In cardiomyocyte hypoxia, insulin-like growth factor-I-induced antiapoptotic signaling requires phosphatidylinositol-3-OH-kinase-dependent and mitogen-activated protein kinase-dependent activation of the transcription factorcAMP response element-binding protein

Background-A variety of pathologic stimuli lead to apoptosis of cardiomyocy tes. Survival factors like insulin-like growth factor-I (IGF-I) exert anti- apoptotic effects in the heart. Yet the underlying signaling pathways are p oorly understood. Methods and Results-In a model of hypoxia-induced apoptosis of cultured neo natal cardiomyocytes, IGF-I prevented cell death in a dose-dependent manner . Antiapoptotic signals induced by IGF-I are mediated by more than one sign aling pathway, because pharmacological inhibition of the phosphatidylinosit ol-3-OH-kinase (PI3K) or the mitogen-activated protein kinase kinase (MEK1) signaling pathway both antagonize the protective effect of IGF-I in an add itive manner. IGF-I-stimulation was followed by a PI3K-dependent phosphoryl ation of AKT and BAD and an MEK1-dependent phosphorylation of extracellular signal-regulated kinase (ERK) 1 and ERK2. IGF-I also induced phosphorylati on of cAMP response element-binding protein (CREB) in a PI3K- and MEK1-depe ndent manner. Ectopic overexpression of a dominant-negative mutant of CREB abolished the antiapoptotic effect of IGF-I. Protein levels of the antiapop totic factor bcl-2 increased after longer periods of IGF-I-stimulation, whi ch could be reversed by pharmacological inhibition of PI3K as well as MEK1 and also by overexpression of dominant-negative CREB. Conclusions-In summary, our data demonstrate that in cardiomyocytes, the an tiapoptotic effect of IGF-I requires both PI3K- and MEK1-dependent pathways leading to the activation of the transcription factor CREB. which then ind uces the expression of the antiapoptotic factor bcl-2.