CSF-1 STIMULATION INDUCES THE FORMATION OF A MULTIPROTEIN COMPLEX INCLUDING CSF-1 RECEPTOR, C-CBL, PI-3-KINASE, CRK-II AND GRB2

Recently c-Cbl has been reported to be phosphorylated upon CSF-1 stimu lation. The product of the c-cbl protooncogene (c-Cbl) is a 120 kDa pr otein harboring several docking sites for Src homology 2 (SH2) domain containing proteins and proline-rich regions that have been shown to a llow its constitutive association with the SH3 domains of Grb2, We dem onstrate here that CSF-1 exposure of stable transfectant CHO cells exp ressing the CSF-1 receptor induced the sustained tyrosine phosphorylat ion of c-Cbl and its subsequent association with Crk-II and the p85 kD a subunit of the PI 3-kinase, while it constitutively associates with Grb2, We demonstrate by in vitro experiments that these associations r equire the SH2 domain of Crk-II and both the C- and N-terminal SH2 dom ains of the p85 subunit of the PI 3-kinase, c-Cbl is the major PI 3-ki nase-containing protein in c-Fms expressing CHO cells upon CSF-1 stimu lation, Thus c-Cbl behaves as a core protein, allowing the formation o f a quaternary complex including, Crk-II, PI 3-kinase and Grb2, We pro vide evidence that this multiprotein complex can interact with the tyr osine phosphorylated CSF-1 receptor through the unoccupied SH2 domain of Grb2.