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

Nitric oxide mediates protein kinase C isoform translocation in rat heart during postischemic reperfusion

It is controversial whether nitric oxide (NO) is protective or deleterious against ischemia-reperfusion injury. We examined the effect of NO on PKC isoform translocation and protection against ischemia-reperfusion injury in perfused heart. An NO synthase inhibitor L-NAME (NG-nitro-L-arginine methyl ester, 3.0 microM), administered only during reperfusion but not during ischemia, inhibited the translocation of PKC-alpha, -delta and -epsilon isoforms to the nucleus-myofibril fraction and the translocation of PKC-alpha to the membrane fraction after ischemia (20 min) and reperfusion (10 min) in the perfused rat heart. NO donors, 3-morpholinosydnonimine (SIN-1) or S-nitroso-N-acetylpenicillamine (SNAP) activated purified PKC in vitro. SIN-1 also induced PKC isoform translocation in perfused heart. On the other hand, PKC selective inhibitor, calphostin C (0.2 microM) or chelerythrine (1.0 microM), aggravated the contractile dysfunction of ischemic heart during reperfusion, when they were perfused during reperfusion. These data suggest that NO generated during reperfusion following ischemia activates PKC isoforms and may protect the heart against contractile dysfunction in the perfused rat heart.

Protein kinase C translocation and PKC-dependent protein phosphorylation during myocardial ischemia

The present study demonstrates that the alpha, epsilon, and iota isozymes of protein kinase C (PKC) are translocated to particulate fractions from the cytosol during brief intervals of global ischemia as well as reperfusion of ischemic rat myocardium. In contrast, phorbol ester treatment of perfused hearts resulted in the translocation of the alpha, delta, and epsilon isozymes of PKC to particulate fractions. Additionally, the alpha, delta, and epsilon isozymes of PKC are translocated to particulate fractions in phorbol ester-stimulated, isolated adult rat cardiac myocytes. Concomitant with the translocation of PKC isozymes to particulate fractions during myocardial ischemia, increased protein phosphorylation was observed, which was blocked by pretreatment of hearts with the selective PKC inhibitor bisindolylmaleimide I (50 nM). In particular, ischemia resulted in the phosphorylation of 26-, 20-, and 17-kDa particulate-associated proteins. Taken together, the present findings are the first to demonstrate that specific PKC isozymes are translocated to particulate fractions in the ischemic and the reperfused ischemic rat heart, resulting in the phosphorylation of specific particulate-associated proteins.

Identification of specific nuclear protein kinase C isozymes and accelerated protein kinase C-dependent nuclear protein phosphorylation during myocardial ischemia

Protein kinase C (PKC) has been suggested to mediate, at least in part, multiple processes in the pathophysiological sequelae of myocardial ischemia. The present study demonstrates that the epsilon, eta and iota isozymes of PKC are translocated to nuclei in response to brief intervals of global ischemia as well as reperfusion of ischemic rat myocardium. Concomitant with the translocation of PKC isozymes to nuclei during ischemia, increased PKC-mediated nuclear protein phosphorylation was observed. Taken together, the present results demonstrate that nuclear signaling mechanisms are activated during myocardial ischemia that include PKC translocation and PKC-mediated nuclear protein phosphorylation.

Applied pressure enhances cell proliferation through mitogen-activated protein kinase activation in mesangial cells

Progressive renal diseases lead to prolonged glomerular hypertension, which induces the proliferation of mesangial cells. This proliferation is thought to be involved in the development of renal injury. Here we investigate mitogen-activated protein kinase (MAPK) activation and cell proliferation in mesangial cells under conditions of high pressure. After pressure-load, the phosphorylation level of MAPK (at Tyr-204) increases rapidly with a peak at 1 min, although the amount of MAPK remains almost constant during pressure-load. To confirm the activation of MAPK, we carried out an immunoprecipitation-kinase assay. MAPK activity during pressure-load shows kinetics similar to that of the tyrosine phosphorylation. In contrast, c-Jun N-terminal kinase 1 (JNK1) phosphorylation falls below basal levels in response to high pressure. Immunocytochemical observations show phosphorylated MAPK in the nucleus at 10 min. The expression of c-Fos, a nuclear transcription factor, is induced by high pressure, and the induction is significantly inhibited by PD98059 (50 microM), an upstream MAPK/extracellular signal-regulated kinase kinase (MEK) inhibitor of MAPK. The expression of the c-Jun that is induced by JNK1 activation remains unchanged during pressure-load. MAPK phosphorylation and cell proliferation by applied pressure are significantly inhibited by genistein, a tyrosine kinase inhibitor in a dose-dependent manner, but not by protein kinase C inhibitors, chelerythrine and GF109203X. Genistein also blocks pressure-induced tyrosine phosphorylation of proteins with molecular masses of 35, 53, and 180 kDa. To clarify the physiological role in MAPK activation under high pressure conditions, we transfected antisense MAPK DNA into mesangial cells. The antisense DNA (2 microM) inhibited MAPK expression by 80% compared with expression in the presence of sense or scrambled DNA, and significantly blocked pressure-induced cell proliferation. Treatment of cells with MEK inhibitor also produced a similar result. MEK inhibitor strongly suppresses DNA synthesis induced by pressure-load. Cyclin D1 expression is significantly increased under high pressure conditions, and the increase is blocked by treatment with MEK inhibitor. These findings show that pressure-load, a novel activator of MAPK, induces the activation of tyrosine kinases, and enhances the proliferation of mesangial cells, probably through cyclin D1 expression.

Ischemic preconditioning: exploring the paradox

Brief transient episodes of nonlethal myocardial ischemia protect or "precondition" the heart and render the myocardium resistant to a subsequent more sustained ischemic insult. The hallmark of this phenomenon--documented in virtually all species and experimental models evaluated to date in countless laboratories worldwide--is the profound reduction in infarct size seen in preconditioned groups versus time-matched controls. Efforts to identify the cellular mechanisms responsible for this paradoxical ischemia-induced cardioprotection, to expand the definition of ischemic preconditioning beyond infarct size reduction, and, perhaps most importantly, to evaluate the efficacy of preconditioning in disease models and in the clinical setting, are all topics of intensive ongoing investigation.

Structure and physiological function of calpains

For a long time now, two ubiquitously expressed mammalian calpain isoenzymes have been used to explore the structure and function of calpain. Although these two calpains, mu- and m-calpains, still attract intensive interest because of their unique characteristics, various distinct homologues to the protease domain of mu- and m-calpains have been identified in a variety of organisms. Some of these 'novel' calpain homologues are involved in important biological functions. For example, p94 (also called calpain 3), a mammalian calpain homologue predominantly expressed in skeletal muscle, is genetically proved to be responsible for limb-girdle muscular dystrophy type 2A. Tra-3, a calpain homologue in nematodes, is involved in the sex determination cascade during early development. PalB, a key gene product involved in the alkaline adaptation of Aspergillus nidulans, is the first example of a calpain homologue present in fungi. These findings indicate various important functional roles for intracellular proteases belonging to the calpain superfamily.

A novel mechanism of JNK1 activation. Nuclear translocation and activation of JNK1 during ischemia and reperfusion

Cytokines and various cellular stresses are known to activate c-Jun NH2-terminal kinase (JNK), which plays a role in conveying signals from the cytosol to the nucleus. Here we investigate the translocation and activation of JNK1 during ischemia and reperfusion in perfused rat heart. Ischemia induces the translocation of JNK1 from the cytosol fraction to the nuclear fraction in a time-dependent manner. Immunohistochemical observation also shows that JNK1 staining in the nucleus is enhanced after ischemia. During reperfusion after ischemia, further nuclear translocation of JNK1 is apparently inhibited. In contrast, JNK1 activity in the nuclear fraction does not increased during ischemia but increases significantly during reperfusion with a peak at 10 min of reperfusion. The activation of JNK1 is confirmed by the phosphorylation of endogenous c-Jun (Ser-73) with similar kinetics. The level of c-jun mRNA also increases during reperfusion but not during ischemia. Based on fractionation and immunohistochemical analyses, an upstream kinase for JNK1, SAPK/ERK kinase 1 (SEK1), is constantly present in both the nucleus and cytoplasm throughout ischemia and reperfusion, whereas an upstream kinase for mitogen-activated protein kinase, MAPK/ERK kinase 1, remains in the cytosol. Furthermore, phosphorylation at Thr-223 of SEK1, necessary for its activation, rapidly increases in the nuclear fraction during postischemic reperfusion. These findings demonstrate that JNK1 translocates to the nucleus during ischemia without activation and is then activated during reperfusion, probably by SEK1 in the nucleus.

Mitogen-activated protein kinase translocates to the nucleus during ischaemia and is activated during reperfusion

Growth factors and various cellular stresses are known to activate mitogen-activated protein (MAP) kinase, which plays a role in conveying signals from the cytosol to the nucleus. The phosphorylation of MAP kinase is thought to be a prerequisite for translocation. Here, we investigate the translocation and activation of MAP kinase during ischaemia and reperfusion in perfused rat heart. Ischaemia (0-40 min) induces the translocation of MAP kinase from the cytosol fraction to the nuclear fraction. Immunohistochemical observation shows that MAP kinase staining in the nucleus is enhanced after ischaemia for 40 min. Unexpectedly, tyrosine phosphorylation of MAP kinase is unchanged in the nuclear fraction during ischaemia, indicating that unphosphorylated MAP kinase translocates from the cytosol to the nucleus. During reperfusion (0-30 min), after ischaemia for 20 min, tyrosine phosphorylation of MAP kinase in the nuclear fraction is increased with a peak at 10 min of reperfusion. The activation is confirmed by MAP kinase activity with similar kinetics to the tyrosine phosphorylation. However, the amount of MAP kinase in the fraction is almost constant during reperfusion for 10 min. Although an upstream kinase for MAP kinase, MAP kinase/extracellular signal-regulated kinase kinase (MEK)-1, remains in the cytosol throughout ischaemia and reperfusion, MEK-2, another upstream kinase for MAP kinase, is constantly present in the nucleus as well as in the cytoplasm, based on analyses by fractionation and immunohistochemistry. Furthermore, MEK-2 activity in the nuclear fraction is rapidly increased during post-ischaemic reperfusion. These findings demonstrate that nuclear MAP kinase is activated by tyrosine phosphorylation during reperfusion, probably by MEK-2.