Expression of protein kinase C isoforms in smooth muscle cells in various states of differentiation

Cigarette smoke extract stimulates rat pulmonary artery smooth muscle cell proliferation via PKC-PDGFB signaling

Accumulating evidence suggests a direct role for cigarette smoke in pulmonary vascular remodeling, which contributes to the development of pulmonary hypertension. However, the molecular mechanisms underlying this process remain poorly understood. Platelet-derived growth factor (PDGF) is a potential mitogen and chemoattractant implicated in several biological processes, including cell survival, proliferation, and migration. In this study, we investigated the effect of cigarette smoke extract (CSE) on cell proliferation of rat pulmonary artery smooth muscle cells (rPASMCs). We found that stimulation of rPASMCs with CSE significantly increased cell proliferation and promoted cell cycle progression from G1 phase to the S and G2 phases. CSE treatment also significantly upregulated the mRNA and protein levels of PDGFB and PDGFRβ. Our study also revealed that Rottlerin, an inhibitor of PKCδ signaling, prevented CSE-induced cell proliferation, attenuated the increase of S and G2 phase populations induced by CSE treatment, and downregulated PDGFB and PDGFRβ mRNA and protein levels in rPASMCs exposed to CSE. Collectively, our data demonstrated that CSE-induced cell proliferation of rPASMCs involved upregulation of the PKCδ-PDGFB pathway.

Determination of PKC isoform-specific protein expression in pulmonary arteries of rats with chronic hypoxia-induced pulmonary hypertension

Background

Evidence indicates that protein kinase C (PKC) plays a pivotal role in hypoxia-induced pulmonary hypertension (PH), but PKC isoform-specific protein expression in pulmonary arteries and their involvement in hypoxia-induced PH are unclear.

Material/Methods

Male SD rats (200–250 g) were exposed to normobaric hypoxia (10% oxygen) for 1, 3, 7, 14 and 21 d (days) to induce PH. PKC isoform-specific membrane translocation and protein expression in pulmonary arteries were determined by using Western blot and immunostaining.

Results

We found that only 6 isoforms of conventional PKC (cPKC) α, βI and βII, and novel PKC (nPKC) δ, ɛ and η were detected in pulmonary arteries of rats by Western blot. Hypoxic exposure (1–21 d) could induce rat PH with right ventricle (RV) hypertrophy and vascular remodeling. The cPKCβII membrane translocation at 3–7 d and protein levels of cPKCα at 3–14 d, βI and βII at 1–21 d decreased, while the nPKCδ membrane translocation at 3–21 d and protein levels at 3–14 d after hypoxic exposure in pulmonary arteries increased significantly when compared with that of the normoxia control group (p<0.05 vs. 0 d, n=6 per group). In addition, the down-regulation of cPKCα, βI and βII, and up-regulation of nPKCδ protein expressions at 14 d after hypoxia were further confirmed by immunostaining.

Conclusions

This study is the first systematic analysis of PKC isoform-specific membrane translocation and protein expression in pulmonary arteries, suggesting that the changes in membrane translocation and protein expression of cPKCα, βI, βII and nPKCδ are involved in the development of hypoxia-induced rat PH.

Thrombin induces EGF receptor expression and cell proliferation via a PKC(delta)/c-Src-dependent pathway in vascular smooth muscle cells

OBJECTIVE

Thrombin upregulates expression of several proteins in vascular smooth muscle cells (VSMCs) which may contribute to atherosclerosis. Here, we investigated the mechanisms underlying thrombin-induced EGF receptor (EGFR) expression and its effect on VSMCs.

METHODS AND RESULTS

Normal rat VSMCs were used. First, Western blotting and RT-PCR analyses showed that thrombin induces the expression of EGFR at transcription and translation levels in VSMCs. Second, pharmacological inhibitors, dominant negative mutants, and short hairpin RNA interference (shRNA) technology enabled us to demonstrate that thrombin-induced EGFR expression is mediated through PKC(delta)/c-Src-dependent transactivation of EGFR linking to PI3K/Akt and ERK1/2. We further investigated whether the transcription factors AP-1 and NF-kappaB are involved in this response by a promoter assay. Finally, data obtained by using EGFR shRNA technology and XTT assay demonstrated that thrombin-enhanced VSMC proliferation was mediated through upregulation of EGFR.

CONCLUSIONS

Our results demonstrate that thrombin-enhanced VSMC proliferation was mediated through upregulation of EGFR via a PKC(delta)/c-Src-dependent transactivation of EGFR, PI3K-Akt, and ERK, and AP-1/NF-kappaB pathway.

Independent beta-arrestin2 and Gq/protein kinase Czeta pathways for ERK stimulated by angiotensin type 1A receptors in vascular smooth muscle cells converge on transactivation of the epidermal growth factor receptor

Recent studies in receptor-transfected cell lines have demonstrated that extracellular signal-regulated kinase (ERK) activation by angiotensin type 1A receptor and other G protein-coupled receptors can be mediated by both G protein-dependent and β-arrestin-dependent mechanisms. However, few studies have explored these mechanisms in primary cultured cells expressing endogenous levels of receptors. Accordingly, here we utilized the β-arrestin biased agonist for the angiotensin type 1A receptor, SII-angiotensin (SII), and RNA interference techniques to investigate angiotensin II (ANG)-activated β-arrestin-mediated mitogenic signaling pathways in rat vascular smooth muscle cells. Both ANG and SII induced DNA synthesis via the ERK activation cascade. Even though SII cannot induce calcium influx (G protein activation) after receptor stimulation, it does cause ERK activation, although less robustly than ANG. Activation by both ligands is diminished by depletion of β-arrestin2 by small interfering RNA, although the effect is more complete with SII. ERK activation at early time points but not later time points is strongly inhibited by those protein kinase C inhibitors that can block protein kinase Cζ. Moreover, ANG- and SII-mediated ERK activation require transactivation of the epidermal growth factor receptor via metalloprotease 2/9 and Src kinase. β-Arrestin2 facilitates ANG and SII stimulation of Src-mediated phosphorylation of Tyr-845 on the EGFR, a known site for Src phosphorylation. These studies delineate a convergent mechanism by which G protein-dependent and β-arrestin-dependent pathways can independently mediate ERK-dependent transactivation of the EGFR in vascular smooth muscle cells thus controlling cellular proliferative responses.

Complex regulation of store-operated Ca2+entry pathway by PKC-ε in vascular SMCs

The role of PKC in the regulation of store-operated Ca2+entry (SOCE) is rather controversial. Here, we used Ca2+-imaging, biochemical, pharmacological, and molecular techniques to test if Ca2+-independent PLA2β (iPLA2β), one of the transducers of the signal from depleted stores to plasma membrane channels, may be a target for the complex regulation of SOCE by PKC and diacylglycerol (DAG) in rabbit aortic smooth muscle cells (SMCs). We found that the inhibition of PKC with chelerythrine resulted in significant inhibition of thapsigargin (TG)-induced SOCE in proliferating SMCs. Activation of PKC by the diacylglycerol analog 1-oleoyl-2-acetyl- sn-glycerol (OAG) caused a significant depletion of intracellular Ca2+stores and triggered Ca2+influx that was similar to TG-induced SOCE. OAG and TG both produced a PKC-dependent activation of iPLA2β and Ca2+entry that were absent in SMCs in which iPLA2β was inhibited by a specific chiral enantiomer of bromoenol lactone ( S-BEL). Moreover, we found that PKC regulates TG- and OAG-induced Ca2+entry only in proliferating SMCs, which correlates with the expression of the specific PKC-ε isoform. Molecular downregulation of PKC-ε impaired TG- and OAG-induced Ca2+influx in proliferating SMCs but had no effect in confluent SMCs. Our results demonstrate that DAG (or OAG) can affect SOCE via multiple mechanisms, which may involve the depletion of Ca2+stores as well as direct PKC-ε-dependent activation of iPLA2β, resulting in a complex regulation of SOCE in proliferating and confluent SMCs.

Endothelin-1 signalling in vascular smooth muscle: pathways controlling cellular functions associated with atherosclerosis

Atherosclerosis is the primary ischaemic vascular condition underlying a majority of cardiovascular disease related deaths. Endothelin-1 is a vasoactive peptide agent upregulated in atherosclerosis and in conjunction with its G protein-coupled receptors exerts diverse actions on all cells of the vasculature in particular vascular smooth muscle cells (VSMC). The effects of endothelin-1 include cell proliferation, migration and contraction, and the induction of extracellular matrix components and growth factors. VSMC as the major component of the neointima in atherosclerotic plaques accordingly play a key role in atherogenesis. In this review we examine classic and novel signalling pathways activated by endothelin-1 in VSMC (including phospholipase C, adenylate cyclase, Rho kinase, transactivation of receptor tyrosine kinases, mitogen activated protein kinase cascades and beta-arrestin) and their likely impact on the development and progression of atherosclerosis.

Protein kinase C isoform expression as a predictor of disease outcome on endocrine therapy in breast cancer

BACKGROUND

Although in vitro breast cancer models have demonstrated a role for protein kinase C (PKC) alpha and delta isoforms in endocrine insensitivity and resistance respectively, there is currently little clinical evidence to support these observations.

AIMS

To define the pattern of PKC alpha and delta expression using breast cancer cell lines, with and without endocrine resistance, and also breast cancer samples, where expression can be correlated with clinicopathological and endocrine therapy outcome data.

METHODS

PKC isoform expression was examined in tamoxifen responsive, oestrogen receptor positive (ER(+)), ER(+) acquired tamoxifen resistant (TAM-R) and oestrogen receptor negative (ER(-)) cell lines by western blotting and immunocytochemical analysis. PKC isoform expression was then examined by immunohistochemistry in archival breast cancer specimens from primary breast cancer patients with known clinical outcome in relation to endocrine response and survival on therapy.

RESULTS

ER(+) breast cancer cell lines expressed considerable PKC-delta but barely detectable levels of PKC-alpha, whereas ER(-) cell lines expressed PKC-alpha but little PKC-delta. ER(+) acquired TAM-R cell lines expressed substantial levels of both PKC-alpha and delta. In clinical samples, high PKC-delta expression correlated to endocrine responsiveness whereas PKC-alpha expression correlated to ER negativity. PKC-delta was an independent predictor of duration of response to therapy. Patients showing a PKC-delta(+)/PKC-alpha(-) phenotype had a six times longer endocrine response than patients with the PKC-delta(+)/ PKC-alpha(+) phenotype (equating to tamoxifen resistance in vitro).

CONCLUSIONS

Levels of PKC-alpha and delta expression appear to be indicative of response to anti-oestrogen therapy and could be useful in predicting a patient's suitability for endocrine therapy.

Possible role of nitric oxide in the pathogenesis of pulmonary hypertension in broilers: a synopsis

Nitric oxide (NO) produced by vascular endothelial cells is an important determinant of the basal tone of small arteries and arterioles. Impaired endothelial NO production has been implicated in the pathophysiology of pulmonary hypertension in humans. Available data suggest that reduction of endothelial NO synthesis, with evidence of reduced endothelial NO synthase expression in pulmonary arterioles, is associated with increased pulmonary vasomotor tone and vascular remodelling in hypertensive broilers. Supplemental l-arginine, a precursor of NO, has been shown to induce flow-dependent pulmonary vasodilation, to prevent reduced endothelial NO synthase expression and to inhibit vascular remodelling in broilers with pulmonary hypertension. Nevertheless, its effect on pulmonary hypertension syndrome incidence is limited. It appears that impaired production of NO is a secondary rather than a causative factor in the pathogenesis of pulmonary hypertension in broilers.

Activation of PKCalpha and pulmonary vascular remodelling in broilers

OBJECTIVE

The present study was conducted to examine the presence of protein kinase Calpha (PKCalpha) in the pulmonary arterioles of broilers during the development of pulmonary hypertension and pulmonary vascular remodelling.

METHOD

One hundred and sixty day-old Avian-2000 broilers were divided equally into a control group and a cold temperature group. All the birds were reared in normal temperatures up to day 14, with the lighting schedule at 24 h per day. Thereafter, birds in the cold temperature group were subjected to low temperature by lowering 1-2 degrees C per day to 12-14 degrees C, and then kept constant until day 49, while birds in the control group were still brooded at normal temperatures. All the birds were fed a diet of pellets throughout the study. Samples of blood were taken from the wing vein, and of heart and lung collected after the birds were killed with an overdose of sodium pentobarbitial, at days 24, 32, 39 and 45 of age, respectively. Right ventricle to total ventricle ratio (RV/TV) and packed cell volume (PCV) were measured. Vessel wall area to vessel total area ratio (WA/TA) and mean media thickness in pulmonary arterioles (mMTPA) was examined using computer-image analytic software. Expression of PKC in pulmonary muscular arterioles was assessed by immunohistochemistry and quantified by measuring optical density (OD) using computer-image analytic software.

RESULTS

The incidence of pulmonary hypertension syndrome (PHS) was 12.5% in birds exposed to cold, and 3.75% in the control group (P<0.05). PCV in the cold temperature group was elevated after day 32 (P<0.05), and RV/TV ratio increased on day 45 (P<0.05). Both the WA/TA and mMTPA of birds subjected to cold were significantly elevated (P<0.05). The OD values were not significantly increased before day 32 (P>0.05), however, one week later (at day 39 of age), the difference between the two groups was significant (P<0.05). The increased PKCalpha expression was positively correlated with the values of mMTPA and WA/TA.

CONCLUSION

PKCalpha expression was up-regulated during the development of pulmonary hypertension. The activation of PKCalpha might be involved in the development of pulmonary vascular remodelling.

Differential regulation by Ca(2+) of calmodulin- and PKC-dependent contractile pathways in cat lower oesophageal sphincter

1. In the present investigation we examined the regulation of calmodulin (CaM)- and protein kinase C (PKC)-dependent pathways by cytosolic Ca(2+) in the contraction of cat lower oesophageal sphincter (LES). 2. Force developed in response to increasing doses of acetylcholine (ACh) was directly related to the increase of the [Ca(2+)](i) measured by fura-2. Thapsigargin, which depletes Ca(2+) stores, reduced the contraction and the [Ca(2+)](i). In addition, contraction in response to maximal ACh was reduced by the CaM inhibitor CGS9343B but not by the PKC inhibitor chelerythrine. The contraction in response to submaximal ACh was reduced by chelerythrine but not by CGS9343B. 3. In permeabilized cells, the contraction in response to low Ca(2+) (0.54 microm) was also reduced by CGS9343B. 4. The response to high Ca(2+) (1.0 microm) was reduced by CGS9343B. ACh also inhibited PKC activation induced by diacylglycerol, which activation is inhibited by the N-myristoylated peptide inhibitor derived from pseudosubstrate sequences of PKCalphabetagamma (myr-PKC-alphabetagamma), but not of myr-PKC-alpha. 5. These data are consistent with the view that activated CaM-dependent pathways inhibit PKC-dependent pathways, this switch mechanism might be regulated by Ca(2+) in the LES.

Angiotensin II-induced protein kinase D activation is regulated by protein kinase Cdelta and mediated via the angiotensin II type 1 receptor in vascular smooth muscle cells

OBJECTIVE

Angiotensin II (Ang II), through its specific signaling cascades, exerts multiple effects on vascular smooth muscle cells (SMCs). It has been shown that Ang II stimulates activation of protein kinase D (PKD), a member of a new class of serine-threonine kinases. However, little is known regarding the upstream cascade of the intracellular signaling that leads to PKD activation. In the present study, we investigated upstream molecules that mediate Ang II-induced PKD activation in SMCs.

METHODS AND RESULTS

Protein kinase C (PKC) inhibitors completely block Ang II-induced PKD activation, and pretreatment with phorbol 12,13-dibutyrate downregulates Ang II-induced PKD activation, indicating that classical or novel isoforms of PKC mediate Ang II-induced PKD activation. Furthermore, the finding that rottlerin, a PKCdelta-specific inhibitor, blocks PKD activation suggests that PKCdelta, a member of novel PKCs, mediates Ang II-induced PKD activation. By using dominant-negative approaches, our results demonstrate that expression of the dominant-negative PKCdelta, but neither the dominant-negative form of PKCepsilon nor PKCzeta, inhibits PKD activation. These results further substantiate the finding that Ang II-induced PKD activation is mediated by PKCdelta. Moreover, using selective Ang II receptor antagonists, our data show that the Ang II type 1 (AT1) receptor but not the AT2 mediates Ang II-stimulated PKD activation.

CONCLUSIONS

This study reveals for the first time that Ang II-induced PKD activation is mediated via AT1 and regulated by PKCdelta in living cells. These data may provide new insights into molecular mechanisms involved in Ang II-induced physiological and pathological events.

Synergistic effects of adenosine A1 and P2Y receptor stimulation on calcium mobilization and PKC translocation in DDT1 MF-2 cells

1. The effect of adenosine analogues and of nucleotides, alone or in combination, on intracellular calcium, accumulation of inositol (1,4,5) trisphosphate (InsP3), and on activation of protein kinase C (PKC) was studied in DDT1 MF2 cells derived from a Syrian hamster myosarcoma. These cells were found to express mRNA for A1 and some as yet unidentified P2Y receptor(s). 2. Activation of either receptor type stimulated the production of InsP3 and raised intracellular calcium in DDT1 MF2 cells. Similarly, the A1 selective agonist N6-cyclopentyladenosine (CPA) increased PKC-dependent phosphorylation of the substrate MBP(4-14) and induced a PKC translocation to the plasma membrane as determined using [3H]-phorbol dibutyrate (PDBu) binding in DDT1 MF-2 cells. However, neither adenosine nor CPA induced a significant translocation of transiently transfected gamma-PKC-GFP from the cytosol to the cell membrane. In contrast to adenosine analogues, ATP and UTP also caused a rapid but transient translocation of gamma-PKC-GFP and activation of PKC. 3. Doses of the A1 agonist CPA and of ATP or UTP per se caused barely detectable increases in intracellular Ca2+ but when combined, they caused an almost maximal stimulation. Similarly, adenosine (0.6 microM) and UTP (or ATP, 2.5 microM), which per se caused no detectable translocation of either gamma- or epsilon-PKC-GFP, caused when combined a very clear-cut translocation of both PKC subforms, albeit with different time courses. These results show that simultaneous activation of P2Y and adenosine A1 receptors synergistically increases Ca2+ transients and translocation of PKC in DDT1 MF-2 cells. Since adenosine is rapidly formed by breakdown of extracellular ATP, such interactions may be biologically important.

Thrombin rapidly induces protein kinase D phosphorylation, and protein kinase C delta mediates the activation

Thrombin plays a critical role in hemostasis, thrombosis, and inflammation. However, the responsible intracellular signaling pathways triggered by thrombin are still not well defined. We report here that thrombin rapidly and transiently induces activation of protein kinase D (PKD) in aortic smooth muscle cells. Our data demonstrate that protein kinase C (PKC) inhibitors completely block thrombin-induced PKD activation, suggesting that thrombin induces PKD activation via a PKC-dependent pathway. Furthermore, our results show that thrombin rapidly induces PKC delta phosphorylation and that the PKC delta-specific inhibitor rottlerin blocks thrombin-induced PKD activation, suggesting that PKC delta mediates the thrombin-induced PKD activation. Using dominant negative approaches, we demonstrated that expression of a dominant negative PKC delta inhibits the phosphorylation and activation of PKD induced by thrombin, whereas neither PKC epsilon nor PKC zeta affects thrombin-induced PKD activation. In addition, our results of co-immunoprecipitation assays showed that PKD forms a complex with PKC delta in smooth muscle cells. Taken together, the findings of the present study demonstrate that thrombin induces activation of PKD and reveal a novel role of PKC delta in mediating thrombin-induced PKD activation in vascular smooth muscle cells.

Induction of apoptosis by protein kinase C delta is independent of its kinase activity

Protein kinase C, a multigene family of phospholipid-dependent and diacylglycerol-activated Ser/Thr protein kinases, is a key component in many signal transduction pathways. The kinase activity was thought to be essential for a plethora of biological processes attributed to these enzymes. Here we show that at least one protein kinase C function, the induction of apoptosis by protein kinase C delta, is independent of the kinase activity. Stimulation of green fluorescent protein-protein kinase C delta fusion protein with phorbol ester or diacylglycerol led to its redistribution within seconds after the stimulus. Membrane blebbing, an early hallmark of apoptosis, was visible as early as 20 min after stimulation, and nuclear condensation was visible after 3-5 h. Apoptosis could be inhibited by expression of Bcl-2 but not by specific protein kinase C inhibitors. In addition, a kinase-negative mutant of protein kinase C delta also induced apoptosis to the same extent as the wild type enzyme. Apoptosis was confined to the protein kinase C delta-overexpressing cells. Stimulation of overexpressed protein kinase C epsilon did not result in increased apoptosis. Our results indicate that distinct protein kinase C isozymes induce apoptosis in vascular smooth muscle cells. More importantly, they show that some protein kinase C effector functions are independent of the catalytic activity.

Activation of protein kinase Czeta is essential for cytokine-induced metalloproteinase-1, -3, and -9 secretion from rabbit smooth muscle cells and inhibits proliferation

Several matrix metalloproteinases (MMPs), including MMP-1, -3, and -9, mediate matrix destruction during chronic inflammatory diseases such as arthritis and atherosclerosis. MMP up-regulation by inflammatory cytokines involves interactions between several transcription factors, including activator protein-1 and nuclear factor kappaB (NF-kappaB). The upstream regulatory pathways are less well understood. We investigated the role of isoforms of protein kinase C (PKC) in basic fibroblast growth factor- and interleukin-1alpha-mediated MMP production from cultured rabbit aortic smooth muscle cells. A synthetic PKC inhibitor, RO318220, inhibited MMP-1, -3, and -9 production by 89 +/- 3, 75 +/- 18, and 89 +/- 9%, respectively. However, down-regulation of conventional and novel isoforms did not inhibit but rather increased MMP-9 production by 48 +/- 16%, implicating an atypical PKC isoform. Consistent with this, PKCzeta protein levels and activity were stimulated 3.3- and 13-fold, respectively, by basic fibroblast growth factor plus interleukin-1alpha and antisense oligonucleotides to PKCzeta significantly decreased MMP-9 formation by 62 +/- 18% compared with scrambled sequences. Moreover, adenovirus-mediated overexpression of a dominant-negative (DN) PKCzeta reduced MMP-1, -3, and -9 production by 78 +/- 9, 76 +/- 8, and 76 +/- 5%, respectively. DN-PKCzeta inhibited NF-kappaB DNA binding but did not affect ERK1/2 activation or AP-1 binding. Antisense PKCzeta oligonucleotides and DN-PKCzeta stimulated cell proliferation by 89 +/- 14% (n = 4) and 305 +/- 74% (n = 3), respectively (both p < 0.05). Our results show that PKCzeta is essential for cytokine-induced up-regulation of MMP-1, -3, and -9, most likely by activating NF-kappaB. Selective inhibition of PKCzeta is therefore a possible strategy to inhibit MMP production in inflammatory diseases such as atherosclerosis.

Protein kinase C isoforms and A1 adenosine receptors in porcine coronary smooth muscle cells

We have previously reported that prolonged exposure of porcine coronary arteries to adenosine agonists upregulates protein kinase C (PKC) through the activation of adenosine A1 receptor-coupled to pertussis toxin sensitive G-protein(s) [Am. J. Physiol. 264 (1993) H1465; Am. J. Physiol. 269 (1995) H1619]. The mechanism(s) by which A1 adenosine receptor upregulates PKC (isoforms) are not yet clearly understood. In the present study, we identified the alpha, beta 1, beta 2, gamma, epsilon, and zeta PKC isoforms that were upregulated by adenosine A1 receptor agonist as a possible mechanism(s) involved for this upregulation. Incubation of porcine coronary smooth muscle cells (PCSMC) with adenosine A1 receptor agonist (2s)-N6-[2-endo-norbornyl]adenosine (ENBA) caused an upregulation of PKC (isoforms), which were blocked by adenosine A1 receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX). Western blot analysis using specific antibodies to PKC isoforms indicated that all the isoforms tested (alpha, beta I, beta II, mu, gamma, delta, epsilon, and zeta) were present in the primary cultured smooth muscle cells from porcine coronary artery. Western blot studies indicated that PKC alpha, beta I, beta II, gamma, epsilon, and zeta isoforms were upregulated in a dose dependent manner by adenosine agonist (ENBA) and PKC delta and mu were not altered.

UDP acts as a growth factor for vascular smooth muscle cells by activation of P2Y(6) receptors

Mitogenic effects of the extracellular nucleotides ATP and UTP are mediated by P2Y(1), P2Y(2), and P2Y(4) receptors. However, it has not been possible to examine the highly expressed UDP-sensitive P2Y(6) receptor because of the lack of stable, selective agonists. In rat aorta smooth muscle cells (vascular smooth muscle cells; VSMC), UDP and UTP stimulated (3)H-labeled thymidine incorporation with similar pEC(50) values (5.96 and 5.69). Addition of hexokinase did not reduce the mitogenic effect of UDP. In cells transfected with P2Y receptors the stable pyrimidine agonist uridine 5'-O-(2-thiodiphosphate) (UDPbetaS) was specific for P2Y(6) with no effect on P2Y(1), P2Y(2), or P2Y(4) receptors. UDPbetaS stimulated [(3)H]thymidine and [(3)H]leucine incorporation and increased cell number in VSMC. Flow cytometry demonstrated that UDP stimulated cell cycle progression to both the S and G(2) phases. The intracellular signal pathways were dependent on phospholipase C, possibly protein kinase C-delta, and a tyrosine kinase pathway but independent of G(i) proteins, eicosanoids, and protein kinase A. The half-life of P2Y(6) receptor mRNA was <1 h by competitive RT-PCR. The mitogen-activated protein kinase kinase inhibitor PD-098059 significantly suppressed, whereas ATP and interleukin-1beta upregulated, expression of P2Y(6) receptor mRNA. The results demonstrate that UDP stimulates mitogenesis through activation of P2Y(6) receptors and that the receptor is regulated by factors important in the development of vascular disease.

Histamine-induced vasoconstriction involves phosphorylation of a specific inhibitor protein for myosin phosphatase by protein kinase C alpha and delta isoforms

Histamine stimulus triggers inhibition of myosin phosphatase-enhanced phosphorylation of myosin and contraction of vascular smooth muscle. In response to histamine stimulation of intact femoral artery, a smooth muscle-specific protein called CPI-17 (for protein kinase C-potentiated inhibitory protein for heterotrimeric myosin light chain phosphatase of 17 kDa) is phosphorylated and converted to a potent inhibitor for myosin phosphatase. Phosphorylation of CPI-17 is diminished by pretreatment with either or GF109203x, suggesting involvement of multiple kinases (Kitazawa, T., Eto, M., Woodsome, T. P., and Brautigan, D. L. (2000) J. Biol. Chem. 275, 9897--9900). Here we purified and identified CPI-17 kinases endogenous to pig artery that phosphorylate CPI-17. DEAE-Toyopearl column chromatography of aorta extracts separated two CPI-17 kinases. One kinase was protein kinase C (PKC) alpha, and the second kinase was purified to homogeneity as a 45-kDa protein, and identified by sequencing as PKC delta. Purified PKC delta was 3-fold more reactive with CPI-17 compared with myelin basic protein, whereas purified PKC alpha and recombinant RhoA-activated kinases (Rho-associated coiled-coil forming protein Ser/Thr kinase and protein kinase N) showed equal activity with CPI-17 and myelin basic protein. inhibited CPI-17 phosphorylation by purified PKC delta with IC(50) of 0.6 microm (in the presence of 0.1 mm ATP) or 14 microm (2.0 mm ATP). significantly suppressed CPI-17 phosphorylation in smooth muscle cells, and the contraction of permeabilized rabbit femoral artery induced by stimulation with phorbol ester. GF109203x inhibited phorbol ester-induced contraction of rabbit femoral artery by 80%, whereas a PKC alpha/beta inhibitor, Go6976, reduced contraction by 47%. The results imply that histamine stimulation elicits contraction of vascular smooth muscle through activation of PKC alpha and especially PKC delta to phosphorylate CPI-17.

Translocation of PKC isoforms in bovine aortic smooth muscle cells exposed to strain

Our laboratory has previously reported that the exposure of smooth muscle cells (SMC) to the cyclic strain results in significant stimulation of protein kinase C (PKC) activity by translocating the enzyme from the cytosol to the particulate fraction. We now sought to examine the strain-induced translocation of individual PKC isoforms in SMC. Confluent bovine aortic SMC grown on collagen type I-coated plates were exposed to cyclic strain for up to 100 s at average 10% strain with 60 cycles/min. Immunoblotting analysis demonstrates that SMC express PKC-alpha, -beta and -zeta in both cytosolic and particulate fractions. Especially, PKC-alpha and -zeta were predominantly expressed in the cytosolic fraction. However, cyclic strain significantly (P < 0.05) increased PKC-alpha and -zeta in the particulate fraction and decreased in the cytosolic fraction. Thus, the cyclic strain-mediated stimulation of PKC activity in SMC may be due to the translocation of PKC-alpha and -zeta from the cytosolic to the particulate fraction. These results demonstrate that mechanical deformation causes rapid translocation of PKC isoforms, which may initiate a cascade of proliferation responses of SMC since NF-kappaB, which is involved in the cellular proliferation has been known to be activated by these PKC isoforms.

Stimulation of nucleoside efflux and inhibition of adenosine kinase by A1 adenosine receptor activation

Adenosine is produced intracellularly during conditions of metabolic stress and is an endogenous agonist for four subtypes of G-protein linked receptors. Nucleoside transporters are membrane-bound carrier proteins that transfer adenosine, and other nucleosides, across biological membranes. We investigated whether adenosine receptor activation could modulate transporter-mediated adenosine efflux from metabolically stressed cells. DDT1 MF-2 smooth muscle cells were incubated with 10 microM [3H]adenine to label adenine nucleotide pools. Metabolic stress with the glycolytic inhibitor iodoacetic acid (1AA, 5 mM) increased tritium release by 63% (P < 0.01), relative to cells treated with buffer alone. The IAA-induced increase was blocked by the nucleoside transport inhibitor nitrobenzylthioinosine (1 microM), indicating that the increased tritium release was primarily a purine nucleoside. HPLC verified this to be [3H]adenosine. The adenosine A1 receptor selective agonist N6-cyclohexyladenosine (CHA, 300 nM) increased the release of [3H]purine nucleoside induced by IAA treatment by 39% (P < 0.05). This increase was blocked by the A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (10 microM). Treatment of cells with UTP (100 microM), histamine (100 microM), or phorbol-12-myristate-13-acetate (PMA, 10 microM) also increased [3H]purine nucleoside release. The protein kinase C inhibitor chelerythrine chloride (500 nM) inhibited the increase in [3H]purine nucleoside efflux induced by CHA or PMA treatment. The adenosine kinase activity of cells treated with CHA or PMA was found to be decreased significantly compared with buffer-treated cells. These data indicated that adenosine A1 receptor activation increased nucleoside efflux from metabolically stressed DDT1 MF-2 cells by a PKC-dependent inhibition of adenosine kinase activity.

Protein kinase c-dependent pathway is critical for the production of pro-inflammatory cytokines (TNF-alpha, IL-1beta, IL-6)

The authors hypothesized that certain PKC isoforms play an important role in the induction of pro-inflammatory cytokine (TNF-alpha, IL-1beta, IL-6) synthesis. To test this hypothesis, the cytosol-to-membrane translocation of select PKC isoforms with tested cytokine production in human monocytes cultured in vitro was correlated. It is reported that in monocytes treated with phorbol ester (PMA), translocation of PKC isoforms alpha, betaII, delta and epsilon precede cytokine synthesis. Moreover, specific inhibition of PKC translocation that occurs in the presence of Calphostin C is reflected in downstream events: lack of MAP kinases phosphorylation, loss of DNA binding ability by AP-1 transcription factor, and the reduction of pro-inflammatory cytokine synthesis. Thus, the cytosol-to-membrane translocation of PKC isoforms alpha, betaII, delta and epsilon with the subsequent activation of: (1) MAP kinases; and (2) AP-1 transcription factor, may represent critical steps in the induction of signalling cascade leading to TNF-alpha, IL-1beta, IL-6 synthesis in human monocytes.

Distribution of active protein kinase C in smooth muscle

To localize activated protein kinase C (PKC) in smooth muscle cells, an antibody directed to the catalytic site of the enzyme was used to assess PKC distribution by immunofluorescence techniques in gastric smooth muscle cells isolated from Bufo marinus. An antibody to vinculin was used to delineate the cell membrane. High-resolution three-dimensional images of immunofluorescence were obtained from a series of images collected through focus with a digital imaging microscope. Cells were untreated or treated with agents that increase PKC activity (10 microM carbachol for 1 min, 1 microM phorbol 12-myristate 13-acetate (PMA) for 10 min), or have no effect on PKC activity (1 micrometer 4-alpha phorbol, 12,13-didecanoate (4-alpha PMA)). In unstimulated cells, activated PKC and vinculin were located and organized at the cell surface. Cell cytosol labeling for activated PKC was sparse and diffuse and was absent for vinculin. After treatment with carbachol, which stimulates contraction and PKC activity, in addition to the membrane localization, the activated PKC exhibited a pronounced cytosolic fibrillar distribution and an increased total fluorescence intensity relative to vinculin. The distributions of activated PKC observed after PMA but not 4-alpha PMA were similar to those observed with carbachol. Our results indicate that in resting cells there is a pool of activated PKC near the cell membrane, and that after stimulation activated PKC is no longer membrane-confined, but is present throughout the cytosol. Active PKC appears to associate with contractile filaments, supporting a possible role in modulation of contraction.

Protein kinase C promotes spontaneous relaxation of streptolysin-O-permeabilized smooth muscle cells from the guinea-pig stomach

Isolated single smooth muscle cells from the fundus of a guinea-pig stomach were permeabilized by use of streptolysin-O (0.5 U/ml). Most of the permeabilized cells responded to 0.6 microM Ca2+, but not to 0.2 microM Ca2+, with a resulting maximal cell shortening to approximately 71% of the resting cell length. These cells were relaxed again by washing with the Ca2+-free solution (2.5 nM free Ca2+) for 3-5 min. Addition of 10 microM acetylcholine (ACh) resulted in both a marked decrease in the concentration of Ca2+ required to trigger a threshold response and an increase in the maximal cell shortening, indicating that the cells retained the muscarinic receptor function. When the cell treated with a protein kinase C (PKC) inhibitor, K-252b (1 microM), for 3 min was exposed to 10 microM ACh in the presence of K-252b, the cell shortened within 2 min with a maximal cell shortening. When the cell shortening was induced by 10 microM ACh plus 1 microM Ca2+ in the presence of K-252b (1 microM) or more selective PKC inhibitors, such as calphostin C (1 microM) or PKC pseudosubstrate peptide (100 microM), the extension of the shortened cells, by washing with the Ca2+-free solution, was significantly inhibited. In contrast, K-252b (1 microM) did not inhibit the relaxation of Ca2+-induced shortened cells. These results suggest that the receptor-mediated activation of PKC in the process of ACh-induced cell shortening plays a role in the subsequent relaxation of the shortened cells.

PKC-dependent signalling mechanisms in differentiated smooth muscle

Protein kinase C (PKC) is now known to play an important physiological role in essentially all cell types. This review will focus on what is known about the kinase in contractile differentiated smooth muscle. Current knowledge on the molecular structure of PKC isoforms will be discussed as they relate to mechanisms of translocation and targeting of the kinase within smooth muscle cells. Studies performed on PKC-dependent signalling pathways in differentiated smooth muscle cells will be discussed with emphasis on studies form our laboratory, especially discussing thin filament linked pathways. Thick filament linked PKC-dependent pathways will be described in more detail elsewhere in this monograph.

Stimulation of melanogenesis in a human melanoma cell line by bistratene A

The polyether toxin, bistratene A, induced morphological and functional differentiation of a human melanoma cell line (MM96E). The cells became blocked at the G2/M transition and elaborated a number of processes. Tyrosinase activity and melanin content were substantially increased. Northern blot analysis showed up-regulation of mRNA for several genes known to be involved in melanin biosynthesis (pmel17, pmel34, and tyrosinase related proteins, TRP-1 and TRP-2). Bistratene A induced the phosphorylation of several proteins as assessed by 2D gel electrophoresis and one of these was identified as stathmin (oncoprotein 18), a cell-cycle regulated phosphoprotein. Bistratene A specifically induced the translocation of protein kinase Cdelta (PKCdelta) from a soluble to a particulate fraction without affecting other isoforms. These results implicate a role for protein kinase Cdelta in the induction of differentiation of this human melanoma cell line.

An in vitro test system for differentiation between antiproliferative and toxic effects in vascular smooth muscle cells

We describe an in vitro test system looking for four endpoints in vascular smooth muscle cells (SMC): toxicity (cell number), DNA synthesis, reversibility of effects, and specificity of effects for SMC. SMC cultures at a low cell density, either actively proliferating or arrested by serum starvation and stimulated with 10% or 2% fetal calf serum (FCS) in parallel to treatment, are subject to a 52-h treatment phase with a test compound. Cultures were labeled with bromodeoxyuridine during the last 4 h of the treatment phase. Thereafter, the cultures are divided into two groups. In the first group, directly following treatment with a test compound, the cell number of the cultures is determined indirectly by using the vital dye neutral red. Subsequently, in the same cultures DNA synthesis is measured with an antibody directed to bromodeoxyuridine. The second group of cultures is reincubated with normal growth medium without test drug for a further 24 h. This recovery period is followed by determination of cell number and DNA synthesis as described above. This procedure allows determination of reversibility of effects observed directly after treatment giving important information for differentiation between toxic and antiproliferative mechanisms resulting in the reduction of DNA synthesis.

Regulation of protein kinase C in the muscular layer of human placental stem villi vessels

Protein kinase C (PKC) activity in the muscular layer of stem villi vessels from the human term placenta was studied. Resting state PKC activity was distributed evenly between the cytosol and the particulate fractions. Upon stimulation by three different activators, phorbol 12-myristate 13-acetate, fluoride and endothelin-1, a translocation of PKC activity from the cytosolic to the particulate fraction was observed. The expression and distribution of PKC isoforms were then examined by Western blot analysis using specific antibodies to PKC isoforms. At least four PKC isoforms, PKCalpha, PKCbeta1, PKCbeta2, PKCzeta, and trace amounts of PKCepsilon were detected in both fractions. Their relative responses to the different agonists were examined by quantifying their subcellular redistribution. No significant differential activation of the four mainly expressed PKC isoforms were observed in response to stimulation with any of the stimuli. Moreover, our results show that endothelin-1 induced translocation/activation of PKC in this vascular smooth muscle.

Protein kinase C mediates increase of Ca2+ sensitivity for contraction by cholinoceptor partial agonist in ileal longitudinal muscle of guinea pig

1. Experiments were designed to study the roles of protein kinase C in carbachol- and pilocarpine-induced contraction and the increase in cytosolic Ca2+ concentration ([Ca2+]i) in guinea pig ileal longitudinal muscle. 2. The protein kinase C inhibitors, GF 109203X (10 microM), calphostin C (10 microM) and H-7 (10 microM), reduced the maximum of the concentration response curve produced by pilocarpine more effectively than that produced by carbachol. 3. The slopes of the regression lines between [Ca2+]i and tension development for pilocarpine and carbachol in tissues treated with GF 109203X were significantly gentler than those for untreated tissues. 4. The protein kinase C alpha- and beta 1 selective inhibitor Goe 6976 (1 microM) decreased both [Ca2+]i and contraction, but did not affect the slopes of the regression lines for pilocarpine and carbachol. 5. These results suggest that protein kinase C (both n- and/or a-type) plays an important role in the increase of Ca2+ sensitivity of the contractile element, and that pilocarpine mainly activates the protein kinase C-dependent pathways for contractile mechanisms in guinea pig ileal longitudinal muscle.

Approaches to determine the specific role of the delta isoform of protein kinase C

Two dimensional gel electrophoresis of proteins from HL-60 human leukaemia cells treated with bistratene A, a specific activator of protein kinase C (PKC) delta, was performed in conjunction with sequencing in order to identify components of the signal transduction pathway of this isoform of PKC. Stathmin (oncoprotein 18) was identified in this way and the phosphorylation of this protein after treatment with bistratene A, was confirmed by Western blotting of 2D gels. Since stathmin has phosphorylation sites for mitogen activated protein (MAP) kinases, cyclin dependent kinases and calcium/calmodulin dependent protein kinases, it is assumed that one of these enzymes, acting downstream from PKC delta, is responsible for the phosphorylation. Another approach to determining the role of PKC delta involves the identification of interacting proteins using the yeast two hybrid screen. The sequence of nine out of ten independently isolated clones from a two hybrid screen showed perfect homology to human ribosomal protein L8. This protein has previously been shown to exist in complexes with ribosomal RNA, aminoacyl-tRNA and elongation factor-1 alpha, a known substrate of PKC delta, suggesting a role for PKC delta in protein synthesis regulation.

Effects of protein kinase C alpha overexpression on A7r5 smooth muscle cell proliferation and differentiation

Smooth muscle cell differentiation and proliferation are increasingly seen to be intimately tied to the etiology of atherosclerosis and hypertension. To determine the role of PKC alpha in the regulation of smooth muscle cell differentiation and proliferation, the rat embryonic smooth muscle cell line A7r5 was transfected with an expression vector containing the full-length PKC alpha cDNA. Neomycin-resistant clones which exhibited increased PKC alpha levels compared to wild-type cells were selected. The A7r5 cells overexpressing PKC alpha had altered morphology and decreased growth rates compared to wild-type cells and cells transfected only with the neomycin resistance gene. Electrophoretic mobility shift assays showed that nuclear extracts from overexpressing clones gave a different pattern of protein-DNA binding to an AP-1 consensus oligonucleotide compared to wild-type cells. In contrast to the growth characteristics of these clones, their levels of cell differentiation marker proteins such as vinculin and desmin were not affected by PKC alpha overexpression. Moreover, the smooth muscle-specific differentiation marker alpha-actin was markedly reduced, while beta-actin levels were found to remain unchanged. Northern blot analysis confirmed that alpha-actin downregulation occurred at the RNA level. Western blot analysis revealed that A7r5 cells have five different PKC isoforms and that these isoform protein levels were not changed by PKC alpha overexpression. These findings suggest that PKC alpha regulates growth and differentiation of A7r5 smooth muscle cells and that these changes might result from altered expression/function of AP-1 transcription factors.

Identification of the protein kinase C isoenzymes in human lung and airways smooth muscle at the protein and mRNA level

The protein kinase C (PKC) isoenzymes expressed by human peripheral lung and tracheal smooth muscle resected from individuals undergoing heart-lung transplantation were identified at the protein and mRNA level. Western immunoblot analyses of human lung identified multiple PKC isoenzymes that were differentially distributed between the soluble and particulate fraction. Thus, PKC alpha, PKC betaII, PKC epsilon, and PKC zeta were recovered predominantly in the soluble fraction whereas the eta isoform was membrane-associated together with trace amounts of PKC alpha and PKC epsilon. PKC beta1-like immunoreactivity was occasionally seen although the intensity of the band was uniformly weak. Immunoreactive bands corresponding to PKCs gamma, delta, or theta were never detected. Reverse transcription-polymerase chain reaction (RT-PCR) of RNA extracted from human lung using oligonucleotide primer pairs that recognise unique sequences in each of the PKC genes amplified cDNA fragments that corresponded to the predicted sizes of PKC alpha, PKC betaI, PKC betaII, PKC epsilon, PKC zeta, and PKC eta (consistent with the expression of PKC isoenzyme protein) and, in addition, mRNA for PKC delta; PCR fragments of the expected size for the supposedly muscle-specific isoform, PKC theta, or the atypical isoenzyme, PKC lambda, were never obtained. The complement and distribution of PKC isoforms in human trachealis were similar, but not identical, to human lung. Thus, immunoreactive bands corresponding to the alpha, betaI, betaII, epsilon, and zeta isoenzymes of PKC were routinely labelled in the cytosolic fraction. In the particulate material PKC alpha, PKC epsilon, PKC alpha, PKC eta, and PKC mu were detected by immunoblotting. With the exception of PKC zeta, RT-PCR analyses confirmed the expression of the PKC isoforms detected at the protein level and, in addition, identified mRNA for PKC delta. Collectively, these data clearly demonstrate the expression of multiple PKC isoenzymes in human lung and tracheal smooth muscle, suggesting that they subserve diverse multifunctional roles in these tissues.

Protein kinase C isoenzymes in airway smooth muscle

The protein kinase C (PKC) isoenzymes expressed by bovine tracheal smooth muscle (BTSM) were identified at the protein and mRNA levels. Western immunoblot analyses reliably identified PKCalpha, PKCbetaI and PKCbetaII. In some experiments immunoreactive bands corresponding to PKCdelta, PKCepsilon and PKCTheta were also labelled, whereas the gamma, eta and zeta isoforms of PKC were never detected. Reverse transcriptase PCR of RNA extracted from BTSM using oligonucleotide primer pairs designed to recognize unique sequences in the PKC genes for which protein was absent or not reproducibly identified by immunoblotting, amplified cDNA fragments that corresponded to the predicted sizes of PKCdelta, PKCepsilon and PKCzeta, which was confirmed by Southern blotting. Anion-exchange chromatography of the soluble fraction of BTSM following homogenization in Ca2+-free buffer resolved two major peaks of activity. Using epsilon-peptide as the substrate, the first peak of activity was dependent upon Ca2+ and 4beta-PDBu (PDBu=phorbol 12, 13-dibutyrate), and represented a mixture of PKCs alpha, betaI and betaII. In contrast, the second peak of activity, which eluted at much higher ionic strength, also appeared to comprise a combination of conventional PKCs that were arbitrarily denoted PKCalpha', PKCbetaI' and PKCbetaII'. However, these novel enzymes were cofactor-independent and did not bind [3H]PDBu, but were equally sensitive to the PKC inhibitor GF 109203X compared with bona fide conventional PKCs, and migrated on SDS/polyacrylamide gels as 81 kDa polypeptides. Taken together, these data suggest that PKCs alpha', betaI' and betaII' represent modified, but not proteolysed, forms of their respective native enzymes that retain antibody immunoreactivity and sensitivity to PKC inhibitors, but have lost their sensitivity to Ca2+ and PDBu when epsilon-peptide is used as the substrate.

Regulation of scavenger receptor expression in smooth muscle cells by protein kinase C: a role for oxidative stress

Phorbol esters increase scavenger-receptor mRNA expression and receptor activity in smooth muscle cells (SMCs). Our present results demonstrate that activation of protein kinase C (PKC) mediates this increase in receptor expression. This conclusion is based on the findings that (1) phorbol esters induced translocation of PKC-alpha from the cytosol to the membrane fraction; (2) PKC inhibitors blocked the effect of phorbol esters on receptor expression; (3) diacylglycerol, a physiological PKC agonist, enhanced scavenger-receptor activity; and (4) in cotransfected human SMCs, constitutively active PKC-alpha stimulated the expression of a reporter gene under control of the scavenger-receptor promoter. Phorbol ester treatment of SMCs increased intracellular reactive oxygen, and the increase in receptor activity was reduced 30% by the antioxidant N-acetyl cysteine (NAC), suggesting a role for reactive oxygen in phorbol ester-mediated receptor regulation. Furthermore, direct treatment of SMCs with reactive oxygen species increased scavenger-receptor activity. In rabbit SMCs, 100 micromol/L H2O2 alone slightly increased scavenger-receptor mRNA and protein expression. In combination, 100 micromol/L H2O2 and 10 micromol/L vanadate, which promotes formation of OH and enhances the inhibition of protein tyrosine phosphatase by H2O2, increased scavenger-receptor mRNA expression 25-fold in rabbit SMCs and 8-fold in human SMCs. NAC reduced the effect of H2O2 and vanadate by 93%. The increase in SMC scavenger-receptor expression occurs at the level of gene transcription. Receptor mRNA half-life was unchanged after treatment with either phorbol esters or reactive oxygen (approximately 14.5 hours), and induction by phorbol esters increased SMC scavenger-receptor mRNA transcription, as determined by nuclear run-on assay. Multiple cytokines and growth factors that contribute to the generation of reactive oxygen species are present in atherosclerotic lesions. These factors may all contribute to the upregulation of SMC scavenger-receptor activity and therefore to the formation of smooth muscle foam cells.

The effect of the PKC inhibitor GF109203X on the release of Ca2+ from internal stores and Ca2+ entry in DDT1 MF-2 cells

1. The effects of the specific protein kinase C (PKC) inhibitor, GF109203X, were measured on the cytoplasmic Ca2+ concentration ([Ca2+]i), and on histamine H1 receptor- and thapsigargin-mediated increases in [Ca2+]i in DDT1 MF-2 smooth muscle cells. 2. After pretreatment of cells with GF109203X (5 microM, 45 min), the histamine (100 microM)-induced initial rise in [Ca2+]i, representing Ca2+ mobilization from internal stores, was inhibited (by 59 +/- 7%). The slowly declining phase of the histamine induced Ca2+ response, reflecting Ca2+ entry, was enhanced (83 +/- 26%) in the presence of the PKC inhibitor. 3. The histamine induced release of Ca2+ from internal stores, measured after blocking Ca2+ entry with LaCl3 was inhibited by GF109203X in a concentration-dependent manner (IC50: 3.1 +/- 1.1 microM). 4. Histamine-induced formation of inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) was not changed in the presence of GF109203X. 5. The PKC activating phorbol ester, phorbol 12-myristate 13-acetate (PMA, 1 microM), strongly reduced histamine-induced Ins(1,4,5)P3 formation (58 +/- 16%). This effect was reversed by GF109203X (5 microM). Furthermore, PMA diminished histamine evoked Ca2+ release (50 +/- 6%) and blocked Ca2+ entry completely. 6. The rise in [Ca2+]i caused by blocking endoplasmic reticulum Ca2(+)-ATPase with thapsigargin (1 microM), was strongly reduced (57 +/- 3%) after pretreatment of cells with GF109203X. Downregulation of PKC by long-term pretreatment of cells with PMA (1 microM, 48 h) did not abolish this effect of GF109203X (48 +/- 3% inhibition). 7. In permeabilized DDT, MF-2 cells preloaded with 45Ca2+ in the presence of GF109203X, the amount of 45Ca2+ released by Ins(1,4,5)P3 (10 microM) was markedly reduced (42 +/- 9%). GF109203X did not release Ca2+ itself and did not impair Ins(1,4,5)P3 receptor function. 8. Uptake of 45Ca2+ by intact cells, representing Ca2+ entry, was enhanced by GF109203X (65 +/- 11%), by histamine (24 +/- 6%) and also by thapsigargin (121 +/- 10%). The GF109203X- and the thapsigargin-induced uptake of 45Ca2+ were not additive. 9. These data suggest that GF109203X reduces the filling-state of intracellular Ins(1,4,5)P3 sensitive Ca2+ stores by inhibiting the Ca2+ uptake into these stores, thereby promoting store-dependent (capacitive) Ca2+ entry.

Endothelial cell tyrosine kinase receptor and G protein-coupled receptor activation involves distinct protein kinase C isoforms

Protein kinase C (PKC) is a family of serine/threonine protein kinase isoforms that is important to intracellular enzymes for both tyrosine kinase receptors and G protein coupled receptors. However, which isoforms are linked to which class of receptors in endothelial cell signaling is not known. Moreover, the PKC isoforms in endothelial cells have not been thoroughly characterized. We tested the hypothesis that specific PKC isoforms are involved in different signaling pathways. PKC isoform expression was assessed by using reverse transcription polymerase chain reaction and Western blotting. The spatial distribution of PKC after stimulation of the cells with basic fibroblast growth factor (bFGF) and thrombin was examined by using confocal microscopy. Expression of PKC alpha, delta, epsilon, theta, and zeta was detectable on both the mRNA and protein levels. In resting cells, PKC alpha and epsilon were mostly distributed in the cytosol, while PKC alpha and epsilon were also present in the nucleus. Nuclear immunoreactivity of PKC alpha and epsilon increased significantly between passages 1 and 3. The phorbol ester TPA induced a rearrangement of PKC delta and a translocation of PKC alpha and epsilon to the nucleus. Treatment of endothelial cells with TPA for 24 hours caused PKC alpha, delta, and epsilon to disappear, while PKC zeta was not influenced by TPA. bFGF induced a rapid assembly of PKC alpha along cytosolic structures, followed by a translocation of the isoform toward the perinuclear region and into the nucleus. bFGF had a smaller effect on PKC epsilon. In contrast, thrombin had a similar effect on nuclear translocation of PKC alpha, did not influence PKC epsilon, and induced a rapid nuclear translocation of PKC zeta. Thus, tyrosine kinase receptor activation via bFGF induced a rapid association of PKC alpha and epsilon with nuclear structures, while activation of the G protein-coupled thrombin receptor increased mostly nuclear PKC zeta. The translocation of PKC isoforms into the nucleus by growth-promoting factors may be important for the induction of endothelial cell growth.

Protein kinase C mediation of Ca(2+)-independent contractions of vascular smooth muscle

Tumour-promoting phorbol esters induce slow, sustained contractions of vascular smooth muscle, suggesting that protein kinase C (PKC) may play a role in the regulation of smooth muscle contractility. In some cases, e.g., ferret aortic smooth muscle, phorbol ester induced contractions occur without a change in [Ca2+]i or myosin phosphorylation. Direct evidence for the involvement of PKC came from the use of single saponin-permeabilized ferret aortic cells. A constitutively active catalytic fragment of PKC induced a slow, sustained contraction similar to that triggered by phenylephrine. Both responses were abolished by a peptide inhibitor of PKC. Contractions of similar magnitude occurred even when the [Ca2+] was reduced to close to zero, implicating a Ca(2+)-independent isoenzyme of PKC. Of the two Ca(2+)-independent PKC isoenzymes, epsilon and zeta, identified in ferret aorta, PKC epsilon is more likely to mediate the contractile response because (i) PKC epsilon, but not PKC zeta, is responsive to phorbol esters; (ii) upon stimulation with phenylephrine, PKC epsilon translocates from the sarcoplasm to the sarcolemma, whereas PKC zeta, translocates from a perinuclear localization to the interior of the nucleus; and (iii) when added to permeabilized single cells of the ferret aorta at pCa 9, PKC epsilon, but not PKC zeta, induced a contractile response similar to that induced by phenylephrine. A possible substrate of PKC epsilon is the smooth muscle specific, thin filament associated protein, calponin. Calponin is phosphorylated in intact smooth muscle strips in response to carbachol, endothelin-1, phorbol esters, or okadaic acid. Phosphorylation of calponin in vitro by PKC (a mixture of alpha, beta, and gamma isoenzymes) dramatically reduces its affinity for F-actin and alleviates its inhibition of the cross-bridge cycling rate. Calponin is phosphorylated in vitro by PKC epsilon but is a very poor substrate of PKC zeta. A signal transduction pathway is proposed to explain Ca(2+)-independent contraction of ferret aorta whereby extracellular signals trigger diacylglycerol production without a Ca2+ transient. The consequent activation of PKC epsilon would result in calponin phosphorylation, its release from the thin filaments, and alleviation of inhibition of cross-bridge cycling. Slow, sustained contraction then results from a slow rate of cross-bridge cycling because of the basal level of myosin light chain phosphorylation (approximately 0.1 mol Pi/mol light chain). We also suggest that signal transduction through PKC epsilon is a component of contractile responses triggered by agonists that activate phosphoinositide turnover; this may explain why smooth muscles often develop more force in response, e.g., to alpha 1-adrenergic agonists than to K+.

Protein kinase C-alpha regulates proliferation but not apoptosis in rat coronary vascular smooth muscle cells

In a previous study (Am. J. Pathol. 1994, 145: 1265-1270) we found rat coronary vascular smooth muscle cell (SMC) proliferation and apoptosis to be regulated by protein kinase C (PKC). In the present study we analysed whether selective depletion of alpha isozyme of PKC would affect SMC proliferation and/or apoptosis. First, using Western blot technique, it was determined that the rat SMC express alpha, delta, epsilon and zeta isozymes of PKC. The selective depletion of PKC-alpha in SMC was achieved by exposing cells to antisense oligodeoxynucleotide to mRNA for PKC-alpha (AS-PKC-alpha). The effect of AS-PKC-alpha on SMC proliferation was analysed by measurement of 3H-thymidine incorporation. The results indicated that a single dose of AS-PKC-alpha at a concentration of 10-100microM caused long-lasting (for at least 4 days) inhibition (up to 55%) of 3H-thymidine incorporation by SMC. This observation indirectly demonstrates that PKC-alpha regulates SMC proliferation. However, it was not possible to induce a significant level of apoptosis in SMC exposed even to the highest dose of AS-PKC-alpha. These data, in conjunction with the previously shown induction of apoptosis in SMC by calphostin C, suggests that another isozyme of PKC is likely to be involved in regulation of SMC apoptosis. Finally, we observed that induction of apoptosis via PKC-dependent mechanism is prevented by supplementing the culture medium with serum. This shows striking similarity with the regulation of apoptosis by the c-myc-dependent pathway. In conclusion, PKC-alpha joins the group of proteins such as c-myc, proliferating-cell nuclear antigen and cdc2 kinase which may be therapeutical targets, for antisense oligodeoxynucleotides, in order to prevent SMC hyperplasia.

Primary structure of a gamma subunit of G protein, gamma 12, and its phosphorylation by protein kinase C

We have determined the primary structure of a novel gamma subunit (gamma 12, previously designated gamma S1) of G protein purified from bovine spleen. The mature gamma 12 protein composed of 68 amino acids had acetylated serine at the N terminus and geranylgeranylated/carboxylmethylated cysteine at the C terminus. This was consistent with the C-terminal prenylation signal in the amino acid sequence, which was predicted from gamma 12 cDNA isolated from a bovine spleen cDNA library. Western blots with the specific antibody against gamma 12 showed that gamma 12 is present in all tissues examined. Among various gamma subunits (gamma 1, gamma 2, gamma 3, gamma 7, and gamma 12), gamma 12 has a unique property to be phosphorylated by protein kinase C. The phosphorylated amino acid residue was Ser1 (or Ser2). The phosphorylated beta gamma 12 associated with Go alpha more tightly than the unphosphorylated form. Exposure of Swiss 3T3 and aortic smooth muscle cells to phorbol 12-myristate 13-acetate and NaF induced phosphorylation of gamma 12. Stimulation of aortic smooth muscle cells with natural vasoactive agents such as angiotensin II and vasopressin also induced phosphorylation of gamma 12. The extent of phosphorylation of beta gamma 12 in vitro was suppressed by a complex formation with Go alpha, which was relieved by the addition of guanosine 5'-O-(3-thiotriphosphate) or aluminum fluoride. These results strongly suggest that gamma 12 is phosphorylated by protein kinase C during activation of receptor(s) and G protein(s) in living cells.

Ca(2+)-dependent and -independent mechanism of cyclic-AMP reduction: mediation by bradykinin B2 receptors

1. Bradykinin caused a transient reduction of about 25% in the cyclic AMP level in forskolin prestimulated DDT1 MF-2 smooth muscle cells (IC50: 36.4 +/- 4.9 nM) and a pronounced, sustained inhibition (40%) of the isoprenaline-stimulated cyclic AMP level (IC50: 37.5 +/- 1.1 nM). 2. The Ca2+ ionophore, ionomycin, mimicked both the bradykinin-induced transient reduction in the forskolin-stimulated cyclic AMP level and the sustained reduction in the isoprenaline-stimulated cyclic AMP level. 3. The Ca(2+)-dependent effect on cyclic AMP induced by bradykinin was mediated solely by Ca2+ release from internal stores, since inhibition of Ca2+ entry with LaCl3 did not reduce the response to bradykinin. 4. The involvement of calmodulin-dependent enzyme activities, protein kinase C or an inhibitory GTP binding protein in the bradykinin-induced responses was excluded since a calmodulin inhibitor, calmidazolium, a PKC inhibitor, staurosporine and pertussis toxin, respectively did not affect the decline in the cyclic AMP level. 5. Bradykinin enhanced the rate of cyclic AMP breakdown in intact cells, which effect was not mimicked by ionomycin. This suggested a Ca(2+)-independent activation of phosphodiesterase activity by bradykinin in DDT1 MF-2 cells. 6. The bradykinin B1 receptor agonist, desArg9-bradykinin, did not affect cyclic AMP formation in isoprenaline prestimulated cells, while the bradykinin B2 receptor antagonists, Hoe 140 (D-Arg[Hyp3, Thi5, D-Tic7, Oic8]-BK) and D-Arg[Hyp3, Thi5,8, D-Phe7]-BK completely abolished the bradykinin response in both forskolin and isoprenaline prestimulated cells. 7. Bradykinin caused an increase in intracellular Ca2+, which was antagonized by the bradykinin B2 receptor antagonists, Hoe 140 and D-Arg[Hyp3, Thi5,8, D-Phe7]-BK. The bradykinin B2 receptor agonist,desArg9-bradykinin, did not evoke a rise in cytoplasmic Ca2 .8. It is concluded, that stimulation of bradykinin B2 receptors causes a reduction in cellular cyclic AMP in DDT1, MF-2 cells. This decline in cyclic AMP is partly mediated by a Ca2+/calmodulin independent activation of phosphodiesterase activity. The increase in [Ca2+], mediated by bradykinin B2 receptors inhibited forskolin- and isoprenaline-activated adenylyl cyclase differently, most likely by interfering with different components of the adenylyl cyclase signalling pathway.

T-cell antigen receptor-induced signal-transduction pathways--activation and function of protein kinases C in T lymphocytes

CONTENTS. T-cell activation--Structure of the T-cell antigen receptor--Modular organisation of the T-cell antigen receptor--T-cell antigen receptor-coupled signaling pathways: Activation of protein-tyrosine kinase by the T-cell antigen receptor; Signal transduction in lymphoid cells involves several protein-tyrosine kinases in parallel; Regulation of T-cell antigen receptor signaling by the phosphoprotein phosphatase CD45--Consequences of T-cell antigen receptor-induced tyrosine phosphorylation: Activation of phosphoinositol-lipid-turnover pathways--Activation of phospholipase C-gamma-1: p59fyn or p56lck?--G-protein motif of CD3-gamma: relevance for signal transduction--Association of lipid kinase with the T-cell antigen receptor--Intracellular signaling by phospholipid metabolites and calcium: activation of protein kinase C--Protein kinase C isoenzymes--Heterogenity of protein kinase C and mode of activation--Phospholipid-derived mediators in activation of protein kinase C in T-cells--Role of phospholipase D metabolites in activation of protein kinase C--Polyunsaturated fatty acids and lysophosphatidylcholine as activators of protein kinase C--Potein kinase C and p21ras function in interdependent and distinct signaling pathways during T-cell activation--Raf-1 kinase: regulator or target of protein kinase C?--Summary and perspectives.

Activation of adenosine A1 and bradykinin receptors increases protein kinase C and phospholipase D activity in smooth muscle cells

Since adenosine A1 receptors activate phospholipase C (PLC) in DDT1 MF-2 smooth muscle cells we have examined whether phospholipase D (PLD) and protein kinase C (PKC) activities are also increased. The formation of diacylglycerol was also measured. PKC activity was determined by measuring the phosphorylation of two peptide substrates after rapidly permeabilizing the cells. PLD activity was determined by measuring the formation of phosphatidylethanol. N6-cyclopentyladenosine, a selective adenosine A1 receptor agonist (100 nM) and bradykinin (1 microM) both stimulated the formation of diacylglycerol. The activation was biphasic with a rapid, transient increase (within 1 min) followed by a second increase. N6-cyclopentyladenosine increased the activity of PKC (EC50 5.6 nM) and PLD (EC50 18.7 nM). This was blocked by treatment of cells with pertussis toxin or the adenosine A1 receptor selective antagonist, 8-cyclopentyl-1,3-dipropylxanthine. Ki values (3 nM for PKC; 0.1 nM for PLD) were consistent with responses mediated via adenosine A1 receptors. Bradykinin (1 microM) also increased PKC and PLD activity, but these responses were insensitive to pertussis toxin treatment. The activation of PKC by N6-cyclopentyladenosine or bradykinin was transient, reaching a maximum at 1-2 min, and was preceded by increases in the formation of diacylglycerol. When adenosine A1 and bradykinin receptors were activated simultaneously, a synergistic activation of PKC was seen. There was no synergistic effect on PLD activity. In summary, the present study shows that activation of adenosine receptors of the A1 subtype increases PKC and PLD activity. Simultaneous activation of adenosine A1 and bradykinin receptors causes a synergistic increase in PKC.

Activation of phospholipase C and phospholipase D by stimulation of adenosine A1, bradykinin or P2U receptors does not correlate well with protein kinase C activation

Activation of adenosine A1-, bradykinin- or P2U-receptors on DDT1 MF-2 smooth muscle cells all increased the formation of inositol 1,4,5-trisphosphate and the mobilization of intracellular calcium. All three types of agents could increase [Ca2+]i in the same cell. Activation of the P2U receptor with ATP or UTP produced larger responses than activation of bradykinin- and adenosine A1-receptors, with bradykinin and N6-cyclopentyladenosine. When agonist-stimulated levels of diacylglycerol were determined, all agonists caused biphasic changes of similar magnitudes. If anything, ATP and UTP tended to give larger increases in the second phase of stimulation. Phospholipase D, measured as the formation of phosphatidylethanol in cells labeled with [3H]palmitic acid and activated in the presence of ethanol, was activated similarly as phospholipase C, i.e. ATP or UTP caused the largest increase in phosphatidylethanol formation, followed by N6-cyclopentyladenosine and bradykinin which caused weaker responses. Activation of PLD by P2U receptors was pertussis toxin insensitive. The activation of PLD by the agonists was only weakly affected by a PKC inhibitor, Ro 31-7549 (3-[1-(3-aminopropanyl)-3- indolyl]-4-(1-methyl-3-indolyl)-1H-pyrrole-2,5-dione). In contrast, ATP or UTP did not activate protein kinase C, determined in a permeabilized cell assay using two specific protein kinase C substrates, whereas N6-cyclopentyladenosine and bradykinin caused a substantial activation.(ABSTRACT TRUNCATED AT 250 WORDS)