IONIZING-RADIATION STIMULATES A GRB2-MEDIATED ASSOCIATION OF THE STRESS-ACTIVATED PROTEIN-KINASE WITH PHOSPHATIDYLINOSITOL 3-KINASE

The stress-activated protein (SAP) kinases are induced by tumor necrosis factor, oncoproteins, and UV light. The present studies demonstrate that ionizing radiation (IR) activates p54 SAP kinase. IR-induced activation of SAP kinase is associated with binding to the SH2/SH3-containing adaptor protein Grb2, This interaction is mediated by the SH3 domains of Grb2 and the proline-rich sequence PPPKIP in the carboxyl terminal region of SAP kinase, We also demonstrate that SAP kinase and the p85 alpha-subunit of phosphatidylinositol (PI) 3-kinase form a complex in irradiated cells, The results indicate that this complex involves binding of the p85 alpha subunit of PI 3-kinase to the SH2 domain of Grb2. The functional role of linking SAP kinase to PI 3-kinase is further supported by the finding that wortmannin, an inhibitor of PI 3-kinase, stimulates SAP kinase activity. These results suggest that the cellular response to IR may include regulation of SAP kinase by a PI 3-kinase-dependent signaling pathway.