DIFFERENT INTERACTIONS OF GRB2 ASH MOLECULE WITH THE NGF AND EGF RECEPTORS IN RAT PHEOCHROMOCYTOMA PC12 CELLS/

We have previously shown that nerve growth factor (NGF) induces a rapi d and relatively continuous activation of pas in rat pheochromocytoma PC12 cells while epidermal growth factor (EGF) activates Ras transient ly, and that tyrosine kinase activity of the NGF receptor is essential for the activation of pas (Muroya et al., Oncogene, 7, 277-281, 1992) . In order to explore the signaling mechanism from tyrosine kinase to Ras activation in more detail, interactions between two adaptor molecu les, She and Grb2/Ash, which contain Src homology regions, and their i nteractions with the NGF and EGF receptors were examined. Both NGF and EGF induced rapid tyrosine phosphorylation of She and its association with both the receptors and with Grb2/Ash. When cells were stimulated with EGF at 4 degrees C, the activation of pas proceeded slowly and M AP kinase activation was quite low. Under such restricted conditions, tyrosine-phosphorylated She formed a complex with Grb2/Ash, suggesting that the complex formation may be one of the immediate early response s. In contrast to She, Grb2/Ash bound to EGF receptor but did not form a stable complex with the NGF receptor. These results suggest that th ere may be an alternative pathway for the activation of Ras in PC12 ce lls.