Reactive oxygen species in mechanical stress-induced cardiac hypertrophy.

Mechanical stress induces various hypertrophic responses including activation of mitogen-activated protein kinases (MAPKs) in cardiac myocytes. Here we examined the role of the small GTP-binding proteins of Rho family and reactive oxygen species (ROS) in stretch-induced activation of p38MAPK in cardiomyocytes. Overexpression of dominant-negative mutants of Rac1 (D.N. Rac1), D.N.RhoA and D.N.Cdc42 suppressed stretch-induced activation of p38MAPK. Overexpression of constitutively active mutants of Rac1 (C.A.Rac1) and C.A.Cdc42 increased the p38MAPK activity in the absence of mechanical stress. Pretreatment with N-acetyl-L-cysteine and N-(2-mercaptopropionyl)-glycine (NAC) suppressed stretch-induced activation of p38MAPK. Mechanical stretch increased intracellular ROS generation, which was abrogated by overexpression of D.N.Rac1 and attenuated by overexpression of D.N.RhoA and D.N.Cdc42. An increase in protein synthesis evoked by mechanical stretch was suppressed by overexpression of D.N.Rac1 and pretreatment with NAC. These results suggest that mechanical stress induces cardiac hypertrophy through the Rac1-ROS-p38MAPK pathway in cardiac myocytes.

Aikawa R ，Nagai T ，Tanaka M ，Zou Y ，Ishihara T ，Takano H ，Hasegawa H ，Akazawa H ，Mizukami M ，Nagai R ，Komuro I ... -  《BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS》

PKC mediates cyclic stretch-induced cardiac hypertrophy through Rho family GTPases and mitogen-activated protein kinases in cardiomyocytes.

Signaling events, including Rho GTPases and protein kinase C (PKC), are involved in cardiac hypertrophy. However, the mechanisms by which these pathways cooperate during the hypertrophic process remain unclear. Using an in vitro cyclic stretch model with neonatal rat cardiomyocytes, we demonstrated that stretch-induced activation of RhoA, Rac1/Cdc42, and phosphorylation of Rho-guanine nucleotide dissociation inhibitor (GDI) were prevented by inhibition or depletion of PKC, using chelerythrine and phorbol 12-myristate 13-acetate, indicating that phorbol ester-sensitive PKC isozymes may be upstream regulators of Rho GTPases. Using adenoviral-mediated gene transfer of wild-type (WT) and dominant-negative (DN) mutants of PKCalpha and delta, we found that stretch-induced activation of Rho GTPases and phosphorylation of Rho-GDI were mainly regulated by PKCalpha. PKCdelta was involved in regulation of the activation of Rac1. Stretch-induced increases in [(3)H]-leucine incorporation, myofibrillar reorganization and cell size, were blocked by inhibition of Rho GTPases, or overexpression of DN PKCalpha and delta, suggesting that PKCalpha and delta are both required in stretch-induced hypertrophy, through Rho GTPases-mediated signaling pathways. The mechanism, whereby PKC and Rho GTPases regulate hypertrophy, was associated with mitogen-activated protein (MAP) kinases. Stretch-stimulated phosphorylation of MEK1/ERK1/2 and MKK4/JNK was inhibited by overexpression of DN PKCalpha and delta, and that of MKK3/p38 inhibited by DN PKCdelta. The phosphorylation of ERK and JNK induced by overexpression of WT PKCalpha, and the phosphorylation of p38 induced by WT PKCdelta, were regulated by Rho GTPases. This study represents the first evidence that PKCalpha and delta are important regulators in mediating activation of Rho GTPases and MAP kinases, in the cyclic stretch-induced hypertrophic process.

Pan J ，Singh US ，Takahashi T ，Oka Y ，Palm-Leis A ，Herbelin BS ，Baker KM ... -  《JOURNAL OF CELLULAR PHYSIOLOGY》

Implication of reactive oxygen species, ERK1/2, and p38MAPK in sodium salicylate-induced heat shock protein 72 expression in C6 glioma cells.

Seo MS ，Oh SY ，Park MJ ，Kim SM ，Kim MY ，Han SI ，Park HG ，Kang HS ... -  《INTERNATIONAL JOURNAL OF MOLECULAR MEDICINE》

Involvement of Rho GTPases and their effectors in the secretory process of PC12 cells.

We investigated the involvement of Rho GTPases in the secretory process of PC12 cells. Overexpression of wild-type RhoA, Rac1, or Cdc42 did affect exocytosis. In contrast, secretion elicited by depolarizing K(+) concentrations was enhanced by the dominant negative mutants RhoA(N19), Rac1(N17), and Cdc42(N17) and was diminished by the constitutively active mutants RhoA(V14), Rac1(V12), and Cdc42(V12). The inhibition observed in the presence of RhoA(V14) was likely a result of the activation of ROK(alpha), since the catalytic domain of this kinase was able to mimic both the reorganization of the actin cytoskeleton and the decrease in exocytosis induced by the RhoA mutant. Part of the effect of Rac1(V12) may be due to POR1 activation. Thus, overexpression of full-length POR1 diminished K(+)-stimulated exocytosis, and a point mutation in the effector domain of Rac1(V12) that prevents the interaction with POR1 abolished the inhibitory effect of the GTPase. We also searched for the Cdc42(V12) target but overexpression of the Cdc42 effector WASP did not mimic the inhibition of exocytosis observed in cells transfected with the activated GTPase. Our findings indicate that different signaling cascades resulting in the activation of RhoA, Rac1, or Cdc42 can modulate the exocytotic process of neuroendocrine cells.

Frantz C ，Coppola T ，Regazzi R 《EXPERIMENTAL CELL RESEARCH》

Rac1 activity is required for cardiac myocyte alignment in response to mechanical stress.

Yamane M ，Matsuda T ，Ito T ，Fujio Y ，Takahashi K ，Azuma J ... -  《-》