Regulation of Protein Kinase B and 4E-BP1 by Oxidative Stress in Cardiac Myocytes

Abstract—Stimulation of phosphatidylinositol 3′-kinase (PI3K) and protein kinase B (PKB) is implicated in the regulation of protein synthesis in various cells. One mechanism involves PI3K/PKB-dependent phosphorylation of 4E-BP1, which dissociates from eIF4E, allowing initiation of translation from the 7-methylGTP cap of mRNAs. We examined the effects of insulin and H2O2 on this pathway in neonatal cardiac myocytes. Cardiac myocyte protein synthesis was increased by insulin, but was inhibited by H2O2. PI3K inhibitors attenuated basal levels of protein synthesis and inhibited the insulin-induced increase in protein synthesis. Insulin or H2O2 increased the phosphorylation (activation) of PKB through PI3K, but, whereas insulin induced a sustained response, the response to H2O2 was transient. 4E-BP1 was phosphorylated in unstimulated cells, and 4E-BP1 phosphorylation was increased by insulin. H2O2 stimulated dephosphorylation of 4E-BP1 by increasing protein phosphatase (PP1/PP2A) activity. This increased the a...