Role of connexin-43 in protective PI3K-Akt-GSK-3β signaling in cardiomyocytes

• Published in: American journal of physiology. Heart and circulatory physiology 2012-06, Vol.302 (12), p.H2536-H2544
• Main Authors: Ishikawa, Satoko, Kuno, Atsushi, Tanno, Masaya, Miki, Takayuki, Kouzu, Hidemichi, Itoh, Takahito, Sato, Tatsuya, Sunaga, Daisuke, Murase, Hiromichi, Miura, Tetsuji
• Format: Article
• Language: English
• Subjects: Analgesics, Opioid - pharmacology; Animals; Cell Line; Connexin 43 - metabolism; Cytoprotection - physiology; Endothelin-1 - pharmacology; Enkephalin, Leucine-2-Alanine - pharmacology; Gap Junctions - metabolism; Glycogen Synthase Kinase 3 - metabolism; Glycogen Synthase Kinase 3 beta; Insulin-Like Growth Factor I - pharmacology; Mitochondria - drug effects; Mitochondria - metabolism; Myocytes, Cardiac - drug effects; Myocytes, Cardiac - enzymology; Myocytes, Cardiac - metabolism; Phosphatidylinositol 3-Kinases - metabolism; Phosphorylation - drug effects; Proto-Oncogene Proteins c-akt - metabolism; Rats; Reactive Oxygen Species - metabolism; RNA, Small Interfering; Signal Transduction - drug effects; Signal Transduction - physiology
• ISSN: 0363-6135; 1522-1539
• DOI: 10.1152/ajpheart.00940.2011

Sarcolemmal connexin-43 (Cx43) and mitochondrial Cx43 play distinct roles: formation of gap junctions and production of reactive oxygen species (ROS) for redox signaling. In this study, we examined the hypothesis that Cx43 contributes to activation of a major cytoprotective signal pathway, phosphoinositide 3-kinase (PI3K)-Akt-glycogen synthase kinase-3β (GSK-3β) signaling, in cardiomyocytes. A δ-opioid receptor agonist {[d-Ala(2),d-Leu(5)]enkephalin acetate (DADLE)}, endothelin-1 (ET-1), and insulin-like growth factor-1 (IGF-1) induced phosphorylation of Akt and GSK-3β in H9c2 cardiomyocytes. Reduction of Cx43 protein to 20% of the normal level by Cx43 small interfering RNA abolished phosphorylation of Akt and GSK-3β induced by DADLE or ET-1 but not that induced by IGF-1. DADLE and IGF-1 protected H9c2 cells from necrosis after treatment with H(2)O(2) or antimycin A. The protection by DADLE or ET-1, but not that by IGF-1, was lost by reduction of Cx43 protein expression. In contrast to Akt and GSK-3β, PKC-ε, ERK and p38 mitogen-activated protein kinase were phosphorylated by ET-1 in Cx43-knocked-down cells. Like diazoxide, an activator of the mitochondrial ATP-sensitive K(+) channel, DADLE and ET-1 induced significant ROS production in mitochondria, although such an effect was not observed for IGF-1. Cx43 knockdown did not attenuate the mitochondrial ROS production by DADLE or ET-1. Cx43 was coimmunoprecipitated with the β-subunit of G protein (Gβ), and knockdown of Gβ mimicked the effect of Cx43 knockdown on ET-1-induced phosphorylation of Akt and GSK-3β. These results suggest that Cx43 contributes to activation of class I(B) PI3K in PI3K-Akt-GSK-3β signaling possibly as a cofactor of Gβ in cardiomyocytes.