Involvement of IGF‐1R and PKCδ in the Protein Kinase B (PKB) phosphorylation induced by Bis(maltolato)‐oxovanadium (IV) (BMOV) in human hepatoma cells (HepG2).

BMOV, an organo‐vanadium compound, is a potent insulinomimetic agent and improves glucose homeostasis in various models of diabetes. We have shown earlier that BMOV stimulates the phosphorylation of PKB in HepG2 which may contribute as one of the mechanism for the insulinmimetic effect of this compound. However, the upstream mechanism of BMOV‐induced PKB phosphorylation remains elusive. Therefore, in this study we have examined the upstream events leading to BMOV‐induced PKB phosphorylation in HepG2. Since BMOV is an inhibitor of Protein Tyrosine Phosphatases and can impact on various Protein tyrosine kinases (PTK), we have investigated the potential role of different receptor or non receptor PTK in mediating BMOV‐induced PKB phosphorylation. Among several pharmacological inhibitors tested, only AG1024, a selective inhibitor of IGF‐1R‐PTK almost completely blocked BMOV‐stimulated phosphorylation of PKB. In contrast, AG 1295, AG 1478 and PP‐2, specific inhibitors of PDGFR, EGFR and c‐Src respectively were unable to block the BMOV response. A role of PKC in BMOV‐induced response was also tested. Chronic treatment with PMA, or pharmacological inhibition with Chelerythrine a non‐selective PKC inhibitor or Rottlerin a PKCδ inhibitor attenuated BMOV‐induced PKB phosphorylation. In contrast, Gö6976 a PKC©α/β selective inhibitor failed to alter BMOV effect. Taken together, these data suggest that IGF‐1R and PKCδ are required to stimulate PKB phosphorylation in response to BMOV in HepG2. (Supported by grants from Canadian Institutes of Health Research).