Translocation of protein kinase C-alpha, delta and epsilon isoforms in ischemic rat heart

Calcium-Sensing Receptor (CaSR)-Mediated Intracellular Communication in Cardiovascular Diseases

The calcium-sensing receptor (CaSR), a G-protein-coupled receptor (GPCR), is a cell-surface-located receptor that can induce highly diffusible messengers (IP3, Ca²⁺, cAMP) in the cytoplasm to activate various cellular responses. Recently, it has also been suggested that the CaSR mediates the intracellular communications between the endoplasmic reticulum (ER), mitochondria, nucleus, protease/proteasome, and autophagy-lysosome, which are involved in related cardiovascular diseases. The complex intracellular signaling of this receptor challenges it as a valuable therapeutic target. It is, therefore, necessary to understand the mechanisms behind the signaling characteristics of this receptor in intracellular communication. This review provides an overview of the recent research progress on the various regulatory mechanisms of the CaSR in related cardiovascular diseases and the heart-kidney interaction; the associated common causes are also discussed.

Targeted inhibition of calpain in mitochondria alleviates oxidative stress-induced myocardial injury

The protein levels and activities of calpain-1 and calpain-2 are increased in cardiac mitochondria under pathological conditions including ischemia, diabetes, and sepsis, and transgenic overexpression of mitochondrial-targeted calpain-1 induces dilated heart failure, which underscores an important role of increased calpain in mitochondria in mediating myocardial injury. However, it remains to be determined whether selective inhibition of calpain in mitochondria protects the heart under pathological conditions. In this study, we generated transgenic mice overexpressing mitochondrial-targeted calpastatin in cardiomyocytes. Their hearts were isolated and subjected to global ischemia/reperfusion. Hyperglycemia was induced in the transgenic mice by injections of STZ. We showed that transgenic calpastatin was expressed exclusively in mitochondria isolated from their hearts but not from other organs including skeletal muscle and lung tissues. Transgenic overexpression of mitochondrial-targeted calpastatin significantly attenuated mitochondrial oxidative stress and cell death induced by global ischemia/reperfusion in isolated hearts, and ameliorated mitochondrial oxidative stress, cell death, myocardial remodeling and dysfunction in STZ-treated transgenic mice. The protective effects of mitochondrial-targeted calpastatin were correlated with increased ATP5A1 protein expression and ATP synthase activity in isolated hearts subjected to global ischemia/reperfusion and hearts of STZ-treated transgenic mice. In cultured rat myoblast H9c2 cells, overexpression of mitochondrial-targeted calpastatin maintained the protein levels of ATP5A1 and ATP synthase activity, prevented mitochondrial ROS production and decreased cell death following hypoxia/reoxygenation, whereas upregulation of ATP5A1 or scavenging of mitochondrial ROS by mito-TEMPO abrogated mitochondrial ROS production and decreased cell death. These results confirm the role of calpain in myocardial injury, suggesting that selective inhibition of calpain in myocardial mitochondria by mitochondrial-targeted calpastatin is an effective strategy for alleviating myocardial injury and dysfunction in cardiac pathologies.

Protein kinase Cα mediates recovery of renal and mitochondrial functions following acute injury

Previously, we have shown that active protein kinase Cα (PKCα) promotes recovery of mitochondrial function after injury in vitro [Nowak G & Bakajsova D (2012) Am J Physiol Renal Physiol 303, F515-F526]. This study examined whether PKCα regulates recovery of mitochondrial and kidney functions after ischemia-induced acute injury (AKI) in vivo. Markers of kidney injury were increased after bilateral ischemia and returned to normal levels in wild-type (WT) mice. Maximum mitochondrial respiration and activities of respiratory complexes and F_o F₁ -ATPase decreased after ischemia and recovered in WT mice. Reperfusion after ischemia was accompanied by translocation of active PKCα to mitochondria. PKCα deletion reduced mitochondrial respiration and activities of respiratory complex I and F_o F₁ -ATPase in noninjured kidneys, indicating that PKCα is essential in developing fully functional renal mitochondria. These changes in PKCα-deficient mice were accompanied by lower levels of complex I subunits (NDUFA9 and NDUFS3) and the γ-subunit of F_o F₁ -ATPase. Also, lack of PKCα exacerbated ischemia-induced decreases in respiration, complex I and F_o F₁ -ATPase activities, and blocked their recovery after injury, indicating a crucial role of PKCα in promoting mitochondrial recovery after AKI. Further, PKCα deletion exacerbated acetylation and succinylation of key mitochondrial proteins of energy metabolism after ischemia due to decreases in deacetylase and desuccinylase (sirtuin3 and sirtuin5) levels in renal mitochondria. Thus, our data show a novel role for PKCα in regulating levels of mitochondrial sirtuins and acetylation and succinylation of key mitochondrial proteins. We conclude that PKCα deletion: (a) affects renal physiology by decreasing mitochondrial capacity for maximum respiration; (b) blocks recovery of mitochondrial functions, renal morphology, and functions after AKI; and (c) decreases survival after AKI. ENZYMES: Protein kinase C: EC 2.7.11.13; NADH : ubiquinone reductase (H⁺ -translocating; complex I): EC 7.1.1.2; FoF1-ATPase (H⁺ -transporting two-sector ATPase): EC 7.1.2.2; Succinate : ubiquinone oxidoreductase (complex II): EC 1.3.5.1; Ubiquinol : cytochrome-c reductase (complex III): EC 7.1.1.8; Cytochrome c oxidase (complex IV): EC 1.9.3.1; NAD-dependent protein deacetylase sirtuin-3, mitochondrial: EC 2.3.1.286; NAD-dependent protein deacetylase sirtuin-5, mitochondrial: EC 3.5.1.-; Proteinase K (peptidase K): EC 3.4.21.64.

Inhibition of Na⁺-H⁺ exchange as a mechanism of rapid cardioprotection by resveratrol

BACKGROUND AND PURPOSE Resveratrol is a polyphenol abundantly found in grape skin and red wine. In the present study, we investigated whether resveratrol exerts protective effects against cardiac ischaemia/reperfusion and also explored its mechanisms. EXPERIMENTAL APPROACH Infarct size and functional recovery in rat isolated perfused hearts subjected to no-flow global ischaemia followed by reperfusion were measured. Cultured neonatal rat cardiomyocytes were exposed to H(2)O(2) (100 µmol·L(-1)) to induce cell injury. Intracellular ion concentrations were measured using specific dyes. Western blotting was used to quantify protein expression levels. KEY RESULTS In rat isolated perfused hearts, treatment with resveratrol (20 and 100 µmol·L(-1)) 15 min before ischaemia considerably improved left ventricular functional recovery and infarct size. In cultured neonatal rat cardiomyocytes, resveratrol significantly attenuated the increase in reactive oxygen species (ROS) and loss of mitochondrial inner membrane potential. Resveratrol also suppressed the increase in intracellular concentrations of Na(+) ([Na(+)](i)) and Ca(2+) ([Ca(2+)](i)) after H(2)O(2) application; however, it did not suppress the ouabain-induced [Ca(2+) ](i) increase. By measuring changes in intracellular pH recovery after acidification, we also confirmed that acid-induced activation of the Na(+)-H(+) exchanger (NHE) was prevented by pretreatment with resveratrol. Furthermore, resveratrol inhibited the H(2)O(2)-induced translocation of PKC-α from the cytosol to the cell membrane; this translocation is believed to activate NHE. CONCLUSION AND IMPLICATIONS Resveratrol exerts cardioprotection by reducing ROS and preserving mitochondrial function. The PKC-α-dependent inhibition of NHE and subsequent attenuation of [Ca(2+)](i) overload may be a cardioprotective mechanism.

Potassium 2-(1-hydroxypentyl)-benzoate attenuated hydrogen peroxide-induced apoptosis in neuroblastoma SK-N-SH cells

Potassium 2-(1-hydroxypentyl)-benzoate (dl-PHPB) has been shown to have potent neuroprotective effects, such as reducing the infarct volume and improving neurobehavioral deficits in the transient focal cerebral ischemic rat model. The present study is to evaluate the neuroprotective effect of dl-PHPB on hydrogen peroxide (H(2)O(2))-induced apoptosis and the possible mechanism in the human neuroblastoma SK-N-SH cells. Our results showed that dl-PHPB significantly attenuated H(2)O(2)-induced cell death, and reduced neuronal apoptosis. Dl-PHPB partially reversed the decrease of B-cell CLL/lymphoma 2 (Bcl-2) protein level induced by H(2)O(2). Furthermore, dl-PHPB inhibited the elevation of pro-apoptotic Bcl-2-associated X protein (Bax) and caspase3, and alleviated the down-regulation of protein kinase C alpha (PKCα). The PKC inhibitor, Calphostin C significantly attenuated the protective effects of dl-PHPB. The findings suggest that dl-PHPB may protect neurons against H(2)O(2)-induced apoptosis by modulating apoptosis-related proteins, and PKC signaling pathway may be involved in the neuroprotection of dl-PHPB.

Restraint stress induces connexin-43 translocation via α-adrenoceptors in rat heart

BACKGROUND

Immobilization (IMO) confers emotional stress in animals and humans. It was recently reported that IMO in rats induced translocation of connexin-43 (Cx43) to gap junctions (GJs) and attenuated arrhythmogenesis with GJ inhibition, and Cx43 translocation in the ischemic heart was also shown. Few reports show the contribution of adrenoceptors to Cx43 upregulation in cardiomyocytes, but the involvement of adrenoceptors and ischemia in Cx43 translocation in IMO remains elusive.

METHODS AND RESULTS

Male Sprague-Dawley rats underwent IMO and the ventricular distribution of Cx43 was examined by western blotting. IMO induced translocation of Cx43 to the GJ-enriched membrane fraction, with a peak at 60min. The IMO-induced Cx43 translocation was inhibited by pretreatment with the α(1)-adrenoceptor blockers, prazosin (1mg/kg, PO) and bunazosin (4mg/kg, PO), but not with either the β(1)-blocker, metoprolol (10mg/kg, IP), or the β(1+2)-blocker, propranolol (1mg/kg, PO). The translocation was inhibited by the nitric oxide, donor isosorbide dinitrate (100µg·kg(-1)·min(-1), IV), possibly through sympathetic inhibition. Hypoxia inducible factor-1α was not redistributed by IMO. The β-blockers, but not the α-blockers, inhibited the premature ventricular contractions (PVCs) induced by IMO.

CONCLUSIONS

Translocation of Cx43 to the GJ-enriched fraction occurs via the α(1)-adrenoceptor pathway, independently of ischemia. The β-adrenoceptor pathway contributes to the inducing of PVCs in IMO.

Endothelial NO Synthase (eNOS) phosphorylation regulates coronary diameter during ischemia-reperfusion in association with oxidative stress

The link between endothelial nitric oxide synthase (eNOS) activation and vascular diameter during ischemia-reperfusion was investigated in the rat heart. After short (<30 min) and long (>45 min) time of ischemia conferred by coronary artery occlusion of the rats, reperfusion caused dilatation and constriction of arterioles, respectively. Partial oxygen pressure (pO2) measurement of the heart by the electrode confirmed the hyper-perfusion and no-reflow phenomena during reperfusion, as well as myocardial ischemia. The vascular diameter was correlated with phosphorylation of Akt and serine 1177 residue of eNOS, and formation of NO-bound guanylate cyclase (GC) by immuoflorescence study. Western blotting confirmed the phosphorylation of eNOS-Ser1177 depending on ischemia time. The constriction during reperfusion after 45 min of ischemia is supposedly caused by the inhibition of Akt-mediated eNOS-Ser1177 phosphorylation, which was suppressed by a PKC inhibitor chelerythrine, or ROS scavengers N-2-mercaptopropionyl glycine (MPG) and 4,5-Dihydroxy-1, 3-benzenedisulfonic acid disodium salt (Tiron). However, an endothelin receptor antagonist BQ123 alleviated the vasoconstriction by increasing NO availability but not eNOS-Ser1177 phosphorylation. Thus, vascular patency is correlated with eNOS-Ser1177 phosphorylation in association with ROS, and PKC during reperfusion. Endothelin inhibits vasodilatation by reducing NO availability during reperfusion.

Pursuing enigmas on ischemic heart disease and sudden cardiac death

This article reviews what our colleagues have found as to how ischemic injury or cell death develop in myocardium through Ca(2+)-dependent protease calpain and how compensatory responses evolve through activation of intracellular signaling molecules including PKC isoforms, MAP kinase family enzymes and PI3 kinase. We also addressed how restraint or other psychological stress evokes hypertension and cardiovascular responses in signaling molecules or genes. Unexpectedly, carbon monoxide protects heart and cardiogenic cells against ischemia-resperfusion injury. When I think back, the unresolved cases of autopsies provided ideas for experimental study, which then taught us how the other cases died.

Potential role and mechanisms of subcellular remodeling in cardiac dysfunction due to ischemic heart disease

Several studies have revealed varying degrees of changes in sarcoplasmic reticular and myofibrillar activities, protein content, gene expression and intracellular Ca-handling during cardiac dysfunction due to ischemia-reperfusion (I/R); however, relatively little is known about the sarcolemmal and mitochondrial alterations, as well as their mechanisms in the I/R hearts. Because I/R is associated with oxidative stress and intracellular Ca-overload, it has been indicated that changes in subcellular activities, protein content and gene expression due to I/R are related to both oxidative stress and Ca-overload. Intracellular Ca-overload appears to induce changes in subcellular activities, protein contents and gene expression (subcellular remodeling) by activation of proteases and phospholipases, as well as by affecting the genetic apparatus, whereas oxidative stress is considered to cause oxidation of functional groups of different subcellular proteins in addition to modifying the genetic machinery. Ischemic preconditioning, which is known to depress the development of both intracellular Ca-overload and oxidative stress due to I/R, was observed to attenuate the I/R-induced subcellular remodeling and improve cardiac performance. It is suggested that a combination therapy with antioxidants and interventions, which reduce the development of intracellular Ca-overload, may improve cardiac function by preventing or attenuating the occurrence of subcellular remodeling due to ischemic heart disease. It is proposed that defects in the activities of subcellular organelles may serve as underlying mechanisms for I/R-induced cardiac dysfunction under acute conditions, whereas subcellular remodeling due to alterations in gene expression may explain the impaired cardiac performance under chronic conditions of I/R.

4-Hydroxynonenal modifies IgA in rat intestine after lipopolysaccharide injection

The lipid peroxide 4-hydroxynonenal (HNE) was measured in rat intestinal mucosa after lipopolysaccharide (LPS) injection (0.5 mg/kg, ip) by a highly sensitive time-resolved fluoroimmunoassay. HNE was increased, with a small peak at 20 min followed by a sustained elevation at 2-4 h, after injection of LPS. Immunohistochemistry demonstrated enhanced labeling with anti-IgA and anti-HNE antibodies in the plasma cells followed by diffusion of the labeled materials into the submucosal tissue after LPS injection. Immunoprecipitation with anti-IgA antibody and Western blotting with anti-HNE antibody showed that IgA is modified with HNE after LPS injection. The HNE (5 microM-5 mM) modification in vitro reduced the bactericidal activity of IgA and anti-Escherichia coli serum. The HNE modification in vitro also promoted polymerization of IgA as shown by nondenaturing gel electrophoresis. This is the first demonstration of the modification of IgA with HNE in an in vivo model of intestinal inflammation as well as in vitro effects of HNE on bactericidal activity and polymerization of IgA. These findings will help in understanding the involvement of oxidative stress in the IgA-mediated immune response exerted by plasma cells in early intestinal inflammation.

Dual mechanism of autoregulation of protein kinase C in myocardial ischemia

BACKGROUND

Recently, a dual activation mechanism of protein kinase C (PKC) in ischemia has been reported, consisting of early translocation and late expressional regulation. Moreover, autophosphorylation of the enzyme has been shown in vitro during its activation. This study aimed to show modes of late activation of PKC in myocardial ischemia in intact hearts.

METHODS AND RESULTS

Isolated perfused hearts of male Wistar rats were used. A: To examine if the early translocation of PKC influences the late transcriptional activation, hearts were treated with the PKC-inhibitor Bisindolylmaleimid (BIS, 0.25 microM) before the onset of ischemia and then subjected to ischemia (30 min). PKC-isoform mRNA was quantified by RT-PCR. In these experiments, ischemia leads to a selective increase of mRNA specific for the isoforms PKC-delta and PKC-epsilon (163% and 168% of control, p<0.05). This ischemia-induced upregulation could be completely blocked by BIS given before the onset of ischemia. B: To test the capacity of PKC to undergo phosphorylation during ischemia, hearts were perfused with [32P]-phosphorus and then subjected to ischemia. Ischemia (30 min) induced a significant 3-fold increase of PKC phosphorylation. Stimulation of heart with the PKC-activator tetradecanoylphorbol-13-acetate (TPA) lead to a comparable phosphorylation, suggesting that ischemia leads to autophosphorylation of PKC.

CONCLUSION

Ischemia activates two distinct forms of autoregulation of PKC. The expressional upregulation of PKC-delta and PKC-epsilon is dependent on early activation of the enzyme. At the same time, processes of enzyme phosphorylation occur. Both the mechanisms may contribute to enzyme activation processes beyond the classical enzyme translocation.

Ischemic preconditioning or p38 MAP kinase inhibition attenuates myocardial TNF α production and mitochondria damage in brief myocardial ischemia

Coronary artery occlusion increased the TNF alpha level in the membrane fraction of the rat heart, almost maximally at 30 min. TNF alpha immunofluorescence labeled streak-like reticular structures inside of the cardiomyocyte but not vascular or interstitial cells in myocardial ischemia. Immuno-electron microscopy confirmed the localization of TNF alpha between myofibrils, mitochondria, or other membrane structures in the ischemic cardiomyocyte. Ischemic preconditioning (IP) is the protection of myocardium conferred by cycles of brief ischemia-reperfusion. The increases in TNF alpha production, as well as phosphorylation of p38 MAP kinase and S6 kinase after ischemia were inhibited by IP or p38 MAP kinase inhibitors (SB203580, FR167653). TNF alpha production appeared to be regulated possibly at the post-transcriptional step by ribosomal S6 phosphorylation given that IP did not suppress TNF alpha mRNA up-regulation and was independent of NFkappaB activation. Electron microscopy (EM) showed mitochondria damage in ischemic cardiomyocyte, which was inhibited either by IP or SB203580. This is the first demonstration of the TNF alpha up-regulation in membrane structures of ischemic cardiomyocyte through p38 MAP kinase-mediated post-transcriptional mechanism, in association with mitochondrial damage.

Na+/Ca2+ exchange inhibition protects the rat heart from ischemia-reperfusion injury by blocking energy-wasting processes

We have recently reported that exposure of rat hearts to high Ca2+ produces a Ca2+ overload-induced contractile failure in rat hearts, which was associated with proteolysis of α-fodrin. We hypothesized that contractile failure after ischemia-reperfusion (I/R) is similar to that after high Ca2+ infusion. To test this hypothesis, we investigated left ventricular (LV) mechanical work and energetics in the cross-circulated rat hearts, which were subjected to 15 min global ischemia and 60 min reperfusion. Sixty minutes after I/R, mean systolic pressure-volume area (PVA; a total mechanical energy per beat) at midrange LV volume (mLVV) (PVAmLVV) was significantly decreased from 5.89 ± 1.55 to 3.83 ± 1.16 mmHg·ml·beat−1·g−1 ( n = 6). Mean myocardial oxygen consumption per beat (Vo2) intercept of (Vo2-PVA linear relation was significantly decreased from 0.21 ± 0.05 to 0.15 ± 0.03 μl O2·beat−1·g−1 without change in its slope. Initial 30-min reperfusion with a Na+/Ca2+ exchanger (NCX) inhibitor KB-R7943 (KBR; 10 μmol/l) significantly reduced the decrease in mean PVAmLVV and Vo2 intercept ( n = 6). Although Vo2 for the Ca2+ handling was finally decreased, it transiently but significantly increased from the control for 10–15 min after I/R. This increase in Vo2 for the Ca2+ handling was completely blocked by KBR, suggesting an inhibition of reverse-mode NCX by KBR. α-Fodrin proteolysis, which was significantly increased after I/R, was also significantly reduced by KBR. Our study shows that the contractile failure after I/R is similar to that after high Ca2+ infusion, although the contribution of reverse-mode NCX to the contractile failure is different. An inhibition of reverse-mode NCX during initial reperfusion protects the heart against reperfusion injury.

Age- and sex-dependent alterations in protein kinase C (PKC) and extracellular regulated kinase 1/2 (ERK1/2) in rat myocardium

Cardiovascular morbidity and mortality increase significantly with advancing age, with proportionally higher rates occurring in aged women when compared to aged men. The signaling alterations responsible for age-related reductions in ischemic stress reserves, particularly in aged women, are poorly understood. Accordingly, we sought to determine whether alterations in the cellular location and formation of specific protein kinase C (PKC)-extracellular regulated 1/2 (ERK1/2) signaling modules (SMS) might provide insight into known age- and sex-related differences in cardiovascular disease outcomes. Cytosolic (Cyto), mitochondrial (Mito) and nuclear (Nuc) fractions were isolated from left ventricles of male (M) and female (F) adult (6 mo), castrated or aged (23 mo) F344 rats by centrifugation. Western blotting was used to assess PKC (alpha, delta, epsilon), p-ERK1/2 and p-Bad(Ser112) levels, and immunoprecipitation to assess PKC-ERK1/2 SMS. Cyto-PKCalpha levels increased with age (p<0.0001), whereas increases in cyto-PKCalpha-ERK1/2 SMS were only observed in aged F (60%; p<0.01). Mito-PKCdelta and Mito-PKCdelta-ERK1/2 SMS increased in M and F with age (p<0.0001); however increases in Cyto-PKCdelta were only observed in aged M (80% p<0.0001). It is important to note that Nuc- and Mito-PKCdelta-ERK1/2 SMS were 3.5- and 4.8-fold greater in males versus females, respectively (p<0001). Increases in Mito-PKCepsilon-ERK1/2 SMS (216%) were also specific to aged M (p<0.0001), however, Mito-p-Bad(Ser112) levels were decreased with age in both M and F. Differences in sex hormone status could not fully account for observed age-related differences in PKC. Collectively, our results provide novel evidence for age and sex-related differences in the magnitude and distribution of cardiac PKC-ERK1/2 SMS consistent with previously described pathological and protective phenotypes, respectively.

Protein kinase C distribution and translocation in rat myocardium: Methodological considerations

INTRODUCTION

Protein kinase C (PKC) is an important modifier of several cardiovascular phenomena, including cardioprotection, apoptosis, and hypertrophy. Although pharmacological activation of PKC is often assessed by translocation, the effects of isolation procedures on left ventricular (LV) PKC distribution have not been systematically examined. Accordingly, we sought to determine whether homogenization methods (Polytron, glass-glass tissue grinder), detergent selection and concentration, or centrifugation protocols affect PKC (alpha, epsilon) distribution or phorbol-12-myristate-13-acetate (PMA)-induced translocation.

METHODS

Hearts of male F344 or Wistar rats were Langendorff perfused with either 100 nM PMA or vehicle, and LV cytosolic and particulate PKC (alpha, epsilon) distributions were assessed by differential centrifugation and Western blotting.

RESULTS

Following 100000 xg centrifugation of the homogenate, resuspension of the pellet (P(1)) in 0.1% sodium dodecyl sulfate (SDS) increased electrophoretic mobility of PKC (alpha, epsilon) such that PKCepsilon comigrated with a nonspecific band. Resuspension of P(1) in Triton X-100 (TX) did not affect mobility but decreased P(1) PKC (alpha, epsilon) levels in a TX-concentration-dependent manner; however, this decrease was found to be due to differential protein solubilization. Decreased levels of PKC (alpha, epsilon) were also noted in soluble and P(2) (supernatant of 100000 xg centrifugation of P(1)) fractions due to increased Polytron burst and total homogenization times. Interestingly, the P(2) fraction also revealed Polytron-dependent decreases (47% vs. glass-glass tissue grinder; p<0.05) in PKCepsilon following an initial 1000 xg centrifugation and an increased PMA-dependent translocation of PKC (alpha, epsilon; 2.4-fold and 1.6-fold, respectively, vs. P(1); p<0.05).

DISCUSSION

Taken together, these results suggest that PKC isolation procedures should be carefully considered when designing or comparing LV PKC studies due to the potential effects isolation may have on PKC distribution and translocation.

The temporal relationship between p38 MAPK and HSP27 activation in ischaemic and pharmacological preconditioning

An ischaemic preconditioning protocol and subsequent sustained ischaemia were characterized by activation and attenuation of p38 MAPK phosphorylation, respectively. However, the significance of events downstream of p38 MAPK needs investigation. Therefore the temporal relationship between phosphorylation of p38 MAPK and its downstream substrate HSP27 was studied during either an ischaemic or beta-adrenergic preconditioning protocol and during sustained ischaemia. Isolated rat hearts were preconditioned (with or without a p38 MAPK inhibitor, SB203580) with 1 x 5 min or 3 x 5 min global ischaemia or 5 min beta-adrenergic stimulation (10(-7) M isoproterenol), followed by 25 min sustained ischaemia and 30 min reperfusion. Hearts were freeze-clamped at different time intervals and fractionated to determine p38 MAPK and HSP27 phosphorylation, via Western blotting. Significant phosphorylation of cytosolic p38 MAPK and membrane (myo-fibrillar) HSP27 occurred at the end of the first preconditioning episode. However, p38 MAPK phosphorylation disappeared during subsequent preconditioning episodes, while HSP27 phosphorylation was maintained for the duration of the protocol. Similar changes in p38 MAPK and HSP27 occurred with 5 min beta-adrenergic preconditioning. After 25 min ischaemia, significant phosphorylation of cytosolic and membrane HSP27 was observed, while p38 MAPK phosphorylation was attenuated in ischaemic and beta-adrenergic preconditioned compared to non-preconditioned hearts. SB203580-induced abolishment of p38 MAPK and HSP27 phosphorylation during the triggering phase of both preconditioning protocols reversed the changes in these parameters seen after sustained ischaemia. The results suggest that p38 MAPK activation triggers HSP27 phosphorylation during both the preconditioning protocols and during sustained ischaemia. Protection of preconditioned hearts during sustained ischaemia was characterized by phosphorylation of both cytosolic and myofibrillar HSP27.

Intermittent hypoxia protects the rat heart against ischemia/reperfusion injury by activating protein kinase C

The aim of this study was to investigate whether and how protein kinase C (PKC) was involved in the protection afforded by intermittent hypoxia (IH) and the subcellular distribution of different PKC isozymes in rat left ventricle. Post-ischemic recovery of left ventricular developed pressure and +/-dP/dtmax in IH hearts were higher than those of normoxic hearts. Chelerythrine (CHE, 5 microM), a PKC antagonist, significantly inhibited the protective effects of IH, but had no influence on normoxic hearts. CHE significantly reduced the effect of IH on the time to maximal contracture (Tmc), but had no significant effect on the amplitude of maximal contracture (Amc) in IH group. In isolated normoxic cardiomyocytes, [Ca(2+)](i), measured as arbitrary units of fluorescence ratio (340 nm/380 nm) of fura-2, gradually increased during 20 min simulated ischemia and kept at high level during 30 min reperfusion. However, [Ca(2+)](i) kept at normal level during simulated ischemia and reperfusion in isolated IH cardiomyocytes. In normoxic myocytes, [Na(+)](i), indicated as actual concentration undergone calibration, gradually increased during 20 min simulated ischemia and quickly declined to almost the same level as that of pre-ischemia during 30 min simulated reperfusion. However, in IH myocytes, [Na(+)](i) increased to a level lower than the corresponding of normoxic myocytes during simulated ischemia and gradually reduced to the similar level as that of normoxic myocytes after simulated reperfusion. 5 microM CHE greatly increased the levels of [Ca(2+)](i) and [Na(+)](i) during ischemia and reperfusion in normoxic and IH myocytes. In addition, we demonstrated that IH up-regulated the baseline protein expression of particulate fraction of PKC-alpha, epsilon, delta isozymes. There is no significant difference of protein expression of PKC-alpha, epsilon, delta isozymes in cytosolic fraction between IH and normoxic group. The above results suggested that PKC contributed to the cardioprotection afforded by IH against ischemia/reperfusion (I/R) injury; the basal up-regulation of the particulate fraction of PKC-alpha, epsilon, delta isozymes in IH rat hearts and the contribution of PKC to the elimination of calcium and sodium overload might underlie the mechanisms of cardioprotection by IH.

ERK1/2 regulates intracellular ATP levels through alpha-enolase expression in cardiomyocytes exposed to ischemic hypoxia and reoxygenation

Extracellular signal-regulated kinase 1/2 (ERK1/2) is known to function in cell survival in response to various stresses; however, the mechanism of cell survival by ERK1/2 remains poorly elucidated in ischemic heart. Here we applied functional proteomics by two-dimensional electrophoresis to identify a cellular target of ERK1/2 in response to ischemic hypoxia. Approximately 1500 spots were detected by Coomassie Brilliant Blue staining of a sample from unstimulated cells. The staining intensities of at least 50 spots increased at 6-h reoxygenation after 2-h ischemic hypoxia. Of the 50 spots that increased, at least 4 spots were inhibited in the presence of PD98059, a MEK inhibitor. A protein with a molecular mass of 52 kDa that is strongly induced by ERK1/2 activation in response to ischemic hypoxia and reoxygenation was identified as alpha-enolase, a rate-limiting enzyme in the glycolytic pathway, by liquid chromatography-mass spectrometry and amino acid sequencing. The expressions of the alpha-enolase mRNA and protein are inhibited during reoxygenation after ischemic hypoxia in the cells containing a dominant negative mutant of MEK1 and treated with a MEK inhibitor, PD98059, leading to a decrease in ATP levels. alpha-Enolase expression is also observed in rat heart subjected to ischemia-reperfusion. The induction of alpha-enolase by ERK1/2 appears to be mediated by c-Myc. The introduction of the alpha-enolase protein into the cells restores ATP levels and prevents cell death during ischemic hypoxia and reoxygenation in these cells. These results show that alpha-enolase expression by ERK1/2 participates in the production of ATP during reoxygenation after ischemic hypoxia, and a decrease in ATP induces apoptotic cell death. Furthermore, alpha-enolase improves the contractility of cardiomyocytes impaired by ischemic hypoxia. Our results reveal that ERK1/2 plays a role in the contractility of cardiomyocytes and cell survival through alpha-enolase expression during ischemic hypoxia and reoxygenation.

Subcellular distribution of protein kinase C isozymes during cardioplegic arrest

BACKGROUND

On the basis of the hypothesis that cardioplegia-associated myocardial depression was due to activation of protein kinase C, we examined whether specific protein kinase C isozymes would translocate to a cellular fraction containing myofilaments.

METHODS

Isolated rat hearts were perfused with Krebs-Ringer bicarbonate buffer for 30 minutes and arrested with 4 degrees C St Thomas No. 2 cardioplegic solution for 0 to 120 minutes (n = 5 per group). The 3 fractions of the left ventricle tissue represented the myofibrillar/nuclear fraction (P1), membranes (P2), and cytosol (supernatant). The distributions of protein kinase C isozymes alpha, delta, epsilon, and eta were examined after separation by electrophoresis, immunoblotting/chemiluminescence, and densitometry.

RESULTS

A significant increase in protein kinase C-delta in the P1 fraction was detected after 5 minutes of cardioplegic arrest and remained increased for 60 minutes. Increases in P1 protein kinase C-alpha and -epsilon were seen transiently at 5 minutes, and protein kinase C-epsilon demonstrated a secondary increase in P1 at 30 to 60 minutes. There was also a significant relative increase in protein kinase C-alpha and protein kinase C-delta in the P2 fraction after 60 minutes of cardioplegia.

CONCLUSIONS

These data are consistent with our hypothesis that activation of protein kinase C isozymes is associated with altered myofilament function after cardioplegic arrest.

Heterogeneous nuclear ribonucleoprotein K interacts with and is proteolyzed by calpain in vivo

Calpain is a cytosolic "modulator protease" that modulates cellular functions in response to Ca2+. To identify in vivo substrates of calpain, yeast two-hybrid screening was done using the 5-EF-hand (penta-EF-hand; PEF) domain of the micro-calpain large subunit (domain IV), since several possible in vivo substrates for calpain have been previously reported to bind to the 5-EF-hand domains. Other than the regulatory subunit of calpain, which binds to the domain IV, heterogeneous nuclear ribonucleoproteins (hnRNP) K and R were identified, and shown to be proteolyzed by micro-calpain in vitro. When expressed in COS7 cells, hnRNP K and micro-calpain co-localized in the cytosol, and Ca2+-ionophore stimulation of the cells resulted in proteolysis of hnRNP K, indicating that hnRNP K is an in vivo substrate for calpain. Now, hnRNP K is considered to function as a scaffold protein for its binding proteins, such as PKCdelta and C/EBPbeta, which were reported to be calpain substrates, suggesting that hnRNP-K is a scaffold for calpain to proteolyze these proteins.

Role of protein kinase C in geranylgeranylacetone-induced expression of heat-shock protein 72 and cardioprotection in the rat heart

We recently demonstrated that oral administration of geranylgeranylacetone (GGA), an antiulcer agent, induces heat-shock protein 72 (HSP72) in the rat heart and renders cardioprotection against ischemia/reperfusion injury. However, the signaling pathways remain to be elucidated. The present study tested the hypothesis that oral GGA would activate protein kinase C (PKC), leading to the phosphorylation and translocation of heat-shock factor 1 (HSF1), and thus, promote the expression of HSP72 protein. Rats were classified into four groups: a control (CNT) group (vehicle administration), a GGA group (GGA 200 mg/kg administration), a chelerythrine (CHE)-CNT group (pretreated with intravenous (i.v.) injection of 5 mg/kg CHE before vehicle administration), and a CHE-GGA group (pretreated with CHE before GGA administration). After 24 h administration, oral GGA-induced overexpression of HSP72, increased amount of the phosphorylated form of HSF1 in the nucleus, produced heat-shock element-specific DNA-HSF1 complex, and caused translocation of protein kinase C (PKC)delta, all of which were prevented by pretreatment with CHE. GGA also increased the PKC activity in a particulate fraction, which was prevented by pretreatment with rottlerin, a specific inhibitor of PKCdelta. Isolated-perfused heart experiments revealed that the better functional recovery observed in the GGA group during the reperfusion period following the 20 min of no-flow global ischemia, compared with the CNT group, was abolished by pretreatment with CHE. These results suggest that activation of PKC (translocation of PKCdelta), which primes the phosphorylation of HSF1, plays an essential role in the cardiac overexpression of HSP72 by GGA that leads to cardioprotection.

On-pump coronary artery bypass surgery activates human myocardial NF-kappaB and increases TNF-alpha in the heart

PURPOSE

Myocardial tumor necrosis factor alpha (TNF) production and nuclear factor kappa B (NF-kappaB) activation has been demonstrated in chronic heart failure and experimental models of acute ischemia-reperfusion injury. Further, a cause and effect relationship has been established between these events and cardiomyocyte apoptosis following such conditions. It remains unknown, however, whether the myocardial injury associated with coronary artery bypass surgery (CAB) results in myocardial NF-kappaB activation and TNF production. We hypothesized that CAB with cardiopulmonary bypass ("on-pump") activates human myocardial NF-kappaB and increases TNF in the heart.

METHODS

Patients, 18 to 65 years of age, scheduled for elective cardiac surgery but without other preexisting disease were considered eligible for the study. Biopsies of human myocardium were obtained before and after cardiopulmonary bypass and myocardial TNF levels were determined by ELISA and cytotoxicity assay, and NF-kappaB activation was determined by electrophoretic mobility shift assay (n = 6 patients). NF-kappaB activation was quantitated with gel densitometry.

RESULTS

The clinical characteristics of the study patients were as follows (means +/- SEM): mean age (y) 50.0 +/- 5.7, male 6 (100%), cardiopulmonary bypass time (min) 107 +/- 37.7, cross-clamp time (min) 68 +/- 17.6, number of CAB 3.0 +/- 1.1, and length of hospital stay (d) 4.8 +/- 0.9. Before CAB, myocardial TNF-alpha levels were 251 +/- 22 pg/g and 33 +/- 9 U/g, as determined by ELISA and cytotoxicity assay, respectively. Following CAB, human myocardial TNF-alpha levels increased to 892 +/- 71 pg/g (P = 0.0008) and 141 +/- 11 U/g (P = 0.0042), as determined by ELISA and cytotoxicity assay, respectively. Before CAB, the ratio of bound to unbound NF-kappaB DNA was 0.009 +/- 0.0007 and after CAB the ratio was 0.24 +/- 0.01 (P < 0.0001).

CONCLUSIONS

This study represents the initial demonstration that coronary artery bypass grafting results in an activation of NF-kappaB and an increase of TNF in the heart.

Dose-dependent effects of acute exercise on PKC levels in rat heart: is PKC the heart's prophylactic?

Epidemiological studies have demonstrated that chronic exercise is cardioprotective, and recent evidence from our laboratory suggests a key role for protein kinase C (PKC)-dependent pathways, at least in part, as a cellular basis for this response. However, the dose-response relationship linking exercise volume and the time course of isoform-specific PKC activation are poorly understood.

AIM

The purpose of this investigation was to determine the effects of acute exercise of varying durations on PKC subcellular distribution and phosphorylation in the rat left ventricle.

METHODS

Adult (5 months) male Fischer-344 more rats were subjected to a single bout (OB) or 7 days (SB) of treadmill running (n = 6/group; 23 m min-1, 20 min), and compared with sedentary controls (SED; n = 8). Hearts were isolated immediately after [early window (EW); n = 3/group] or 24 h after the last exercise bout [late window (LW); n = 3/group] in OB and SD, respectively. Total PKC and subcellular distribution for the alpha, delta, epsilon, betaI, and betaII isoforms, as well as phosphorylated (phospho-) PKC epsilon (pSer729), PKC alpha (pSer657) and PKCdelta (pThr507) levels were assessed by western blotting. Protein kinase C epsilon and PKC alpha mRNA levels were assessed by real time polymerase chain reaction.

RESULTS

Following OB, PKCbetaI protein levels were reduced, while total phospho-PKC epsilon (pSer729), PKC alpha (pSer657) and PKC delta (pThr507) levels were increased during EW (P < 0.05). Interestingly, total PKC delta (31%) and membrane-associated PKC alpha (24%) levels decreased from EW to LW (P < 0.05). In contrast, SB yielded chronic increases in total PKC epsilon (80.5%) levels and PKC delta (20.0%) levels (P < 0.03), with reversal of effects on phospho-PKC epsilon (Ser729), phospho-PKC alpha (Ser657) and phospho-PKC delta (Thr507) levels observed with OB. Reductions in total phospho-PKC alpha (Ser657) persisted at SB (26.1%; P < 0.02). Interestingly, mRNA levels for PKC epsilon were significantly increased following SB while PKC alpha mRNA levels were reduced, respectively.

CONCLUSION

These data suggest that divergent patterns of PKC activation occur following OB and SB at both the transcriptional and translational levels. That similar patterns of PKC translocation are observed in experimental models of ischaemic preconditioning and genetic PKC manipulation provide evidence for a dose-dependent cardioprotective phenotype induced by physical activity.

Mechanisms of myocardial remodeling: ramiprilat blocks the expressional upregulation of protein kinase C-epsilon in the surviving myocardium early after infarction

Inhibition of angiotensin-converting enzyme (ACEI) after myocardial infarction reduces remodeling of the surviving myocardium. The cellular signaling mechanisms contributing to remodeling are not fully elucidated. Goal of the current study was to test whether protein kinase C (PKC) is regulated in the surviving myocardium shortly after infarction and whether this regulation is influenced by ACEI. Rats were subjected to anterior wall myocardial infarction in vivo or sham operation. After 15-45 min, mRNA levels and protein expression of the major cardiac PKC isoforms were measured in the ischemic and the remote myocardium. The influence of ACEI on PKC was tested by pretreating the rats with ramiprilat. In the ischemic region of the myocardium, a significant increase of the mRNA for PKC-delta and PKC-epsilon was observed in close correlation with increased isoform protein expression. In the surviving, remote myocardium, however, only PKC-epsilon expression was significantly augmented both at the mRNA level (158%) and at the protein level (149%). PKC-delta and PKC-alpha were unchanged. Treatment with ramiprilat could abolish this isoform-specific PKC regulation in both areas. These data characterize for the first time an isoform-specific transcriptional regulation process of PKC in the surviving myocardium after infarction. This induction of PKC-epsilon can be prevented by ACEI. It is speculated that PKC-epsilon plays a role in the signal transduction of early remodeling after infarction.

Protein kinase C-epsilon protects PC12 cells against methamphetamine-induced death: possible involvement of suppression of glutamate receptor

The involvement of PKC isoform in the methamphetamine (MA)-induced death of neuron-like PC12 cell was studied. The death and the enhanced terminal dUTP nick end labeling (TUNEL) staining were inhibited by a caspase inhibitor, z-Val-Ala-Asp- (OMe)-CH(2)F (z-VAD-fmk). However, the cell death shows neither morphological nor biochemical features of apoptosis or necrosis. The cell death was suppressed by a protein kinase C (PKC) activator, 12,13-phorbol myristate acetate, but was enhanced by PKC specific inhibitor calphostin C or bisindolylmaleimide, not by PKC inhibitor relatively specific for PKC-alpha (safingol) or PKC-delta (rottlerin). Western blotting demonstrated the expression of PKC-alpha, gamma, delta, epsilon and zeta, of which PKC-epsilon translocated from the soluble to the particulate fraction after MA-treatment. Antisense to PKC-epsilon enhanced MA-induced death. A glutamate receptor antagonist MK801 abrogated the cell death, which is reversed by PKC inhibition. These data suggest that PKC-epsilon promotes PC12 cell survival through glutamate receptor suppression.

Protective effects of protein kinase C during myocardial ischemia require activation of phosphatidyl-inositol specific phospholipase C

BACKGROUND

Protein kinase C (PKC) activation during myocardial ischemia is thought to be cardioprotective. However, the mechanism of ischemia-induced PKC activation remains unclear. We hypothesized that ischemic PKC activation occurs through activation of phosphatidyl-inositol specific phospholipase C (PI-PLC) and protects the heart from ischemic injury.

METHODS

Isolated rabbit hearts were subjected to 20 minutes of normothermic ischemia and reperfusion. The PI-PLC inhibitor U73122 (0.5 micromol/L), its inactive analogue U73343 (0.5 micromol/L), or the PKC inhibitor chelerythrine (2 micromol/L) were given just before ischemia. Another group received U73122 plus the direct PKC activator phorbol 12-myristate-13-acetate (PMA, 10 pmol/L). Measurements included contractile function, intracellular calcium, PI-PLC activity, and translocation of PKC isoforms.

RESULTS

PI-PLC activity increased during myocardial ischemia and was inhibited by U73122. PI-PLC inhibition prevented the ischemic translocation of PKC-alpha, PKC-epsilon, and PKC-eta, and impaired cardiac recovery and cytosolic calcium regulation without significant changes in energy metabolism. PMA restored both contractile function and PKC translocation pattern in U73122-treated hearts. Direct PKC inhibition with chelerythrine mimicked the effects of U73122.

CONCLUSIONS

PI-PLC mediates PKC translocation during myocardial ischemia. Inhibition of PI-PLC or PKC activation, or both, during ischemia significantly impairs postischemic myocardial recovery.

Activation of alpha 1-adrenoceptors is not essential for the mediation of ischaemic preconditioning in rat heart

1. The aim of the present study was to clarify the role of alpha1-adrenoceptors in the mechanism of ischaemic preconditioning (IP). 2. Rat isolated perfused hearts were either non- preconditioned, preconditioned with 5 min ischaemia or treated for 5 min with alpha1-adrenoceptor agonists (50 micromol/L phenylephrine; 0.1, 0.5 and 1 micromol/L methoxamine) before being subjected to 45 min of sustained ischaemia followed by 60 min reperfusion. 3. Within each of the above protocols, hearts were divided into groups to which alpha1-adrenoceptor antagonists (prazosin, 5'-methyl urapidil and chloroethylclonidine (CEC)) were administered. Functional recovery and infarct size were used as indices of the effects of ischaemia. Ischaemic contracture characteristics and maximal diastolic pressure during reflow were also assessed. 4. Blockade of alpha(1)-adrenoceptors with prazosin or the subtype-selective antagonists 5'-methyl urapidil and CEC did not abolish the protective effect of IP with respect to both functional recovery and infarct size reduction. 5. Protection afforded by phenylephrine was attenuated in hearts treated with prazosin or the alpha(1B)-adrenoceptor- selective antagonist CEC, but not in those treated with the alpha(1A)-adrenoceptor-selective antagonist 5'-methyl urapidil. 6. Treatment with low concentrations of methoxamine, considered to be alpha(1A)-adrenoceptor selective, did not confer any protection to the ischaemic myocardium. 7. A close relationship between accelerated ischaemic contracture and enhanced cardioprotection was observed. 8. The results suggest that alpha1-adrenoceptor stimulation mimics IP, but it is not an essential component in the mechanism behind the protective effect of IP in rat heart. In addition, the present study demonstrates that stimulation of the alpha(1B)- but not the alpha(1A)-adrenoceptor subtype is responsible for the catecholamine-induced protection of ischaemic myocardium in rat.

Phosphorylation of proteins and apoptosis induced by c-Jun N-terminal kinase1 activation in rat cardiomyocytes by H(2)O(2) stimulation

Cytokines and various cellular stresses are known to activate c-Jun N-terminal kinase-1 (JNK1), which is involved in physiological function. Here, we investigate the activation of JNK1 by oxidative stress in H9c2 cells derived from rat cardiomyocytes. H(2)O(2) (100 microM) significantly induces the tyrosine phosphorylation of JNK1 with a peak 25 min after the stimulation. The amount of JNK1 protein remains almost constant during stimulation. Immunocytochemical observation shows that JNK1 staining in the nucleus is enhanced after H(2)O(2) stimulation. To clarify the physiological role of JNK1 activation under these conditions, we transfected antisense JNK1 DNA into H9c2 cells. The antisense DNA (2 microM) inhibits JNK1 expression by 80% as compared with expression in the presence of the sense DNA, and significantly blocks H(2)O(2)-induced cell death. Consistent with the decrease in cell number, we detected condensation of the nuclei, a hallmark of apoptosis, 3 h after H(2)O(2) stimulation in the presence of the sense DNA for JNK1. The antisense DNA of JNK1 inhibits the condensation of nuclei by H(2)O(2). Under these conditions, the H(2)O(2)-induced phosphorylation of proteins with molecular masses of 55, 72, and 78 kDa is blocked by treatment with the antisense DNA for JNK1 as compared with the sense DNA for JNK1. These findings suggest that JNK1 induces apoptotic cell death in response to H(2)O(2), and that the cell death may be involved in the phosphorylations of 55, 72, and 78 kDa proteins induced by JNK1 activation.

Rat cardiac contractile dysfunction induced by Ca2+ overload: possible link to the proteolysis of alpha-fodrin

The aim of the present study was to examine the mechanisms of Ca2+ overload-induced contractile dysfunction in rat hearts independent of ischemia and acidosis. Experiments were performed on 30 excised cross-circulated rat heart preparations. After hearts were exposed to high Ca2+, there was a contractile failure associated with a parallel downward shift of the linear relation between myocardial O(2) consumption per beat and systolic pressure-volume area (index of a total mechanical energy per beat) in left ventricles from all seven hearts that underwent the protocol. This result suggested a decrease in O(2) consumption for total Ca2+ handling in excitation-contraction coupling. In the hearts that underwent the high Ca2+ protocol and had contractile failure, we found marked proteolysis of a cytoskeleton protein, alpha-fodrin, whereas other proteins were unaffected. A calpain inhibitor suppressed the contractile failure by high Ca2+, the decrease in O(2) consumption for total Ca2+ handling, and membrane alpha-fodrin degradation. We conclude that the exposure to high Ca2+ may induce contractile dysfunction possibly by suppressing total Ca2+ handling in excitation-contraction coupling and degradation of membrane alpha-fodrin via activation of calpain.

Src tyrosine kinase is the trigger but not the mediator of ischemic preconditioning

The signal cascade that triggers and mediates ischemic preconditioning (IPC) remains unclear. The present study investigated the role of the Src family of tyrosine kinases in IPC. Isolated and buffer-perfused rat hearts underwent IPC with three cycles of 5-min ischemia and 5-min reperfusion, followed by 30-min ischemia and 120-min reperfusion. The Src tyrosine kinase family-selective inhibitor PP1 was administered between 45 and 30 min before ischemia (early PP1 treatment) or for 15 min before IPC [early PP1-preconditioning (PC) treatment]. PP1 was also administered for 5 min before the sustained ischemia (late PP1 treatment) or after IPC (late PP1-PC treatment). Src kinase was activated after 30 min of ischemia in both the membrane and cytosolic fractions. Src kinase was also activated by IPC but was attenuated after the sustained ischemia. Early and late PP1 treatment inhibited Src activation after the sustained ischemia and reduced infarct size. Early PP1-PC inhibited Src activation after IPC but not after the sustained ischemia and blocked cardioprotection afforded by IPC. Late PP1-PC treatment abrogated IPC-induced activation of Src and protein kinase C (PKC)-epsilon in the membrane but not in the cytosolic fraction. This treatment modality abrogated Src activation after the sustained ischemia and failed to block cardioprotection afforded by IPC. These results suggest that Src kinase activation mediates ischemic injury but triggers IPC in the position either upstream of or parallel to membrane-associated PKC-epsilon.

Role of protein kinase C in the reduction of infarct size by N-methyl-1-deoxynojirimycin, an alpha-1,6-glucosidase inhibitor

Preischaemic treatment with N-methyl-1-deoxynojirimycin (MOR-14), an alpha-1,6-glucosidase inhibitor, attenuates glycogenolysis and lactate accumulation during ischaemia and markedly reduces infarct size in rabbit hearts. In the present study, we have investigated whether protein kinase C (PKC), a principal mediator of ischaemic preconditioning, is also involved in the cardioprotective effect of MOR-14. To assess the effect of PKC inhibition on infarct size in MOR-14-treated hearts, 38 rabbits were subjected to 30 min of ischaemia followed by 48 h of reperfusion. Infarct size, as a per cent of area at risk, was significantly smaller in rabbits administered 100 mg kg(-1) of MOR-14 10 min before ischaemia (17+/-2%, n=10), than in a control group (46+/-5%, n=10). This beneficial effect of MOR-14 was abolished when 5 mg kg(-1) of chelerythrine, a PKC inhibitor, was given 10 min prior to MOR-14 injection (39+/-4%, n=10), although chelerythrine alone did not alter infarct size (43+/-4%, n=8). Further, chelerythrine had no effect on MOR-14-induced attenuation of glycogen breakdown and lactate accumulation in hearts excised at 30 min of ischaemia. Immunoblot analysis of PKC in homogenates of Langendorff-perfused rabbit hearts revealed that MOR-14 significantly increased levels of PKC-epsilon in the particulate fraction at 20 and 30 min of ischaemia and in the cytosolic fraction at 30 min of ischaemia. Taken as a whole, our data suggest that PKC acts downstream of the inhibition of glycogenolysis by MOR-14 to reduce infarct size. Thus, activation of PKC is a more direct mediator of the cardioprotection afforded by MOR-14 than is inhibition of glycogenolysis.

Localization and kinetics of protein kinase C-epsilon anchoring in cardiac myocytes

Protein kinase C-epsilon (PKC-epsilon) plays a central role in cardiac cell signaling, but mechanisms of translocation and anchoring upon activation are poorly understood. Conventional PKC isoforms rely on a rapid Ca2+-mediated recruitment to cell membranes, but this mechanism cannot be employed by PKC-epsilon or other PKC isoforms lacking a Ca2+-binding domain. In this study, we used recombinant green fluorescent protein (GFP) fusion constructs and confocal microscopy to examine the localization, kinetics, and reversibility of PKC-epsilon anchoring in permeabilized rat cardiac myocytes. PKC-epsilon-GFP bound with a striated pattern that co-localized with alpha-actinin, a marker of the Z-line of the sarcomere. Binding required activation of PKC and occurred slowly but reversibly with apparent rate constants of k(on) = 4.6 +/- 1.2 x 10(3) M(-1) x s(-1) and k(off) = 1.4 +/- 0.5 x 10(-3) s(-1) (t1/2 = 8 min) as determined by fluorescence recovery after photobleaching and by perfusion experiments. A truncated construct composed of the N-terminal 144-amino-acid variable region of PKC-epsilon (epsilonV1-GFP), but not an analogous N-terminal domain of PKC-delta, mimicked the Z-line decoration and slow binding rate of the full-length enzyme. These findings suggest that the epsilonV1 domain is important in determining PKC-epsilon localization and translocation kinetics in cardiac muscle. Moreover, PKC-epsilon translocation is not a diffusion-controlled binding process but instead may be limited by intramolecular conformational changes within the V1 domain. The k(off) for epsilonV1-GFP was two- to threefold faster than for full-length enzyme, indicating that other domains in PKC-epsilon contribute to anchoring by prolonging the bound state.

Ischemic preconditioning upregulates vascular endothelial growth factor mRNA expression and neovascularization via nuclear translocation of protein kinase C epsilon in the rat ischemic myocardium

Ischemic preconditioning (IP) exerts cardioprotection through protein kinase C (PKC) activation, whereas myocardial ischemia enhances vascular endothelial growth factor (VEGF) mRNA expression. However, the IP effect or the involvement of PKC on the VEGF expression is unknown in myocardial infarction. We investigated whether IP enhances VEGF gene expression and angiogenesis through PKC activation in the in vivo myocardial infarction model. Sprague-Dawley rats were assigned into the following 3 groups: the sham group; the IP group, which underwent 3 cycles of 3 minutes of ischemia and 5 minutes of reperfusion (IP procedure); and the non-IP group. The latter 2 groups were subsequently subjected to left anterior descending coronary artery occlusion. To examine the involvement of PKC, the PKC inhibitor chelerythrine (5 mg/kg) or bisindolylmaleimide (1 mg/kg) was injected intravenously before the IP procedures. PKCepsilon was translocated to the nucleus after 10 minutes of ischemia after the IP procedure but was not translocated in the non-IP and the sham groups. VEGF mRNA expression 3 hours after infarction was significantly higher in the IP group than in the non-IP and the sham groups. Capillary density in the infarction was significantly higher, whereas the infarct size was smaller in the IP group than in the non-IP group at 3 days of infarction. Chelerythrine but not bisindolylmaleimide blocked all of the IP effects on the nuclear translocation of PKCepsilon, enhancement of VEGF mRNA expression and angiogenesis, and infarct size limitation. These results show that IP may enhance VEGF gene expression and angiogenesis through nuclear translocation of PKCepsilon in the infarcted myocardium.

Protein kinase C isoform-dependent myocardial protection by ischemic preconditioning and potassium cardioplegia

OBJECTIVE

Ischemic preconditioning combined with potassium cardioplegia does not always confer additive myocardial protection. This study tested the hypothesis that the efficacy of ischemic preconditioning under potassium cardioplegia is dependent on protein kinase C isoform.

METHODS

Isolated and crystalloid-perfused rat hearts underwent 5 cycles of 1 minute of ischemia and 5 minutes of reperfusion (low-grade ischemic preconditioning) or 3 cycles of 5 minutes of ischemia and 5 minutes of reperfusion (high-grade ischemic preconditioning) or time-matched continuous perfusion. These hearts received a further 5 minutes of infusion of normal buffer or oxygenated potassium cardioplegic solution. The isoform nonselective protein kinase C inhibitor chelerythrine (5 micromol/L) was administered throughout the preischemic period. All hearts underwent 35 minutes of normothermic global ischemia followed by 30 minutes of reperfusion. Isovolumic left ventricular function and creatine kinase release were measured as the end points of myocardial protection. Distribution of protein kinase C alpha, delta, and epsilon in the cytosol and the membrane fractions were analyzed by Western blotting and quantified by a densitometric assay.

RESULTS

Low-grade ischemic preconditioning was almost as beneficial as potassium cardioplegia in improving functional recovery; left ventricular developed pressure 30 minutes after reperfusion was 70 +/- 15 mm Hg (P <.01) in low-grade ischemic preconditioning and 77 +/- 14 mm Hg (P <.001) in potassium cardioplegia compared with values found in unprotected control hearts (39 +/- 12 mm Hg). Creatine kinase release during reperfusion was also equally inhibited by low-grade ischemic preconditioning (18.2 +/- 10.6 IU/g dry weight, P <.05) and potassium cardioplegia (17.6 +/- 6.7 IU/g, P <.01) compared with control values. However, low-grade ischemic preconditioning in combination with potassium cardioplegia conferred no significant additional myocardial protection; left ventricular developed pressure was 80 +/- 17 mm Hg, and creatine kinase release was 14.8 +/- 11.0 IU/g. In contrast, high-grade ischemic preconditioning with potassium cardioplegia conferred better myocardial protection than potassium cardioplegia alone; left ventricular developed pressure was 121 +/- 16 mm Hg (P <.001), and creatine kinase release was 8.3 +/- 5.8 IU/g (P <.05). Chelerythrine itself had no significant effect on functional recovery and creatine kinase release in the control hearts, but it did inhibit the salutary effects not only of low-grade and high-grade ischemic preconditioning but also those of potassium cardioplegia. Low-grade ischemic preconditioning and potassium cardioplegia enhanced translocation of protein kinase C alpha to the membrane, whereas high-grade ischemic preconditioning also enhanced translocation of protein kinase C delta and epsilon. Chelerythrine inhibited translocation of all 3 protein kinase C isoforms.

CONCLUSIONS

These results suggest that myocardial protection by low-grade ischemic preconditioning and potassium cardioplegia are mediated through enhanced translocation of protein kinase C alpha to the membrane. It is therefore suggested that activation of the novel protein kinase C isoforms is necessary to potentiate myocardial protection under potassium cardioplegia.

cis-9,10-Methylenehexadecanoic acid inhibits contractility and actomyosin ATPase activity of guinea pig myocardium

Superfusion with a cyclopropane fatty acid, cis-9, 10-methylenehexadecanoic acid (10-300 microM), reduced the contractility of papillary muscle isolated from guinea pigs in a dose-dependent manner. cis-9,10-Methylenehexadecanoic acid also inhibited the Mg(2+)-ATPase activity of guinea pig papillary myocardium by about 40% at 400 microM. Since cis-9, 10-methylenehexadecanoic acid 4 microM inhibited the K(+)-EDTA-ATPase activity inherent in myosin's catalytic activity by about 25%, the fatty acid was thought to interact with the catalytic center of the myosin molecule.

Nuclear mitogen-activated protein kinase activation by protein kinase czeta during reoxygenation after ischemic hypoxia

We examined the upstream kinases for mitogen-activated protein kinase (MAPK) activation during ischemic hypoxia and reoxygenation using H9c2 cells derived from rat cardiomyocytes. Protein kinase C (PKC)zeta, an atypical PKC isoform mainly expressed in rat heart, has been shown to act as an upstream kinase of MAPK during ischemic hypoxia and reoxygenation by analyses with PKC inhibitors, antisense DNA, a dominant negative kinase defective mutant, and constitutively active mutants of PKCzeta. Immunocytochemical observations show PKCzeta staining in the nucleus during ischemic hypoxia and reoxygenation when phosphorylated MAPK is also detected in the nucleus. This nuclear localization of PKCzeta is inhibited by treatment with wortmannin, a phosphoinositide 3-kinase inhibitor that also inhibits MAPK activation in a dose-dependent manner. This is supported by the inhibition of MAPK phosphorylation by another blocker of phosphoinositide 3-kinase, LY294002. An upstream kinase of MAPK, MEK1/2, is significantly phosphorylated 15 min after reoxygenation and observed mainly in the nucleus, whereas it is present in the cytoplasm in serum stimulation. The phosphorylation of MEK is blocked by PKC inhibitors and phosphoinositide 3-kinase inhibitors, as observed in the case of MAPK phosphorylation. These observations indicate that PKCzeta, which is activated by phosphoinositide 3-kinase, induces MAPK activation through MEK in the nucleus during reoxygenation after ischemic hypoxia.

Translocation of HSP27 to sarcomere induced by ischemic preconditioning in isolated rat hearts

We investigated the role of the 27-kDa heat shock protein (HSP27) in cardiac protection using Langendorff-perfused rat hearts. After preconditioning (a single episode of 5 min global ischemia followed by 5 min of reperfusion), HSP27 redistributed from the cytosol to the sarcomere and recovery of the contractile function, after 40 min of global ischemia and 50 min of reperfusion, was significantly enhanced. Both SB203580, a p38 MAP kinase inhibitor, and bisindolylmaleimide I, a protein kinase C inhibitor, prevented the effects of preconditioning. Both 2-chloro-N(6)-cyclopentyladenosine (adenosine A1 agonist) and anisomycin (activator of p38 MAP kinase and c-jun N-terminal kinase) mimicked preconditioning. These results suggest that activation of protein kinase C followed by activation of p38 MAP kinase elicits translocation of HSP27 to the sarcomere, a process which may be involved in the cardioprotective mechanism afforded by ischemic preconditioning in rat heart.

The effect of protein kinase C activation on colonic epithelial cellular integrity

We have investigated whether activation of protein kinase C has a direct cytotoxic effect on colonic mucosal epithelial cells and whether oxidant-induced damage to colonocytes is mediated by activation of cellular protein kinase C. Incubation of freshly harvested cells from rat colon with the protein kinase C activator, phorbol 12-myristate, resulted in a concentration-dependent increase in the extent of cell injury. Phorbol 12-myristate acetate (0.1-10 microM) also increased cellular protein kinase C activity and this was reduced significantly by treating cells with the antagonists staurosporine or 2-[1-(3-dimethylaminopropyl)-indol-3-yl]3-(-indol-3-yl)maleimide (GF 109203X; 10 microM). Phorbol 12-myristate acetate treatment also resulted in increased translocation of proteins for protein kinase C isoforms alpha, delta and epsilon from cytosol to membrane particulate fractions. The antagonists reduced the extent of cell damage in response to phorbol 12-myristate acetate. Furthermore, cell injury in response to the phorbol acetate was also inhibited by the addition of the oxidant scavengers, superoxide dismutase or catalase to the cell suspension. Addition of H(2)O(2) to the incubation medium (0.1-100 microM) resulted in an increase in cellular protein kinase C activity, an increase in the expression of the alpha, beta and zeta isoforms and a reduction in cell integrity. The cellular damaging actions of H(2)O(2) were significantly reduced by the protein kinase C antagonists, staurosporine or 2-[1-(3-dimethylaminopropyl)-indol-3-yl]-3-(-indol-3-yl)maleimide (GF 109203X). These findings suggest that protein kinase C activation results in colonic cellular injury and this damage is mediated, at least in part, by release of reactive oxidants. Furthermore, oxidant-mediated damage to these cells also involves protein kinase C activation.

Protein kinase C expression and subcellular distribution in chronic myocardial ischemia. Comparison of two different canine models

We studied protein kinase C (PKC) isozyme expression and activity distribution in two models of chronically ischemic canine myocardium: (1) single vessel obstruction (SVO), produced by tight stenosis of LAD followed by preconditioning and acute ischemia (40 min); (2) three vessel obstruction (3VO), produced by LAD-stenosis and gradual occlusion of right coronary artery and left circumflex. In both models after 8 weeks of chronic ischemia the dogs were either sacrificed or had PTCA of the LAD with a follow up of another 4 weeks. Control dogs were sham operated. PKC activity was measured in subcellular fractions of tissue samples from anterior and posterior regions in the presence of histone and gamma-[32P]-ATP. PKC isozymes were detected by Western blotting. All regions perfused by the obstructed coronaries were dysfunctional at 8 weeks when compared to baseline, with improvement of anterior wall function after PTCA of LAD. PKC activity was elevated in the membrane fraction of SVO, but unchanged in the 3VO model. PKCs alpha, epsilon, and zeta prevailed in cytosol fraction of the controls (cytosol/membrane ratios were +/- 3.34, 1.38 and 4.56 for alpha, epsilon and zeta, respectively), consistent with PKC activity distribution, while delta was not detected. There was no significant difference between the groups concerning the relative membrane amount of the isozymes. PKCs alpha and epsilon were decreased in the cytosol fraction of both models at 8 weeks (for anterior region, by 56 and 57% in SVO and by 49 and 46% in 3VO, respectively) without there being any differences between anterior and posterior regions, and were low also in the PTCA group. PKC zeta distribution however varied between the two models. The amount of PKC zeta isozyme was downregulated by 45% after 8 weeks of chronic ischemia and returned towards the control values after PTCA in the anterior region of SVO, while it did not change in anterior wall after 8 weeks in 3VO but was significantly decreased (by 47%) in posterior region after PTCA. In conclusion, our results suggest modified PKC signalling in chronically ischemic canine myocardium.

Protein kinase C regulation of K+ currents in rat ventricular myocytes and its modification by hormonal status

1. The effects of protein kinase C (PKC) activation on cardiac K+ currents were studied in rat ventricular myocytes, using whole-cell voltage clamp methods. Control rats were compared to hypothyroid or diabetic rats, in which PKC expression and activity were enhanced. 2. In control myocytes, two calcium-independent outward K+ currents, the transient It and the sustained Iss, were attenuated by 18.9 +/- 2.0 and 16.8 +/- 3.5 %, respectively (mean +/- s.e.m.), following addition of a synthetic analogue of diacylglycerol, DiC8 (20 microM). In myocytes from hypothyroid or diabetic rats, It and Iss were not affected by DiC8. 3. The effects of DiC8 were restored in myocytes from thyroidectomized rats by injection of physiological doses of tri-iodothyronine (T3; 10 microg kg-1 for 6-8 days). Incubating cells from diabetic rats with 100 nM insulin for 5-9 h also restored the ability of DiC8 to attenuate It and Iss. 4. The attenuation of K+ currents by DiC8 in control cells was absent in the presence of a peptide known to inhibit the translocation of the isoform PKCepsilon (EAVSKPLT, 24 microM introduced through the recording pipette). A scrambled peptide (LSETKPAV) was without effect. 5. Under hypothyroid conditions the inhibitory peptide restored the effects of DiC8 on It and Iss. These currents were attenuated by 11.9 +/- 1. 5 and 9.8 +/- 1.5 %, respectively, which was significantly (P < 0. 001) more than without the peptide or with the scrambled peptide. 6. These results show that the PKC-mediated suppression of cardiac K+ currents is normally mediated by PKCepsilon translocation. This effect is absent under hypothyroid and diabetic conditions, presumably due to prior PKC activation and translocation. A PKCepsilon translocation inhibitor restores the ability of DiC8 to attenuate K+ currents under hypothyroid conditions. This presumably reflects a (partial) reversal of a chronic translocation and a shift in the balance between PKC and its anchoring proteins.

Modulation of protein kinase C isoforms by PAF in cerebral cortex

The effect of platelet activating factor (PAF) on subcellular distribution of protein kinase C isoforms in rat cerebral cortex was investigated. PAF induced an increase in levels of protein kinase C epsilon and gamma in membrane fraction. Results also indicate that PAF induced an increase in protein kinase C delta levels in both cytosolic and membrane fraction. This effect is possibly due to an increase in enzyme synthesis, as indicated by the results obtained from the experiments performed in the presence of cycloheximide and actinomycin. All the effects induced by PAF were time- and dose-dependent, and were mediated through the activation of PAF receptor. These findings indicate that the three isoforms may be involved in signal transduction of PAF in the brain.

Two distinct mechanisms mediate a differential regulation of protein kinase C isozymes in acute and prolonged myocardial ischemia

An activation of protein kinase C (PKC) in acute myocardial ischemia has been shown previously using its translocation to the plasma membrane as an indirect parameter. However, whether PKC remains activated or whether other mechanisms such as altered gene expression may mediate an isozyme-specific regulation in prolonged ischemia have not been investigated. In isolated perfused rat hearts, PKC activity and the expression of PKC cardiac isozymes were determined on the protein level using enzyme activities and Western blot analyses and on the mRNA level using reverse transcriptase-polymerase chain reaction after various periods of global ischemia (1 to 60 minutes). As early as 1 minute after the onset of ischemia, PKC activity is translocated from the cytosol to the particulate fraction without change in total cardiac enzyme activity. This translocation involves all major cardiac isozymes of PKC (ie, PKCalpha, PKCdelta, PKCepsilon, and PKCzeta). This rapid, nonselective activation of PKCs is only transient. In contrast, prolonged ischemia (>/=15 minutes) leads to an increased cardiac PKC activity (119+/-7 versus 190+/-8 pmol/min per mg protein) residing in the cytosol. This is associated with an augmented, subtype-selective isozyme expression of PKCdelta and PKCvarepsilon (163% and 199%, respectively). The specific mRNAs for PKCdelta (948+/-83 versus 1501+/-138 ag/ng total RNA, 30 minutes of ischemia) and PKCepsilon (1597+/-166 versus 2611+/-252 ag/ng total RNA) are selectively increased. PKCalpha and PKCzeta remain unaltered. In conclusion, two distinct activation and regulation processes of PKC are characterized in acute myocardial ischemia. The early, but transient, translocation involves all constitutively expressed cardiac isozymes of PKC, whereas in prolonged ischemia an increased total PKC activity is associated with an isozyme-selective induction of PKCepsilon and PKCdelta. Whether these fundamentally different activation processes interact remains to be elucidated.

Translocation and down-regulation of protein kinase C-alpha, -beta, and -gamma isoforms during ischemia-reperfusion in rat brain

We investigated the distribution of protein kinase C (PKC) isoforms in the subcellular fractions (P1, 1,000-g pellet; P2, 10,000-g pellet; P3, 100,000-g pellet; S, 100,000-g supernatant) of rat forebrain after ischemia or reperfusion by immunoblotting. PKC-delta and -epsilon isoforms were predominant in the P2 (synaptosome-rich) fraction, whereas PKC-alpha, -beta, -gamma, -epsilon, and -zeta isoforms were rich in the S (cytosolic) fraction. With time of ischemia (5-30 min), PKC-alpha, -beta, and -gamma translocated to the P2 and P3 fractions, whereas reperfusion for 60 min after 30 min of ischemia reduced PKC-beta activity greatly and PKC-alpha and -gamma activities to a lesser extent. There was no redistribution of PKC-delta, -epsilon, and -zeta after ischemia or reperfusion. A calpain inhibitor, acetylleucylleucylnorleucinal, inhibited the down-regulation of PKC-beta, through intravenous injection. The PKC translocation to the P2 fraction was accompanied by their dephosphorylation, transition of PKC-alpha from dimer to trimer, and the decrease in activity. These data show that PKC-alpha, -beta, and -gamma isoforms translocate chiefly to the synaptosome in ischemic brain in association with the dephosphorylation, multimeric change, and inactivation, followed by the proteolysis of PKC-beta by calpain after postischemic reperfusion.

Calcium antagonists ameliorate ischemia-induced endothelial cell permeability by inhibiting protein kinase C

BACKGROUND

Dihydropyridines block calcium channels; however, they also influence endothelial cells, which do not express calcium channels. We tested the hypothesis that nifedipine can prevent ischemia-induced endothelial permeability increases by inhibiting protein kinase C (PKC) in cultured porcine endothelial cells.

METHODS AND RESULTS

Ischemia was induced by potassium cyanide/deoxyglucose, and permeability was measured by albumin flux. Ion channels were characterized by patch clamp. [Ca2+]i was measured by fura 2. PKC activity was measured by substrate phosphorylation after cell fractionation. PKC isoforms were assessed by Western blot and confocal microscopy. Nifedipine prevented the ischemia-induced increase in permeability in a dose-dependent manner. Ischemia increased [Ca2+]i, which was not affected by nifedipine. Instead, ischemia-induced PKC translocation was prevented by nifedipine. Phorbol ester also increased endothelial cell permeability, which was dose dependently inhibited by nifedipine. The effects of non-calcium-channel-binding dihydropyridine derivatives were similar. Analysis of the PKC isoforms showed that nifedipine prevented ischemia-induced translocation of PKC-alpha and PKC-zeta. Specific inhibition of PKC isoforms with antisense oligodeoxynucleotides demonstrated a major role for PKC-alpha.

CONCLUSIONS

Nifedipine exerts a direct effect on endothelial cell permeability that is independent of calcium channels. The inhibition of ischemia-induced permeability by nifedipine seems to be mediated primarily by PKC-alpha inhibition. Anti-ischemic effects of dihydropyridine calcium antagonists could be due in part to their effects on endothelial cell permeability.

Transcriptional activation of the glucose transporter GLUT1 in ventricular cardiac myocytes by hypertrophic agonists

Myocardial hypertrophy is associated with increased basal glucose metabolism. Basal glucose transport into cardiac myocytes is mediated by the GLUT1 isoform of glucose transporters, whereas the GLUT4 isoform is responsible for regulatable glucose transport. Treatment of neonatal cardiac myocytes with the hypertrophic agonist 12-O-tetradecanoylphorbol-13-acetate or phenylephrine increased expression of Glut1 mRNA relative to Glut4 mRNA. To study the transcriptional regulation of GLUT1 expression, myocytes were transfected with luciferase reporter constructs under the control of the Glut1 promoter. Stimulation of the cells with 12-O-tetradecanoylphorbol-13-acetate or phenylephrine induced transcription from the Glut1 promoter, which was inhibited by cotransfection with the mitogen-activated protein kinase phosphatases CL100 and MKP-3. Cotransfection of the myocytes with constitutively active versions of Ras and MEK1 or an estrogen-inducible version of Raf1 also stimulated transcription from the Glut1 promoter. Hypertrophic induction of the Glut1 promoter was also partially sensitive to inhibition of the phosphatidylinositol 3-kinase pathway and was strongly inhibited by cotransfection with dominant-negative Ras. Thus, Ras activation and pathways downstream of Ras mediate induction of the Glut1 promoter during myocardial hypertrophy.

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.