G-protein-mediated signaling in cholesterol-enriched arterial smooth muscle cells. 2. Role of protein kinase C-delta in the regulation of eicosanoid production

Exercise and hypercholesterolemia produce disparate shifts in coronary PKC expression

INTRODUCTION

Sedentary lifestyle and high-fat, high-cholesterol diets are each associated with elevated risk for coronary heart disease (CHD); however, the mechanisms by which they increase risk are unclear. Specific PKC isoforms have been implicated in the development of CHD, regulation of coronary vasoreactivity, as well as exercise-induced cardioprotection. Thus, diet and physical inactivity may increase CHD risk by altering coronary protein kinase C (PKC) isoform profiles.

PURPOSE

To determine whether coronary PKC isoform profiles are altered in a model of early CHD and whether exercise can prevent these changes.

METHODS

Male and female Yucatan miniature swine were either fed a normal (NF) or high-fat (HF) diet (8 vs 46% kilocalories from fat) and remained sedentary (Sed) or were treadmill-trained (Ex) at 75% of; VO2max (6 mph, 60 min) for 16 wk. Groups were as follows: NFSed (N=8/N=7), NFEx (N=8/N=7), HFSed (N=8/N=7), and HFEx (N=8/N=7). Western blotting was performed on right coronary conduit artery (CCA) segments (>1 mm I.D.) to measure total protein levels of PKC-alpha, -betaI, -betaII, -delta, -epsilon, and -zeta.

RESULTS

HF diet increased total cholesterol by more than sixfold with no increase in triglycerides. Hypercholesterolemia increased PKC-betaII and -epsilon protein levels in CCA of both male and female pig; Ex had no effect on this response. Ex-induced increases in PKC-betaI, PKC-delta, and PKC-zeta were observed in HF male pigs. Female pigs had higher baseline amounts of PKC-alpha (25%), PKC-betaI (33%), PKC-betaII (39%), and PKC-epsilon (29%), whereas male pigs had higher amounts of PKC-delta (308%). Further analyses revealed a direct relationship between androgens and PKC-delta levels.

CONCLUSION

Hypercholesterolemia and exercise exert disparate effects on coronary PKC expression. Observed sex differences in PKC protein profiles may also contribute to altered cardiovascular risk patterns in males versus females.

Oxysterol and 9-cis-retinoic acid stimulate the group IIA secretory phospholipase A2 gene in rat smooth-muscle cells

The inflammation that occurs during rheumatoid arthritis or atherosclerosis is characterized by the release of large amounts of sPLA(2) (group IIA secretory phospholipase A(2)). We have shown previously that the sPLA(2) promoter in SMC (smooth-muscle cells) is activated by interleukin-1beta and cAMP-signalling pathways, through the interplay of multiple transcription factors [Antonio, Brouillet, Janvier, Monne, Bereziat, Andreani, and Raymondjean (2002) Biochem. J. 368, 415-424]. In the present study, we have investigated the regulation of sPLA(2) gene expression in rat aortic SMCs by oxysterols. We found that oxysterol ligands that bind to the LXR (liver X receptor), including 25-HC (25-hydroxycholesterol) and 22( R )-HC, cause the accumulation of sPLA(2) mRNA and an increased enzyme activity. Transient transfection experiments demonstrated that the sPLA(2) promoter is synergistically activated by 22( R )-HC in combination with 9- cis -retinoic acid, a ligand for the LXR heterodimeric partner RXR (retinoid X receptor). Promoter activity was also increased in a sterol-responsive fashion when cells were co-transfected with LXRalpha/RXRalpha or LXRbeta/RXRalpha. Mutagenesis studies and gel mobility-shift assays revealed that LXR/RXR heterodimers regulate sPLA(2) transcription directly, by interacting with a degenerated LXRE (LXR response element) at position [-421/-406] of the sPLA(2) promoter. Chromatin immunoprecipitation revealed the in vivo occupancy of LXR on the sPLA(2) promoter. In addition, the orphan nuclear receptor LRH-1 (liver receptor homologue-1) potentiated the sterol-dependent regulation of the sPLA(2) promoter by binding to an identified promoter element (TCAAGGCTG). Finally, we have demonstrated that oxysterols act independent of interleukin-1beta and cAMP pathways to activate the sPLA(2) promoter. In the present study, we have identified a new pathway activating sPLA(2) gene expression in SMCs.

Mechanical stress-activated PKCdelta regulates smooth muscle cell migration

Vascular smooth muscle cells (SMCs) are exposed to altered mechanical stress that may contribute to SMC migration in the development of atherosclerosis. Signal transduction pathways in SMCs activated by mechanical stress that instigate cell migration are undefined. Herein, we provide evidence that mechanical stress enhances SMC migration, which is mediated, at least in part, by protein kinase C (PKC)delta. When rat SMCs cultivated on a flexible membrane were subjected to cyclic strain stress (60 cycles/min, 5, 15, or 20% elongation), PKCdelta was translocated to the Triton-insoluble fraction, whereas PKCalpha was translocated to the membrane, which was confirmed by PKC kinase assays. Immunofluorescence and actin staining revealed a cytoskeleton translocation of PKCdelta in SMCs stimulated by cyclic strain. PKCdelta-deficient SMCs cultivated from PKCdelta-/- mice showed an abnormal cytoskeleton structure, which was related to a diminished phosphorylation of paxillin, focal adhesion kinase, and vinculin in response to mechanical stress. Mechanical stress enhanced SMC migration, which was diminished in PKCdelta-/- SMCs. Taken together, our data demonstrated that mechanical stress activates PKCdelta translocation to the cytoskeleton, which is related to decreased SMC migration and indicates that PKCdelta is a key signal transducer between mechanical stress and cell migration.

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.

Differential effects of protein kinase C on human vascular smooth muscle cell proliferation and migration

Vascular smooth muscle cell (SMC) migration and proliferation contribute to intimal hyperplasia, and protein kinase C (PKC) may be required for both events. In this report, we investigated the role of PKC in proliferation and migration of SMC derived from the human saphenous vein. Activation of PKC by phorbol-12,13-dibutyrate (PDBu) or (-)-indolactam [(-)-ILV] increases SMC proliferation. Downregulation of PKC activity by prolonged incubation with phorbol ester or inhibition of PKC with chelerythrine in SMC diminished agonist-stimulated proliferation. In contrast, stimulation of PKC with PDBu or (-)-ILV inhibited basal and agonist-induced SMC chemotaxis. Moreover, downregulation of PKC or inhibition with chelerythrine accentuated migration. We postulated that the inhibitory effect of PKC on SMC chemotaxis was mediated through cAMP-dependent protein kinase (protein kinase A, PKA). In support of this hypothesis, we found that activation of PKC in SMC stimulated PKA activity. The cAMP agonist forskolin significantly inhibited SMC chemotaxis. Furthermore, the inhibitory effect of PKC on SMC chemotaxis was completely reversed by cAMP or PKA inhibitors. In search of the PKC isotype(s) underlying these differential effects of PKC in SMC, we identified eight isotypes expressed in human SMC. Only PKC-alpha, -beta I, -delta, and -epsilon were eliminated by downregulation, suggesting that one or more of these four enzymes facilitate the observed phorbol ester-dependent effects of PKC in SMC. In summary, we found that PKC activation enhances proliferation but inhibits migration of human vascular SMC. These differential effect of PKC on vascular cells appears to be mediated through PKC-alpha, -beta I, -delta, and/or -epsilon.