Oxidative stress and vanadate induce tyrosine phosphorylation of phosphoinositide-dependent kinase 1 (PDK1)

Phosphoinositide-dependent kinase (PDK1) regulates a number of pathways inv olved in responses to stress and in growth factor signaling; however, littl e is known concerning the mechanisms governing the activity of PDK1. In thi s report, we find that oxidative stress (H2O2) and vanadate induce tyrosine phosphorylation of PDK1. These effects of H2O2 and vanadate were found in 293T cells and CH310T1/2 cells expressing exogenous PDK1 and in A20 lymphom a cells expressing endogenous PDK1. Exogenously expressed PDK1 was also tyr osine-phosphorylated in response to NGF treatment of 293T expressing TrkA. H2O2 induced a more rapid tyrosine phosphorylation of PDK1 relative to vana date, and only vanadate-induced tyrosine phosphorylation of PDK1 was sensit ive to pretreatment of cells with wortmannin. In vitro, PDK1 could be tyros ine-phosphorylated by both the c-Src and Abl tyrosine kinases. Both H2O2 an d vanadate treatments increased the activity of PDK1 when the serum/glucoco rticoid regulated kinase (SGK) was used as substrate. Vanadate treatment ap peared to bypass the requirement for phosphatidylinositol 3,4,5-trisphospha te when Akt was used as substrate for PDK1. Tyrosine phosphorylation of PDK 1 by the Abl tyrosine kinase also increased the activity of PDK1 toward SGK and Akt. These data suggest a novel mechanism through which PDK1 activity may be regulated.