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1.  Gambogic Acid Inhibits STAT3 Phosphorylation Through Activation of Protein Tyrosine Phosphatase SHP-1: Potential Role in Proliferation and Apoptosis 
The transcription factor, signal transducer and activator of transcription 3 (STAT3), is associated with proliferation, survival, and metastasis of cancer cells. We investigated whether gambogic acid (GA), a xanthone derived from the resin of traditional Chinese medicine, Gamboge hanburyi (mangosteen), can regulate the STAT3 pathway, leading to suppression of growth and sensitization of cancer cells. We found that GA induced apoptosis in human multiple myeloma cells that correlated with the inhibition of both constitutive and inducible STAT3 activation. STAT3 phosphorylation at both tyrosine residue 705 and serine residue 727 was inhibited by GA. STAT3 suppression was mediated through the inhibition of activation of the protein tyrosine kinases Janus-activated kinase (JAK) 1, and JAK2. Treatment with the protein tyrosine phosphatase (PTP) inhibitor pervanadate reversed the GA-induced down-regulation of STAT3, suggesting the involvement of a PTP. We also found that GA induced the expression of the PTP SHP-1. Deletion of the SHP-1 gene by small interfering RNA suppressed the ability of GA to inhibit STAT3 activation and to induce apoptosis, suggesting the critical role of SHP-1 in its action. Moreover, GA down-regulated the expression of STAT3-regulated antiapoptotic (Bcl-2, Bcl-xL, and Mcl-1), proliferative (cyclin D1), and angiogenic (VEGF) proteins, and this correlated with suppression of proliferation and induction of apoptosis. Overall, these results suggest that GA blocks STAT3 activation, leading to suppression of tumor cell proliferation and induction of apoptosis.
PMCID: PMC3131433  PMID: 21490133
Gambogic acid; STAT3; Apoptosis; Proliferation; Cancer
2.  Exploration of the antiplatelet activity profile of betulinic acid on human platelets 
Betulinic acid, a natural pentacyclic triterpene acid, presents a diverse mode of biological actions including anti-retroviral, antibacterial, antimalarial and anti-inflammatory activities. The potency of betulinic acid as an inhibitor of human platelet activation was evaluated and its antiplatelet profile against in vitro platelet aggregation, induced by several platelet agonists (Adenosine Diphosphate, Thrombin Receptor Activator Peptide-14 and Arachidonic Acid), was explored. Flow cytometric analysis was performed to examine the effect of betulinic acid on P-selectin membrane expression and PAC-1 binding to activated platelets. Betulinic acid potently inhibits platelet aggregation and also reduced PAC-1 binding and the membrane expression of P-selectin. Principal component analysis was used to screen, on the chemical property space, for potential common pharmacophores of betulinic acid with approved antithrombotic drugs. A common pharmacophore was defined between the NMR derived structure of betulinic acid and prostacyclin agonists (PGI2) and the importance of its carboxylate group in its antiplatelet activity was determined. The present results indicate that betulinic acid has potential use as an antithrombotic compound and suggest that the mechanism underlying the antiplatelet effects of betulinic acid is similar to that of the PGI2 receptor agonists, a hypothesis that reserves further investigation.
PMCID: PMC3676635  PMID: 22720759
betulinic acid; platelet aggregation; ADP; antithrombotics
3.  Suppression of STAT3 and HIF-1 Alpha Mediates Anti-Angiogenic Activity of Betulinic Acid in Hypoxic PC-3 Prostate Cancer Cells 
PLoS ONE  2011;6(6):e21492.
Signal transducer and activator of transcription 3 (STAT3) is a transcription factor that regulates various cellular processes such as cell survival, angiogenesis and proliferation. In the present study, we examined that betulinic acid (BA), a triterpene from the bark of white birch, had the inhibitory effects on hypoxia-mediated activation of STAT3 in androgen independent human prostate cancer PC-3 cells.
Methodology/Principal Findings
BA inhibited the protein expression and the transcriptional activities of hypoxia-inducible factor-1α (HIF-1α) under hypoxic condition. Consistently, BA blocked hypoxia-induced phosphorylation, DNA binding activity and nuclear accumulation of STAT3. In addition, BA significantly reduced cellular and secreted levels of vascular endothelial growth factor (VEGF), a critical angiogenic factor and a target gene of STAT3 induced under hypoxia. Furthermore, BA prevented in vitro capillary tube formation in human umbilical vein endothelial cells (HUVECs) maintained in conditioned medium of hypoxic PC-3 cells, implying anti-angiogenic activity of BA under hypoxic condition. Of note, chromatin immunoprecipitation (ChiP) assay revealed that BA inhibited binding of HIF-1α and STAT3 to VEGF promoter. Furthermore, silencing STAT3 using siRNA transfection effectively enhanced the reduced VEGF production induced by BA treatment under hypoxia.
Taken together, our results suggest that BA has anti-angiogenic activity by disturbing the binding of HIF-1α and STAT3 to the VEGF promoter in hypoxic PC-3 cells.
PMCID: PMC3123343  PMID: 21731766
4.  Study of the betulin enriched birch bark extracts effects on human carcinoma cells and ear inflammation 
Pentacyclic triterpenes, mainly betulin and betulinic acid, are valuable anticancer agents found in the bark of birch tree. This study evaluates birch bark extracts for the active principles composition.
New improved extraction methods were applied on the bark of Betula pendula in order to reach the maximum content in active principles. Extracts were analyzed by HPLC-MS, Raman, SERS and 13C NMR spectroscopy which revealed a very high yield of betulin (over 90%). Growth inhibiting effects were measured in vitro on four malignant human cell lines: A431 (skin epidermoid carcinoma), A2780 (ovarian carcinoma), HeLa (cervix adenocarcinoma) and MCF7 (breast adenocarcinoma), by means of MTT assay. All of the prepared bark extracts exerted a pronounced antiproliferative effect against human cancer cell lines. In vivo studies involved the anti-inflammatory effect of birch extracts on TPA-induced model of inflammation in mice.
The research revealed the efficacy of the extraction procedures as well as the antiproliferative and anti-inflammatory effects of birch extracts.
PMCID: PMC3527166  PMID: 23158079
Betulin; Birch extract; Anticancer; Raman; SERS; 13C NMR
5.  Boswellic Acid Blocks STAT3 Signaling, Proliferation, and Survival of Multiple Myeloma via the Protein Tyrosine Phosphatase SHP-1 
Molecular cancer research : MCR  2009;7(1):118-128.
Activation of signal transducers and activators of transcription (STAT)-3 factors has been linked with survival, proliferation, chemoresistance and angiogenesis of tumor cells, including human multiple myeloma (MM). Thus agents that can suppress STAT3 activation have potential as cancer therapeutics. In our search for such agents, we identified acetyl-11-keto-β-boswellic acid (AKBA), originally isolated from Boswellia serrata. Our results show that AKBA inhibited constitutive STAT3 activation in human MM cells. AKBA suppressed IL-6-induced STAT3 activation, and the inhibition was reversible. The phosphorylation of both Jak 2 and Src, constituents of the STAT3 pathway, was inhibited by AKBA. Interestingly, treatment of cells with pervanadate suppressed AKBA’s effect to inhibit the phosphorylation of STAT3, thus suggesting the involvement of a protein tyrosine phosphatase. We found that AKBA induced Src homology region 2 domain-containing phosphatase 1 (SHP-1), which may account for its role in dephosphorylation of STAT3. Moreover, deletion of SHP-1 gene by SiRNA abolished the ability of AKBA to inhibit STAT3 activation. The inhibition of STAT3 activation by AKBA led to the suppression of gene products involved in proliferation (cyclin D1), survival (Bcl-2, Bcl-xL and Mcl-1), and angiogenesis (VEGF). This affect correlated with the inhibition of proliferation and apoptosis in MM cells. Consistent with these results, overexpression of constitutive active STAT3 significantly reduced the AKBA induced apoptosis. Overall, our results suggest that AKBA is a novel inhibitor of STAT3 activation and has potential in the treatment of cancer.
PMCID: PMC2677182  PMID: 19147543
Acetyl-11-Keto-{beta}-Boswellic Acid; STAT3; c-Src; JAK2; SHP-1; Apoptosis
6.  Dysregulation of JAK-STAT pathway in hematological malignancies and JAK inhibitors for clinical application 
Biomarker Research  2013;1:5.
JAK-STAT (Janus associated kinase-signal transducer and activator of transcription) pathway plays a critical role in transduction of extracellular signals from cytokines and growth factors involved in hematopoiesis, immune regulation, fertility, lactation, growth and embryogenesis. JAK family contains four cytoplasmic tyrosine kinases, JAK1-3 and Tyk2. Seven STAT proteins have been identified in human cells, STAT1-6, including STAT5a and STAT5b. Negative regulators of JAK–STAT pathways include tyrosine phosphatases (SHP1 and 2, CD45), protein inhibitors of activated STATs (PIAS), suppressors of cytokine signaling (SOCS) proteins, and cytokine-inducible SH2-containing protein (CIS). Dysregulation of JAK-STAT pathway have been found to be key events in a variety of hematological malignancies. JAK inhibitors are among the first successful agents reaching clinical application. Ruxolitinib (Jakafi), a non-selective inhibitor of JAK1 & 2, has been approved by FDA for patients with intermediate to high risk primary or secondary myelofibrosis. This review will also summarize early data on selective JAK inhibitors, including SAR302503 (TG101348), lestaurtinib (CEP701), CYT387, SB1518 (pacritinib), LY2784544, XL019, BMS-911543, NS-018, and AZD1480.
PMCID: PMC3776247  PMID: 24252238
7.  Betulinic Acid for Cancer Treatment and Prevention 
Betulinic acid is a natural product with a range of biological effects, for example potent antitumor activity. This anticancer property is linked to its ability to induce apoptotic cell death in cancer cells by triggering the mitochondrial pathway of apoptosis. In contrast to the cytotoxicity of betulinic acid against a variety of cancer types, normal cells and tissue are relatively resistant to betulinic acid, pointing to a therapeutic window. Compounds that exert a direct action on mitochondria present promising experimental cancer therapeutics, since they may trigger cell death under circumstances in which standard chemotherapeutics fail. Thus, mitochondrion-targeted agents such as betulinic acid hold great promise as a novel therapeutic strategy in the treatment of human cancers.
PMCID: PMC2658785  PMID: 19325847
apoptosis; cancer; betulinic acid; mitochondria; AIF, apoptosis inducing factor; Apaf-1, Apoptotic protease activating factor-1; BA, betulinic acid; DIABLO, direct IAP Binding protein with Low PI; HtrA2, high temperature requirement protein A; IAPs, Inhibitor of Apoptosis Proteins; MOMP, mitochondrial outer membrane permeabilization; ROS, reactive oxygen species; PARP, Poly (ADP-ribose) Polymerase; Smac, second mitochondria-derived activator of caspase; TNF, tumor necrosis factor; TRAIL, tumor necrosis factor-related apoptosis-inducing ligand; zVAD.fmk, N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone
8.  Targeting Inflammatory Pathways by Triterpenoids for Prevention and Treatment of Cancer 
Toxins  2010;2(10):2428-2466.
Traditional medicine and diet has served mankind through the ages for prevention and treatment of most chronic diseases. Mounting evidence suggests that chronic inflammation mediates most chronic diseases, including cancer. More than other transcription factors, nuclear factor-kappaB (NF-κB) and STAT3 have emerged as major regulators of inflammation, cellular transformation, and tumor cell survival, proliferation, invasion, angiogenesis, and metastasis. Thus, agents that can inhibit NF-κB and STAT3 activation pathways have the potential to both prevent and treat cancer. In this review, we examine the potential of one group of compounds called triterpenes, derived from traditional medicine and diet for their ability to suppress inflammatory pathways linked to tumorigenesis. These triterpenes include avicins, betulinic acid, boswellic acid, celastrol, diosgenin, madecassic acid, maslinic acid, momordin, saikosaponins, platycodon, pristimerin, ursolic acid, and withanolide. This review thus supports the famous adage of Hippocrates, “Let food be thy medicine and medicine be thy food”.
PMCID: PMC3153165  PMID: 22069560
triterpenoids; nuclear factor-κB; inflammation; tumor cell proliferation; invasion; angiogenesis; apoptosis
9.  Plumbagin, Vitamin K3 Analogue, Suppresses STAT3 Activation Pathway through Induction of Protein Tyrosine Phosphatase, SHP-1: Potential Role in Chemosensitization 
Molecular cancer research : MCR  2010;8(1):107-118.
The activation of STAT3 has been linked with carcinogenesis through survival, proliferation, and angiogenesis of tumor cells. Agents that can suppress STAT3 activation have potential not only for prevention but also for treatment of cancer. In the present report, we investigated whether plumbagin (5-hydroxy-2-methyl-1,4-naphthoquinone), an analogue of Vitamin K and isolated from chitrak (Plumbago zeylanica), an Ayurvedic medicinal plant, can modulate the STAT3 pathway. We found that plumbagin inhibited both constitutive and IL-6-inducible STAT3 phosphorylation in multiple myeloma (MM) cells and this correlated with the inhibition of c-Src, JAK1, and JAK2 activation. Vanadate, however, reversed the plumbagin-induced downregulation of STAT3 activation, suggesting the involvement of a protein tyrosine phosphatase. Indeed, we found that plumbagin induced the expression of the protein tyrosine phosphatase, SHP-1; and silencing of the SHP-1 abolished the effect of plumbagin. This agent also downregulated the expression of STAT3-regulated cyclin D1, Bcl-xL, and VEGF, activated caspase-3, induced PARP cleavage, and increased the sub-G1 population of MM cells. Consistent with these results, overexpression of constitutive active STAT3 significantly reduced the plumbagin-induced apoptosis. When compared with AG490, a rationally designed STAT3/JAK2 inhibitor, plumbagin was found more potent in suppressing proliferation of cells. Plumbagin also significantly potentiated the apoptotic effects of thalidomide and bortezomib in MM cells. Overall, these results suggest that the plumbagin inhibits STAT3 activation pathway through induction of SHP-1 and this may mediate sensitization of STAT3 overexpressing cancers to chemotherapeutic agents.
PMCID: PMC2808447  PMID: 20068065
Plumbagin; STAT3; JAK1; JAK2; SHP-1; Apoptosis
10.  A Discoidin Domain Receptor 1/SHP-2 Signaling Complex Inhibits α2β1-Integrin–mediated Signal Transducers and Activators of Transcription 1/3 Activation and Cell Migration 
Molecular Biology of the Cell  2006;17(6):2839-2852.
Regulation of cell migration is an important step for the development of branching tubule morphogenesis in collagen gel. Here, we showed that discoidin domain receptor (DDR) 1a/b inhibited collagen-induced tyrosine phosphorylation of signal transducers and activators of transcription (Stat) 1/3 and cell migration triggered by α2β1-integrin. Overexpression of DDR1a/b increased the interaction of DDR1 with SHP-2 and up-regulated the tyrosine phosphatase activity of SHP-2. Expression of catalytically inactive SHP-2 in DDR1-transfected cells restored the tyrosine phosphorylation of Stat3 and cell migration. We demonstrated that the Src homology-2 (SH2)-SH2 and phosphotyrosyl phosphatase (PTP) domains of SHP-2 were responsible for interaction with DDR1 and that both tyrosine phosphorylation sites 703 and 796 of DDR1 were essential for it to bind with SHP-2. Mutation of tyrosine 703 or 796 of DDR1 abolished the ability of DDR1 to inhibit the tyrosine phosphorylation of Stat1 and Stat3 and restored collagen-induced cell migration and hepatocyte growth factor-induced branching tubulogenesis in collagen gel. Together, these results demonstrate that SHP-2 is required for the DDR1-induced suppression of Stat1 and Stat3 tyrosine phosphorylation, cell migration, and branching tubulogenesis.
PMCID: PMC1474786  PMID: 16611743
11.  Betulinic Acid Inhibits Growth of Cultured Vascular Smooth Muscle Cells In Vitro by Inducing G1 Arrest and Apoptosis 
Betulinic acid is a widely available plant-derived triterpene which is reported to possess selective cytotoxic activity against cancer cells of neuroectodermal origin and leukemia. However, the potential of betulinic acid as an antiproliferative and cytotoxic agent on vascular smooth muscle (VSMC) is still unclear. This study was carried out to demonstrate the antiproliferative and cytotoxic effect of betulinic acid on VSMCs using 3-[4,5-dimethylthizol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay, flow cytometry cell cycle assay, BrdU proliferation assay, acridine orange/propidium iodide staining, and comet assay. Result from MTT and BrdU assays indicated that betulinic acid was able to inhibit the growth and proliferation of VSMCs in a dose-dependent manner with IC50 of 3.8 μg/mL significantly (P < 0.05). Nevertheless, betulinic acid exhibited G1 cell cycle arrest in flow cytometry cell cycle profiling and low level of DNA damage against VSMC in acridine orange/propidium iodide and comet assay after 24 h of treatment. In conclusion, betulinic acid induced G1 cell cycle arrest and dose-dependent DNA damage on VSMC.
PMCID: PMC3463985  PMID: 23056140
12.  Anti-Human Immunodeficiency Virus Activity of YK-FH312 (a Betulinic Acid Derivative), a Novel Compound Blocking Viral Maturation 
Betulinic acid, a triterpenoid isolated from the methyl alcohol extract of the leaves of Syzigium claviflorum, was found to have a potent inhibitory activity against human immunodeficiency virus type 1 (HIV-1). Betulinic acid derivatives were synthesized to enhance the anti-HIV activity. Among the derivatives, 3-O-(3′,3′-dimethylsuccinyl) betulinic acid, designated YK-FH312, showed the highest activity against HIV-induced cytopathic effects in HIV-1-infected MT-4 cells. To determine the step(s) of HIV replication affected by YK-FH312, a syncytium formation inhibition assay in MOLT-4/HIV-1IIIB and MOLT-4 coculture, a multinuclear-activation-of-galactosidase-indicator (MAGI) assay in MAGI-CCR5 cells, electron microscopic observation, and a time-of-addition assay were performed. In the syncytium formation inhibition assay or in the MAGI assay for de novo infection, the compound did not show inhibitory effects against HIV replication. Conversely, no virions were detected in HIV-1-infected cell cultures treated with YK-FH312 either by electron microscopic observation or by viral yield in the supernatant. In accordance with a p24 enzyme-linked immunosorbent assay of culture supernatant in the time-of-addition assay, YK-FH312 inhibited virus expression in the supernatant when it was added 18 h postinfection. However, Western blot analysis of the cells in the time-of-addition assay revealed that the production of viral proteins in the cells was not inhibited completely by YK-FH312. These results suggest that YK-FH312 might affect the step(s) of virion assembly and/or budding of virions, and this is a novel mechanism of action of an anti-HIV compound.
PMCID: PMC90447  PMID: 11257038
13.  Signal transducer and activator of transcription 5 as a key signaling pathway in normal mammary gland developmental biology and breast cancer 
STAT5 consists of two proteins, STAT5A/B, that impact mammary cell differentiation, proliferation, and survival. In normal development, STAT5 expression and activity are regulated by prolactin signaling with JAK2/ELF5, EGF signaling networks that include c-Src, and growth hormone, insulin growth factor, estrogen, and progesterone signaling pathways. In cancer, erythropoietin signaling can also regulate STAT5. Activation levels are influenced by AKT, caveolin, PIKE-A, Pak1, c-Myb, Brk, beta-integrin, dystroglycan, other STATs, and STAT pathway molecules JAK1, Shp2, and SOCS. TGF-β and PTPN9 can downregulate prolactin- and EGF-mediated STAT5 activation, respectively. IGF, AKT, RANKL, cyclin D1, BCL6, and HSP90A lie downstream of STAT5.
PMCID: PMC3262193  PMID: 22018398
14.  Differential regulation of the alpha/beta interferon-stimulated Jak/Stat pathway by the SH2 domain-containing tyrosine phosphatase SHPTP1. 
Molecular and Cellular Biology  1995;15(12):7050-7058.
Interferons (IFNs) induce early-response genes by stimulating Janus family (Jak) tyrosine kinases, leading to tyrosine phosphorylation of Stat transcription factors. Previous studies implicated protein-tyrosine phosphatase (PTP) activity in the control of IFN-regulated Jak/Stat signaling, but the specific PTPs responsible remained unidentified. We have found that SH2 domain-containing PTP1 (SHPTP1; also called PTP1C, HCP, or SHP) reversibly associates with the IFN-alpha receptor complex upon IFN addition. Compared with macrophages from normal littermate controls, macrophages from motheaten mice, which lack SHPTP1, show dramatically increased Jak1 and Stat1 alpha tyrosine phosphorylation, whereas Tyk2 and Stat2 activation is largely unaffected. These findings correlate with selectively increased complex formation on a gamma response element, but not an IFN-stimulated response element, in motheaten macrophages. Our results establish that SHPTP1 selectively regulates distinct components of Jak/Stat signal transduction pathways in vivo.
PMCID: PMC230960  PMID: 8524272
15.  Sorafenib Inhibits Signal Transducer and Activator of Transcription-3 Signaling in Cholangiocarcinoma Cells by Activating the Phosphatase Shatterproof 2 
Hepatology (Baltimore, Md.)  2009;50(6):1861-1870.
The Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway is one of the key signaling cascades in cholangiocarcinoma (CCA) cells, mediating their resistance to apoptosis. Our aim was to ascertain if sorafenib, a multikinase inhibitor, may also inhibit JAK/STAT signaling and, therefore, be efficacious for CCA. Sorafenib treatment of three human CCA cell lines resulted in Tyr705 phospho-STAT3 dephosphorylation. Similar results were obtained with the Raf-kinase inhibitor ZM336372, suggesting sorafenib promotes Tyr705 phospho-STAT3 dephosphorylation by inhibiting Raf-kinase activity. Sorafenib treatment enhanced an activating phosphorylation of the phosphatase SHP2. Consistent with this observation, small interfering RNA–mediated knockdown of phosphatase shatterproof 2 (SHP2) inhibited sorafenib-induced Tyr705 phospho-STAT3 dephosphorylation. Sorafenib treatment also decreased the expression of Mcl-1 messenger RNA and protein, a STAT3 transcriptional target, as well as sensitizing CCA cells to tumor necrosis factor–related apoptosis-inducing ligand (TRAIL)-mediated apoptosis. In an orthotopic, syngeneic CCA model in rats, sorafenib displayed significant tumor suppression resulting in a survival benefit for treated animals. In this in vivo model, sorafenib also decreased tumor Tyr705 STAT3 phosphorylation and increased tumor cell apoptosis.
Sorafenib accelerates STAT3 dephosphorylation by stimulating phosphatase SHP2 activity, sensitizes CCA cells to TRAIL-mediated apoptosis, and is therapeutic in a syngeneic rat, orthotopic CCA model that mimics human disease.
PMCID: PMC2891152  PMID: 19821497
16.  Betulinic acid-induced Mcl-1 expression in human melanoma--mode of action and functional significance. 
Molecular Medicine  2002;8(12):877-884.
BACKGROUND: Currently there is no information on the regulation of expression and physiological role of the anti-apoptotic protein Mcl-1 in cells of the melanocytic lineage. This study investigates the regulation and expression of Mcl-1 in human melanoma cells, which was recently found to be induced by betulinic acid, a compound with anti-melanoma and apoptosis-inducing potential. MATERIALS AND METHODS: Mcl-1 phosphorthioate antisense oligonucleotides were used to investigate the effect of downregulating the expression of Mcl-1. Regulation of Mcl-1 expression was analyzed with the specific PI3-kinase inhibitors LY294002 and wortmannin and the inhibitor of MAP-kinase activation, PD98059. Western blot analysis was performed with anti ERK1/2, Mcl-1, Bak, Bcl-x and Bax antibodies. Activation status of PI-3 kinase and MAP-kinase pathways was investigated using phospho-Akt and phosphorylation-state independent Akt as well as phospho-MAP kinase, phospho-MEK and phospho-GSK-3alpha/beta antibodies. RESULTS: Upregulation of Mcl-1 in human melanoma cells by betulinic acid is mediated via a signal-transduction pathway that is inhibited by LY294002 and wortmannin. Betulinic acid-induced phosphorylation and activation of the Akt protein kinase was inhibited by LY294002. The inhibitor PD98059 reduced expression levels of Mcl-1 in melanoma cells and this effect was counteracted by betulinic acid. Downregulation of Mcl-1 by antisense oligodeoxynucleotides in combination with betulinic treatment led to a synergistic effect regarding growth inhibition. CONCLUSIONS: These results suggest that in human melanoma cells Mcl-1 is (i) of functional relevance for survival and (ii) subject to dual regulation by the MAP- kinase pathway and a pathway involving protein kinase B/Akt, the latter of which is modulated in response to betulinic acid. This study provides an experimental foundation for future therapeutic strategies using anti-Mcl-1 antisense oligonucleotides in human melanoma.
PMCID: PMC2039966  PMID: 12606824
17.  Structure-guided studies of the SHP-1/JAK1 interaction provide new insights into phosphatase catalytic domain substrate recognition 
Journal of structural biology  2013;181(3):243-251.
SHP-1 (PTPN6) is a member of the SHP sub-family of protein tyrosine phosphatases and plays a critical role in the regulation of the JAK/STAT signaling pathway. Previous studies suggested that SHP-1 contains a PTP1B-like second phosphotyrosine pocket that allows for binding of tandem phosphotyrosine residues, such as those found in the activation loop of JAK kinases. To discover the structural nature of the interaction between SHP-1 and the JAK family member, JAK1, we determined the 1.8 Å co-crystal structure of the SHP-1 catalytic domain and a JAK1-derived substrate peptide. This structure reveals electron density for only one bound phosphotyrosine residue. To investigate the role of the predicted second site pocket we determined the structures of SHP-1 in complex with phosphate and sulfate to 1.37 Å and 1.7 Å, respectively, and performed anomalous scattering experiments for a selenate-soaked crystal. These crystallographic data suggest that SHP-1 does not contain a PTP1B-like second site pocket. This conclusion is further supported by analysis of the relative dephosphorylation and binding affinities of mono-and tandem-phosphorylated peptide substrates. The crystal structures instead indicate that SHP-1 contains an extended C-terminal helix α2′ incompatible with the predicted second phosphotyrosine binding site. This study suggests that SHP-1 defines a new category of PTP1B-like protein tyrosine phosphatases with a hindered second phosphotyrosine pocket.
PMCID: PMC3578099  PMID: 23296072
phosphatase; cytokine signaling; protein-protein interaction; crystal structure; JAK-STAT; PTP1B
18.  Inhibition of STAT3 signaling and induction of SHP1 mediate antiangiogenic and antitumor activities of ergosterol peroxide in U266 multiple myeloma cells 
BMC Cancer  2012;12:28.
Ergosterol peroxide (EP) derived from edible mushroom has been shown to exert anti-tumor activity in several cancer cells. In the present study, anti-angiogenic activity of EP was investigated with the underlying molecular mechanisms in human multiple myeloma U266 cells.
Despite weak cytotoxicity against U266 cells, EP suppressed phosphorylation, DNA binding activity and nuclear translocalization of signal transducer and activator of transcription 3 (STAT3) in U266 cells at nontoxic concentrations. Also, EP inhibited phosphorylation of the upstream kinases Janus kinase 2 (JAK2) and Src in a time-dependent manner. Furthermore, EP increased the expression of protein tyrosine phosphatase SHP-1 at protein and mRNA levels, and conversely silencing of the SHP-1 gene clearly blocked EP-mediated STAT3 inactivation. In addition, EP significantly decreased vascular endothelial growth factor (VEGF), one of STAT3 target genes at cellular and protein levels as well as disrupted in vitro tube formation assay. Moreover, EP significantly suppressed the growth of U266 cells inoculated in female BALB/c athymic nude mice and immunohistochemistry revealed that EP effectively reduced the expression of STAT3 and CD34 in tumor sections compared to untreated control.
These findings suggest that EP can exert antitumor activity in multiple myeloma U266 cells partly with antiangiogenic activity targeting JAK2/STAT3 signaling pathway as a potent cancer preventive agent for treatment of multiple myeloma cells.
PMCID: PMC3292511  PMID: 22260501
ergosterol peroxide; JAK2; STAT3; angiogenesis; multiple myeloma
19.  "Shping 2" different cellular localizations - a potential new player in aging processes 
Aging  2009;1(7):664-668.
The functions of the ubiquitously expressed protein tyrosine phosphatase Shp-2 are dependent on its localization. Cytosolic Shp-2 is known to modulate different pathways involved in cell growth, cell development, tissue inflammation and cellular chemotaxis. But Shp-2 is also localized in the nucleus and the mitochondria. Nuclear Shp-2 forms a complex with the signal transducer and activator of transcription 5 (STAT5) which then binds to DNA and regulates transcription of milk genes. In contrast, nuclear Shp-2 dephosphorylates STAT1 and thereby inhibits gene transcription. In addition, it counteracts the oxidative stress dependent nuclear export of Telomerase Reverse Transcriptase (TERT) mediated by members of the Src kinase family, a process leading to replicative senescence. For the recently found mitochondrial Shp-2 an involvement in the regulation of the cellular redox balance is discussed. Shp-2 shows the ability to regulate reactive oxygen species formation in the mitochondria. There are hints that mitochondrial Shp-2 and Src are involved in the regulation of respiratory chain activity. Since a substantial fraction of TERT has been found in the mitochondria, it is hypothesized that mitochondrial Shp-2 acts as a positive regulator of TERT in the mitochondria, similar to its nuclear role. Taken together, Shp-2 seems to be a new player in aging processes.
PMCID: PMC2806037  PMID: 20157547
Shp-2; nucleus; mitochondria; Telomerase Reverse Transcriptase
20.  Betulinic Acid Suppresses Constitutive and TNFα-induced NF-κB Activation and Induces Apoptosis in Human Prostate Carcinoma PC-3 Cells 
Molecular carcinogenesis  2008;47(12):964-973.
Development of chemoresistance in androgen-refractory prostate cancer cells is partly due to constitutive activation of Rel/NF-κB transcription factors that regulate several cell survival and anti-apoptotic genes. In this study we examined whether betulinic acid (BetA), a pentacyclic triterpene from the bark of white birch, is effective in inhibiting NF-κB expression in androgen-refractory human prostate cancer cells exhibiting high constitutive NF-κB expression. Treatment of PC-3 cells with BetA inhibited DNA binding and reduced nuclear levels of the NF-κB/p65. BetA-mediated NF-κB inhibition involved decreased IKK activity and phosphorylation of IκBα at serine 32/36 followed by its degradation. Reporter assays revealed that NF-κB inhibition by BetA is transcriptionally active. These effects were found to correlate with a shift in Bax/Bcl-2 ratio and cleavage of poly(ADP)ribose polymerase more towards apoptosis. BetA also inhibited TNFα-induced activation of NF-κB via the IκBα pathway, thereby sensitizing the cells to TNFα-induced apoptosis. Our studies demonstrate that BetA effectively inhibits constitutive NF-κB activation and supports the rationale for targeting NF-κB through combination protocols with BetA in androgen-refractory prostate cancer.
PMCID: PMC2864721  PMID: 18444250
transcription factor; betulinic acid; IκBα; IKK; prostate cancer
21.  Sensitization for Anticancer Drug-Induced Apoptosis by Betulinic Acid1 
Neoplasia (New York, N.Y.)  2005;7(2):162-170.
We previously described that betulinic acid (BetA), a naturally occurring pentacyclic triterpenoid, induces apoptosis in tumor cells through the mitochondrial pathway. Here, for the first time, we provide evidence that BetA cooperated with anticancer drugs to induce apoptosis and to inhibit clonogenic survival of tumor cells. Combined treatment with BetA and anticancer drugs acted in concert to induce loss of mitochondrial membrane potential and the release of cytochrome c and Smac from mitochondria, resulting in activation of caspases and apoptosis. Overexpression of Bcl-2, which blocked mitochondrial perturbations, also inhibited the cooperative effect of BetA and anticancer drugs, indicating that cooperative interaction involved the mitochondrial pathway. Notably, cooperation of BetA and anticancer drugs was found for various cytotoxic compounds with different modes of action (e.g., doxorubicin, cisplatin, Taxol, VP16, or actinomycin D). Importantly, BetA and anticancer drugs cooperated to induce apoptosis in different tumor cell lines, including p53 mutant cells, and also in primary tumor cells, but not in human fibroblasts indicating some tumor specificity. These findings indicate that using BetA as sensitizer in chemotherapy-based combination regimens may be a novel strategy to enhance the efficacy of anticancer therapy, which warrants further investigation.
PMCID: PMC1501129  PMID: 15802021
Apoptosis; betulinic acid; cancer; mitochondria; resistance
22.  Ionic derivatives of betulinic acid as novel HIV-1 protease inhibitors 
Betulinic acid is a natural product possessing abundant and favourable biological activity, including anti-cancer, anti-malarial, anti-inflammatory and anti-HIV properties, while causing minimal toxicity to unaffected cells. The full biological potency of betulinic acid cannot be fully unlocked, however, for a number of reasons, a primary one being its limited solubility in aqueous and biologically pertinent organic media. Aiming to improve the water solubility of betulinic acid without disrupting its structurally related bioactivity, we have prepared different ionic derivatives of betulinic acid. Inhibition bioassays on HIV-1 protease-catalysed peptide hydrolysis indicate significantly improved performance resulting from converting the betulinic acid to organic salt form. Indeed, for one particular cholinium-based derivative, its water solubility is improved more than 100 times and the half maximal inhibitory concentration (IC50) value (22 μg mL−1) was one-third that of wide-type betulinic acid (60 μg mL−1). These encouraging results advise that additional studies of ionic betulinic acid derivatives as a therapeutic solution against HIV-1 infection are warranted.
PMCID: PMC3438379  PMID: 21985312
Betulinic acid; anti-HIV; ionic liquid; HIV-1 protease; derivative
23.  Protein tyrosine phosphatases in the JAK/STAT pathway 
The Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway is crucial in controlling cellular activities in response to extracellular cytokines. Dysfunctions of the JAK/STAT pathway result in various hematopoietic and immune disorders. The central events in regulating this pathway are tyrosine phosphorylation and dephosphorylation of the signaling components, which are carried out by protein tyrosine kinases and protein tyrosine phosphatases (PTP), respectively. Here, we review recent advances in the regulatory roles of PTPs, in particular, SHP2 phosphatase, in the JAK/STAT signaling pathway.
PMCID: PMC2599796  PMID: 18508557
JAK; STAT; SHP2; Cytokine; Signal transduction; Hematopoiesis
24.  Redox-sensitive Signaling by Angiotensin II Involves Oxidative Inactivation and Blunted Phosphorylation of Protein Tyrosine Phosphatase SHP-2 in Vascular Smooth Muscle Cells from SHR 
Circulation research  2008;103(2):149-158.
Angiotensin II (Ang II) signaling in vascular smooth muscle cells (VSMC) involves reactive oxygen species (ROS) through unknown mechanisms. We propose that Ang II induces phosphorylation of growth signaling kinases by redox-sensitive regulation of protein tyrosine phosphatases (PTP) in VSMCs and that augmented Ang II signaling in spontaneously hypertensive rats (SHR) involves oxidation/inactivation and blunted phosphorylation of the PTP, SHP-2. PTP oxidation was assessed by the in-gel PTP method. SHP-2 expression and activity were evaluated by immunoblotting and by a PTP activity assay respectively. SHP-2 and Nox1 were downregulated by siRNA. Ang II induced oxidation of multiple PTPs, including SHP-2. Basal SHP-2 content was lower in SHR versus WKY. Ang II increased SHP-2 phosphorylation and activity with blunted responses in SHR. Ang II-induced SHP-2 effects were inhibited by valsartan (AT1R blocker), apocynin (NAD(P)H oxidase inhibitor) and Nox1 siRNA. Ang II stimulation increased activation of ERK1/2, p38MAPK and AKT, with enhanced effects in SHR. SHP-2 knockdown resulted in increased AKT phosphorylation, without effect on ERK1/2 or p38MAPK. Nox1 downregulation attenuated Ang II-mediated AKT activation in SHR. Hence, Ang II regulates PTP/SHP-2 in VSMCs through AT1R and Nox1-based NAD(P)H oxidase via two mechanisms, oxidation and phosphorylation. In SHR Ang II-stimulated PTP oxidation/inactivation is enhanced, basal SHP-2 expression is reduced and Ang II-induced PTP/SHP-2 phosphorylation is blunted. These SHP-2 actions are associated with augmented AKT signaling. We identify a novel redox-sensitive SHP-2-dependent pathway for Ang II in VSMCs. SHP-2 dysregulation by increased Nox1-derived ROS in SHR is associated with altered Ang II-AKT signaling.
PMCID: PMC2758103  PMID: 18566342
Redox signaling; protein tyrosine phosphatases; SHP-2; MAP kinases; AKT; vascular smooth muscle cells
25.  Design, synthesis and biological evaluation of novel betulinic acid derivatives 
Tumor, is one of the major reason for human death, due to its widespread occurrence. Betulinic acid derivatives have attracted considerable attention as cancer chemopreventive agents and also as cancer therapeutics. Many of its derivatives inhibit the growth of human cancer cell lines by triggering apoptosis. With this background, we planned to synthesize a series of betulinic acid derivatives to assess their antiproliferation efficacy on human cancer cell lines.
A series of novel betulinic acid derivatives were designed and synthesized as highlighted by the preliminary antitumor evaluation against MGC-803, PC3, A375, Bcap-37 and A431 human cancer cell lines in vitro. The pharmacological results showed that some of the compounds displayed moderate to high levels of antitumor activities with most of new exhibiting higher inhibitory activities compared to BA. The IC50 values of compound 3c on the five cancer cell lines were 2.3, 4.6, 3.3, 3.6, and 4.3 μM, respectively. Subsequent fluorescence staining and flow cytometry analysis (FCM) indicated that compound 3c could induce apoptosis in MGC-803 and PC3 cell lines, and the apoptosis ratios reached the peak (37.38% and 33.74%) after 36 h of treatment at 10 μM.
This study suggests that most of betulinic acid derivatives could inhibit the growth of human cancer cell lines. Furthermore, compound 3c could induce apoptosis of cancer cells.
PMCID: PMC3541990  PMID: 23174002

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