SHC, GRB2, SOS1, AND A 150-KILODALTON TYROSINE-PHOSPHORYLATED PROTEINFORM COMPLEXES WITH FMS IN HEMATOPOIETIC-CELLS

Fms, the macrophage colony-stimulating factor (M-CSF) receptor, is nor mally expressed in myeloid cells and initiates signals for both growth and development along the monocyte/macrophage lineage. We have examin ed Fms signal transduction pathways in the murine myeloid progenitor c ell line FDC-P1. hl-CSF stimulation of FDC-P1 cells expressing exogeno us Fms resulted in tyrosine phosphorylation of a variety of cellular p roteins in addition to Fms. M-CSF stimulation also resulted in Fms ass ociation with two of these tyrosine-phosphorylated proteins, one of wh ich was identified as the 55-kDa She, which is shown in other systems to be involved in growth stimulation, and the other was a previously u ncharacterized 150-kDa protein (p150). Fms also formed complexes with Grb2 and Sos1, and neither contained phosphotyrosine. Whereas both Grb 2 and Sos1 complexed with Fms only after M-CSF stimulation, the amount of Sos1 complexed with GRb2 was not M-CSF dependent. She coimmunoprec ipitated Sos1, Grb2, and tyrosine-phosphorylated p150, while Grb2 immu noprecipitates contained mainly phosphorylated p150, Fmns, Shc, and So s1. She interacted with tyrosine-Dhosphorylated p150 via its SH2 domai n, and the Grb2 SH2 domain likewise bound tyrosincphosphorglated Fms a nd p150. Analysis of Fms mutated at each of four tyrosine autophosphor ylation sites indicated that none of these sites dramatically affected p150 phosphorylation or its association with She and Grb2. M-CSF stim ulation of fibroblast cell lines expressing esogenous murine Fms did n ot phosphorylate p150, and this protein was not detected either in cel l Ivsates or in Grb2 or She immunoprecipttntes. The p150 protein is no t related to known signal transduction molecules and mag be myeloid ce ll specific. These results suggest that M-CSF stimulation of myeloid c ells could activate Ras through the nucleotide exchange factor Sosl by Grb2 binding to either Fms, She, or p150 and that Fms signal transduc tion in mgeloid cells differs from that in fibroblasts.