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

E-cigarette exposure augments murine abdominal aortic aneurysm development: role of Chil1

AIMS

Abdominal aortic aneurysm (AAA) is a common cardiovascular disease with a strong correlation to smoking, although underlying mechanisms have been minimally explored. Electronic cigarettes (e-cigs) have gained recent broad popularity and can deliver nicotine at comparable levels to tobacco cigarettes, but effects on AAA development are unknown.

METHODS AND RESULTS

We evaluated the impact of daily e-cig vaping with nicotine on AAA using two complementary murine models and found that exposure enhanced aneurysm development in both models and genders. E-cigs induced changes in key mediators of AAA development including cytokine chitinase-3-like protein 1 (CHI3L1/Chil1) and its targeting microRNA-24 (miR-24). We show that nicotine triggers inflammatory signalling and reactive oxygen species while modulating miR-24 and CHI3L1/Chil1 in vitro and that Chil1 is crucial to e-cig-augmented aneurysm formation using a knockout model.

CONCLUSIONS

In conclusion our work shows increased aneurysm formation along with augmented vascular inflammation in response to e-cig exposure with nicotine. Further, we identify Chil1 as a key mediator in this context. Our data raise concerns regarding the potentially harmful long-term effects of e-cig nicotine vaping.

Protein Kinase C Inhibitors as Modulators of Vascular Function and their Application in Vascular Disease

Blood pressure (BP) is regulated by multiple neuronal, hormonal, renal and vascular control mechanisms. Changes in signaling mechanisms in the endothelium, vascular smooth muscle (VSM) and extracellular matrix cause alterations in vascular tone and blood vessel remodeling and may lead to persistent increases in vascular resistance and hypertension (HTN). In VSM, activation of surface receptors by vasoconstrictor stimuli causes an increase in intracellular free Ca(2+) concentration ([Ca(2+)]i), which forms a complex with calmodulin, activates myosin light chain (MLC) kinase and leads to MLC phosphorylation, actin-myosin interaction and VSM contraction. Vasoconstrictor agonists could also increase the production of diacylglycerol which activates protein kinase C (PKC). PKC is a family of Ca(2+)-dependent and Ca(2+)-independent isozymes that have different distributions in various blood vessels, and undergo translocation from the cytosol to the plasma membrane, cytoskeleton or the nucleus during cell activation. In VSM, PKC translocation to the cell surface may trigger a cascade of biochemical events leading to activation of mitogen-activated protein kinase (MAPK) and MAPK kinase (MEK), a pathway that ultimately increases the myofilament force sensitivity to [Ca(2+)]i, and enhances actin-myosin interaction and VSM contraction. PKC translocation to the nucleus may induce transactivation of various genes and promote VSM growth and proliferation. PKC could also affect endothelium-derived relaxing and contracting factors as well as matrix metalloproteinase (MMPs) in the extracellular matrix further affecting vascular reactivity and remodeling. In addition to vasoactive factors, reactive oxygen species, inflammatory cytokines and other metabolic factors could affect PKC activity. Increased PKC expression and activity have been observed in vascular disease and in certain forms of experimental and human HTN. Targeting of vascular PKC using PKC inhibitors may function in concert with antioxidants, MMP inhibitors and cytokine antagonists to reduce VSM hyperactivity in certain forms of HTN that do not respond to Ca(2+) channel blockers.

Therapeutic potential for protein kinase C inhibitor in vascular restenosis

Vascular restenosis, an overreaction of biological response to injury, is initialized by thrombosis and inflammation. This response is characterized by increased smooth muscle cell migration and proliferation. Available pharmacological treatments include anticoagulants, antiplatelet agents, immunosuppressants, and antiproliferation agents. Protein kinase C (PKC), a large family of serine/threonine kinases, has been shown to participate in various pathological stages of restenosis. Consequently, PKC inhibitors are expected to exert a wide range of pharmacological activities therapeutically beneficial for restenosis. In this review, the roles of PKC isozymes in platelets, leukocytes, endothelial cells, and smooth muscle cells are discussed, with emphasis given to smooth muscle cells. We will describe cellular and animal studies assessing prevention of restenosis with PKC inhibitors, particularly targeting -α, -β, -δ, and -ζ isozymes. The delivery strategy, efficacy, and safety of such PKC regulators will also be discussed.

Changes of protein kinase Calpha and cyclin D1 expressions in pulmonary arteries from smokers with and without chronic obstructive pulmonary disease

The purpose of this study was to investigate the changes of protein kinase Calpha (PKCalpha) and cyclin D1 expressions in pulmonary arteries from smokers with normal lung function and smokers with mild to moderate chronic obstructive pulmonary disease (COPD). The peripheral lung tissues were obtained from 10 non-smokers with normal lung function (non-smoker group), 14 smokers with normal lung function (smoker group), 11 smokers with mild to moderate COPD (COPD group). The morphological changes of pulmonary arteries were observed by HE-staining. The expressions of alpha-smooth muscle actin (alpha-SMA), proliferating cell nuclear antigen (PCNA), PKCalpha and cyclin D1 proteins in pulmonary artery smooth muscle cells (PASMCs) were immunohistochemically determined. The percentages of PCNA-positive cells were taken as the smooth muscle cells proliferation index (PI). The mRNA expressions of PKCalpha and cyclin D1 in PASMCs were evaluated by real-time fluorescence PCR. Morphometrical analysis showed that the ratio of pulmonary artery wall area to total area (WA%) in smoker group and COPD group was significantly greater than that in non-smoker group (P<0.01). The PASMCs proliferation index in smoker group and COPD group was significantly higher than that in nonsmoker group (P<0.01). The protein levels of PKCalpha and cyclin D1 in PASMCs were significantly increased in smoker group and COPD group as compared with non-smoker group (P<0.01). The mRNA expressions of PKCalpha and cyclin D1 in PASMCs were significantly elevated in smoker group and COPD group as compared with non-smoker group (P<0.01). Significant correlations were found between PKCalpha protein and WA% or PI (P<0.01). Correlations between cyclin D1 protein and WA% or PI also existed (P<0.01). The expression of PKCalpha was positively correlated with the expression of cyclin D1 at both protein and mRNA levels (P<0.01). In conclusion, increased expressions of PKCalpha and cyclin D1 might be involved in the pathogenesis of abnormal proliferation of PASMCs in smokers with normal lung function and smokers with mild to moderate COPD.

Plectin deposition at podosome rings requires myosin contractility

Metalloproteinase-dependent tissue invasion requires the formation of podosomes and invadopodia for localized matrix degradation. Actin cytoskeleton remodeling via Arp2/3-mediated actin polymerization is essential for podosome formation, and dynamic microtubules have an important role in maintaining podosome turnover in macrophages and osteoclasts. Little is known, however, about the involvement of the intermediate filament cytoskeleton in formation, stabilization, and turnover of podosomes. Here we show that vimentin intermediate filaments colocalize with the early sites of podosome formation at the stress fiber - focal adhesion interface in cultured vascular smooth muscle cells, but do not directly contribute to podosome formation, or stabilization. In unstimulated A7r5 cells the cytolinker protein plectin poorly colocalized with vimentin and the microdomains, but following induction by phorbol ester accumulated in the rings that surround the podosomes. In plectin-deficient A7r5 cells actin stress fiber remodelling is reduced in response to PDBu, and small podosomes remain localized at stable actin stress fibres. Pharmacological inhibition of actomyosin contractility by blebbistatin leads to an aberrant localization of podosomes away from the cell periphery and induces failure of plectin to surround the outer perimeter of these invasive adhesions. Taken together, we conclude that plectin is involved in growth and maturation of podosomes by reducing focal adhesion and stress fiber turnover, and that actomyosin-dependent contractility is required for the peripheral localization and specific deposition of plectin at the podosome rings.

Reduced PKCα expression in pulmonary arterioles of broiler chickens is associated with early feed restriction

OBJECTIVE

The present study was conducted to investigate the effect of early feed restriction on protein kinase Calpha (PKCalpha) expression in pulmonary arterioles, which has been revealed to promote pulmonary vascular remodeling in pulmonary hypertensive broilers.

METHODS

A total of 270day-old mixed sex commercial broilers were randomly distributed to a normal temperature control group (NT), a low temperature control group (LT) and a low temperature plus feed restriction group (LR). The PHS incidence, the right/total ventricular weight ratio (RV/TV), the vessel wall area/vessel total area ratio (WA/TA), the mean media thickness in pulmonary arterioles (mMTPA) and the expression of PKCalpha in the pulmonary arterioles were measured weekly.

RESULTS

Low temperature treatment significantly increased the PHS mortality. The RV/TV, WA/TA and mMTPA values of group LT were significantly elevated compared with those of group NT on d 35 and 42. The LT chickens had increased PKCalpha expression compared with their NT counterparts on d 28 and afterwards. Feed restriction reduced the PHS mortality, RV/TV, WA/TA and mMTPA in cold-exposed broilers. The LR chickens had much lower PKCalpha expression in pulmonary arterioles than the LT chickens.

CONCLUSION

Early time feed restriction inhibited pulmonary vascular remodeling in broilers, which might be partly attributed to reduced PKCalpha expression in pulmonary arterioles.

Expression and characterization of the human alpha 2B-adrenoceptor in a vascular smooth muscle cell line

A vascular smooth muscle cell line stably expressing the human alpha 2B-adrenoceptor at a density of 1.5 pmol/mg membrane protein was generated by transfection of rat A7r5 cells. [35S]GTPgammaS binding experiments and [3H]thymidine incorporation experiments indicated that the expressed receptors were functional, had the expected pharmacological characteristics and efficiently stimulated smooth muscle cell proliferation. Confocal fluorescence microscopy was used to visualize alpha2B-adrenoceptors in A7r5-alpha 2B cells and indicated that the receptors were mainly localized in the plasma membrane. The expression of the smooth muscle-specific marker alpha-actin was similar in transfected A7r5-alpha 2B cells and in non-transfected A7r5 wild-type cells. The generated A7r5-alpha 2B cell line will be a useful tool for studying the function and regulation of alpha 2B-adrenoceptors in vascular smooth muscle cells.

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.

Phenotype-specific inhibition of the vascular smooth muscle cell cycle by high glucose treatment

AIMS/HYPOTHESIS

Diabetes accelerates the development of atherosclerosis, which critically involves the proliferation of vascular smooth muscle cells (SMCs). However, how high glucose treatment regulates SMC proliferation is controversial. Considering the established SMC heterogeneity, we hypothesised that glucose treatment may have distinct effects on proliferation of the various phenotypic SMCs.

MATERIALS AND METHODS

We tested this possibility using cloned spindle-shaped and epithelioid SMCs and laser scanning cytometry.

RESULTS

Our results showed that glucose treatment significantly inhibited the serum-independent proliferation of epithelioid SMCs, but had no effect on the proliferation of spindle-shaped cells either with or without serum stimulation. Furthermore, glucose treatment inhibited DNA synthesis, as detected by bromodeoxyuridine (BrdU) incorporation, and increased the production of reactive oxygen species in epithelioid SMCs. The inhibition of BrdU incorporation by glucose treatment was mimicked by glucosamine and phorbol 2,13-dibutyrate, a protein kinase C (PKC) activator, and reversed by azaserine, an inhibitor of the hexosamine pathway. In addition, the inhibitory effects of glucose treatment were blocked by GF 109203X (a PKC inhibitor) and PD98058 (a MAPK/ERK kinase, MEK inhibitor), and by knockdown of MEK1 by small interfering RNA (siRNA). The addition of either GF 109203X or PD98058 also reduced the phosphorylation of MAP kinase induced by glucose treatment.

CONCLUSIONS/INTERPRETATION

Glucose treatment inhibits the proliferation of epithelioid, but not spindle-shaped, vascular SMCs through the activation of PKC and the MAP kinase pathway, suggesting that the effects of hyperglycaemia on vascular disease depend on the phenotype of SMCs involved.

Characterisation of the complement susceptibility of the rat aortic smooth muscle cell line A7r5

Complement (C) activation is thought to contribute to the initiation and progression of atherosclerosis. Proliferation of smooth muscle cells plays an important role in atherosclerotic plaque formation. Our aim was to investigate the suitability of the rat aortic smooth muscle cell line A7r5 as an in vitro model to study C-induced events in smooth muscle cells. A7r5 cells abundantly expressed membrane bound C-regulators (CReg) Crry and CD59 as assessed by flow-cytometry, but no DAF or MCP was detected. Using RT-PCR in addition to Crry and CD59, also mRNA for rat DAF but not for MCP was detected. Flow-cytometry of cells removed by EDTA instead of trypsin demonstrated that A7r5 did express cell surface DAF. Upon prolonged culturing under either logarithmic growing conditions or under conditions where cells were kept over-confluent, two different sub cell lines were obtained, one which had lost the expression of CD59, while the other showed increased expression of DAF and Crry. The change in expression of these CReg resulted in a change in C-susceptibility. Incubation of the A7r5 cells with human serum induced membrane attack complex dependent proliferation. Transfection with human CD59 efficiently protected the cells from C-mediated killing and C-induced cell proliferation. Our results show that A7r5 cells can be used as an in vitro model for C-induced events, but care has to be taken to use the cells at an early stage of passaging as they readily change their phenotype.

PKC pathway associated with the expression of an A-type K+ channel induced by TGF-β1 in rat vascular myofibroblasts

Our previous study indicated that TGF-beta1 induced the expression of a transient outward K+ channel (A-type) during the phenotypic transformation of vascular fibroblasts to myofibroblasts. Here, we studied the relevant signal transduction pathway using whole cell recording and a quantitative RT-PCR technique. Results indicate that the protein kinase C (PKC) agonist phorbol-12-myristate-13-acetate (PMA, 1 microM) could mimic the effect of TGF-beta1 (20 ng/ml) on the expression of an A-type K+ channel and induced a similar A-type K+ current. Moreover, a PKC inhibitor, bisindolylmaleimide I (1 microM), could abrogate the effect of TGF-beta1 on K(V)4.2 expression. This result suggests that a PKC pathway may be involved in the expression of an A-type K+ channel induced by TGF-beta1 in rat vascular myofibroblasts.

Protein kinase C isoforms as specific targets for modulation of vascular smooth muscle function in hypertension

Vascular contraction is an important determinant of the peripheral vascular resistance and blood pressure. The mechanisms underlying vascular smooth muscle (VSM) contraction and the pathological changes that occur in hypertension have been the subject of numerous studies and interpretations. Activation of VSM by vasoconstrictor stimuli at the cell surface causes an increase in [Ca(2+)](i), Ca(2+)-dependent activation of myosin light chain (MLC) kinase, MLC phosphorylation, actin-myosin interaction and VSM contraction. Additional signaling pathways involving Rho-kinase and protein kinase C (PKC) may increase the myofilament force sensitivity to [Ca(2+)](i) and MLC phosphorylation, and thereby maintain vascular contraction. PKC is a particularly intriguing protein kinase as it comprises a family of Ca(2+)-dependent and Ca(2+)-independent isoforms, which have different tissue and subcellular distribution, and undergo differential translocation during cell activation. PKC translocation to the cell surface may trigger a cascade of protein kinases, such as mitogen-activated protein kinase (MAPK) and MAPK kinase (MEK) that ultimately interact with the contractile myofilaments and cause VSM contraction. Also, PKC translocation to the nucleus may promote VSM growth and proliferation. Increased PKC expression and activity have been identified in several forms of hypertension. The subcellular location of PKC may determine the state of VSM activity, and may be useful in the diagnosis/prognosis of hypertension. Vascular PKC isoforms may represent specific targets for modulation of VSM hyperactivity, and isoform-specific PKC inhibitors may be useful in treatment of Ca(2+) antagonist-resistant forms of hypertension.

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.

Protein Kinase C in Cardiac Disease and as a Potential Therapeutic Target

Protein kinase C (PKC) is a member of a large family of serine/threonine kinases that plays an integral role in many of the signaling cascades that govern cellular behavior. As such, it is intricately involved in the processes that mediate disease pathogenesis. Strategies that serve to alter PKC function may prove to be useful in the treatment of numerous disease states. This article reviews the various roles PKC may play in cardiovascular disease, specifically with regard to ischemic heart disease, cardiac hypertrophy, heart failure, hypertension, and atherosclerosis, and suggests the potential for developing therapeutic approaches that can target PKC activity.

Regulation of expression and activity of four PKC isozymes in confluent and mechanically stimulated UMR-108 osteoblastic cells

The transcript (mRNA), protein levels, enzyme activity, and cellular localization of four protein kinase C (PKC) isozymes identified in rat osteogenic sarcoma cells (UMR-108) were studied at confluent density and during mechanical stress (cyclic stretch). Western blot analysis indicated that growth to confluent density significantly increased the protein levels of cPKC-alpha (11.6-fold), nPKC-delta (5.3-fold), and nPKC-epsilon (22.0-fold) but not aPKC-zeta. Northern blot analysis indicated a significant (2.3-fold) increase in the 10 kb transcript of cPKC-alpha, a slight (1.3-fold) increase in that of nPKC-epsilon but no detectable change in that of the remaining isozymes. Enzyme activity assays of the individually immunoprecipitated isozymes yielded detectable kinase activity only for PKC-alpha, PKC-delta, and PKC-epsilon and only in confluent cells, corroborating the selective increase of these isozymes at confluent density. The UMR-108 cells showed a dramatic orientation response to mechanical stress with cell reshaping and alignment of the cell long axis perpendicular to the axis of force, remodeling of the actin cytoskeleton, and the appearance of multiple peripheral sites which stained for actin, vinculin, and PKC in separate experiments. Longer term mechanical stress beyond 24 h, however, resulted in no significant change in the mRNA level, protein level, or enzyme activity of any of the four PKC isozymes investigated. The results indicate that there are isozyme-selective increases in the protein levels of PKC isozymes of osteoblastic UMR-108 cells upon growth to confluence which may be regulated at the transcriptional or the post-transcriptional level. The results from UMR-108 cells support the earlier proposal (Carvalho RS, Scott JE, Suga DM, Yen EH. 1994. J Bone Miner Res 9(7):999-1011) that PKC could be involved in the early phase of mechanotransduction in osteoblasts through the activation of focal adhesion assembly/disassembly and the remodeling of the actin cytoskeleton.

Proliferative effect of lipoprotein lipase on human vascular smooth muscle cells

Vascular smooth muscle cell (VSMC) proliferation is a key event in the development and progression of atherosclerotic lesions. Accumulating evidence suggests that lipoprotein lipase (LPL) produced in the vascular wall may exert proatherogenic effects. The aim of the present study was to examine the effect of LPL on VSMC proliferation. Incubation of growth-arrested human VSMCs with purified endotoxin-free bovine LPL for 48 and 72 hours, in the absence of any added exogenous lipoproteins, resulted in a dose-dependent increase in VSMC growth. Addition of VLDLs to the culture media did not further enhance the LPL effect. Treatment of growth-arrested VSMCs with purified human or murine LPL (1 microg/mL) led to a similar increase in cell proliferation. Neutralization of bovine LPL by the monoclonal 5D2 antibody, irreversible inhibition, or heat inactivation of the lipase suppressed the LPL stimulatory effect on VSMC growth. Moreover, preincubation of VSMCs with the specific protein kinase C inhibitors calphostin C and chelerythrine totally abolished LPL-induced VSMC proliferation. In LPL-treated VSMCs, a significant increase in protein kinase C activity was observed. Treatment of VSMCs with heparinase III (1 U/mL) totally inhibited LPL-induced human VSMC proliferation. Taken together, these data indicate that LPL stimulates VSMC proliferation. LPL enzymatic activity, protein kinase C activation, and LPL binding to heparan sulfate proteoglycans expressed on VSMC surfaces are required for this effect. The stimulatory effect of LPL on VSMC proliferation may represent an additional mechanism through which the enzyme contributes to the progression of atherosclerosis.

The effect of protein kinase C and its alpha subtype on human vascular smooth muscle cell proliferation, migration and fibronectin production

BACKGROUND

Vascular smooth muscle cell (SMC) migration, proliferation and extracellular matrix protein production are key steps in the formation of intimal hyperplasia, a process that leads to failure of vascular reconstructions. Protein kinase C (PKC) may be involved in all 3 cellular events. PKC consists of a family of 11 isotypes, 8 of which we have identified in human vascular SMCs. In this study we evaluate the role of PKCalpha as a second messenger for proliferation, migration and fibronectin production induced by human saphenous vein SMCs.

METHODS

DNA synthesis was evaluated by using (3)H-thymidine incorporation. Mitogen-activated protein kinase (MAP-K) activation was quantified by Western blotting with an antibody to its phosphorylated substrate, Elk-1. Chemotaxis was evaluated by using a microchemotaxis chamber. SMC fibronectin was measured by Western blotting. For all experiments, PKCalpha was blocked with a selective inhibitor, Gö6976.

RESULTS

Gö6976, at concentrations that allow selective inhibition of PKCalpha, inhibited platelet-derived growth factor-stimulated SMC proliferation and MAP-K activation by 30% to 40% and 30% to 60%, respectively. SMC chemotaxis was stimulated approximately 2-fold by the PKCalpha inhibitor. Neither basal nor transforming growth factor-betaI induced fibronectin production was affected by Gö6976.

CONCLUSIONS

Our data suggest that PKCalpha is a positive mediator of SMC proliferation and MAP-K activity, a negative regulator of migration and has no effect on SMC fibronectin production. These data suggest that modulating activities of specific PKC isotypes might be useful in both the study and control of intimal hyperplasia.

Changes in protein kinase C isoforms in association with vascular hyporeactivity in cirrhotic rat aortas

BACKGROUND & AIMS

Although protein kinase C (PKC) alterations may play a role in the abnormal reactivity of cirrhotic rat aortas, its isoforms and cellular distribution are unknown. We therefore studied the protein expression and cellular distribution of PKC isoforms and their activation in cirrhotic rat aortas.

METHODS

Endothelium-denuded aortas from control and cirrhotic rats were examined. Immunoblots were performed with PKC isoform-specific antibodies. Aortic reactivity was determined for phorbol myristate acetate and phenylephrine after PKC down-regulation.

RESULTS

PKC-alpha expression was reduced in both the cytosolic and membrane fractions in cirrhotic aortas. Trace amounts of PKC-beta were detected in cirrhotic aortas. PKC-delta was detected in the cytosolic fraction of control and cirrhotic aortas. PKC-zeta was detected in the membrane fraction in control aortas and in the cytosolic fraction in cirrhotic aortas. Phorbol myristate acetate and phenylephrine triggered translocation of PKC-alpha and PKC-delta isoforms from the cytosol to the membrane in control aortas; in cirrhotic aortas, only PKC-alpha was translocated. Aortic reactivities were reduced after PKC down-regulation. PKC-alpha and -delta activities were reduced in cirrhotic aortas.

CONCLUSIONS

These results suggest that a change in PKC isoforms may be responsible in part for the abnormal reactivity and intracellular transduction through the PKC pathway in cirrhotic rat aortas.

Ca2+ signalling in rat vascular smooth muscle cells: a role for protein kinase C at physiological vasoconstrictor concentrations of vasopressin

Physiological vasoconstrictor concentrations of Arg8-vasopressin (AVP, 10-100 pM) stimulate oscillations (spikes) in cytosolic free Ca2+ concentration ([Ca2+]i) in A7r5 rat vascular smooth muscle cells. These Ca2+ spikes are dependent on L-type voltage-sensitive Ca2+ channels and increase in frequency with increasing AVP concentration. The signal transduction pathway responsible for this effect was examined in fura-2-loaded A7r5 cell monolayers. The serine/threonine phosphatase inhibitor calyculin A (5 nM) sensitized A7r5 cells to AVP, resulting in the stimulation of Ca2+ spiking by 1-10 pM AVP. Calyculin A alone did not stimulate Ca2+ spiking. The protein kinase C (PKC) activator 4beta-phorbol 12-myristate 13-acetate (PMA, 100 pM to 200 nM), also stimulated Ca2+ spiking and this effect was additive with a submaximal concentration of AVP (50 pM). The PKC inhibitors Ro-31-8220 (1 microM) and calphostin C (250 nM) completely blocked the stimulation of Ca2+ spiking by either PMA or AVP. alpha, beta, gamma, delta, epsilon, zeta and &lamdda; isoforms of PKC were detected in A7r5 cells by Western blot analysis. Time-dependent redistribution of PKC-alpha, -delta and -epsilon isoforms between the membrane and cytosolic fractions occurred in response to 100 pM AVP. Pretreatment for 24 h with 1 microM PMA downregulated expression of PKC-alpha and -delta, but not PKC-epsilon, and prevented the Ca2+-spiking responses to either 1 nM PMA or 100 pM AVP. Neither the release of intracellular Ca2+ by 1 microM AVP nor the increase in [Ca2+]i in response to elevated extracellular [K+] was prevented by the PMA pretreatment. We conclude that PKC activation is a necessary step in the signal transduction pathway linking low concentrations of AVP to Ca2+ spiking in A7r5 cells.

Antisense inhibition of protein kinase Calpha reverses the transformed phenotype in human lung carcinoma cells

The protein kinase C (PKC) family, which functions through serine/threonine kinase activity, is involved in signal transduction pathways necessary for cell proliferation and differentiation. Its critical role in processes relevant to neoplastic transformation and tumor invasion renders PKC a potentially suitable target for anticancer therapy. To explore whether antisense blocking of PKCalpha would inhibit the neoplastic properties in tumor cells, human lung carcinoma LTEPa-2 cells were transfected with a recombinant plasmid, pXJ41-CKPalpha, with PKCalpha cDNA inserted in the antisense orientation. In LT.AS4 cell clones stably expressing antisense PKCalpha mRNA, the amounts of PKCalpha protein and total PKC activity were decreased when compared to control cells. The expression of antisense PKCalpha markedly inhibited the cell proliferation rate, colony forming efficiency in soft agar, and tumorigenecity in nude mice. Furthermore, the mRNA levels of oncogenes (Ha-ras, c-jun, and c-fos) were seen to decrease to varying degrees. Reduced DNA binding activity of transcription factor AP-1 was also observed using gel shift analysis, suggesting that one major molecular mechanism by which PKCalpha can exert its effects on cell growth and transformation is through regulation of AP-1 transcription factor activity. Taken together, these data provide evidence for the ability of antisense PKCalpha expression to reverse the transformed phenotype of human lung carcinoma cells and support the development of PKCalpha inhibitors for the clinical treatment of cancers.

Differentiation of human monocytes to monocyte-derived macrophages is associated with increased lipoprotein lipase-induced tumor necrosis factor-alpha expression and production: a process involving cell surface proteoglycans and protein kinase C

The aim of the present study was to (1) evaluate the responsiveness of human mononuclear cells to lipoprotein lipase (LPL), as assessed by tumor necrosis factor-alpha (TNFalpha) production, during the process of differentiation of monocytes to macrophages, and (2) determine the mechanisms by which LPL exerts its effect on these cells. Treatment of human monocytes with purified endotoxin-free bovine LPL (1 microgram/mL) resulted in a 161+/-15% increase in TNFalpha production over control values (P<0.01). A further increase in TNFalpha production was observed after treatment of monocyte-derived macrophages (MDMs) with LPL (490+/-81% over control values, P<0.01). Increased TNFalpha mRNA expression and protein kinase C activity were also observed in LPL-treated human monocytes and MDMs. These LPL effects were abrogated by the specific protein kinase C inhibitor calphostin C (1 micromol/L). Although heparinase totally abolished LPL-induced TNFalpha production in human monocytes, this agent did not significantly inhibit LPL effect in human MDMs. In contrast, treatment of MDMs with chondroitinase suppressed LPL-induced TNFalpha production. Taken together, these data suggest that (1) differentiation of human monocytes to MDMs is associated with increased LPL-induced TNFalpha mRNA expression and production, (2) a protein kinase C-dependent pathway is involved in the induction of TNFalpha by LPL in these cells, and (3) LPL effect is mediated by cell surface proteoglycans. As MDMs secrete LPL in the vascular wall, we propose that LPL, by acting as an autocrine activator of MDM function, may contribute to the high level of TNFalpha found in the atheromatous lesion.

Heparin down-regulates the phorbol ester-induced protein kinase C gene expression in human endothelial cells: enzyme-mediated autoregulation of protein kinase C-alpha and -delta genes

Overexpression of protein kinase C-alpha and protein kinase C-delta has been shown to modulate a number of biological effects, including the cell growth and differentiation. We hypothesized that heparin, a potent antimitogenic drug, could affect the cell proliferation by inhibiting the expression of specific protein kinase C genes. Heparin, markedly but not completely, inhibited the serum-stimulated protein kinase C-alpha and -delta mRNA expression. Protein kinase C inhibition or down-regulation significantly decreased the serum-induced protein kinase C isoenzyme gene expression. Heparin failed to inhibit the residual effect of serum that was resistant to the above-mentioned treatments. Phorbol 12-myristate 13-acetate elicited an increase of protein kinase C isoenzyme gene expression that was completely prevented by protein kinase C inhibition or down-regulation. Heparin dose-dependently counteracted and ultimately abolished the increase in the protein kinase C isoenzyme gene expression elicited by phorbol 12-myristate 13-acetate. These results suggest that the inhibition of an autoregulatory role wielded by protein kinase C on the protein kinase C-alpha and -delta gene expression might represent a possible mechanism by which glycosaminoglycans modulate the cell growth.

Contribution of protein kinase C to ET-1-induced proliferation in human myometrial cells

The role of protein kinase C (PKC) in endothelin-1 (ET-1)-induced proliferation of human myometrial cells was investigated. ET-1 dose dependently stimulated DNA synthesis and the number of cultured myometrial cells. Inhibition of PKC by calphostin C or Ro-31-8220 or downregulation of PKC eliminated the proliferative effects of ET-1. The failure of two protein tyrosine kinase (PTK) inhibitors (tyrphostin 51 and tyrphostin 23) to affect ET-1-induced proliferation supports the hypothesis of noninvolvement of the tyrosine kinase signaling pathway in this process. The expression and distribution of PKC isoforms were examined by Western blot analysis. The five PKC isoforms (PKC-alpha, -beta1, -beta2, -zeta, -epsilon) evidenced in human myometrial tissue were found to be differentially expressed in myometrial cells, with a predominant expression of PKC-alpha and PKC-zeta. Treatment with phorbol 12, 13-dibutyrate (PDBu) resulted in the translocation of all five isoforms to the particulate fraction, whereas ET-1 induced a selective increase in particulate PKC-beta1, PKC-beta2, and PKC-epsilon. Our findings that multiple PKC isoforms are differentially responsive to ET-1 or PDBu suggest that they play distinct roles in the myometrial growth process.

Protein kinase C: modulation of vasopressin-induced calcium influx and release in A7r5 vascular smooth muscle cells

This study was guided by the hypothesis that specific isoforms of protein kinase C may participate in modulating increases in intracellular Ca2+ that are induced by stimulation of vascular smooth muscle cells with vasopressin. Immunoblot analysis revealed that A7r5 vascular smooth muscle cells expressed conventional (alpha), novel (delta and epsilon), and atypical (iota/lambda and mu) isoforms of protein kinase C. Stimulation of fura-2-loaded cells with 20 nM vasopressin induced a rapid transient increase in the intracellular concentration of calcium that was followed by a slowly declining component which was above baseline throughout the period of observation. Cell fractionation studies showed that the calcium response was associated with (a) transient translocation of the alpha and delta isoforms of protein kinase C from the cytosolic fraction to the particulate-membrane fraction, (b) sustained translocation of the epsilon isoform, and (c) no translocation of iota/lambda or mu isoforms. Ratiometric and isobestic fluorescence analysis showed that vasopressin-induced Ca2+ influx and release were markedly inhibited in cells that were preincubated with either 1 microM phorbol 12-myristate 13-acetate, or 10 microM 1, 2 dioctanoyl-sn-glycerol, two structurally different activators of protein kinase C. In contrast, vasopressin-induced increases in intracellular Ca2+ were not significantly altered following preincubation with either 1 microM 4alpha-phorbol or 4alpha-phorbol 12,13-didecanoate, analogs of phorbol 12-myristate 13-acetate that do not activate protein kinase C. Moreover, the inhibitory effects of phorbol 12-myristate 13-acetate were prevented by treatment with 1 microM GF109203X, a potent inhibitor of protein kinase C. Taken together, these results show that direct activation of protein kinase C can negatively modulate vasopressin-induced Ca2+ influx and release in cultured vascular smooth muscle cells. They also show that stimulation with vasopressin induces translocation of specific isoforms of protein kinase C, an observation suggesting that one or more of these isoforms may participate in modulation of vasopressin-induced increases in intracellular Ca2+.