The current study aimed to understand the anti-apoptotic effect of overexpressed gap junction forming protein connexin (Cx) 43 in C6 glioma cells. C6 cells exposed to hydrogen peroxide (H2O2) or staurosporine demonstrated morphological and biochemical changes consistent with apoptosis, whereas C6 cells expressing Cx43 demonstrated relative resistance to H2O2, but not to staurosporine. This selective protection against H2O2 was due to inhibition of caspase-3 activation in Cx43 expressing cells. siRNA knockdown experiments in rat primary astrocytes confirmed the presence of endogenous Cx43-mediated anti-apoptotic effect. Cx43 interacts with the upstream apoptosis signal-regulating kinase I known to mediate H2O2-induced apoptosis providing a possible mechanism for protection. These findings provided new evidence for regulation of the mitogen activated protein kinase pathway and apoptosis by Cx43 implicating this protein in intracellular signaling beyond its role as a gap junction forming protein on the plasma membrane. (c) 2007 Elsevier Inc. All rights reserved.