Novel roles of specific isoforms of protein kinase C in activation of the c-fos serum response element

Calcium receptor-induced serotonin secretion by parafollicular cells: role of phosphatidylinositol 3-kinase-dependent signal transduction pathways

Elevation of extracellular Ca2+ (increase[Ca2+]e) stimulates the Ca2+ receptor (CaR) to induce secretion of 5-hydroxytryptamine (5-HT) from the calcium-sensing parafollicular (PF) cells. The CaR has been reported to couple to Galpha(q) with subsequent activation of protein kinase C-gamma (PKCgamma). We have identified a parallel transduction pathway in primary cultures of sheep PF cells by using a combinatorial approach in which we expressed adenoviral-encoded dominant-negative signaling proteins and performed in vitro kinase assays. The role of the CaR was established by expression of a dominant-negative CaR that eliminated calcium-induced 5-HT secretion but not secretion in response to KCl or phorbol esters. The calcium-induced secretion was inhibited by a dominant-negative p85 regulatory subunit of phosphatidylinositol 3-kinase (PI3-K). PI3-K activity was also assayed using isoform-specific antibodies. The activity of p85/p110beta (PI3-Kbeta) immunocomplexes was elevated by increase[Ca2+]e and activated by Gbetagamma subunits. In addition, secretion of 5-HT was antagonized by the expression of a minigene encoding a peptide scavenger of Gbetagamma subunits (C-terminal fragment peptide of bovine beta-adrenergic receptor kinase). One target of PI3-K activity is phosphoinositide-dependent kinase-1 (PDK1), which in turn activated PKCzeta. Expression of a dominant-negative PKCzeta in PF cells reduced 5-HT secretion. Together, these observations establish that increase[Ca2+]e evokes 5-HT secretion from PF cells by stimulating both Galpha(q)- and Gbetagamma-signaling pathways downstream of the CaR. The betagamma cascade subsequently activates PI3-Kbeta-dependent signaling that is coupled to PDK1 and the downstream effector PKCzeta, and results in an increase in 5-HT release.

PKC epsilon -mediated ERK1/2 activation involved in radiation-induced cell death in NIH3T3 cells

Protein kinase C (PKC) isoforms play distinct roles in cellular functions. We have previously shown that ionizing radiation activates PKC isoforms (alpha, delta, epsilon, and zeta), however, isoform-specific sensitivities to radiation and its exact mechanisms in radiation mediated signal transduction are not fully understood. In this study, we showed that overexpression of PKC isoforms (alpha, delta, epsilon, and zeta) increased radiation-induced cell death in NIH3T3 cells and PKC epsilon overexpression was predominantly responsible. In addition, PKC epsilon overexpression increased ERK1/2 activation without altering other MAP-kinases such as p38 MAPK or JNK. Co-transfection of dominant negative PKC epsilon (PKC epsilon -KR) blocked both PKC epsilon -mediated ERK1/2 activation and radiation-induced cell death, while catalytically active PKC epsilon construction augmented these phenomena. When the PKC epsilon overexpressed cells were pretreated with PD98059, MEK inhibitor, radiation-induced cell death was inhibited. Co-transfection of the cells with a mutant of ERK1 or -2 (ERK1-KR or ERK2-KR) also blocked these phenomena, and co-transfection with dominant negative Ras or Raf cDNA revealed that PKC epsilon -mediated ERK1/2 activation was Ras-Raf-dependent. In conclusion, PKC epsilon -mediated ERK1/2 activation was responsible for the radiation-induced cell death.

Effect of HCV NS3 on proliferation and phosphorylation of MAPK in human hepatocytes

AIM: To study effects of HCV NS3 protein on proliferation and transformation of normal human liver cell line.

METHODS: QSG7701 cells were transfected with pRcHCNS3-5' pRcHCNS3-3'and pRcCMV using liposome transfecting technique and selected with G418; Expression of HCV NS3 protein was determined by immunohistochemistry; Biological characters of transfected cells were evaluated by population doubling time and soft agar assays; activation of MAPK was analyzed by western blot.

RESULTS: QSG7701 cells transfected with pRcHCNS3-5'showed strong intracellular expression of HCVNS3 protein, and the positive signal was localized in cytoplasm. The level of expressed HCVNS3 protein in pRcHCNS3-3'transfected cells was lower than that in pRcHCNS3-5'transfected cells. The population doubling time in pRcHCNS3-5'ransfected cells (12 h) was significantly shorter than that in pRcHCNS3-3'ransfected cells (24 h), pRcCMV transfected cells (26h) and normal cells (28 h) (P < 0.01). The cells transfected with pRcHCNS3-5'showed much more anchorage independent colonies than those with pRcHCNS3-3'and pRcCMV (P < 0.01). The cloning efficiencies of transfected cells with pRcHCNS3-5' pRcHCNS3-3' pRcCMV and controls were 33%, 1.33%, 1.46%, 1.11%, respectively. The level of phosphorylated MAPK in cells with pRcHCNS3-5'was much higher than those with pRcHCNS3-3'nd cell transfected with pRcCMV and normal cells (8 858 ± 877, 5 612 ± 656, 2 212 ± 245, 989 ± 188, P < 0.01).

CONCLUSION: QSG7701 is the good human liver cell line for investigating the pathogenesis of HCV NS3 protein. 5'region of the HCV genome segment encoding NS3 is involved in cell growth and cell phenotype. N-terminal peptide of HCV NS3 protein may up-regulate the activation of MAPK.

Monocytic activation of protein tyrosine kinase, protein kinase A and protein kinase C induced by porins isolated from Salmonella enterica serovar Typhimurium

OBJECTIVES

In the present study a monocytic cell line, U937, was used to investigate the possible involvement of protein tyrosine kinases (NT-PTKs), protein kinase A (PKA) and protein kinase C (PKC) in cell signaling pathways following Salmonella enterica serovar Typhimurium porin stimulation.

METHODS

Different concentrations of porins and lipopolysaccharide (LPS) were analysed to evaluate changes in PTK activity by a non radioactive tyrosine kinase assay and in PKA and PKC phosphorylation by Western blotting analysis. The inhibitors of PTK, PKA and PKC activation used, were: 3,4-dihydroxybenzylidene-malononitrile (tyrphostin 23), inhibitor of epidermal growth factor (EGF) receptor tyrosine kinase activity; dihychloride (H-89), a selective inhibitor of PKA which is useful to discriminate between the effects of PKC and PKA; diacylglycerol kinase inhibitor II (R59949), which is useful for elucidating roles of PKC; calphostin C, a specific inhibitor of PKC.

RESULTS

Porins of the outer membrane of the ST were isolated to be used as a stimulus in the performed experiments. Following porin treatment, a dose-dependent increase in PTK, PKA and PKC activation was observed. U937 monocytes pretreated with inhibitors induced an evident decrease in PTK activity and PKA and PKC phosphorylation pattern in porin stimulated monocytes.

CONCLUSIONS

Our data support the important role played by NT-PTK, PKA and PKC in transducing the activating signal in macrophages stimulated with porins through the activation of the mitogen-activated protein kinase (MAPK) pathway that participate in the regulation of gene expression.

Dependence of gonadotropin-releasing hormone-induced neuronal MAPK signaling on epidermal growth factor receptor transactivation

The hypothalamic decapeptide, gonadotropin-releasing hormone (GnRH), utilizes multiple signaling pathways to activate extracellularly regulated mitogen-activated protein kinases (ERK1/2) in normal and immortalized pituitary gonadotrophs and transfected cells expressing the GnRH receptor. In immortalized hypothalamic GnRH neurons (GT1-7 cells), which also express GnRH receptors, GnRH, epidermal growth factor (EGF), and phorbol 12-myristate 13-acetate (PMA) caused marked phosphorylation of ERK1/2. This action of GnRH and PMA, but not that of EGF, was primarily dependent on activation of protein kinase C (PKC), and the ERK1/2 responses to all three agents were abolished by the selective EGF receptor kinase inhibitor, AG1478. Consistent with this, both GnRH and EGF increased tyrosine phosphorylation of the EGF receptor. GnRH and PMA, but not EGF, caused rapid phosphorylation of the proline-rich tyrosine kinase, Pyk2, at Tyr(402). This was reduced by Ca(2+) chelation and inhibition of PKC, but not by AG1478. GnRH stimulation caused translocation of PKC alpha and -epsilon to the cell membrane and enhanced the association of Src with PKC alpha and PKC epsilon, Pyk2, and the EGF receptor. The Src inhibitor, PP2, the C-terminal Src kinase (Csk), and dominant-negative Pyk2 attenuated ERK1/2 activation by GnRH and PMA but not by EGF. These findings indicate that Src and Pyk2 act upstream of the EGF receptor to mediate its transactivation, which is essential for GnRH-induced ERK1/2 phosphorylation in hypothalamic GnRH neurons.

The protein kinase C pathway plays a central role in the fibroblast growth factor-stimulated expression and transactivation activity of Runx2

Fibroblast growth factor (FGF)/FGF receptor (FGFR) signaling induces the expression of Runx2, a key transcription factor in osteoblast differentiation, but little is known about the molecular signaling mechanisms that mediate this. Here we examined the role of the protein kinase C (PKC) pathway in regulating Runx2 gene expression and its transactivation function. Treatment with FGF2 or FGF4, or transfection with a vector expressing a mutant FGFR2 that is constitutively activated in the absence of ligand, strongly stimulates Runx2 expression. Electrophoretic mobility shift assays also showed that FGF2 treatment increases the specific binding of Runx2 to the cognate response element in the osteocalcin gene promoter. Blocking PKC completely inhibited FGF2-induced Runx2 expression, whereas mitogen-activate protein kinase inhibitors had no effect. The FGF/FGFR-stimulated 6xOSE2 promoter activity was also blocked by inhibiting PKC, as was the FGF2 stimulation of the DNA-binding activity of Runx2. Experiments with PKC isoform-specific inhibitors and dominant negative isoforms of PKC indicate that PKCdelta is one of key isoforms involved in the FGF2-stimulated Runx2 expression. In addition, experiments with Runx2-knockout cells showed that, although the PKC pathway largely regulates FGF2-stimulated Runx2 activity by up-regulating Runx2 expression, it also modifies Runx2 protein post-translationally and thereby increases its transcriptional activity. Thus, we show for the first time that FGF/FGFR signaling stimulates the DNA-binding and transcriptional activities of Runx2 as well as its expression, and these are largely regulated by the PKC pathway.

The herpes simplex virus type 2 R1 protein kinase (ICP10 PK) functions as a dominant regulator of apoptosis in hippocampal neurons involving activation of the ERK survival pathway and upregulation of the antiapoptotic protein Bag-1

Herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) can trigger or block apoptosis in a cell type-dependent manner. We have recently shown that the protein kinase activity of the large subunit of the HSV-2 ribonucleotide reductase (R1) protein (ICP10 PK) blocks apoptosis in cultured hippocampal neurons by activating the extracellular signal-regulated kinase (ERK) survival pathway (Perkins et al., J. Virol. 76:1435-1449, 2002). The present studies were designed to better elucidate the mechanism of ICP10 PK-induced neuroprotection and determine whether HSV-1 has similar activity. The data indicate that apoptosis inhibition by ICP10 PK involves a c-Raf-1-dependent mechanism and induction of the antiapoptotic protein Bag-1 by the activated ERK survival pathway. Also associated with neuroprotection by ICP10 PK are increased activation/stability of the transcription factor CREB and stabilization of the antiapoptotic protein Bcl-2. HSV-1 and the ICP10 PK-deleted HSV-2 mutant ICP10DeltaPK activate JNK, c-Jun, and ATF-2, induce the proapoptotic protein BAD, and trigger apoptosis in hippocampal neurons. c-Jun activation and apoptosis are inhibited in hippocampal cultures infected with HSV-1 in the presence of the JNK inhibitor SP600125, suggesting that JNK/c-Jun activation is required for HSV-1-induced apoptosis. Ectopically delivered ICP10 PK (but not its PK-negative mutant p139) inhibits apoptosis triggered by HSV-1 or ICP10DeltaPK. Collectively, the data indicate that ICP10 PK-induced activation of the ERK survival pathway results in Bag-1 upregulation and overrides the proapoptotic JNK/c-Jun signal induced by other viral proteins.

Regulation of caveolin-1 expression and secretion by a protein kinase cepsilon signaling pathway in human prostate cancer cells

Caveolin-1, androgen receptor, c-Myc, and protein kinase Cepsilon (PKCepsilon) proteins are overrepresented in most advanced prostate cancer tumors. Previously, we demonstrated that PKCepsilon has the capacity to enhance the expression of both caveolin-1 and c-Myc in cultured prostate cancer cells and is sufficient to induce the growth of androgen-independent tumors. In this study, we have uncovered further evidence of a functional interplay among these proteins in the CWR22 model of human prostate cancer. The results demonstrated that PKCepsilon expression was naturally up-regulated in recurrent CWR22 tumors and that this oncoprotein was required to sustain the androgen-independent proliferation of CWR-R1 cells in culture. Gene transfer experiments demonstrated that PKCepsilon had the potential to augment the expression and secretion of a biologically active caveolin-1 protein that supports the growth of the CWR-R1 cell line. Antisense and pharmacological experiments provided additional evidence that the sequential activation of PKCepsilon, mitogen-activated protein kinases, c-Myc, and androgen receptor signaling drove the downstream expression of caveolin-1 in CWR-R1 cells. Finally, we demonstrate that mitogen-activated protein kinases were required downstream of PKCepsilon to derepress the transcriptional elongation of the c-myc gene. Our findings support the hypothesis that PKCepsilon may advance the recurrence of human prostate cancer by promoting the expression of several important downstream effectors of disease progression.

Inhibition of histone acetyltransferase function of p300 by PKCdelta

Protein kinase Cdelta (PKCdelta) is one of the functionally distinct isoforms in PKC family. p300 is a histone acetyltransferase/transcription coactivator. They share certain properties, such as ubiquitous expression, growth and tumor suppression, and ability to enhance differentiation and apoptosis. In this study, we found that PKCdelta but not classical PKC, specifically phosphorylates p300 at serine 89 in vitro and in vivo. This phosphorylation causes inhibition of p300 intrinsic HAT activity. Subsequently, the targeted acetylation of nucleosomal histones is markedly reduced, which causes repression of p300 transcription coactivator function. These findings identify a new signal transduction pathway by which PKCdelta may inhibit cell growth and promote cellular differentiation.

Regulation of tumor invasion and metastasis in protein kinase C epsilon-transformed NIH3T3 fibroblasts

Protein kinase C epsilon is an oncogenic, actin nucleating protein that coordinately regulates changes in cell growth and shape. Cells constitutively expressing PKCepsilon spontaneously acquire a polarized morphology and extend long cellular membrane protrusions. Here we report that the regulatory C1 domain of PKCepsilon contains an actin binding site that is essential for the formation of elongate invadopodial-like structures, increased pericellular metalloproteinase activity, in vitro invasion of a Matrigel barrier, and the invasion and metastasis of tumors grown in vivo by PKCepsilon-transformed NIH3T3 fibroblasts in nude mice. While removing this small actin binding motif caused a dramatic reversion of tumor invasion, the deletion mutant of PKCepsilon remained oncogenic and tumorigenic in this experimental system. We propose that PKCepsilon directly interacts with actin to stimulate polymerization and the extension of membrane protrusions that transformed NIH3T3 cells use in vivo to penetrate and degrade surrounding tissue boundaries.

CTGF expression in mesangial cells: involvement of SMADs, MAP kinase, and PKC

BACKGROUND

The induction of excess matrix in renal fibrosis seems to be mediated, at least in part, by the transforming growth factor-beta (TGF-beta)-mediated induction of connective tissue growth factor (CTGF) in mesangial cells.

METHODS

By examining CTGF protein and mRNA expression and promoter activity in the presence or absence of TGF-beta or inhibitors, the signaling pathways controlling basal and TGF-beta-induced CTGF expression in mesangial cells were investigated.

RESULTS

TGF-beta enhances CTGF mRNA and protein expression in mesangial cells. Mutation of a consensus SMAD binding element in the CTGF promoter completely abolished TGF-beta-induced CTGF expression and reduced basal CTGF expression. The previously identified basal control element-1 (BCE-1) site, but not Sp1 contributes to basal CTGF promoter activity. Ras/MEK/ERK, protein kinase C (PKC) and tyrosine kinase activity also contribute to basal and TGF-beta-induced CTGF promoter activity in cultured mesangial cells.

CONCLUSIONS

The TGF-beta-induction of CTGF in mesangial cells requires SMADs and PKC/ras/MEK/ERK pathways. SMADs are involved in basal CTGF expression, which presumably reflects the fact that mesangial cells express TGF-beta endogenously. TGF-beta also induces CTGF through ras/MEK/ERK. Inhibiting ras/MEK/ERK seems not to reduce phosphorylation (that is, activation) of SMADs, suggesting that SMADs, although necessary, are insufficient for the TGF-beta-stimulation of the CTGF promoter through ras/MEK/ERK. Thus, maximal TGF-beta induction of CTGF requires synergy between SMAD and ras/MEK/ERK signaling.

The hexosamine pathway regulates the plasminogen activator inhibitor-1 gene promoter and Sp1 transcriptional activation through protein kinase C-beta I and -delta

Increased flux through the hexosamine biosynthesis pathway (HBP) has been shown to stimulate the expression of a number of genes. We previously demonstrated in glomerular mesangial and endothelial cells that both high glucose concentrations and glucosamine activated the plasminogen activator inhibitor-1 (PAI-1) gene promoter through the transcription factor, Sp1; and that the glutamine:fructose-6-phosphate amidotransferase inhibitor, 6-diazo-5-oxonorleucine, inhibited the effect of high glucose, but not that of glucosamine. Here, we examined the role of protein kinase C (PKC) isoforms in the regulation of the PAI-1 promoter and Sp1 transcriptional activity by the HBP. In transient transfections, exposure to 2 mm glucosamine or 20 mm glucose for 4 days increased the activities of a PAI-1 promoter-luciferase reporter gene as well as the Sp1 transcriptional activation domain fused to the GAL4 DNA-binding domain cotransfected with a GAL4 promoter-luciferase reporter. Cotransfected dominant negative PKC-betaI and -delta completely blocked the induction of PAI-1 promoter transcription by both sugars, whereas only dominant negative PKC-betaI interfered with Sp1-GAL4 activation. Both glucosamine and high glucose stimulated the in vitro kinase activity of immunoprecipitated PKC-betaI and -delta. Furthermore, 6-diazo-5-oxonorleucine suppressed high glucose-induced PKC kinase activity and Sp1-GAL4 transcriptional activation. These findings demonstrate a requirement for the PKC-betaI and -delta signal transduction pathways in HBP-induced transcription.

p38 kinase-dependent and -independent Inhibition of protein kinase C zeta and -alpha regulates nitric oxide-induced apoptosis and dedifferentiation of articular chondrocytes

In articular chondrocytes, nitric oxide (NO) production triggers dedifferentiation and apoptotic cell death that is regulated by the converse functions of two mitogen-activated protein kinase subtypes, extracellular signal-regulated kinase (ERK) and p38 kinase. Since protein kinase C (PKC) transduces signals that influence differentiation, survival, and apoptosis of various cell types, we investigated the roles and underlying molecular mechanisms of action of PKC isoforms in NO-induced dedifferentiation and apoptosis of articular chondrocytes. We report here that among the expressed isoforms, activities of PKCalpha and -zeta were reduced during NO-induced dedifferentiation and apoptosis. Inhibition of PKCalpha activity was independent of NO-induced activation of ERK or p38 kinase and occurred due to blockage of expression. On the other hand, PKCzeta activity was inhibited as a result of NO-induced p38 kinase activation and was observed prior to proteolytic cleavage by a caspase-mediated process to generate enzymatically inactive fragments. Inhibition of PKCalpha or -zeta activities potentiated NO-induced apoptosis, whereas ectopic expression of these isoforms significantly reduced the number of apoptotic cells and blocked dedifferentiation. Ectopic expression of PKCalpha or -zeta did not affect p38 kinase or ERK but inhibited the p53 accumulation and caspase-3 activation that are required for NO-induced apoptosis of chondrocytes. Therefore, our results collectively indicate that p38 kinase-independent and -dependent inhibition of PKCalpha and -zeta, respectively, regulates NO-induced apoptosis and dedifferentiation of articular chondrocytes.

Regulation of airway smooth muscle cyclin D1 transcription by protein kinase C-delta

The precise mechanism by which protein kinase C-delta (PKCdelta) inhibits cell cycle progression is not known. We investigated the regulation of cyclin D1 transcription by PKCdelta in primary bovine airway smooth muscle cells. Overexpression of the active catalytic subunit of PKCdelta attenuated platelet-derived growth factor (PDGF)-mediated transcription from the cyclin D1 promoter, whereas overexpression of a dominant-negative PKCdelta increased promoter activity. A PKCdelta-specific pseudosubstrate increased cyclin D1 protein abundance. To determine the transcriptional mechanism by which PKCdelta negatively regulates cyclin D1 expression, we transiently transfected cells with cDNAs encoding cyclin D1 promoter 5' deletions and site mutations in the context of a -66 promoter fragment. We found that the -57 to -52 CRE/ATF2 site functions as a basal level and PDGF enhancer, whereas the -39 to -30 nuclear factor-kappaB site functions as a basal level suppressor. Further, PDGF and PKCdelta responsiveness of the cyclin D1 promoter was maintained following 5' deletion to the Ets-containing -22 minimal promoter. Finally, using electrophoretic mobility gel shift and reporter assays, we determined that PKCdelta inhibits CRE/ATF2 binding and transactivation, activates nuclear factor-kappaB binding and transactivation, and attenuates Ets transactivation. These data suggest that PKCdelta attenuates cyclin D1 promoter activity via the regulation of three distinct cis-acting regulatory elements.

Mechanism of 17-beta-estradiol-induced Erk1/2 activation in breast cancer cells. A role for HER2 AND PKC-delta

Activation of mitogen-activated protein kinase (Erk/MAPK) is a critical signal transduction event for estrogen (E(2))-mediated cell proliferation. Recent studies from our group and others have shown that persistent activation of Erk plays a major role in cell migration and tumor progression. The signaling mechanism(s) responsible for persistent Erk activation are not fully characterized, however. In this study, we have shown that E(2) induces a slow but persistent activation of Erk in MCF-7 breast carcinoma cells. The E(2)-induced Erk activation is dependent on new protein synthesis, suggesting that E(2)-induced growth factors play a major role in Erk activation. When MCF-7 cells were treated with E(2) in the presence of an anti-HER-2 monoclonal antibody (herceptin), 60-70% of E(2)-induced Erk activation is blocked. In addition, when untreated MCF-7 cells were exposed to conditioned medium from E(2)-treated cells, Erk activity was significantly enhanced. Furthermore Erk activity was blocked by an antibody against HER-2 or by heregulin (HRG) depletion from the conditioned medium through immunoprecipitation. In contrast, epidermal growth factor receptor (Ab528) antibody only blocked 10-20% of E(2)-induced Erk activation, suggesting that E(2)-induced Erk activation is predominantly mediated through the secretion of HRG and activation of HER-2 by an autoctine/paracrine mechanism. Inhibition of PKC-delta-mediated signaling by a dominant negative mutant or the relatively specific PKC-delta inhibitor rottlerin blocked most of the E(2)-induced Erk activation but had no effect on TGF alpha-induced Erk activation. By contrast inhibition of Ras, by inhibition of farnesyl transferase (Ftase-1) or dominant negative (N17)-Ras, significantly inhibited both E(2)- and TGF alpha-induced Erk activation. This evaluation of downstream signaling revealed that E(2)-induced Erk activation is mediated by a HRG/HER-2/PKC-delta/Ras pathway that could be crucial for E(2)-dependent growth-promoting effects in early stages of tumor progression.

PKCzeta regulates TNF-alpha-induced activation of NADPH oxidase in endothelial cells

Although oxidant generation by NADPH oxidase is known to play an important role in signaling in endothelial cells, the basis of activation of NADPH oxidase is incompletely understood. The atypical isoform of protein kinase C, PKCzeta, has been implicated in the mechanism of tumor necrosis factor-alpha (TNF-alpha)-induced oxidant generation in endothelial cells; thus, in the present study, we have addressed the role of PKCzeta in regulating NADPH oxidase function. We showed by immunoblotting and confocal microscopy the presence of the major cytosolic NADPH oxidase subunits, p47(phox) and membrane-bound gp91(phox) in human pulmonary artery endothelial (HPAE) cells. TNF-alpha failed to activate oxidant generation in lung vascular endothelial cells derived from p47(phox-/-) and gp91(phox-/-) mice, indicating the requirement of NADPH oxidase in mediating the oxidant generation in endothelial cells. Stimulation of HPAE cells with TNF-alpha resulted in the phosphorylation of p47(phox) and its association with gp91(phox). Inhibition of PKCzeta by multiple pharmacological and genetic approaches prevented the TNF-alpha-induced phosphorylation of p47(phox), and its translocation to the membrane. PKCzeta was shown to colocalize with p47(phox), and inhibition of PKCzeta activation prevented the interaction of p47(phox) with gp91(phox) induced by TNF-alpha. Furthermore, inhibition of association of p47(phox) with gp91(phox) prevented the oxidant generation in endothelial cells. These data demonstrate a novel function of PKCzeta in signaling oxidant generation in endothelial cells by the activation of NADPH oxidase, which may be important in mediating endothelial activation responses.

Calcium-dependent involucrin expression is inversely regulated by protein kinase C (PKC)alpha and PKCdelta

Calcium is an important physiologic regulator of keratinocyte function that may regulate keratinocyte differentiation via modulation of protein kinase C (PKC) activity. PKCalpha and PKCdelta are two PKC isoforms that are expressed at high levels in keratinocytes. In the present study, we examine the effect of PKCdelta and PKCalpha on calcium-dependent keratinocyte differentiation as measured by effects on involucrin (hINV) gene expression. Our studies indicate that calcium increases hINV promoter activity and endogenous hINV gene expression. This response requires PKCdelta, as evidenced by the observation that treatment with dominant-negative PKCdelta inhibits calcium-dependent hINV promoter activity, whereas wild type PKCdelta increases activity. PKCalpha, in contrast, inhibits calcium-dependent hINV promoter activation, a finding that is consistent with the ability of dominant-negative PKCalpha and the PKCalpha inhibitor, Go6976, to increase hINV gene expression. The calcium-dependent regulatory response is mediated by an AP1 transcription factor-binding site located within the hINV promoter distal regulatory region that is also required for PKCdelta-dependent regulation; moreover, both calcium and PKCdelta produce similar, but not identical, changes in AP1 factor expression. A key question is whether calcium directly influences PKC isoform function. Our studies show that calcium does not regulate PKCalpha or delta levels or cause a marked redistribution to membranes. However, tyrosine phosphorylation of PKCdelta is markedly increased following calcium treatment. These findings suggest that PKCalpha and PKCdelta are required for, and modulate, calcium-dependent keratinocyte differentiation in opposing directions.

Protein kinase C-delta (PKC-delta ) is activated by type I interferons and mediates phosphorylation of Stat1 on serine 727

It is well established that engagement of the Type I interferon (IFN) receptor results in activation of JAKs (Janus kinases), which in turn regulate tyrosine phosphorylation of STAT proteins. Subsequently, the IFN-dependent tyrosine-phosphorylated/activated STATs translocate to the nucleus to regulate gene transcription. In addition to tyrosine phosphorylation, phosphorylation of Stat1 on serine 727 is essential for induction of its transcriptional activity, but the IFNalpha-dependent serine kinase that regulates such phosphorylation remains unknown. In the present study we provide evidence that PKC-delta, a member of the protein kinase C family of proteins, is activated during engagement of the Type I IFN receptor and associates with Stat1. Such an activation of PKC-delta appears to be critical for phosphorylation of Stat1 on serine 727, as inhibition of PKC-delta activation diminishes the IFNalpha- or IFNbeta-dependent serine phosphorylation of Stat1. In addition, treatment of cells with the PKC-delta inhibitor rottlerin or the expression of a dominant-negative PKC-delta mutant results in inhibition of IFNalpha- and IFNbeta-dependent gene transcription via ISRE or GAS elements. Interestingly, PKC-delta inhibition also blocks activation of the p38 MAP kinase, the function of which is required for IFNalpha-dependent transcriptional regulation, suggesting a dual mechanism by which this kinase participates in the generation of IFNalpha responses. Altogether, these findings indicate that PKC-delta functions as a serine kinase for Stat1 and an upstream regulator of the p38 MAP kinase and plays an important role in the induction of Type I IFN-biological responses.

Regulation of protein kinase C in Escherichia coli K1 invasion of human brain microvascular endothelial cells

Escherichia coli is one of the most important pathogens involved in the development of neonatal meningitis in many parts of the world. Traversal of E. coli across the blood-brain barrier is a crucial event in the pathogenesis of E. coli meningitis. Our previous studies have shown that outer membrane protein A (OmpA) expression is necessary in E. coli for a mechanism involving actin filaments in its passage through the endothelial cells. Focal adhesion kinase (FAK) and phosphatidylinositol 3-kinase (PI3K) have also been activated in host cells during the process of invasion. In an attempt to elucidate the mechanisms leading to actin filament condensation, we have focused our attention on protein kinase C (PKC), an enzyme central to many signaling events, including actin rearrangement. In the current study, specific PKC inhibitors, bisindolmaleimide and a PKC-inhibitory peptide, inhibited E. coli invasion of human brain microvascular endothelial cells (HBMEC) by more than 75% in a dose-dependent manner, indicating a significant role played by this enzyme in the invasion process. Our results further showed that OmpA+ E. coli induces significant activation of PKC in HBMEC as measured by the PepTag nonradioactive assay. In addition, we identified that the PKC isoform activated in E. coli invasion is a member of the conventional family of PKC, PKC-alpha, which requires calcium for activation. Immunocytochemical studies have indicated that the activated PKC-alpha is associated with actin condensation beneath the bacterial entry site. Overexpression of a dominant negative mutant of PKC-alpha in HBMEC abolished the E. coli invasion without significant changes in FAK phosphorylation or PI3K activity patterns. In contrast, in HBMEC overexpressing the mutant forms of either FAK or PI3K, E. coli-induced PKC activation was significantly blocked. Furthermore, our studies showed that activation of PKC-alpha induces the translocation of myristoylated alanine-rich protein kinase C substrate, an actin cross-linking protein and a substrate for PKC-alpha, from the membrane to cytosol. This is the first report of FAK- and PI3K-dependent PKC-alpha activation in bacterial invasion related to cytoskeletal reorganization.

Dopamine-induced exocytosis of Na,K-ATPase is dependent on activation of protein kinase C-epsilon and -delta

The purpose of this study was to define mechanisms by which dopamine (DA) regulates the Na,K-ATPase in alveolar epithelial type 2 (AT2) cells. The Na,K-ATPase activity increased by twofold in cells incubated with either 1 microM DA or a dopaminergic D(1) agonist, fenoldopam, but not with the dopaminergic D(2) agonist quinpirole. The increase in activity paralleled an increase in Na,K-ATPase alpha1 and beta1 protein abundance in the basolateral membrane (BLM) of AT2 cells. This increase in protein abundance was mediated by the exocytosis of Na,K-pumps from late endosomal compartments into the BLM. Down-regulation of diacylglycerol-sensitive types of protein kinase C (PKC) by pretreatment with phorbol 12-myristate 13-acetate or inhibition with bisindolylmaleimide prevented the DA-mediated increase in Na,K-ATPase activity and exocytosis of Na,K-pumps to the BLM. Preincubation of AT2 cells with either 2-[1-(3-dimethylaminopropyl)-5-methoxyindol-3-yl]-3-(1H-indol-3-yl)maleimide (Gö6983), a selective inhibitor of PKC-delta, or isozyme-specific inhibitor peptides for PKC-delta or PKC-epsilon inhibited the DA-mediated increase in Na,K-ATPase. PKC-delta and PKC-epsilon, but not PKC-alpha or -beta, translocated from the cytosol to the membrane fraction after exposure to DA. PKC-delta- and PKC-epsilon-specific peptide agonists increased Na,K-ATPase protein abundance in the BLM. Accordingly, dopamine increased Na,K-ATPase activity in alveolar epithelial cells through the exocytosis of Na,K-pumps from late endosomes into the basolateral membrane in a mechanism-dependent activation of the novel protein kinase C isozymes PKC-delta and PKC-epsilon.

The role of protein kinase C-delta in PTH stimulation of IGF-binding protein-5 mRNA in UMR-106-01 cells

We have investigated the role of protein kinase C (PKC) signal transduction pathways in parathyroid hormone (PTH) regulation of insulin-like growth factor-binding protein-5 (IGFBP-5) gene expression in the rat osteoblast-like cell line UMR-106-01. Involvement of the PKC pathway was determined by the findings that bisindolylmaleimide I inhibited 40% of the PTH effect, and 1 microM bovine PTH-(3-34) stimulated a 10-fold induction of IGFBP-5 mRNA. PTH-(1-34) and PTH-(3-34) (100 nM) both stimulated PKC-delta translocation from the membrane to the nuclear fraction. Rottlerin, a PKC-delta-specific inhibitor, and a dominant negative mutant of PKC-delta were both able to significantly inhibit PTH-(1-34) and PTH-(3-34) induction of IGFBP-5 mRNA, suggesting a stimulatory role for PKC-delta in the effects of PTH. Phorbol 12-myristate 13-acetate (PMA) stimulated PKC-alpha translocation from the cytosol to the membrane and inhibited approximately 50% of the PTH-(1-34), forskolin, and 8-bromoadenosine 3',5'-cyclic monophosphate-stimulated IGFBP-5 mRNA levels, suggesting that PKC-alpha negatively regulates protein kinase A (PKA)-mediated induction of IGFBP-5 mRNA. These results suggest that the induction of IGFBP-5 by PTH is both PKA and PKC dependent and PKC-delta is the primary mediator of the effects of PTH via the PKC pathway.

The roles of JNK1 and Stat3 in the response of head and neck cancer cell lines to combined treatment with all-trans-retinoic acid and 5-fluorouracil

We have used a combination of vitamin A (all-trans-retinyl palmitate), 5-fluorouracil (5-FU) and radiation to treat human head and neck squamous cell carcinoma (HNSCC). This chemoradiotherapy is called "FAR therapy." In this study we examined the effects of all-trans-retinoic acid (ATRA), the active metabolite of vitamin A, and ATRA plus 5-FU on two HNSCC cell lines (YCU-N861 and YCU-H891) to gain insight into the molecular mechanisms of FAR therapy. ATRA at 1 mM (the order of concentration found in HNSCC tumors treated with FAR therapy) inhibited cell proliferation and caused G1 cell cycle arrest in both cell lines. This was associated with a decrease in cyclin D1, an increase in p27(Kip1) and a reduction in the hyperphosphorylated form of retinoblastoma protein (pRB). With YCU-N861 cells, ATRA also caused a decrease in Bcl-2 and Bcl-X(L) and an increase in Bax. Both ATRA and 5-FU activated c-Jun N-terminal kinase (JNK) 1 and the combination of both agents resulted in additive or synergistic activation of JNK1, and also enhanced the induction of apoptosis. The YCU-H891 cells, in which the epidermal growth factor receptor (EGFR)-signal transducer and activator of transcription 3 (Stat3) pathway is constitutively activated, were more resistant to treatments with ATRA, 5-FU and the combination of both agents than YCU-N861 cells. A dominant negative Stat3 construct strongly enhanced the cellular sensitivity of this cell line to 5-FU but not to ATRA. In addition there is evidence that activation of Stat3 is associated with cellular resistance to radiation in HNSCC. Therefore, the addition to FAR therapy of agents that inhibit activation of the Stat3 pathway may enhance the clinical response of patients with HNSCC to FAR therapy.

Biochemical and morphogenic effects of the interaction between protein kinase C-epsilon and actin in vitro and in cultured NIH3T3 cells

Protein kinase C-epsilon coordinately regulates changes in cell growth and shape. Cells overproducing protein kinase C-epsilon spontaneously acquire a polarized morphology and extend long cellular membrane protrusions that are reminiscent of the morphology observed in ras-transformed fibroblasts. Here we report that the regulatory C1 domain contains an actin binding hexapeptide motif that is essential for the morphogenic effects of protein kinase C-epsilon in cultured NIH3T3 murine fibroblasts. The extension of elongate processes by protein kinase C-epsilon transformed fibroblasts appeared to be driven by a kinase-independent mechanism that required organized networks of both actin and microtubules. Flow cytometry of phalloidin-stained cells demonstrated that protein kinase C-epsilon significantly increased the cellular content of polymerized actin in NIH3T3 cells. Studies with a cell-free system suggest that protein kinase C-epsilon inhibits the in vitro disassembly of actin filaments, is capable of desequestering actin monomers from physiologically relevant concentrations of thymosin beta4, and increases the rate of actin filament elongation by decreasing the critical concentration of actin. Based on these and other observations, it is proposed that protein kinase C-epsilon may function as a terminal downstream effector in at least one of the signaling pathways that mitogens engage to initiate outgrowth of cellular protrusions.

Effect of protein kinase C on endoplasmic reticulum cholesterol

Plasma membrane cholesterol both regulates and is regulated by effector proteins in the endoplasmic reticulum (ER) through a feedback system that is poorly understood. We now show that ER cholesterol varies over a fivefold range in response to experimental agents that act upon protein kinase C (PKC). Agents that activate Ca(2+)-dependent PKC [phorbol-12-myristate-13-acetate (PMA) and bryostatin 1] increased the level of ER cholesterol; inhibitors such as staurosporine and calphostin C decreased it. Rottlerin, a selective inhibitor of the PKC-delta isoform, also increased ER cholesterol. The esterification of plasma membrane cholesterol was altered by protein kinase C-directed agents in a corresponding fashion. Furthermore, the regulatory effect of plasma membrane cholesterol on the esterification of ER cholesterol was blocked by PKC-directed agents. These findings suggest that multiple protein kinase C isoforms participate in the regulation of ER cholesterol and therefore in cholesterol homeostasis.

Antisense oligonucleotides targeted against protein kinase c alpha inhibit proliferation of cultured avian myoblasts

Protein kinase C (PKC) has been implicated in the control of proliferation and differentiation of many cell types. There is evidence indicating that it plays a role in signal transduction mechanisms related to myogenesis, but little is known about the individual functions of PKC isoforms in muscle cell development. Data obtained in previous studies using cultured chick embryo skeletal muscle cells suggested that PKC alpha is linked to the regulation of myoblast proliferation. However, this causal relationship could not be definitively established as no experiments based on selective inhibition of this isoform were carried out. In the present work, specific inhibition of the expression of PKC alpha in cultured myoblasts by using antisense oligonucleotide technology resulted in a significant decrease of culture cell density and DNA synthesis, clearly showing that this isoenzyme is involved in signalling pathways which promote muscle cell proliferation.

The ups and downs of MEK kinase interactions

MEK kinases (MEKKs) comprise a family of related serine-threonine protein kinases that regulate mitogen-activated protein kinase (MAPK) signalling pathways leading to c-Jun NH2-terminal kinase (JNK) and p38 activation, induced by cellular stress (e.g., UV and gamma irradiation, osmotic stress, heat shock, protein synthesis inhibitors), inflammatory cytokines (e.g., tumour necrosis factor alpha, TNFalpha, and interleukin-1, IL1) and G protein-coupled receptor agonists (e.g., thrombin). These stress-activated kinases have been implicated in apoptosis, oncogenic transformation, and inflammatory responses in various cell types. At present, the signalling events involving MEKKs are not well understood. This review summarises our current knowledge concerning the regulation and function of MEKK family members, with particular emphasis on those factors capable of directly interacting with distinct MEKK isoforms.

Phosphorylation is involved in the activation of metal-regulatory transcription factor 1 in response to metal ions

We have studied the role of phosphorylation in the activation of metal-regulatory transcription factor-1 (MTF-1) and metallothionein (MT) gene expression. We showed that MTF-1 is phosphorylated in vivo and that zinc stimulates MTF-1 phosphorylation 2-4-fold. Several kinase inhibitors were used to examine the possible involvement of kinase cascades in the activation of MTF-1. Metal-induced MT gene expression was abrogated by protein kinase C (PKC), c-Jun N-terminal kinase (JNK), phosphoinositide 3-kinase, and tyrosine-specific protein kinases inhibitors, as assayed by Northern analysis and by cotransfection experiments using a metal regulatory element-luciferase reporter plasmid. The extracellular signal-activated protein kinase and the p38 kinase cascades did not appear to be essential for the activation of MT gene transcription by metals. By using dominant-negative mutants of PKC, JNK, mitogen-activated kinase kinase 4 (MKK4), and MKK7, we provide further evidence supporting a role for PKC and JNK in the activation of MTF-1 in response to metals. Notably, increased MTF-1 DNA binding in response to zinc and MTF-1 nuclear localization was not inhibited in cells preincubated with the different kinase inhibitors despite strong inhibition of MTF-1-mediated gene expression. This suggests that phosphorylation is essential for MTF-1 transactivation function. We hypothesize that metal-induced phosphorylation of MTF-1 is one of the primary events leading to increased MTF-1 activity. Thus, metal ions such as cadmium could activate MTF-1 and induce MT gene expression by stimulating one or several kinases in the MTF-1 signal transduction pathway.

Early postnatal cardiac changes and premature death in transgenic mice overexpressing a mutant form of serum response factor

Serum response factor (SRF) is a key regulator of a number of extracellular signal-regulated genes important for cell growth and differentiation. A form of the SRF gene with a double mutation (dmSRF) was generated. This mutation reduced the binding activity of SRF protein to the serum response element and reduced the capability of SRF to activate the atrial natriuretic factor promoter that contains the serum response element. Cardiac-specific overexpression of dmSRF attenuated the total SRF binding activity and resulted in remarkable morphologic changes in the heart of the transgenic mice. These mice had dilated atrial and ventricular chambers, and their ventricular wall thicknesses were only 1/2 to 1/3 the thickness of that of nontransgenic mice. Also these mice had smaller cardiac myocytes and had less myofibrils in their myocytes relative to nontransgenic mice. Altered gene expression and slight interstitial fibrosis were observed in the myocardium of the transgenic mice. All the transgenic mice died within the first 12 days after birth, because of the early onset of severe, dilated cardiomyopathy. These results indicate that dmSRF overexpression in the heart apparently alters cardiac gene expression and blocks normal postnatal cardiac growth and development.

High glucose-enhanced mesangial cell extracellular signal-regulated protein kinase activation and alpha1(IV) collagen expression in response to endothelin-1: role of specific protein kinase C isozymes

High glucose (HG) stimulates glomerular mesangial cell (MC) expression of extracellular matrix, a process involving protein kinase C (PKC) isozymes and enhanced signaling by autocrine peptides such as endothelin-1 (ET-1). The purpose of this study was to identify the specific PKC isozymes mediating the effects of HG on MC extracellular signal-regulated protein kinase (ERK1/2) signaling and alpha1(IV) collagen expression in response to ET-1. HG (30 mmol/l for 72 h) enhanced ET-1-stimulated alpha1(IV) collagen mRNA expression from 1.2 +/- 0.1-fold to 1.9 +/- 0.2-fold (P < 0.05 vs. normal glucose [NG] + ET-1), and the effect was significantly reduced by Calphostin C or the MEK (mitogen-activated protein kinase kinase) inhibitor PD98059. In transiently transfected MCs, dominant-negative (DN)-PKC-delta, -epsilon, or -zeta inhibited ET-1 activation of ERK1/2. Likewise, downstream of ERK1/2, ET-1 stimulated Elk-1-driven GAL4 luciferase activity to 11 +/- 1-fold (P < 0.002 vs. NG + ET-1) in HG, and DN-PKC-delta, -epsilon, or -zeta attenuated this response to NG levels. HG enhanced ET-1-stimulated intracellular alpha1(IV) collagen protein expression, assessed by confocal immunofluorescence imaging, showed that individual DN-PKC-delta, -epsilon, -zeta, as well as DN-PKC-alpha and -beta, attenuated the response. Thus, HG-enhanced ET-1 stimulation of alpha1(IV) collagen expression requires PKC-delta, -epsilon, and -zeta to act through an ERK1/2-dependent pathway and via PKC-alpha and -beta, which are independent of ERK1/2.

Endothelial exposure to hypoxia induces Egr-1 expression involving PKCalpha-mediated Ras/Raf-1/ERK1/2 pathway

Hypoxia induces endothelial dysfunction that results in a series of cardiovascular injuries. Early growth response-1 (Egr-1) has been indicated as a common theme in vascular injury. Here we demonstrates that in bovine aortic endothelial cells (ECs) subjected to hypoxia (PO(2) approximately 23 mmHg), rapidly increased Egr-1 mRNA expression which peaked within 30 min and decreased afterwards. Treatment of ECs with PD98059, a specific inhibitor to mitogen-activated protein kinase (MAPK/ERK), inhibited this hypoxia-induced Egr-1 expression. The involvement of ERK pathway was further substantiated by the inhibition of Egr-1 promoter activities when ECs were co-transfected with a dominant negative mutant of Ras (RasN17), Raf-1 (Raf 301), or a catalytically inactive mutant of ERK2 (mERK). In addition, the hypoxia-induced transcriptional activity of Elk-1, an ERK substrate, was abolished by administration of PD98059. Addition of calphostin C, a protein kinase C (PKC) inhibitor, completely blocked the hypoxia-augmented Egr-1 expression. The likewise occurred while exposing ECs to D609 to inhibit phospholipase C and BAPTA/AM to chelate intracellular calcium. Hypoxia to ECs increased ERK phosphorylation within 10 min and which was abolished by administration of PD98095, calphostin C, and BAPTA/AM. Hypoxia triggered a transient translocation of PKCalpha from cytosol to membrane fraction concurrent with the association of PKCalpha to Raf-1. Involvement of PKCalpha in mediating ERK activation was further confirmed by the inhibition of ERK and the subsequent Egr-1 gene induction with antisense oligonucleotides to PKCalpha. These results indicate that ECs under hypoxia induce Egr-1 expression and this induction requires calcium, phospholipase C activation, and PKCalpha-mediated Ras/Raf-1/ERK1/2 signaling pathway. Our finding support the importance of specific PKC isozyme linked to MAPK pathway in the regulation of endothelial responses to hypoxia.

Sequential activation of protein kinase C (PKC)-alpha and PKC-epsilon contributes to sustained Raf/ERK1/2 activation in endothelial cells under mechanical strain

Endothelial cells (ECs) are constantly subjected to hemodynamic forces including cyclic pressure-induced strain. The role of protein kinase C (PKC) in cyclic strain-treated ECs was studied. PKC activities were induced as cyclic strain was initiated. Cyclic strain to ECs caused activation of PKC-alpha and -epsilon. The translocation of PKC-alpha and -epsilon but not PKC-beta from the cytosolic to membrane fraction was observed. An early transient activation of PKC-alpha versus a late but sustained activation of PKC-epsilon was shown after the onset of cyclic strain. Consistently, a sequential association of PKC-alpha and -epsilon with the signaling molecule Raf-1 was shown. ECs treated with a PKC inhibitor (calphostin C) abolished the cyclic strain-induced Raf-1 activation. ECs under cyclic strain induced a sustained activation of extracellular signal-regulated protein kinases (ERK1/2), which was inhibited by treating ECs with calphostin C. ECs treated with a specific Ca(2+)-dependent PKC inhibitor (Go 6976) showed an inhibition in the early phase of ERK1/2 activation but not in the late and sustained phase. ECs transfected with the antisense to PKC-alpha, the antisense to PKC-epsilon, or the inhibition peptide to PKC-epsilon reduced strain-induced ERK1/2 phosphorylation in a temporal manner. PKC-alpha mediated mainly the early ERK1/2 activation, whereas PKC-epsilon was involved in the sustained ERK1/2 activation. Strained ECs increased transcriptional activity of Elk1 (an ERK1/2 substrate). ECs transfected with the antisense to each PKC isoform reduced Elk1 and monocyte chemotactic protein-1 promotor activity. Our findings conclude that a sequential activation of PKC isoform (alpha and epsilon) contribute to Raf/ERK1/2 activation, and PKC-epsilon appears to play a key role in endothelial adaptation to hemodynamic environment.

Stromal inhibition of megakaryocytic differentiation correlates with blockade of signaling by protein kinase C-epsilon and ERK/MAPK

Contact with bone marrow stromal cells maintains normal and leukemic hematopoietic progenitors in an undifferentiated state. Recently, stromal contact has been shown to diminish the yield of megakaryocytes in cultures of primary human hematopoietic stem cells. This inhibition may explain the poor megakaryocytic engraftment frequently observed after bone marrow transplantation. In the current study, stromal co-culture is shown to render K562 cells refractory to megakaryocytic induction. This stromal inhibition correlated with the selective down-regulation in K562 cells of protein kinase C-epsilon (PKC-epsilon), which has recently been implicated in regulation of megakaryocytic lineage commitment. In addition, the stromal inhibition correlated with inactivation of the ERK/MAPK pathway, which has also been implicated in promoting megakaryocytic development. Forced expression of PKC-epsilon by retroviral transduction was insufficient to reverse the stromal blockade of ERK/MAPK signaling or of megakaryocytic induction. Thus stromal interruption of ERK/MAPK signaling occurred independently of PKC-epsilon levels and correlated more closely with megakaryocytic blockade. These findings provide potential mechanisms for stromal inhibition of hematopoietic differentiation and possibly for the poor megakaryocytic engraftment seen after bone marrow transplantation.

Protein kinase C-delta regulates thrombin-induced ICAM-1 gene expression in endothelial cells via activation of p38 mitogen-activated protein kinase

The procoagulant thrombin promotes the adhesion of polymorphonuclear leukocytes to endothelial cells by a mechanism involving expression of intercellular adhesion molecule 1 (ICAM-1) via an NF-kappaB-dependent pathway. We now provide evidence that protein kinase C-delta (PKC-delta) and the p38 mitogen-activated protein (MAP) kinase pathway play a critical role in the mechanism of thrombin-induced ICAM-1 gene expression in endothelial cells. We observed the phosphorylation of PKC-delta and p38 MAP kinase within 1 min after thrombin challenge of human umbilical vein endothelial cells. Pretreatment of these cells with the PKC-delta inhibitor rottlerin prevented the thrombin-induced phosphorylation of p38 MAP kinase, suggesting that p38 MAP kinase signals downstream of PKC-delta. Inhibition of PKC-delta or p38 MAP kinase by pharmacological and genetic approaches markedly decreased the thrombin-induced NF-kappaB activity and resultant ICAM-1 expression. The effects of PKC-delta inhibition were secondary to inhibition of IKKbeta activation and of subsequent NF-kappaB binding to the ICAM-1 promoter. The effects of p38 MAP kinase inhibition occurred downstream of IkappaBalpha degradation without affecting the DNA binding function of nuclear NF-kappaB. Thus, PKC-delta signals thrombin-induced ICAM-1 gene transcription by a dual mechanism involving activation of IKKbeta, which mediates NF-kappaB binding to the ICAM-1 promoter, and p38 MAP kinase, which enhances transactivation potential of the bound NF-kappaB p65 (RelA).

Role of protein kinase Cdelta in transmitting hypoxia signal to HSF and HIF-1

An hypoxic microenvironment is an important modulator of gene expression in many pathophysiological conditions. In this study, we show a coordinate activation of heat shock transcription factor (HSF) and hypoxia-inducible factor-1 (HIF-1) in RIF tumor cells by hypoxia. Since heat shock protein (hsp) and angiogenic factor genes that are regulated by HSF and HIF-1 are thought to contribute to the malignant progression of hypoxic tumor cells, it was of our major interest to identify the components that are responsible for the activation of both HSF and HIF-1. Our finding that a bioflavonoid quercetin (QCT), a well known inhibitor of hsp gene expression, significantly inhibited the transcriptional activation of HSF and HIF-1 strongly suggests that QCT-sensitive molecule(s) is involved in the transcriptional activation of HSF and HIF-1 by hypoxia. Our results revealed that PCKalpha, delta and epsilon isoforms are expressed in RIF cells, but only PKCdelta was specifically translocated to the membrane by hypoxia. Our results also revealed that the translocation of PKCdelta was completely abrogated by QCT. Moreover, inhibiting the PKCdelta activation, either pharmacologically with phorbol 12-myristate 13-acetate or with bisindolymaleimide II or genetically by transient transfection of a dominant negative PKCdelta, significantly inhibited the transcriptional activation of HSF and HIF-1 by hypoxia. These results strongly substantiate a view that the PKCdelta isozyme is the QCT-sensitive molecule that plays an important role in transmitting hypoxia signals to both HSF and HIF-1. Here we show that the membrane translocation of PKCdelta is dependent on the activation of phosphoinositol 3-kinase (PI3K). Treatment with PI3K inhibitor, wortmannin or LY294002, abrogated not only PKCdelta translocation but the subsequent transcriptional activation of HSF and HIF-1 by hypoxia. Together, our study shows that the PKCdelta isozyme acts as a shared component in transmitting hypoxia-induced signals to both HSF and HIF-1, and that the upstream regulator of PKCdelta is PI3K.

The 5' UTR of protein kinase C epsilon confers translational regulation in vitro and in vivo

We have examined translational regulation conferred by the 5' untranslated region (UTR) of PKCepsilon on expression of the luciferase reporter gene in vitro, using rabbit reticulocyte lysates and in vivo, in contact-inhibiting mouse Swiss 3T3 fibroblasts and non-contact-inhibiting Swiss 3T6 fibroblasts. In rabbit reticulocyte lysates, the 5' UTR of PKCepsilon significantly represses translation. In 3T3 and 3T6 cells, the 5' UTR of PKCepsilon reduces luciferase activity, but not to the same extent as it does in vitro. In rabbit reticulocyte lysate, the degree of repression mediated by different PKCepsilon 5' UTR-deletion constructs correlates with the free energy (DeltaG) of their predicted secondary structures. However, in cells, secondary structure is not the only determinant of repression; an internal region of the 5' UTR is both necessary and sufficient for repression. Mutation of an upstream AUG (uAUG) motif in this region partially relieves repression. We conclude that the 5' UTR of PKCepsilon can mediate translational regulation and that translation inhibition in vivo involves the uAUG motif. Our findings also suggest that there are factors present in fibroblasts, but not in rabbit reticulocyte lysates that substantially overcome the repressive qualities of the long, structured 5' UTR. Thus, we have identified a potential new level of regulation of PKC in mammalian cells.

Protein kinase C-alpha signals rho-guanine nucleotide dissociation inhibitor phosphorylation and rho activation and regulates the endothelial cell barrier function

The Rho-GDP guanine nucleotide dissociation inhibitor (GDI) complexes with the GDP-bound form of Rho and inhibits its activation. We investigated the role of protein kinase C (PKC) isozymes in the mechanism of Rho activation and in signaling the loss of endothelial barrier function. Thrombin and phorbol 12-myristate 13-acetate induced rapid phosphorylation of GDI and the activation of Rho-A in human umbilical venular endothelial cells. Inhibition of PKC by chelerythrine chloride abrogated the thrombin-induced GDI phosphorylation and Rho activation. Depletion of PKC prevented the thrombin-induced GDI phosphorylation and Rho activation, thereby indicating that these events occurred downstream of phorbol ester-sensitive PKC isozyme activation. The depletion of PKC or inhibition of Rho by C3 toxin also prevented the thrombin-induced decrease in transendothelial electrical resistance (a measure of increased transendothelial permeability), thus indicating that PKC-induced barrier dysfunction was mediated through Rho-dependent pathway. Using inhibitors and dominant-negative mutants, we found that Rho activation was regulated by PKC-alpha. Moreover, the stimulation of human umbilical venular endothelial cells with thrombin induced rapid association of PKC-alpha with Rho. Activated PKC-alpha but not PKC-epsilon induced marked phosphorylation of GDI in vitro. Taken together, these results indicate that PKC-alpha is critical in regulating GDI phosphorylation, Rho activation, and in signaling Rho-dependent endothelial barrier dysfunction.

Ca2+-independent protein kinase C Apl II mediates the serotonin-induced facilitation at depressed aplysia sensorimotor synapses

At nondepressed Aplysia sensory to motor synapses, serotonin (5-HT) facilitates transmitter release primarily through a protein kinase A pathway. In contrast, at depressed Aplysia sensory to motor synapses, 5-HT facilitates transmitter release primarily through a protein kinase C (PKC)-dependent pathway. It is known that only two phorbol ester-activated PKC isoforms, the Ca(2+)-dependent PKC Apl I and the Ca(2+)-independent PKC Apl II, exist in the Aplysia nervous system. For the first time, we have now been able to functionally determine which isoform of PKC is involved in a particular form of plasticity. We microinjected cultured sensorimotor pairs of neurons with various PKC constructs tagged with the enhanced green fluorescent protein as a reporter for successful plasmid expression. Our results demonstrate that short-term facilitation of depressed synapses is mediated by PKC Apl II. Dominant-negative PKC Apl II, but not dominant-negative PKC Apl I, disrupted the normal kinetics of 5-HT-induced facilitation by completely blocking its rapid onset. This effect was specific to depressed synapses, because dominant-negative PKC Apl II did not inhibit 5-HT-mediated facilitation of nondepressed synapses. Our results suggest that not only different signal transduction pathways but also different isoforms of a specific cascade may mediate physiological responses according to the state of a synapse.

Gα16Couples Chemoattractant Receptors to NF-κB Activation

The guanine nucleotide-binding regulatory protein alpha-subunit, Galpha(16), is primarily expressed in hemopoietic cells, and interacts with a large number of seven-membrane span receptors including chemoattractant receptors. We investigated the biological functions resulting from Galpha(16) coupling of chemoattractant receptors in a transfected cell model system. HeLa cells expressing a kappaB-driven luciferase reporter, Galpha(16), and the formyl peptide receptor responded to fMLP with a approximately 7- to 10-fold increase in luciferase activity. This response was accompanied by phosphorylation of IkappaBalpha and elevation of nuclear kappaB-DNA binding activity, indicating activation of NF-kappaB. In contrast to Galpha(16), expression of Galpha(q), Galpha(13), and Galpha(i2) resulted in a marginal increase in kappaB luciferase activity. A GTPase-deficient, constitutively active Galpha(16) mutant (Q212L) could replace agonist stimulation for activation of NF-kappaB. Furthermore, expression of Galpha(16) (Q212L) markedly enhanced TNF-alpha-induced kappaB reporter activity. The Galpha(16)-mediated NF-kappaB activation was paralleled by an increase in phospholipase C-beta activity, and was blocked by pharmacological inhibitors of protein kinase C (PKC) and by buffering of intracellular Ca(2+). The involvement of a conventional PKC isoform was confirmed by the finding that expression of PKCalpha enhanced the effect of Galpha(16), and a dominant negative PKCalpha partially blocked Galpha(16)-mediated NF-kappaB activation. In addition to formyl peptide receptor, Galpha(16) also enhanced NF-kappaB activation by the C5a and C3a receptors, and by CXC chemokine receptor 2 and CCR8. These results suggest a potential role of Galpha(16) in transcriptional regulation downstream of chemoattractant receptors.

Estrogen receptor-mediated activation of the serum response element in MCF-7 cells through MAPK-dependent phosphorylation of Elk-1

17beta-Estradiol (E2) induces c-fos protooncogene expression in MCF-7 human breast cancer cells, and deletion analysis of the c-fos promoter showed that the serum response element (SRE) at -325 to -296 was E2-responsive. The mechanism of ligand-activated estrogen receptor alpha (ERalpha)-dependent activation of gene expression through the SRE was determined by mutational analysis of the promoter, analysis of mitogen-activated protein kinase (MAPK) pathway activation by E2, and transforming growth factor alpha (TGF-alpha) as a positive control. In addition, ERalpha-negative MDA-MB-231 breast cancer and Chinese hamster ovary cells were used as reference cell lines. The results showed that transcriptional activation of the SRE by E2 was due to ERalpha activation of the MAPK pathway and increased binding of the serum response factor and Elk-1 to the SRE. Subsequent studies with dominant negative Elk-1, wild type, and variant GAL4-Elk-1 fusion proteins confirmed that phosphorylation of Elk-1 at serines 383 and 389 in the C-terminal region of Elk-1 is an important downstream target associated with activation of an SRE by E2. Both E2 (ERalpha-dependent) and growth factors (ERalpha-independent) activated the SRE in breast cancer cells via the Ras/MAPK pathway; however, in ER-negative CHO cells that do not express a receptor for TGF-alpha, only hormone-induced activation was observed in cells transfected with ERalpha.

Protein kinase C mu selectively activates the mitogen-activated protein kinase (MAPK) p42 pathway

Here we show that human protein kinase C mu (PKC mu) activates the mitogen-activated protein kinase (MAPK). Transient expression of constitutive active PKC mu leads to an activation of Raf-1 kinase as demonstrated by in vitro phosphorylation of MAPK. PKC mu enhances transcriptional activity of a basal thymidine kinase promotor containing serum response elements (SREs) as shown by luciferase reporter gene assays. SRE driven gene activation by PKC mu is triggered by the Elk-1 ternary complex factor. PKC mu-mediated activation of SRE driven transcription can be inhibited by the MEK1 inhibitor PD98059. In contrast to the activation of the p42/ERK1 MAPK cascade, transient expression of constitutive active PKC mu does neither affect c-jun N-terminal kinase nor p38 MAPK.

Gene expression profiling of rat brain neurons reveals angiotensin II-induced regulation of calmodulin and synapsin I: possible role in neuromodulation

Angiotensin (Ang II) activates neuronal AT(1) receptors located in the hypothalamus and the brainstem and stimulates noradrenergic neurons that are involved in the control of blood pressure and fluid intake. In this study we used complementary DNA microarrays for high throughput gene expression profiling to reveal unique genes that are linked to the neuromodulatory actions of Ang II in neuronal cultures from newborn rat hypothalamus and brainstem. Of several genes that were regulated, we focused on calmodulin and synapsin I. Ang II (100 nM; 1-24 h) elicited respective increases and decreases in the levels of calmodulin and synapsin I messenger RNAs, effects mediated by AT(1) receptors. This was associated with similar changes in calmodulin and synapsin protein expression. The actions of Ang II on calmodulin expression involve an intracellular pathway that includes activation of phospholipase C, increased intracellular calcium, and stimulation of protein kinase C. Taken together with studies that link calmodulin and synapsin I to axonal transport and exocytotic processes, the data suggest that Ang II regulates these two proteins via a Ca(2+)-dependent pathway, and that this may contribute to longer term or slower neuromodulatory actions of this peptide.

PKC delta mediates ionizing radiation-induced activation of c-Jun NH(2)-terminal kinase through MKK7 in human thyroid cells

The thyroid gland is one of the most sensitive organs in ionizing radiation (IR)-induced carcinogenesis. To determine, therefore, the specific cascade of IR-induced signal transduction in human thyroid cells, we investigated the functional role of protein kinase C (PKC), especially its interlocking activation of c-Jun NH(2)-terminal kinase (JNK) pathway. In the present study, using adenovirus expression vectors for diverse dominant-negative (DN) types of PKC isoforms (alpha, beta2, delta, epsilon and zeta) expressed in primary cultured human thyroid cells, only DN/PKC delta suppressed IR-induced JNK activation. In addition, Rottlerin, a PKC delta specific inhibitor, inhibited IR-induced JNK activation. IR-induced activation of transcription factor AP-1, downstream target of JNK, was also attenuated by DN/PKC delta. To examine the involvement of upstream kinases of JNK, we performed immune-complex kinase assays of mitogen-activated protein kinase kinase 4 (MKK4) and MKK7. IR activated MKK7 but not MKK4, and this activation was inhibited by Rottlerin. Furthermore, IR-induced JNK activation was suppressed by overexpression of kinase-deficient MKK7. Our results indicate that IR selectively activates the cascade of PKC delta-MKK7-JNK-AP-1 in human thyroid cells, suggesting a not apoptotic but radio-resistant role of PKC delta in human thyroid cells following IR.

Ca2+-independent protein kinase C Apl II mediates the serotonin-induced facilitation at depressed aplysia sensorimotor synapses

At nondepressed Aplysia sensory to motor synapses, serotonin (5-HT) facilitates transmitter release primarily through a protein kinase A pathway. In contrast, at depressed Aplysia sensory to motor synapses, 5-HT facilitates transmitter release primarily through a protein kinase C (PKC)-dependent pathway. It is known that only two phorbol ester-activated PKC isoforms, the Ca(2+)-dependent PKC Apl I and the Ca(2+)-independent PKC Apl II, exist in the Aplysia nervous system. For the first time, we have now been able to functionally determine which isoform of PKC is involved in a particular form of plasticity. We microinjected cultured sensorimotor pairs of neurons with various PKC constructs tagged with the enhanced green fluorescent protein as a reporter for successful plasmid expression. Our results demonstrate that short-term facilitation of depressed synapses is mediated by PKC Apl II. Dominant-negative PKC Apl II, but not dominant-negative PKC Apl I, disrupted the normal kinetics of 5-HT-induced facilitation by completely blocking its rapid onset. This effect was specific to depressed synapses, because dominant-negative PKC Apl II did not inhibit 5-HT-mediated facilitation of nondepressed synapses. Our results suggest that not only different signal transduction pathways but also different isoforms of a specific cascade may mediate physiological responses according to the state of a synapse.

Effect of protein kinase C inhibitor (PKCI) on radiation sensitivity and c-fos transcription

PURPOSE

The human genetic disorder ataxia-telangiectasia (AT) is a multisystem disease characterized by extreme radiosensitivity. Although ionizing radiation was known to induce c-fos transcription and cellular protein kinase C (PKC) induces the expression of this immediate response gene, little is known about how mutated AT (ATM) or PKC-mediated signal transduction pathway modulates the c-fos gene transcription and gene expression. Here we have studied the effect of PKC inhibitor (PKCI) on radiation sensitivity and c-fos transcription in normal and AT cells, and also studied whether PKCI effect on c-fos occurs in Ras-dependent pathway.

METHODS AND MATERIALS

Normal (LM217) and AT (AT5BIVA) cells were transfected with PKCI expression plasmid and integration and overexpression of PKCI was evaluated by polymerase chain reaction and northern blotting, respectively. Cells were irradiated at a dose of 5 Gy/min with 137Cs irradiator and harvested 48 h after irradiation and investigated apoptosis with TUNEL method. The c-fos transcription activity was studied by performing compute assisted tomography (CAT) assay of reporter gene after transfection of c-fos CAT plasmid into LM and AT cells. Overexpression of Ras protein in transfected cells was shown by western blotting.

RESULTS

Our results demonstrated for the first time a role of PKCI on the radiation sensitivity and c-fos transcription in LM and AT cells. PKCI increased radiation induced apoptosis in LM cells (5% to 20%) but reduced apoptosis slightly in AT cells. The basal c-fos transcription activity is 70 times lower in AT cells than in LM cells. This c-fos transcription activity was repressed by overexpression of PKCI in LM cells but not in AT cells. After induction of c-fos by Ras protein, overexpression of PKCI repressed c-fos transcription in LM cells but not in AT cells.

CONCLUSIONS

Overexpression of PKCI increased radiation sensitivity and repressed c-fos transcription in LM cells but not in AT cells, and this is related with Ras. These results suggest that the effect of PKCI on c-fos transcription activity is related with Ras dependent signal transduction pathways and these mechanisms are different between normal fibroblasts, LM and ATM mutated, AT cells. The data obtained by this study provided evidence for novel transcriptional difference between LM and AT cells and this may be a reason for increased radiation sensitivity of AT cells.

Allelic exclusion and differentiation by protein kinase C-mediated signals in immature thymocytes

Pre-T cell receptor (preTCR)-derived signals mediate the transition of thymocytes from the CD4(-) CD8(-) double-negative (DN) to CD4(+) CD8(+) double-positive stage of T lymphocyte development. This progression, termed beta-selection, is limited to thymocytes that have generated a functional TCR-beta chain able to associate with pTalpha to form the preTCR complex. Formation of the preTCR complex not only induces differentiation, survival, and proliferation of DN thymocytes; it also inhibits further TCR-beta gene rearrangement through an ill-defined process known as allelic exclusion. The signaling pathways controlling this critical developmental checkpoint have not been characterized. Here we demonstrate that formation of the preTCR complex leads to the activation of protein kinase C (PKC), and that activation of PKC is necessary for the differentiation and expansion of DN thymocytes. Importantly, we also show that allelic exclusion at the TCR-beta gene loci is enforced by PKC-mediated signals. These results define PKC as a central mediator of both differentiation and allelic exclusion during thymocyte development.

Allelic exclusion and differentiation by protein kinase C-mediated signals in immature thymocytes

Pre-T cell receptor (preTCR)-derived signals mediate the transition of thymocytes from the CD4(-) CD8(-) double-negative (DN) to CD4(+) CD8(+) double-positive stage of T lymphocyte development. This progression, termed beta-selection, is limited to thymocytes that have generated a functional TCR-beta chain able to associate with pTalpha to form the preTCR complex. Formation of the preTCR complex not only induces differentiation, survival, and proliferation of DN thymocytes; it also inhibits further TCR-beta gene rearrangement through an ill-defined process known as allelic exclusion. The signaling pathways controlling this critical developmental checkpoint have not been characterized. Here we demonstrate that formation of the preTCR complex leads to the activation of protein kinase C (PKC), and that activation of PKC is necessary for the differentiation and expansion of DN thymocytes. Importantly, we also show that allelic exclusion at the TCR-beta gene loci is enforced by PKC-mediated signals. These results define PKC as a central mediator of both differentiation and allelic exclusion during thymocyte development.

Expression of the high molecular weight fibroblast growth factor-2 isoform of 210 amino acids is associated with modulation of protein kinases C delta and epsilon and ERK activation

The high molecular weight (HMW) fibroblast growth factor (FGF)-2 isoform of 210 amino acids initiated at a CUG start codon possesses a nuclear localization sequence and is not secreted. In contrast, the low molecular weight (LMW) isoform of 155 amino acids initiated at the AUG start codon can be secreted and activates the cell surface FGF receptors. The two isoforms possess different biological properties; however, little is known about the intracrine regulatory mechanisms involved in the biological effects of the HMW FGF-2 isoform. Using pancreatic cells stably transfected with cDNAs leading to the expression of either the HMW FGF-2 (A3 cells) or the LMW form (A5 cells), we provide evidence that the two FGF-2 isoforms differentially modulate PKC levels. The LMW FGF-2 up-regulated the PKC epsilon levels by 1.6-fold; by contrast the HMW isoform down-regulated the level of this PKC isotype by about 3-fold and increased the amount of PKC delta by 1.7-fold. PKC mRNAs were also modified, suggesting that PKC expression was regulated at a pretranslational level. Additionally, expression of different levels of the HMW FGF-2 with an inducible expression system confirmed the role of this isoform on PKC delta and epsilon expressions. Increased activation of ERK-1 and -2 was also observed in cells expressing the HMW FGF-2. By using different PKC inhibitors and a dominant negative PKC delta, it was found that ERK activation was PKC delta-dependent. These data indicate that expression of HMW FGF-2 can modify PKC levels by acting at the intracellular level and that the overexpression of PKC delta induces ERK-1/2 activation. The expression of a dominant negative FGFR1 did not reduce ERK-1/2 activation by the HMW FGF-2, suggesting that ERK activation does not require FGFR activity. The signaling cascade downstream of ERK might be involved in the known mitogenic effect exerted by this FGF-2 isoform.

A potential role for protein kinase C-epsilon in regulating megakaryocytic lineage commitment

Multiple studies have shown that intracellular signal transduction by the protein kinase C (PKC) family participates in the initiation of megakaryocyte differentiation. In this study, multiple approaches addressed the functional contributions by specific PKC isozymes to megakaryocytic lineage commitment of two independent cell lines, K562 and human erythroleukemia (HEL). Pharmacologic profiles of induction and inhibition of megakaryocytic differentiation in both cell lines suggested a role for the calcium-independent novel PKCs, in particular PKC-epsilon. In transfection studies, the isolated variable domain of PKC-epsilon selectively blocked exogenous activation of the megakaryocyte-specific alpha IIb promoter. Constitutively active mutants of PKC-epsilon, but not of other PKC isozymes, cooperated with the transcription factor GATA-1 in the activation of the alpha IIb promoter. The functional cooperation between GATA-1 and PKC-epsilon displayed dependence on cellular milieu, as well as on the promoter context of GATA binding sites. In aggregate, the data suggest that PKC-epsilon specifically participates in megakaryocytic lineage commitment through functional cooperation with GATA-1 in the activation of megakaryocytic promoters.

Gps2, a protein partner for human papillomavirus E6 proteins

We have used the yeast two-hybrid system to screen a cDNA library prepared from normal human epidermal keratinocytes and identified protein partners for human papilloma virus (HPV) E6 proteins. A clone that encoded Gps2 interacted with E6 proteins from HPVs of high and low oncogenic risk. The specificity of these reactions was verified and the regions of E6 that were required for interaction were mapped. Steady-state and pulse-chase analyses of cells cotransfected with DNAs expressing E6 from either HPV6 or HPV18 and Gps2 demonstrated that the E6 proteins induced the degradation of Gps2 in vivo but not in vitro. Gps2 exhibited transcriptional activation activity, and high-risk E6 suppressed this activity.