Protein kinase C βII (PKCβII) levels increase in the myocardium of patients with end-stage heart failure (HF). Also targeted over-expression of PKCβII in the myocardium of mice leads to dilated cardiomyopathy associated with inflammation, fibrosis and myocardial dysfunction. These reports suggest a deleterious role of PKCβII in HF development. Using a post-myocardial infarction (MI) model of heart failure in rats, we determined the benefit of chronic inhibition of PKCβII on the progression of heart failure over a period of 6 weeks after the onset of symptoms and the cellular basis for these effects. Four weeks after MI, rats with HF signs that were treated for 6 weeks with the PKCβII selective inhibitor (βIIV5-3 conjugated to TAT47-57 alone) (3mg/kg/day) showed improved fractional shortening (from 21% to 35%) compared to control (TAT47-57 alone). Formalin-fixed mid-ventricle tissue sections stained with picrosirius red, hematoxylin-eosin and toluidine blue dyes exhibited a 150% decrease in collagen deposition, a two-fold decrease in inflammation and a 30% reduction in mast cell degranulation, respectively, in rat hearts treated with the selective PKCβII inhibitor. Further, a 90% decrease in active TGFβ1 and a significant reduction in SMAD2/3 phosphorylation indicated that the selective inhibition of PKCβII attenuates cardiac remodeling mediated by the TGF-SMAD signaling pathway. Therefore, sustained selective inhibition of PKCβII in a post-MI HF rat model improves cardiac function and is associated with inhibition of pathological myocardial remodeling.
Protein kinase; PKCβII inhibitor peptide; cardiac remodeling; heart failure; myocardial infarction; mast cells, myocardial fibrosis; inflammation
Significant up-regulation of the protein kinase CβII (PKCβII) develops during heart failure and yet divergent functional outcomes are reported in animal models. The goal here is to investigate PKCβII modulation of contractile function and gain insights into downstream targets in adult cardiac myocytes. Increased PKCβII protein expression and phosphorylation developed after gene transfer into adult myocytes while expression remained undetectable in controls. The PKCβII was distributed in a perinuclear pattern and this expression resulted in diminished rates and amplitude of shortening and re-lengthening compared to controls and myocytes expressing dominant negative PKCβII (PKCβDN). Similar decreases were observed in the Ca2+ transient and the Ca2+ decay rate slowed in response to caffeine in PKCβII-expressing myocytes. Parallel phosphorylation studies indicated PKCβII targets phosphatase activity to reduce phospholamban (PLB) phosphorylation at residue Thr17 (pThr17-PLB). The PKCβ inhibitor, LY379196 (LY) restored pThr17-PLB to control levels. In contrast, myofilament protein phosphorylation was enhanced by PKCβII expression, and individually, LY and the phosphatase inhibitor, calyculin A each failed to block this response. Further work showed PKCβII increased Ca2+- activated, calmodulin-dependent kinase IIδ (CaMKIIδ) expression and enhanced both CaMKIIδ and protein kinase D (PKD) phosphorylation. Phosphorylation of both signaling targets also was resistant to acute inhibition by LY. These later results provide evidence PKCβII modulates contractile function via intermediate downstream pathway(s) in cardiac myocytes.
Protein kinase C; cardiac myocyte; contractile function; gene transfer
Angiogenesis is critical in the progression of prostate cancer. However, the interplay between the proliferation kinetics of tumor endothelial cells (angiogenesis) and tumor cells has not been investigated. Also, protein kinase C (PKC) regulates various aspects of tumor cell growth but its role in prostate cancer has not been investigated in detail. Here, we found that the proliferation rates of endothelial and tumor cells oscillate asynchronously during the growth of human prostate cancer xenografts. Furthermore, our analyses suggest that PKCβII was activated during increased angiogenesis and that PKCβII plays a key role in the proliferation of endothelial cells and tumor cells in human prostate cancer; treatment with a PKCβII-selective inhibitor, βIIV5-3, reduced angiogenesis and tumor cell proliferation. We also find a unique effect of PKCβII inhibition on normalizing pericentrin (a protein regulating cytokinesis), especially in endothelial cells as well as in tumor cells. PKCβII inhibition reduced the level and mislocalization of pericentrin and normalized microtubule organization in the tumor endothelial cells. Although pericentrin has been known to be upregulated in epithelial cells of prostate cancers, its level in tumor endothelium has not been studied in detail. We found that pericentrin is upregulated in human tumor endothelium compared with endothelium adjacent to normal glands in tissues from prostate cancer patients. Our results suggest that a PKCβII inhibitor such as βIIV5-3 may be used to reduce prostate cancer growth by targeting both angiogenesis and tumor cell growth.
Elevated protein kinase C βII (PKCβII) expression develops during heart failure and yet the role of this isoform in modulating contractile function remains controversial. The present study examines the impact of agonist-induced PKCβII activation on contractile function in adult cardiac myocytes. Diminished contractile function develops in response to low dose phenylephrine (PHE, 100 nM) in controls, while function is preserved in response to PHE in PKCβII-expressing myocytes. PHE also caused PKCβII translocation and a punctate distribution pattern in myocytes expressing this isoform. The preserved contractile function and translocation responses to PHE are blocked by the inhibitor, LY379196 (30 nM) in PKCβII-expressing myocytes. Further analysis showed downstream protein kinase D (PKD) phosphorylation and phosphatase activation are associated with the LY379196-sensitive contractile response. PHE also triggered a complex pattern of end-target phosphorylation in PKCβII-expressing myocytes. These patterns are consistent with bifurcated activation of downstream signaling activity by PKCβII.
The priming of eosinophils by cytokines leading to augmented response to chemoattractants and degranulating stimuli is a characteristic feature of eosinophils in the course of allergic inflammation and asthma. Actin reorganization and integrin activation are implicated in eosinophil priming by GM-CSF but their molecular mechanism of action is unknown. In this regard, we investigated the role of L-plastin, an eosinophil phosphoprotein which we identified from eosinophil proteome analysis. Phosphoproteomic analysis demonstrated the upregulation of phosphorylated L-plastin after eosinophil stimulation with GM-CSF. In addition, co-immunoprecipitation studies demonstrated a complex formation of phosphorylated L-plastin with Protein Kinase C βII (PKCβII), GM-CSF receptor α chain, and two actin associated proteins, paxilin and cofilin. Inhibition of PKCβII with 4,5-bis (4-fluoroanilino)phtalimide or PKCβII specific siRNA blocked GM-CSF induced phosphorylation of L-plastin. Furthermore, flow cytometric analysis also showed an upregulation of αMβ2 integrin which was sensitive to PKCβII inhibition. In chemotaxis assay, GM-CSF treatment allowed eosinophils to respond to lower concentrations of eotaxin which was abrogated by the above mentioned PKCβII inhibitors. Similarly, inhibition of PKCβII blocked GM-CSF induced priming for degranulation as assessed by release of ECP and EPX in response to eotaxin. Importantly, eosinophil stimulation with a synthetic L-plastin peptide (residues 2–19) phosphorylated on Ser5 upregulated αMβ2 integrin expression and increased eosinophil migration in response to eotaxin independent of GM-CSF stimulation. Our results establish a causative role for PKCβII and L-plastin in linking GM-CSF-induced eosinophil priming for chemotaxis and degranulation to signaling events associated with integrin activation via induction of PKCβII -mediated L-plastin phosphorylation.
Eosinophils; Cytokines; Signal Transduction; Priming
The phosphorylation state of several cardiac myofilament proteins changes with the level of stretch in intact, twitch-contracting cardiac muscles. It remains unclear which kinases are involved in the length-dependent phosphorylation of these proteins. We set out to investigate which kinases are involved after a step-wise change in cardiac muscle length. We hypothesize that myofilament protein phosphorylation by PKCβII and PKA alters contractile kinetics during length-dependent activation. Right ventricular intact trabeculae were isolated from New Zealand White rabbit hearts and stimulated to contract at 1 Hz. Twitch force recordings where taken at taut and optimal muscle lengths before and after administration of kinase inhibitors at 37 °C. PKCβII inhibition significantly decreased time from stimulation to peak force (TTP), time from peak force to 50% relaxation (RT50), and 90% relaxation (RT90) at optimal muscle length. This led to a loss in the length-dependent increase of RT50 and RT90 in the presence of the PKCβII inhibitor, whereas the length-dependent increase in RT50 and RT90 was seen in the controls. PKA inhibition using H-89 significantly decreased TTP at both taut and optimal muscle lengths. Detection of Ser/Thr phosphorylation with ProQ-diamond staining indicates a role for PKCβII in the phosphorylation of tropomyosin and myosin light chain-2 (MLC2) and PKA for tropomyosin, troponin-I, MLC2, myosin binding protein-C, troponin-T (TnT) 3 and TnT4. Our data provide evidence for two signaling kinases acting upon myofilament proteins during length-dependent activation, and provide further insight for length-dependent myofilament function.
Frank-Starling mechanism; Contraction; Kinetics; Protein kinase C; Protein kinase A; Phosphorylation; Rabbit
Serine/threonine protein kinase C βII isoform (PKCβII) or the pain receptor transient receptor potential vanilloid 1 (TRPV1) have been separately implicated in mediating heat hyperalgesia during inflammation or diabetic neuropathy. However, detailed information on the role of PKC βII in nociceptive signaling mediated by TRPV1 is lacking. This study presents evidence for activation and translocation of the PKC βII isoform as a signaling event in nociception mediated by activation of TRPV1 by capsaicin. We show that capsaicin induces translocation of cytosolic PKCβII isoform fused with enhanced green fluorescence protein (PKCβII-EGFP) in dorsal root ganglion (DRG) neurons. We also show capsaicin-induced translocation in Chinese Hamster Ovarian (CHO) cells co-transfected with TRPV1 and PKCβII-EGFP, but not in CHO cells expressing PKCβII-EGFP alone. By contrast, the PKC activator phorbol-12-myristate-13-acetate (PMA) induced translocation of PKCβII-EGFP which was sustained and independent of calcium or TRPV1. In addition PMA-induced sensitization of TRPV1 to capsaicin response in DRG neurons was attenuated by PKCβII blocker CGP 53353. Capsaicin response via TRPV1 in the DRG neurons was confirmed by TRPV1 antagonist AMG 9810. These results suggested a novel and potential signaling link between PKCβII and TRPV1. These cell culture models provide a platform for investigating mechanisms of painful neuropathies mediated by nociceptors expressing the pain sensing gene TRPV1, and its regulation by the PKC isoform PKCβII.
pain; protein kinase C; transient receptor potential vanilloid-1; real-time translocation; dorsal root ganglion neurons; nociceptive signaling
Insulin stimulates phosphorylation cascades, including phosphatidylinositol-3-kinase (PI3K), phosphatidylinositol-dependent kinase (PDK1), Akt, and protein kinase C (PKC). Myristoylated alanine-rich C-kinase substrate (MARCKS), a PKCβII substrate, could link the effects of insulin to insulin-stimulated glucose transport (ISGT) via phosphorylation of its effector domain since MARCKS has a role in cytoskeletal rearrangements.
We examined phosphoPKCβII after insulin treatment of L6 myocytes, and cytosolic and membrane phosphoMARCKS, MARCKS and phospholipase D1 in cells pretreated with LY294002 (PI3K inhibitor), CG53353 (PKCβII inhibitor) or W13 (calmodulin inhibitor), PI3K, PKCβII and calmodulin inhibitors, respectively, before insulin treatment, using western blots. ISGT was examined after cells had been treated with inhibitors, small inhibitory RNA (siRNA) for MARCKS, or transfection with MARCKS mutated at a PKC site. MARCKS, PKCβII, GLUT4 and insulin receptor were immunoblotted in subcellular fractions with F-actin antibody immunoprecipitates to demonstrate changes following insulin treatment. GLUT4 membrane insertion was followed after insulin with or without CG53353.
Insulin increased phosphoPKCβII(Ser660 and Thr641); LY294002 blocked this, indicating its activation by PI3K. Insulin treatment increased cytosolic phosphoMARCKS, decreased membrane MARCKS and increased membrane phospholipase D1 (PLD1), a protein regulating glucose transporter vesicle fusion resulted. PhosphoMARCKS was attenuated by CG53353 or MARCKS siRNA. MARCKS siRNA blocked ISGT. Association of PKCβII and GLUT4 with membrane F-actin was enhanced by insulin, as was that of cytosolic and membrane MARCKS. ISGT was attenuated in myocytes transfected with mutated MARCKS (Ser152Ala), whereas overproduction of wild-type MARCKS enhanced ISGT. CG53353 blocked insertion of GLUT4 into membranes of insulin treated cells.
The results suggest that PKCβII is involved in mediating downstream steps of ISGT through MARCKS phosphorylation and cytoskeletal remodelling.
F-actin; Glucose transporter 4; Insulin-stimulated glucose uptake; L6 myocytes; MARCKS; Phospholipase D1; PKCβ
Colon cancer develops over a period of 10 to 15 years, providing a window of opportunity for chemoprevention and early intervention. However, few molecular targets for effective colon cancer chemoprevention have been characterized and validated. Protein kinase CβII (PKCβII) plays a requisite role in the initiation of colon carcinogenesis in a preclinical mouse model by promoting proliferation and increased β-catenin accumulation. In this study, we test the hypothesis that PKCβII is an effective target for colon cancer chemoprevention using enzastaurin (LY317615), a PKCβ-selective inhibitor, in a mouse model of colon carcinogenesis. We find that enzastaurin potently reduces azoxymethane-induced colon tumor initiation and progression by inhibiting PKCβII-mediated tumor cell proliferation and β-catenin accumulation. Biochemically, enzastaurin reduces expression of the PKCβII- and β-catenin/T-cell factor–regulated genes PKCβII, cyclooxygenase II, and vascular endothelial growth factor, three genes implicated in colon carcinogenesis. Our results show that enzastaurin is an effective chemopreventive agent in a mouse model of sporadic colon cancer that significantly reduces both tumor initiation and progression by inhibiting expression of proproliferative genes. Thus, PKCβII is an important target for colon cancer chemoprevention and the PKCβ-selective inhibitor enzastaurin may represent an effective chemopreventive agent in patients at high risk for colon cancer.
Interleukin-33 (IL-33) is a new member of the IL-1 cytokine family. The objectives of present study are to assess whether IL-33 can protect cardiomyocytes from anoxia/reoxygenation (A/R)-induced injury and the mechanism involved in the protection.
Cardiomyocytes derived from either wild type or JNK1−/− mice were challenged with an A/R with or without IL-33. Myocyte apoptosis was assessed by measuring caspase 3 activity, fragmented DNA and TUNEL staining. In addition, cardiomyocyte oxidative stress was assessed by measuring DHR123 oxidation; PKCβII and JNK phosphorylation were assessed with Western blot.
Challenge of cardiomyocytes with an A/R resulted in cardiomyocyte oxidative stress, PKCβII and JNK phosphorylation, and myocyte apoptosis. Treatment of the cardiomyocytes with IL-33 attenuated the A/R-induced myocyte oxidative stress, prevented PKCβII and JNK phosphorylation and attenuated the A/R-induced myocyte apoptosis. The protective effect of the IL-33 did not show in cardiac myocytes with siRNA specific to PKCβII or myocytes deficient in JNK1. Inhibition of PKCβII prevented the A/R-induced JNK phosphorylation, but inhibition of JNK1 showed no effect on A/R-induced PKCβII phosphorylation.
Our results indicate that IL-33 prevents the A/R-induced myocyte apoptosis through inhibition of PKCβ/JNK pathway.
Încreasing evidence demonstrates that protein kinase C βII (PKCβII) promotes colon carcinogenesis. We previously reported that colonic PKCβII is induced during colon carcinogenesis in rodents and humans, and that elevated expression of PKCβII in the colon of transgenic mice enhances colon carcinogenesis. Here, we demonstrate that PKCβII represses transforming growth factor β receptor type II (TGFβRII) expression and reduces sensitivity to TGF-β–mediated growth inhibition in intestinal epithelial cells. Transgenic PKCβII mice exhibit hyperproliferation, enhanced colon carcinogenesis, and marked repression of TGFβRII expression. Chemopreventive dietary ω-3 fatty acids inhibit colonic PKCβII activity in vivo and block PKCβII-mediated hyperproliferation, enhanced carcinogenesis, and repression of TGFβRII expression in the colonic epithelium of transgenic PKCβII mice. These data indicate that dietary ω-3 fatty acids prevent colon cancer, at least in part, through inhibition of colonic PKCβII signaling and restoration of TGF-β responsiveness.
protein kinase C; colon carcinogenesis; ω-3 fatty acids; transforming growth factor β; hyperproliferation
Many viruses take advantage of receptor-mediated endocytosis in order to enter target cells. We have utilized influenza virus and Semliki Forest virus (SFV) to define a role for protein kinase C βII (PKCβII) in endocytic trafficking. We show that specific PKC inhibitors prevent influenza virus infection, suggesting a role for classical isoforms of PKC. We also examined virus entry in cells overexpressing dominant-negative forms of PKCα and -β. Cells expressing a phosphorylation-deficient form of PKCβII (T500V), but not an equivalent mutant form of PKCα, inhibited successful influenza virus entry—with the virus accumulating in late endosomes. SFV, however, believed to enter cells from the early endosome, was unaffected by PKCβII T500V expression. We also examined the trafficking of two cellular ligands, transferrin and epidermal growth factor (EGF). PKCβII T500V expression specifically blocked EGF receptor trafficking and degradation, without affecting transferrin receptor recycling. As with influenza virus, in PKCβII kinase-dead cells, EGF receptor was trapped in a late endosome compartment. Our findings suggest that PKCβII is an important regulator of a late endosomal sorting event needed for influenza virus entry and infection.
We previously demonstrated that elevated expression of either protein kinase CβII (PKCβII) or PKCι/λ enhances colon carcinogenesis in mice. Here we use novel bi-transgenic mice to determine the relative importance of PKCβII and PKCι/λ in colon carcinogenesis in two complimentary models of colon cancer in vivo. Bi-transgenic mice over-expressing PKCβII and constitutively active PKCι (PKCβII/caPKCι) or kinase-deficient, dominant negative PKCι (PKCβII/kdPKCι) in the colon exhibit a similar increase in colon tumor incidence, tumor size and tumor burden in response to azoxymethane (AOM) when compared to non-transgenic littermates. However, PKCβII/kdPKCι mice develop predominantly benign colonic adenomas whereas PKCβII/caPKCι mice develop malignant carcinomas. In contrast, PKCβ deficient (PKCβ−/−) mice fail to develop tumors even in the presence of caPKCι. Our previous data indicated that PKCβII drives tumorigenesis and proliferation by activating β-catenin/Apc signaling. Consistent with this conclusion, genetic deletion of PKCβ has no effect on spontaneous tumorigenesis in APCmin/+ mice. In contrast, tissue-specific knock out of PKCλ significantly suppresses intestinal tumor formation in APCmin/+ mice. Our data demonstrate that PKCβII and PKCι/λ serve distinct, non-overlapping functions in colon carcinogenesis. PKCβII is required for AOM-induced tumorigenesis, but is dispensable for tumor formation in ApcMin/+ mice. PKCι/λ promotes tumor progression in both AOM- and APCmin/+-induced tumorigenesis. Thus PKCβII and PKCι, whose expression is elevated in both rodent and human colon tumors, collaborate to drive colon tumor formation and progression, respectively.
colon carcinogenesis; transgenic mice; β-catenin; proliferation; Adenomatous polyposis coli (Apc); intestinal tumorigenesis
The ubiquitous enzyme Protein Kinase C (PKC) has been linked to the pathogenesis of vascular injury, but the cell-specific and discrete functions of the βII isoform have yet to be discovered in this setting. Our previous findings demonstrated significantly increased PKCβII in the membrane fraction of injured femoral arteries in wild type (WT) mice and revealed reduction of neointimal expansion in PKCβ-/- mice after acute vascular injury. As PKCβ-/- mice are globally devoid of PKCβ, we established novel transgenic (Tg) mice to test the hypothesis that the action of PKCβII specifically in smooth muscle cells (SMCs) mediates the formation of neointimal lesions in response to arterial injury.
Tg mice expressing SM22α promoter-targeted mouse carboxyl-terminal deletion mutant PKCβII were produced using standard techniques, subjected to femoral artery injury and compared with littermate controls. Smooth muscle cells (SMC) were isolated from wild-type (WT) and Tg mice and exposed to a prototypic stimulus, tumor necrosis factor (TNF)-α. Multiple strategies were employed in vivo and in vitro to examine the molecular mechanisms underlying the specific effects of SMC PKCβII in neointimal expansion.
In vivo and in vitro analyses demonstrated that PKCβII activity in SMCs was critical for neointimal expansion in response to arterial injury, at least in part via regulation of ERK1/2, Egr-1 and induction of MMP-9.
These data identify the SMC-specific regulatory role of PKCβII in neointimal expansion in response to acute arterial injury, and suggest that targeted inactivation of PKCβII may be beneficial in limiting restenosis via suppression of the neointima-mediating effects of Egr-1 and MMP-9.
arterial injury; transgenic mouse; mutant PKCβII; signal transduction; SMC
Phosphorylation of the adaptor protein p66shc is essential for p66shc-mediated oxidative stress. We investigated the role of the reducing protein/DNA repair enzyme apurinic/apyrimidinic endonuclease1 (APE1) in modulating protein kinase CβII (PKCβII)-mediated p66shc phosphorylation in cultured endothelial cells and PKC-mediated vasoconstriction of arteries.
Methods and results
Oxidized low-density lipoprotein (oxLDL)induced p66shc phosphorylation at serine 36 residue and PKCβII phosphorylation in mouse endothelial cells. Adenoviral overexpression of APE1 resulted in reduction of oxLDL-induced p66shc and PKCβII phosphorylation. Phorbol 12-myristate 13-acetate (PMA), which stimulates PKCs, induced p66shc phosphorylation and this was inhibited by a selective PKCβII inhibitor. Adenoviral overexpression of PKCβII also increased p66shc phosphorylation. Overexpression of APE1 suppressed PMA-induced p66shc phosphorylation. Moreover, PMA-induced p66shc phosphorylation was augmented in cells in which APE1 was knocked down. PMA increased cytoplasmic APE1 expression, compared with the basal condition, suggesting the role of cytoplasmic APE1 against p66shc phosphorylation. Finally, vasoconstriction induced by phorbol-12,13, dibutylrate, another PKC agonist, was partially inhibited by transduction of Tat-APE1 into arteries.
APE1 suppresses oxLDL-induced p66shc activation in endothelial cells by inhibiting PKCβII-mediated serine phosphorylation of p66shc, and mitigates vasoconstriction induced by activation of PKC.
p66shc; Apurinic/apyrimidinic endonuclease1; Oxidized LDL; Protein kinase C; Endothelial cells
Activation of PKCβII is associated with the response to ischemia/reperfusion (I/R), though its role, either pathogenic or protective, has not been determined. In a murine model of single-lung I/R, evidence linking PKCβ to maladaptive responses is shown in the following studies. Homozygous PKCβ-null mice and WT mice fed the PKCβ inhibitor ruboxistaurin subjected to I/R displayed increased survival compared with controls. In PKCβ-null mice, phosphorylation of extracellular signal–regulated protein kinase-1 and -2 (ERK1/2), JNK, and p38 MAPK was suppressed in I/R. Expression of the immediate early gene, early growth response-1 (Egr-1), and its downstream target genes was significantly increased in WT mice in I/R, particularly in mononuclear phagocytes (MPs), whereas this expression was attenuated in PKCβ-null mice or WT mice fed ruboxistaurin. In vitro, hypoxia/reoxygenation-mediated induction of Egr-1 in MPs was suppressed by inhibition of PKCβ, ERK1/2, and JNK, but not by inhibition of p38 MAPK. These findings elucidate key roles for PKCβII activation in I/R by coordinated activation of MAPKs (ERK1/2, JNK) and Egr-1.
mTORC2 has been shown to be involved in cytoskeletal regulation, but the mechanisms by which this takes place are poorly understood. This study shows that PKCβII is specifically required for mTORC2-dependent activation of adenylyl cyclase 9 and back retraction during neutrophil chemotaxis to chemoattractants.
Chemotaxis is a process by which cells polarize and move up a chemical gradient through the spatiotemporal regulation of actin assembly and actomyosin contractility, which ultimately control front protrusions and back retractions. We previously demonstrated that in neutrophils, mammalian target of rapamycin complex 2 (mTORC2) is required for chemoattractant-mediated activation of adenylyl cyclase 9 (AC9), which converts ATP into cAMP and regulates back contraction through MyoII phosphorylation. Here we study the mechanism by which mTORC2 regulates neutrophil chemotaxis and AC9 activity. We show that inhibition of protein kinase CβII (PKCβII) by CPG53353 or short hairpin RNA knockdown severely inhibits chemoattractant-induced cAMP synthesis and chemotaxis in neutrophils. Remarkably, PKCβII-inhibited cells exhibit specific and severe tail retraction defects. In response to chemoattractant stimulation, phosphorylated PKCβII, but not PKCα, is transiently translocated to the plasma membrane, where it phosphorylates and activates AC9. mTORC2-mediated PKCβII phosphorylation on its turn motif, but not its hydrophobic motif, is required for membrane translocation of PKCβII. Inhibition of mTORC2 activity by Rictor knockdown not only dramatically decreases PKCβII activity, but it also strongly inhibits membrane translocation of PKCβII. Together our findings show that PKCβII is specifically required for mTORC2-dependent AC9 activation and back retraction during neutrophil chemotaxis.
A major mechanism by which cancers escape control by the immune system is by blocking the differentiation of myeloid cells into dendritic cells (DCs), immunostimulatory cells that activate anti-tumor T cells. Tumor-dependent activation of signal transducer and activator of transcription 3 (STAT3) signaling in myeloid progenitor cells is thought to cause this block in their differentiation. In addition, a signaling pathway through protein kinase C βII (PKCβII) is essential for the differentiation of myeloid cells into DCs. Here, we found in humans and mice that breast cancer cells substantially decreased the abundance of PKCβII in myeloid progenitor cells through a mechanism involving the enhanced activation of STAT3 signaling by soluble, tumor-derived factors (TDFs). STAT3 bound to previously undescribed negative regulatory elements within the promoter of PRKCB, which encodes PKCβII. We also found a previously undescribed counter-regulatory mechanism through which the activity of PKCβII inhibited tumor-dependent STAT3 signaling by decreasing the abundance of cell-surface receptors, such as cytokine and growth factor receptors, that are activated by TDFs. Together, these data suggest that a previously unrecognized crosstalk mechanism between the STAT3 and PKCβII signaling pathways provides the molecular basis for the tumor-induced blockade in the differentiation of myeloid cells, and suggest that enhancing PKCβII activity may be a therapeutic strategy to alleviate cancer-mediated suppression of the immune system.
Functional adipocyte glucose disposal is a key component of global glucose homeostasis. PKCβII is involved in rat skeletal muscle cell ISGT. Western blot analysis and Real-Time PCR revealed 3T3-L1 cells developmentally regulated PKCβ splicing such that PKCβI was downregulated and PKCβII was upregulated during the course of differentiation. An initial glucose uptake screen using PKC inhibitor LY379196 pointed to a PKC isozyme other than PKCζ mediating 3T3-L1 adipocyte ISGT. Subsequent use of PKCβII inhibitor CGP53353 pointed to a role for PKCβII in ISGT. Western blot analysis showed that CGP53353 specifically inhibited phosphorylation of PKCβII Serine 660. Subcellular fractionation and immunofluorescence demonstrated that PKCβII regulates GLUT4 translocation. Further western blot, immunofluorescence and co-immunoprecipitation analysis reveal that PKCβII inhibition does not affect mTORC2 activity yet abrogates phosphorylation of Akt Serine 473. PKCβII regulates GLUT4 translocation by regulating Akt phosphorylation and thus activity.
PKCβII; GLUT4; Akt; mTORC2
The aim of this study was to examine the endothelial distribution and activity of selected PKC isoforms in coronary vessels with respect to their functional impact on endothelial permeability under the experimental conditions relevant to diabetes.
Methods and Results
En face immunohistochemistry demonstrated a significant increase of PKCβII and decrease of PKCδ expression in coronary arterial endothelium of Zucker diabetic rats. To test whether changes in PKC expression alter endothelial barrier properties, we measured the transcellular electric resistance in human coronary microvascular endothelial monolayers and found that either PKCβII overexpression or PKCδ inhibition disrupted the cell–cell adhesive barrier. Three-dimensional fluorescence microscopy revealed that hyperpermeability was caused by altered PKC activity in association with distinct translocation of PKCβII to the cell–cell junction and PKCδ localization to the cytosol. Further analyses in fractionated endothelial lysates confirmed the differential redistribution of these isozymes. Additionally, FRET analysis of PKC subcellular dynamics demonstrated a high PKCβII activity at the cell surface and junction, whereas PKCδ activity is concentrated in intracellular membrane organelles.
Taken together, these data suggest that PKCβII and PKCδ counter-regulate coronary endothelial barrier properties by targeting distinctive subcellular sites. Imbalanced PKCβII/PKCδ expression and activity may contribute to endothelial hyperpermeability and coronary dysfunction in diabetes.
diabetes; inflammation; permeability; protein kinase; FRET
The development of adipocytes from their progenitor cells requires the action of growth factors signaling to transcription factors to induce the expression of adipogenic proteins leading to the accumulation of lipid droplets, induction of glucose transport, and secretion of adipokines signaling metabolic events throughout the body. Murine 3T3-L1 pre-adipocytes sequentially express all the proteins necessary to become mature adipocytes throughout an 8–10 day process initiated by a cocktail of hormones. We examined the role of Clk/STY or Clk1, a cdc2-like kinase, in adipogenesis since it is known to be regulated by Akt, a pivotal kinase in development. Inhibition of Clk1 by a specific inhibitor, TG003, blocked alternative splicing of PKCβII and expression of PPARγ1 and PPARγ2. SiRNA depletion of Clk1 resulted in early expression of PKCβII and sustained PKCβI expression. Since Clk1 is a preferred Akt substrate, required for phosphorylation of splicing factors, mutation of Clk1 Akt phosphorylation sites was undertaken. Akt sites on Clk1 are in the serine/arginine-rich domain and not the kinase domain. Mutation of single and multiple sites resulted in dysregulation of PKCβII, PKCβI, and PPARγ1&2 expression. Additionally, adipogenesis was blocked as assessed by Oil Red O staining, adiponectin, and Glut1 and 4 expression. Immunofluorescence microscopy revealed that Clk1 triple mutant cDNA, transfected into pre-adipocytes, resulted in excluding SRp40 (SFSR6) from co-localizing to the nucleus with PFS, a perispeckle specific protein. This study demonstrates the role of Akt and Clk1 kinases in the early differentiation of 3T3-L1 cells to adipocytes.
The RhoA/ROCK pathway contributes to diabetic cardiomyopathy in part by promoting the sustained activation of PKCβ2 but the details of their interaction are unclear. The purpose of this study was to investigate if over-activation of ROCK in the diabetic heart leads to direct phosphorylation and activation of PKCβ2, and to determine if their interaction affects PDK-1/Akt signaling.
Regulation by ROCK of PKCβ2 and related kinases was investigated by Western blotting and co-immunoprecipitation in whole hearts and isolated cardiomyocytes from 12 to 14-week diabetic rats. Direct ROCK2 phosphorylation of PKCβ2 was examined in vitro. siRNA silencing was used to confirm role of ROCK2 in PKCβ2 phosphorylation in vascular smooth muscle cells cultured in high glucose. Furthermore, the effect of ROCK inhibition on GLUT4 translocation was determined in isolated cardiomyocytes by confocal microscopy.
Expression of ROCK2 and expression and phosphorylation of PKCβ2 were increased in diabetic hearts. A physical interaction between the two kinases was demonstrated by reciprocal immunoprecipitation, while ROCK2 directly phosphorylated PKCβ2 at T641 in vitro. ROCK2 siRNA in vascular smooth muscle cells or inhibition of ROCK in diabetic hearts reduced PKCβ2 T641 phosphorylation, and this was associated with attenuation of PKCβ2 activity. PKCβ2 also formed a complex with PDK-1 and its target AKT, and ROCK inhibition resulted in upregulation of the phosphorylation of PDK-1 and AKT, and increased translocation of glucose transporter 4 (GLUT4) to the plasma membrane in diabetic hearts.
This study demonstrates that over-activation of ROCK2 contributes to diabetic cardiomyopathy by multiple mechanisms, including direct phosphorylation and activation of PKCβ2 and interference with the PDK-1-mediated phosphorylation and activation of AKT and translocation of GLUT4. This suggests that ROCK2 is a critical node in the development of diabetic cardiomyopathy and may be an effective target to improve cardiac function in diabetes.
This study examined the role of protein kinase C (PKC) isozymes in methamphetamine (MA)-induced dopaminergic toxicity. Multiple-dose administration of MA did not significantly alter PKCα, PKCβI, PKCβII, or PKCζ expression in the striatum, but did significantly increase PKCδ expression. Gö6976 (a co-inhibitor of PKCα and -β), hispidin (PKCβ inhibitor), and PKCζ pseudosubstrate inhibitor (PKCζ inhibitor) did not significantly alter MA-induced behavioral impairments. However, rottlerin (PKCδ inhibitor) significantly attenuated behavioral impairments in a dose-dependent manner. In addition, MA-induced behavioral impairments were not apparent in PKCδ knockout (–/–) mice. MA-induced oxidative stress (i.e., lipid peroxidation and protein oxidation) was significantly attenuated in rottlerin-treated mice and was not apparent in PKCδ (–/–) mice. Consistent with this, MA-induced apoptosis (i.e., terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling-positive apoptotic cells) was significantly attenuated in rottlerin-treated mice. Furthermore, MA-induced increases in the dopamine (DA) turnover rate and decreases in tyrosine hydroxylase (TH) activity and the expression of TH, dopamine transporter (DAT), and vesicular monoamine transporter 2 (VMAT2) were not significantly observed in rottlerin-treated or PKCδ (–/–) mice. Our results suggest that PKCδ gene expression is a key mediator of oxidative stress and dopaminergic damage induced by MA. Thus, inhibition of PKCδ may be a useful target for protection against MA-induced neurotoxicity.
Methamphetamine; PKC isozymes; PKCδ gene deletion; Rottlerin; dopamine; oxidative stress
Protein kinase C (PKC)β2 is preferably overexpressed in the diabetic myocardium, which induces cardiomyocyte hypertrophy and contributes to diabetic cardiomyopathy, but the underlying mechanisms are incompletely understood. Caveolae are critical in signal transduction of PKC isoforms in cardiomyocytes. Caveolin (Cav)-3, the cardiomyocyte-specific caveolar structural protein isoform, is decreased in the diabetic heart. The current study determined whether PKCβ2 activation affects caveolae and Cav-3 expression. Immunoprecipitation and immunofluorescence analysis revealed that high glucose (HG) increased the association and colocalization of PKCβ2 and Cav-3 in isolated cardiomyocytes. Disruption of caveolae by methyl-β-cyclodextrin or Cav-3 small interfering (si)RNA transfection prevented HG-induced PKCβ2 phosphorylation. Inhibition of PKCβ2 activation by compound CGP53353 or knockdown of PKCβ2 expression via siRNA attenuated the reductions of Cav-3 expression and Akt/endothelial nitric oxide synthase (eNOS) phosphorylation in cardiomyocytes exposed to HG. LY333531 treatment (for a duration of 4 weeks) prevented excessive PKCβ2 activation and attenuated cardiac diastolic dysfunction in rats with streptozotocin-induced diabetes. LY333531 suppressed the decreased expression of myocardial NO, Cav-3, phosphorylated (p)-Akt, and p-eNOS and also mitigated the augmentation of O2−, nitrotyrosine, Cav-1, and iNOS expression. In conclusion, hyperglycemia-induced PKCβ2 activation requires caveolae and is associated with reduced Cav-3 expression in the diabetic heart. Prevention of excessive PKCβ2 activation attenuated cardiac diastolic dysfunction by restoring Cav-3 expression and subsequently rescuing Akt/eNOS/NO signaling.
Rapid repair of epithelial wounds is essential for intestinal homeostasis, and involves cell proliferation and migration, which in turn are mediated by multiple cellular signaling events including PKC activation. PKC isoforms have been implicated in regulating cell proliferation and migration, however, the role of PKCs in intestinal epithelial cell (IEC) wound healing is still not completely understood. In the current work we used phorbol 12-myristate 13-acetate (PMA), a well recognized agonist of classical and non-conventional PKC subfamilies to investigate the effect of PKC activation on IEC wound healing. We found that PMA treatment of wounded IEC monolayers resulted in 5.8±0.7-fold increase in wound closure after 24 hours. The PMA effect was specifically mediated by PKCβII, as its inhibition significantly diminished the PMA-induced increase in wound closure. Furthermore, we show that the PKCβII-mediated increase in IEC wound closure after PMA stimulation was mediated by increased cell spreading/cell migration but not proliferation. Cell migration was mediated by PKCβII dependent actin cytoskeleton reorganization, enhanced formation of lamellipodial extrusions at the leading edge and increased activation of the focal adhesion protein, paxillin. These findings support a role for PKCβII in IEC wound repair and further demonstrate the ability of epithelial cells to migrate as a sheet thereby efficiently covering denuded surfaces to recover the intestinal epithelial barrier.