α-thrombin activates Akt via a nonreceptor tyrosine kinase in IIC9 cells

Previous data from our laboratory show that PI 3-kinase is required for α-thrombin-stimulated G₁ progression in IIC9 cells. In IIC9 cells, PI 3-kinase acts downstream of Ras to activate Akt, in a pathway parallel to ERK1. Here we show that α-thrombin does not transactivate either the EGF receptor or the PDGF receptor as measured by tyrosine phosphorylation, suggesting that activation of PI 3-kinase by α-thrombin is not the result of an RTK. Interestingly, both genistein and PP1 block α-thrombin-stimulated Akt phosphorylation, suggesting the involvement of a member of the Src family of non-receptor tyrosine kinases.