overexpression of cadherin, which binds free β-catenin, blocks the axis-inducing activity of membrane- tethered β-catenin. The mechanism by which ectopic membrane-tethered β-catenin increases the level of endogenous β-catenin likely involves competition for the adenomatous polyposis coli (APC) protein, which in other systems has been shown to play a role in degradation of β-catenin. Consistent with this hypothesis, membrane-tethered β-catenin coimmunoprecipitates with APC and relocalizes APC to the membrane in cells. Similar results are observed with ectopic plakoglobin, casting doubt on a normal role for plakoglobin in axis specification and indicating that ectopic proteins that interact with APC can artifactually elevate the level of endogenous β-catenin, likely by interfering with its degradation. These results highlight the difficulty in interpreting the activity of an ectopic protein when it is assayed in a background containing the endogenous protein. We next investigated whether the ability of β-catenin to interact with potential protein partners in the cell may normally be regulated by phosphorylation. Compared with nonphosphorylated β-catenin, β-catenin phosphorylated by glycogen synthase kinase-3 preferentially associates with microsomal fractions expressing the cytoplasmic region of N-cadherin. These results suggest that protein–protein interactions of β-catenin can be influenced by its state of phosphorylation, in addition to prior evidence that this phosphorylation modulates the stability of β-catenin.
PMCID: PMC2139814  PMID: 9314542
7.  The Akt signaling pathway contributes to postconditioning’s protection against stroke; the protection is associated with the MAPK and PKC pathways 
Journal of neurochemistry  2008;105(3):943-955.
We previously reported that ischemic postconditioning with a series of mechanical interruptions of reperfusion reduced infarct volume 2 days after focal ischemia in rats. Here, we extend this data by examining long-term protection and exploring underlying mechanisms involving the Akt, mitogen-activated protein kinase (MAPK) and protein kinase C (PKC) signaling pathways. Post-conditioning reduced infarct and improved behavioral function assessed 30 days after stroke. Additionally, postconditioning increased levels of phosphorylated Akt (Ser473) as measured by western blot and Akt activity as measured by an in vitro kinase assay. Inhibiting Akt activity by a phosphoinositide 3-kinase inhibitor, LY294002, enlarged infarct in postconditioned rats. Postconditioning did not affect protein levels of phosphorylated-phosphatase and tensin homologue deleted on chromosome 10 or -phosphoinositide-dependent protein kinase-1 (molecules upstream of Akt) but did inhibit an increase in phosphorylated-glycogen synthase kinase 3β, an Akt effector. In addition, postconditioning blocked β-catenin phosphorylation subsequent to glycogen synthase kinase, but had no effect on total or non-phosphorylated active β-catenin protein levels. Furthermore, postconditioning inhibited increases in the amount of phosphorylated-c-Jun N-terminal kinase and extracellular signal-regulated kinase 1/2 in the MAPK pathway. Finally, postconditioning blocked death-promoting δPKC cleavage and attenuated reduction in phosphorylation of survival-promoting εPKC. In conclusion, our data suggest that postconditioning provides long-term protection against stroke in rats. Additionally, we found that Akt activity contributes to postconditioning’s protection; furthermore, increases in εPKC activity, a survival-promoting pathway, and reductions in MAPK and δPKC activity; two putative death-promoting pathways correlate with postconditioning’s protection.
PMCID: PMC2746404  PMID: 18182053
Akt; cerebral ischemia; mitogen-activated protein kinase; postconditioning; protein kinase C; β-catenin
8.  Reperfusion Differentially Induces Caspase-3 Activation in Ischemic Core and Penumbra After Stroke in Immature Brain 
Background and Purpose
Different strategies for neuroprotection of neonatal stroke may be required because the developing brain responds differently to hypoxia-ischemia than the mature brain. This study was designed to determine the role of caspase-dependent injury in the pathophysiology of pure focal cerebral ischemia in the immature brain.
Postnatal day 7 rats were subjected to permanent or transient middle cerebral artery (MCA) occlusion. Diffusion-weighted MRI was used during occlusion to noninvasively map the evolving ischemic core. The time course of caspase-3 activation in ischemic brain tissue was determined with the use of an Asp-Glu-Val-Asp-aminomethylcoumarin cleavage assay. The anatomy of caspase-3 activation in the ischemic core and penumbra was mapped immunohistochemically with an anti–activated caspase-3 antibody in coronal sections that matched the imaging planes on diffusion-weighted MRI.
A marked increase in caspase-3 activity occurred within 24 hours of reperfusion after transient MCA occlusion. In contrast, caspase-3 activity remained significantly lower within 24 hours of permanent MCA occlusion. Cells with activated caspase-3 were prominent in the penumbra beginning at 3 hours after reperfusion, while a more delayed but marked caspase-3 activation was observed in the ischemic core by 24 hours after reperfusion.
In the neonate, caspase-3 activation is likely to contribute substantially to cell death not only in the penumbra but also in the core after ischemia with reperfusion. Furthermore, persistent perfusion deficits result in less caspase-3 activation and appear to favor caspase-independent injury.
PMCID: PMC2262098  PMID: 12511776
apoptosis; caspases; cerebral ischemia; magnetic resonance imaging, diffusion-weighted; neonate
9.  Phosphorylation and ubiquitination of oncogenic mutants of β-catenin containing substitutions at Asp32 
Oncogene  2004;23(28):4839-4846.
β-Catenin, a member of the Wnt signaling pathway, is downregulated by glycogen synthase kinase-3β (GSK-3β)-dependent phosphorylation of Ser/Thr residues in the N-terminus of the protein, followed by ubiquitination and proteosomal degradation. In human and rodent cancers, mutations that substitute one of the critical Ser/Thr residues in the GSK-3β region of β-catenin stabilize the protein and activate β-catenin/TCF/LEF target genes. This study examined three oncogenic β-catenin mutants from rat colon tumors containing substitutions adjacent to amino-acid residue Ser33, a key target for phosphorylation by GSK-3β. Compared with wild-type β-catenin (WT), the β-catenin mutants D32G, D32N, and D32Y strongly activated TCF-4-dependent transcription in HEK293 cells, and there was accumulation of β-catenin in the cell lysates. Immunoblotting with phosphospecific antibodies indicated that there was little if any effect on the phosphorylation of Ser37, Thr41 or Ser45; however, the phosphorylation of Ser33 appeared to be affected in the β-catenin mutants. Specifically, antiphospho-β-catenin 33/37/41 antibody identified high, intermediate and low expression levels of phosphorylated β-catenin in cells transfected with D32G, D32N and D32Y, respectively. Experiments with the proteosome inhibitor N-acetyl-Leu-Leu-norleucinal (ALLN) revealed ubiquitinated bands on all three mutant β-catenins, as well as on WT β-catenin. The relative order of ubiquitination was WT > D32G > D32N > D32Y, in parallel with findings from the phosphorylation studies. These results are discussed in the context of previous studies, which indicated that amino-acid residue D32 lies within the ubiquitination recognition motif of β-catenin.
PMCID: PMC2267883  PMID: 15064718
β-catenin; TCF/LEF; APC; Wnt signaling; colorectal cancer; CTNNB1; human β-catenin gene; Ctnnb1; rat β-catenin gene
10.  Caspase-3-dependent and -independent apoptosis in focal brain ischemia. 
Molecular Medicine  2002;8(7):347-352.
BACKGROUND: Although extensive caspase-3 activation has been demonstrated in experimental brain ischemia produced in neonatal rat, the role this caspase plays in the focal ischemia of adult brain is not clear, as the levels of caspase-3 in adult rat brain are extremely low. This raises the question whether caspase-3 synthesis and activation are essential for execution of the apoptotic program and DNA fragmentation in permanent brain ischemia, a condition that impairs cellular protein synthesis. MATERIALS AND METHODS: Rat middle cerebral artery was permanently occluded and histochemical detection of procaspase-3, active caspase-3 and DFF 40/CAD and apoptotic morphology analysis were performed at 6, 24, 48, and 72 hours after occlusion. RESULTS: Necrosis and two types of programmed cell death (PCD) are identified in this study of permanent focal brain ischemia. The first type of PCD is represented by active caspase-3 and DFF 40/CAD-positive cells. The second type of PCD is represented by caspase-3 and DFF40/CAD negative cells, which display morphological signs of apoptosis-like PCD: namely, nuclear chromatin condensation in lump masses and apoptotic body formation. The cells of the first type have a maximum number noted after 24 hours of ischemia. The cells of the second type are primarily seen after 48 and 72 hours of ischemia. Necrotic cells, which are also detected in the stroke, are caspase-3 negative, and have swollen nuclei, without chromatin condensation and apoptotic body formation. CONCLUSIONS: Our results indicate that in permanent brain ischemia in adult rats, PCD processes occur differently in various parts of ischemic zone. In conditions of severe energy depletion, the reactions of cellular disassembly and packaging into apoptotic bodies are accomplished without either caspase-3 expression or the activation of caspase-3-dependent deoxyribonuclease.
PMCID: PMC2040004  PMID: 12393932
11.  Beta-Catenin Signaling Plays a Disparate Role in Different Phases of Fracture Repair: Implications for Therapy to Improve Bone Healing 
PLoS Medicine  2007;4(7):e249.
Delayed fracture healing causes substantial disability and usually requires additional surgical treatments. Pharmacologic management to improve fracture repair would substantially improve patient outcome. The signaling pathways regulating bone healing are beginning to be unraveled, and they provide clues into pharmacologic management. The β-catenin signaling pathway, which activates T cell factor (TCF)-dependent transcription, has emerged as a key regulator in embryonic skeletogenesis, positively regulating osteoblasts. However, its role in bone repair is unknown. The goal of this study was to explore the role of β-catenin signaling in bone repair.
Methods and Findings
Western blot analysis showed significant up-regulation of β-catenin during the bone healing process. Using a β-Gal activity assay to observe activation during healing of tibia fractures in a transgenic mouse model expressing a TCF reporter, we found that β-catenin-mediated, TCF-dependent transcription was activated in both bone and cartilage formation during fracture repair. Using reverse transcription-PCR, we observed that several WNT ligands were expressed during fracture repair. Treatment with DKK1 (an antagonist of WNT/β-catenin pathway) inhibited β-catenin signaling and the healing process, suggesting that WNT ligands regulate β-catenin. Healing was significantly repressed in mice conditionally expressing either null or stabilized β-catenin alleles induced by an adenovirus expressing Cre recombinase. Fracture repair was also inhibited in mice expressing osteoblast-specific β-catenin null alleles. In stark contrast, there was dramatically enhanced bone healing in mice expressing an activated form of β-catenin, whose expression was restricted to osteoblasts. Treating mice with lithium activated β-catenin in the healing fracture, but healing was enhanced only when treatment was started subsequent to the fracture.
These results demonstrate that β-catenin functions differently at different stages of fracture repair. In early stages, precise regulation of β-catenin is required for pluripotent mesenchymal cells to differentiate to either osteoblasts or chondrocytes. Once these undifferentiated cells have become committed to the osteoblast lineage, β-catenin positively regulates osteoblasts. This is a different function for β-catenin than has previously been reported during development. Activation of β-catenin by lithium treatment has potential to improve fracture healing, but only when utilized in later phases of repair, after mesenchymal cells have become committed to the osteoblast lineage.
In a study in mice Benjamin Alman and colleagues show that β-catenin functions differently in different stages of fracture repair; moreover, activation of β-catenin by lithium improves fracture healing when used in later phases of repair.
Editors' Summary
Most people break at least one bone during their life. If the damaged bone is immobilized with a plaster cast or with metal plates and pins, most fractures heal naturally and quickly. Soon after a bone is damaged, cells called pluripotent mesenchymal cells collect at the injury site. Here, they multiply and change (differentiate) into osteoblasts (cells that make bone) and chondrocytes (cells that make cartilage, the dense connective tissue that covers joints). Osteoblasts and chondrocytes mend the fracture by making new bone, a process called ossification. Bone healing involves two types of ossification. In intramembranous ossification, mesenchymal cells and osteoblast progenitor cells make bone directly, forming a hard “callus” within the fracture. In endochondral ossification, mesenchymal cells differentiate into chondrocytes and make cartilage at the fracture site, which osteoblasts turn into bone. Finally, the bone made by both types of ossification is remodeled so that it closely resembles the damaged bone's original shape and strength.
Why Was This Study Done?
Unfortunately, fractures do not always heal efficiently. If healing is delayed, additional surgery may be needed to repair the break. But surgery can be risky, so drug-based ways of encouraging bone repair would be very useful. To develop such treatments, researchers need to understand what controls the differentiation and activity of osteoblasts and chondrocytes during normal healing. In this study, the researchers have investigated the role of the β-catenin signaling pathway in bone repair. This pathway regulates bone formation during embryonic development, a process that closely resembles bone healing. β-catenin is usually degraded rapidly in cells. However, if a member of a particular family of proteins known as the WNT family binds to a WNT receptor on the surface of a cell, β-catenin moves into the cell's nucleus where it interacts with a protein called T cell factor (TCF). This interaction activates the transcription (the copying of DNA into messenger RNA, which is used to make proteins) of numerous genes and alters the behavior of the cell.
What Did the Researchers Do and Find?
The researchers first measured β-catenin levels in mouse and human bones. In both species, much more β-catenin was made in bones undergoing repair than in intact bones. Then they studied TCF reporter mice—animals in which TCF controls the expression of a marker gene. β-catenin-mediated TCF-dependent transcription, they report, was activated during both bone and cartilage formation after a fracture in these mice. Next, the researchers made mice that could be induced to express an inactive form of β-catenin or a stabilized (permanently active) form of β-catenin in all the cells in a bone fracture. Expression of inactive β-catenin slowed the rate of healing but, unexpectedly, so did expression of stabilized β-catenin. Osteoblast-specific expression of inactive β-catenin also delayed bone healing, whereas osteoblast-specific expression of stabilized β-catenin enhanced the process. Finally, treatment of wild-type mice with lithium (which prevents the degradation of β-catenin) enhanced bone healing if given after a fracture, but interfered with it if given before.
What Do These Findings Mean?
These findings indicate that β-catenin signaling (which, the researchers show, is mainly activated by WNT signaling) has different effects at different stages of bone repair. Early in the process, it controls the ratio of osteoblasts and chondrocytes made from the pluripotent mesenchymal cells. Consequently, too much or too little β-catenin interferes with bone healing at this stage. Later on, β-catenin promotes the differentiation of osteoblasts and enhances their ability to make bone, and so too little β-catenin at this stage prevents healing, whereas increased β-catenin levels stimulate healing. These findings need to be confirmed in people before testing agents that affect β-catenin signaling for their effects on human bone healing. Nevertheless, the researchers' final discovery that lithium improves bone healing if given at the right time is particularly encouraging; lithium is widely used to treat one form of depression so could be readily tested in clinical trials.
Additional Information.
Please access these Web sites via the online version of this summary at
MedlinePlus encyclopedia contains pages on broken bones and on bone fracture repair (in English and Spanish)
Wikipedia has pages on bone fracture and on bone healing (note: Wikipedia is a free online encyclopedia that anyone can edit; available in several languages)
The UK National Health Service Direct encyclopedia provides pages on broken bones
Animations of intramembranous and endochondral ossification are available from the Ministry of Advanced Education, Training and Technology, Province of British Columbia, Canada
The American Academy of Orthopedic Surgeons has an informative discussion of fractures
The Hospital for Sick Children in Toronto (where the authors of this study are affiliated) has a Web site called SickKids, which contains a page on child physiology, including diagrams of bone development
PMCID: PMC1950214  PMID: 17676991
12.  Post-ischemic estradiol treatment reduced glial response and triggers distinct cortical and hippocampal signaling in a rat model of cerebral ischemia 
Estradiol has been shown to exert neuroprotective effects in several neurodegenerative conditions, including cerebral ischemia. The presence of this hormone prior to ischemia attenuates the damage associated with such events in a rodent model (middle cerebral artery occlusion (MCAO)), although its therapeutic value when administered post-ischemia has not been assessed. Hence, we evaluated the effects of estradiol treatment after permanent MCAO (pMCAO) was induced in rats, studying the PI3K/AKT/GSK3/β-catenin survival pathway and the activation of SAPK-JNK in two brain areas differently affected by pMCAO: the cortex and hippocampus. In addition, we analyzed the effect of estradiol on the glial response to injury.
Male rats were subjected to pMCAO and estradiol (0.04 mg/kg) was administered 6, 24, and 48 h after surgery. The animals were sacrificed 6 h after the last treatment, and brain damage was evaluated by immunohistochemical quantification of ‘reactive gliosis’ using antibodies against GFAP and Iba1. In addition, Akt, phospho-AktSer473, phospho-AktThr308, GSK3, phospho-GSK3Ser21/9, β-catenin, SAPK-JNK, and pSAPK-JNKThr183/Tyr185 levels were determined in western blots of the ipsilateral cerebral cortex and hippocampus, and regional differences in neuronal phospho-Akt expression were determined by immunohistochemistry.
The increases in the percentage of GFAP- (5.25-fold) and Iba1- (1.8-fold) labeled cells in the cortex and hippocampus indicate that pMCAO induced ‘reactive gliosis’. This effect was prevented by post-ischemic estradiol treatment; diminished the number of these cells to those comparable with control animals. pMCAO down-regulated the PI3K/AkT/GSK3/β-catenin survival pathway to different extents in the cortex and hippocampus, the activity of which was restored by estradiol treatment more efficiently in the cerebral cortex (the most affected region) than in the hippocampus. No changes in the phosphorylation of SAPK-JNK were observed 54 h after inducing pMCAO, whereas pMCAO did significantly decrease the phospho-AktSer473 in neurons, an effect that was reversed by estradiol.
The present study demonstrates that post-pMCAO estradiol treatment attenuates ischemic injury in both neurons and glia, events in which the PI3K/AKT/GSK3/β-catenin pathway is at least partly involved. These findings indicate that estradiol is a potentially useful treatment to enhance recovery after human ischemic stroke.
PMCID: PMC3414748  PMID: 22747981
MCAO; Focal ischemia; Rat; Estradiol; Brain; Estrogen; Neuroprotection; Stroke; Western blot; Immunohistochemistry; Akt
13.  Silymarin Targets β-Catenin Signaling in Blocking Migration/Invasion of Human Melanoma Cells 
PLoS ONE  2011;6(7):e23000.
Metastatic melanoma is a leading cause of death from skin diseases, and is often associated with activation of Wnt/β-catenin signaling pathway. We have examined the inhibitory effect of silymarin, a plant flavanoid from Silybum marianum, on cell migration of metastasis-specific human melanoma cell lines (A375 and Hs294t) and assessed whether Wnt/β-catenin signaling is the target of silymarin. Using an in vitro invasion assay, we found that treatment of human melanoma cell lines with silymarin resulted in concentration-dependent inhibition of cell migration, which was associated with accumulation of cytosolic β-catenin, while reducing the nuclear accumulation of β-catenin (i.e., β-catenin inactivation) and reducing the levels of matrix metalloproteinase (MMP) -2 and MMP-9 which are the down-stream targets of β-catenin. Silymarin enhanced: (i) the levels of casein kinase 1α, glycogen synthase kinase-3β and phosphorylated-β-catenin on critical residues Ser45, Ser33/37 and Thr41, and (ii) the binding of β-transducin repeat-containing proteins (β-TrCP) with phospho forms of β-catenin in melanoma cells. These events play important roles in degradation or inactivation of β-catenin. To verify whether β-catenin is a potent molecular target of silymarin, the effect of silymarin was determined on β-catenin-activated (Mel 1241) and β-catenin-inactivated (Mel 1011) melanoma cells. Treatment of Mel 1241 cells with silymarin or FH535, an inhibitor of Wnt/β-catenin pathway, significantly inhibited cell migration of Mel 1241 cells, which was associated with the elevated levels of casein kinase 1α and glycogen synthase kinase-3β, and decreased accumulation of nuclear β-catenin and inhibition of MMP-2 and MMP-9 levels. However, this effect of silymarin and FH535 was not found in Mel 1011 melanoma cells. These results indicate for the first time that silymarin inhibits melanoma cell migration by targeting β-catenin signaling pathway.
PMCID: PMC3145779  PMID: 21829575
14.  Influenza A virus infection of vascular endothelial cells induces GSK-3β-mediated β-catenin degradation in adherens junctions, with a resultant increase in membrane permeability 
Archives of Virology  2014;160:225-234.
Multiorgan failure with vascular hyperpermeability is the final outcome in the progression of seasonal influenza virus pneumonia and influenza-associated encephalopathy, and it is also common in infection with highly pathogenic avian influenza virus. However, the precise molecular mechanism by which influenza virus infection causes vascular endothelial cell hyperpermeability remains poorly defined. We investigated the mechanisms of hyperpermeability of human umbilical vein endothelial cells infected with influenza A virus (IAV)/Puerto Rico/8/34 (PR8) (H1N1). The levels of β-catenin, a key regulatory component of the vascular endothelial-cadherin cell adhesion complex, were markedly decreased during infection for 28 h, with increments of vascular hyperpermeability measured by transendothelial electrical resistance. Lactacystin (at 2 μM), a proteasome inhibitor, inhibited the decrease in β-catenin levels. Since the N-terminal phosphorylation of β-catenin by glycogen synthase kinase (GSK)-3β is the initiation step of proteasome-dependent degradation, we examined the effects of GSK-3β suppression by RNA interference in endothelial cells. IAV-infection-induced β-catenin degradation was significantly inhibited in GSK-3β-knockdown cells, and transfection of cells with recombinant β-catenin significantly suppressed IAV-induced hyperpermeability. These findings suggest that IAV infection induces GSK-3β-mediated β-catenin degradation in the adherens junctional complexes and induces vascular hyperpermeability. The in vitro findings of β-catenin degradation and activation of GSK-3β after IAV infection were confirmed in lungs of mice infected with IAV PR8 during the course of infection from day 0 to day 6. These results suggest that GSK-3β-mediated β-catenin degradation in adherens junctions is one of the key mechanisms of vascular hyperpermeability in severe influenza.
PMCID: PMC4284391  PMID: 25385175
15.  Activation of the Wnt pathway through use of AR79, a glycogen synthase kinase 3β inhibitor, promotes prostate cancer growth in soft tissue and bone 
Molecular cancer research : MCR  2013;11(12):10.1158/1541-7786.MCR-13-0332-T.
Due to its bone anabolic activity, methods to increase Wnt activity, such as inhibitors of dickkopf-1 and sclerostin, are being clinically explored. Glycogen synthase kinase (GSK3β) inhibits Wnt signaling through inducing β-catenin degradation. Therefore, AR79, an inhibitor of GSK3β, is being evaluated as a bone anabolic agent. However, Wnt activation has potential to promote tumor growth. The goal of this study was to determine if AR79 impacted progression of prostate cancer (PCa). PCa tumors were established in subcutaneous and bone sites of mice followed by AR79 administration. Tumor growth, β-catenin activation, proliferation (Ki67 expression) and apoptosis (caspase 3 activity) were measured. Additionally, PCa and osteoblast cell lines were treated with AR79 and β-catenin status, proliferation (with β-catenin knocked down in some cases) and proportion of the ALDH+CD133+ stem-like cells was determined. AR79 promoted PCa growth, decreased phospho-β-catenin expression and increased total and nuclear β-catenin expression in tumors and increased tumor-induced bone remodeling. Additionally, it decreased caspase 3 and increased Ki67 expression. In addition, AR79 increased bone formation in normal mouse tibiae. AR79 inhibited β-catenin phosphorylation, increased nuclear β-catenin accumulation in PCa and osteoblast cell lines and increased proliferation of PCa cells in vitro through β-catenin. Furthermore, AR79 increased the ALDH+CD133+ cancer stem cell-like proportion of the PCa cell lines. We conclude that AR79, while being bone anabolic, promotes PCa cell growth through Wnt pathway activation.
PMCID: PMC3869871  PMID: 24088787
Wnt; glycogen synthase kinase 3β; prostate cancer; bone metastases; cancer stem cell
16.  Phosphorylation of β-Catenin by Cyclic AMP-Dependent Protein Kinase Stabilizes β-Catenin through Inhibition of Its Ubiquitination 
Molecular and Cellular Biology  2005;25(20):9063-9072.
The mechanism of cross talk between the Wnt signaling and cyclic AMP (cAMP)-dependent protein kinase (protein kinase A [PKA]) pathways was studied. Prostaglandin E1 (PGE1), isoproterenol, and dibutyryl cAMP (Bt2cAMP), all of which activate PKA, increased the cytoplasmic and nuclear β-catenin protein level, and these actions were suppressed by a PKA inhibitor and RNA interference for PKA. PGE1 and Bt2cAMP also increased T-cell factor (Tcf)-dependent transcription through β-catenin. Bt2cAMP suppressed degradation of β-catenin at the protein level. Although PKA did not affect the formation of a complex between glycogen synthase kinase 3β (GSK-3β), β-catenin, and Axin, phosphorylation of β-catenin by PKA inhibited ubiquitination of β-catenin in intact cells and in vitro. Ser675 was found to be a site for phosphorylation by PKA, and substitution of this serine residue with alanine in β-catenin attenuated inhibition of the ubiquitination of β-catenin by PKA, PKA-induced stabilization of β-catenin, and PKA-dependent activation of Tcf. These results indicate that PKA inhibits the ubiquitination of β-catenin by phosphorylating β-catenin, thereby causing β-catenin to accumulate and the Wnt signaling pathway to be activated.
PMCID: PMC1265785  PMID: 16199882
17.  Nek2 phosphorylates and stabilizes β-catenin at mitotic centrosomes downstream of Plk1 
Molecular Biology of the Cell  2014;25(7):977-991.
Plk1 regulates Nek2 activity in stabilizing β-catenin at mitotic centrosomes and in promoting centrosome separation. Nek2 phosphorylates the same regulatory sites (S33/S37/T41) as GSK3β in β-catenin, as well as additional sites, and inhibits binding of the E3 ligase β-TrCP to β-catenin, thereby preventing β-catenin ubiquitination and degradation.
β-Catenin is a multifunctional protein with critical roles in cell–cell adhesion, Wnt signaling, and the centrosome cycle. Whereas the regulation of β-catenin in cell–cell adhesion and Wnt signaling are well understood, how β-catenin is regulated at the centrosome is not. NIMA-related protein kinase 2 (Nek2), which regulates centrosome disjunction/splitting, binds to and phosphorylates β-catenin. Using in vitro and cell-based assays, we show that Nek2 phosphorylates the same regulatory sites in the N-terminus of β-catenin as glycogen synthase kinase 3β (GSK3β), which are recognized by a specific phospho-S33/S37/T41 antibody, as well as additional sites. Nek2 binding to β-catenin appears to inhibit binding of the E3 ligase β-TrCP and prevents β-catenin ubiquitination and degradation. Thus β-catenin phosphorylated by Nek2 is stabilized and accumulates at centrosomes in mitosis. We further show that polo-like kinase 1 (Plk1) regulates Nek2 phosphorylation and stabilization of β-catenin. Taken together, these results identify a novel mechanism for regulating β-catenin stability that is independent of GSK3β and provide new insight into a pathway involving Plk1, Nek2, and β-catenin that regulates the centrosome cycle.
PMCID: PMC3967981  PMID: 24501426
18.  Honokiol Inhibits Non-Small Cell Lung Cancer Cell Migration by Targeting PGE2-Mediated Activation of β-Catenin Signaling 
PLoS ONE  2013;8(4):e60749.
Lung cancer remains a leading cause of death due to its metastasis to distant organs. We have examined the effect of honokiol, a bioactive constituent from the Magnolia plant, on human non-small cell lung cancer (NSCLC) cell migration and the molecular mechanisms underlying this effect. Using an in vitro cell migration assay, we found that treatment of A549, H1299, H460 and H226 NSCLC cells with honokiol resulted in inhibition of migration of these cells in a dose-dependent manner, which was associated with a reduction in the levels of cyclooxygenase-2 (COX-2) and prostaglandin E2 (PGE2). Celecoxib, a COX-2 inhibitor, also inhibited cell migration. Honokiol inhibited PGE2-enhanced migration of NSCLC cells, inhibited the activation of NF-κB/p65, an upstream regulator of COX-2, in A549 and H1299 cells, and treatment of cells with caffeic acid phenethyl ester, an inhibitor of NF-κB, also inhibited migration of NSCLC cells. PGE2 has been shown to activate β-catenin signaling, which contributes to cancer cell migration. Therefore, we checked the effect of honokiol on β-catenin signaling. It was observed that treatment of NSCLC cells with honokiol degraded cytosolic β-catenin, reduced nuclear accumulation of β-catenin and down-regulated matrix metalloproteinase (MMP)-2 and MMP-9, which are the down-stream targets of β-catenin and play a crucial role in cancer cell metastasis. Honokiol enhanced: (i) the levels of casein kinase-1α, glycogen synthase kinase-3β, and (ii) phosphorylation of β-catenin on critical residues Ser45, Ser33/37 and Thr41. These events play important roles in degradation or inactivation of β-catenin. Treatment of celecoxib also reduced nuclear accumulation of β-catenin in NSCLC cells. FH535, an inhibitor of Wnt/β-catenin pathway, inhibited PGE2-enhanced cell migration of A549 and H1299 cells. These results indicate that honokiol inhibits non-small cell lung cancer cells migration by targeting PGE2-mediated activation of β-catenin signaling.
PMCID: PMC3620279  PMID: 23580348
19.  Regulation of vascular endothelial growth factor expression by homeodomain-interacting protein kinase-2 
Homeodomain-interacting protein kinase-2 (HIPK2) plays an essential role in restraining tumor progression as it may regulate, by itself or within multiprotein complexes, many proteins (mainly transcription factors) involved in cell growth and apoptosis. This study takes advantage of the recent finding that HIPK2 may repress the β-catenin transcription activity. Thus, we investigated whether HIPK2 overexpression may down-regulate vascular endothelial growth factor (VEGF) levels (a β-catenin target gene) and the role of β-catenin in this regulation, in order to consider HIPK2 as a tool for novel anti-tumoral therapeutical approaches.
The regulation of VEGF expression by HIPK2 was evaluated by using luciferase assay with VEGF reporter construct, after overexpression of the β-catenin transcription factor. Relative quantification of VEGF and β-catenin mRNAs were assessed by reverse-transcriptase-PCR (RT-PCR) analyses, following HIPK2 overexpression, while β-catenin protein levels were evaluated by western immunoblotting.
HIPK2 overexpression in tumor cells downregulated VEGF mRNA levels and VEGF promoter activity. The VEGF downregulation was partly depending on HIPK2-mediated β-catenin regulation. Thus, HIPK2 could induce β-catenin protein degradation that was prevented by cell treatment with proteasome inhibitor MG132. The β-catenin degradation was dependent on HIPK2 catalytic activity and independent of p53 and glycogen synthase kinase 3β (GSK-3β) activities.
These results suggest that VEGF might be a target of HIPK2, at least in part, through regulation of β-catenin activity. These findings support the function of HIPK2 as tumor suppressor and hypothesise a role for HIPK2 as antiangiogenic tool in tumor therapy approaches.
PMCID: PMC2494538  PMID: 18644116
20.  KCTD1 Suppresses Canonical Wnt Signaling Pathway by Enhancing β-catenin Degradation 
PLoS ONE  2014;9(4):e94343.
The canonical Wnt signaling pathway controls normal embryonic development, cellular proliferation and growth, and its aberrant activity results in human carcinogenesis. The core component in regulation of this pathway is β-catenin, but molecular regulation mechanisms of β-catenin stability are not completely known. Here, our recent studies have shown that KCTD1 strongly inhibits TCF/LEF reporter activity. Moreover, KCTD1 interacted with β-catenin both in vivo by co-immunoprecipitation as well as in vitro through GST pull-down assays. We further mapped the interaction regions to the 1-9 armadillo repeats of β-catenin and the BTB domain of KCTD1, especially Position Ala-30 and His-33. Immunofluorescence analysis indicated that KCTD1 promotes the cytoplasmic accumulation of β-catenin. Furthermore, protein stability assays revealed that KCTD1 enhances the ubiquitination/degradation of β-catenin in a concentration-dependent manner in HeLa cells. And the degradation of β-catenin mediated by KCTD1 was alleviated by the proteasome inhibitor, MG132. In addition, KCTD1-mediated β-catenin degradation was dependent on casein kinase 1 (CK1)- and glycogen synthase kinase-3β (GSK-3β)-mediated phosphorylation and enhanced by the E3 ubiquitin ligase β-transducin repeat-containing protein (β-TrCP). Moreover, KCTD1 suppressed the expression of endogenous Wnt downstream genes and transcription factor AP-2α. Finally, we found that Wnt pathway member APC and tumor suppressor p53 influence KCTD1-mediated downregulation of β-catenin. These results suggest that KCTD1 functions as a novel inhibitor of Wnt signaling pathway.
PMCID: PMC3988066  PMID: 24736394
21.  Ischemic preconditioning reduces ischemic brain injury by suppressing nuclear factor kappa B expression and neuronal apoptosis☆ 
Neural Regeneration Research  2013;8(7):633-638.
Ischemic stroke induces a series of complex pathophysiological events including blood-brain barrier disruption, inflammatory response and neuronal apoptosis. Previous studies demonstrate that ischemic preconditioning attenuates ischemic brain damage via inhibiting blood-brain barrier disruption and the inflammatory response. Rats underwent transient (15 minutes) occlusion of the bilateral common carotid artery with 48 hours of reperfusion, and were subjected to permanent middle cerebral artery occlusion. This study explored whether ischemic preconditioning could reduce ischemic brain injury and relevant molecular mechanisms by inhibiting neuronal apoptosis. Results found that at 72 hours following cerebral ischemia, myeloperoxidase activity was enhanced, malondialdehyde levels increased, and neurological function was obviously damaged. Simultaneously, neuronal apoptosis increased, and nuclear factor-κB and cleaved caspase-3 expression was significantly increased in ischemic brain tissues. Ischemic preconditioning reduced the cerebral ischemia-induced inflammatory response, lipid peroxidation, and neurological function injury. In addition, ischemic preconditioning decreased nuclear factor-κB p65 and cleaved caspase-3 expression. These results suggested that ischemic preconditioning plays a protective effect against ischemic brain injury by suppressing the inflammatory response, reducing lipid peroxidation, and neuronal apoptosis via inhibition of nuclear factor-κB and cleaved caspase-3 expression.
PMCID: PMC4145988  PMID: 25206708
neural regeneration; brain injury; ischemic preconditioning; neural cells; apoptosis; nuclear factor kappa-B; cleaved caspase-3; grants-supported paper; photographs-containing paper; neuroregeneration
22.  β-Catenin Directly Sequesters Adipocytic and Insulin Sensitizing Activities but Not Osteoblastic Activity of PPARγ2 in Marrow Mesenchymal Stem Cells 
PLoS ONE  2012;7(12):e51746.
Lineage allocation of the marrow mesenchymal stem cells (MSCs) to osteoblasts and adipocytes is dependent on both Wnt signaling and PPARγ2 activity. Activation of PPARγ2, an essential regulator of energy metabolism and insulin sensitivity, stimulates adipocyte and suppresses osteoblast differentiation and bone formation, and correlates with decreased bone mass and increased fracture rate. In contrast, activation of Wnt signaling promotes osteoblast differentiation, augments bone accrual and reduces total body fat. This study examined the cross-talk between PPARγ2 and β-catenin, a key mediator of canonical Wnt signaling, on MSC lineage determination. Rosiglitazone-activated PPARγ2 induced rapid proteolytic degradation of β-catenin, which was prevented by either inhibiting glycogen synthase kinase 3 beta (GSK3β) activity, or blocking pro-adipocytic activity of PPARγ2 using selective antagonist GW9662 or mutation within PPARγ2 protein. Stabilization of β-catenin suppressed PPARγ2 pro-adipocytic but not anti-osteoblastic activity. Moreover, β-catenin stabilization decreased PPARγ2-mediated insulin signaling as measured by insulin receptor and FoxO1 gene expression, and protein levels of phosphorylated Akt (pAkt). Cellular knockdown of β-catenin with siRNA increased expression of adipocyte but did not affect osteoblast gene markers. Interestingly, the expression of Wnt10b was suppressed by anti-osteoblastic, but not by pro-adipocytic activity of PPARγ2. Moreover, β-catenin stabilization in the presence of activated PPARγ2 did not restore Wnt10b expression indicating a dominant role of PPARγ2 in negative regulation of pro-osteoblastic activity of Wnt signaling. In conclusion, β-catenin and PPARγ2 are in cross-talk which results in sequestration of pro-adipocytic and insulin sensitizing activity. The anti-osteoblastic activity of PPARγ2 is independent of this interaction.
PMCID: PMC3525589  PMID: 23272157
23.  Tumor Suppressor Pten Inhibits Nuclear Accumulation of β-Catenin and T Cell/Lymphoid Enhancer Factor 1–Mediated Transcriptional Activation 
The Journal of Cell Biology  2001;153(6):1161-1174.
β-Catenin is a protein that plays a role in intercellular adhesion as well as in the regulation of gene expression. The latter role of β-catenin is associated with its oncogenic properties due to the loss of expression or inactivation of the tumor suppressor adenomatous polyposis coli (APC) or mutations in β-catenin itself. We now demonstrate that another tumor suppressor, PTEN, is also involved in the regulation of nuclear β-catenin accumulation and T cell factor (TCF) transcriptional activation in an APC-independent manner. We show that nuclear β-catenin expression is constitutively elevated in PTEN null cells and this elevated expression is reduced upon reexpression of PTEN. TCF promoter/luciferase reporter assays and gel mobility shift analysis demonstrate that PTEN also suppresses TCF transcriptional activity. Furthermore, the constitutively elevated expression of cyclin D1, a β-catenin/TCF–regulated gene, is also suppressed upon reexpression of PTEN. Mechanistically, PTEN increases the phosphorylation of β-catenin and enhances its rate of degradation. We define a pathway that involves mainly integrin-linked kinase and glycogen synthase kinase 3 in the PTEN-dependent regulation of β-catenin stability, nuclear β-catenin expression, and transcriptional activity. Our data indicate that β-catenin/TCF–mediated gene transcription is regulated by PTEN, and this may represent a key mechanism by which PTEN suppresses tumor progression.
PMCID: PMC2192018  PMID: 11402061
integrin-linked kinase; glycogen synthase kinase 3; cyclin D1; prostate cancer; protein kinase B
24.  Arterialization of a vein graft promotes cell cycle progression through Akt and p38 mitogen-activated protein kinase pathways: Impact of the preparation procedure 
The Canadian Journal of Cardiology  2007;23(14):1147-1154.
Vein arterialization following bypass surgery often leads to graft occlusion, but the underlying cellular mechanisms have been poorly studied.
Cell cycle progression and the activation of proliferation signalling were compared in arterialized grafts prepared either according to the conventional procedure or using pharmacological relaxation with the native vein.
Using the porcine carotid-jugular bilateral interposition graft model on one side, a segment of porcine jugular vein was prepared for grafting using the conventional procedure, with pressure distention at 300 mmHg; the segment grafted on the other side was treated with a combination of pharmacological vasodilators. Both veins were grafted into the carotid artery for two weeks.
On the immunolabelling of proliferation cell nuclear antigen, a greater number of proliferating cells was found in the conventionally prepared grafts compared with pharmacologically prepared grafts. Cyclin D1 expression and phosphorylation of retinoblastoma increased after implantation, coinciding with nuclear accumulation of beta-catenin, activation of the Akt and mitogen-activated protein kinase cascades, and upregulated phosphatase and tensin homologue phosphorylation. Replacement of distention with pharmacological relaxation reduced the increase in cyclin D1 expression, phosphorylation of retinoblastoma, Akt-Thr308, glycogen synthase kinase 3 beta and p38, but not extracellular signal-regulated kinases. This technique preserved the active phosphatase and tensin homologue, as well as the expression of cyclin-dependent kinase inhibitor p21Cip1, while elevating the expression of p27Kip1.
It was concluded that two-week arterial implantation stimulates proliferation signalling and promotes the cell cycle in vein grafts. Replacement of the conventional preparation procedures with pharmacological vasorelaxation restricts the activation of proliferation and cell cycle progression, and can be beneficial for improving vein graft patency.
PMCID: PMC2652006  PMID: 18060101
Bypass; Grafting; Signal transduction; Smooth muscle; Veins
25.  Human T-Cell Leukemia Virus Type 1 Tax Dysregulates β-Catenin Signaling▿  
Journal of Virology  2006;80(21):10497-10505.
Dysregulation of β-catenin signaling has been implicated in the malignant transformation of cells. However, the role of β-catenin in the human T-cell leukemia virus type 1 (HTLV-1)-induced transformation of T cells is unknown. Here we found that β-catenin protein was overexpressed in the nucleus and that β-catenin-dependent transcription was significantly enhanced in Tax-positive HTLV-1-infected T-cell lines compared to that in Tax-negative HTLV-1-infected T-cell lines. Transfection with β-catenin-specific small interfering RNA inhibited the growth of the Tax-positive HTLV-1-infected T-cell line HUT-102. Transient transfection of Tax appeared to enhance β-catenin-dependent transcription by stabilizing the β-catenin protein via activation of the cyclic AMP (cAMP) response element-binding protein. HTLV-1-infected T-cell lines overexpressing β-catenin also showed increased Akt activity via Tax activation of the cAMP response element-binding protein, resulting in the phosphorylation and inactivation of glycogen synthase kinase 3β, which phosphorylates β-catenin for ubiquitination. The phosphatidylinositol 3-kinase inhibitor LY294002 reduced β-catenin expression in Tax-positive T-cell lines, and inactivation of glycogen synthase kinase 3β by lithium chloride restored β-catenin expression in Tax-negative T-cell lines. Finally, we showed that dominant-negative Akt inhibited Tax-induced β-catenin-dependent transcription. These results indicate that Tax activates β-catenin through the Akt signaling pathway. Our findings suggest that activation of β-catenin by Tax may be important in the transformation of T cells by HTLV-1 infection.
PMCID: PMC1641756  PMID: 16920823

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