The signal transduction of colony-stimulating factor-1 (CSF-1)--the role of protein tyrosine phosphorylation

Abstract

The mechanism of transmembrane activation of the CSF-1 receptor tyrosine kinase upon ligand binding and the possible role of the CSF-1 induced cellular protein tyrosine phosphorylation have been studied. By using kinetic and cross-linking appoaches to study CSF-1-induced changes in the structure and function of the CSF-1R, it is demonstrated that in the absence of CSF-1, CSF-1Rs are clustered in either aggregated or dynamic interactive states. Addition of CSF-1 to cells stimulates or stabilizes non-covalent CSF-1R dimerization resulting in activation of the CSF-1R kinase and the tyrosine phosphorylation of the receptor and certain cytoplasmic proteins. The non-covalent dimers become covalently linked via disulfide bonds and/or are subsequently further modified. These latter forms are selectively internalized. It is proposed that ligand-induced non-covalent dimerization activates the CSF-1R kinase, whereas the covalent linkage between monomeric subunits of the dimer and the subsequent modification lead to kinase inactivation, phosphotyrosine dephosphorylation and internalization of the receptor-ligand complex. A common {dollar}\alpha{dollar}PY-reactive 57-kDa protein has been identified in the macrophage cell line BAC1.2F5 and in NIH 3T3 cells in response to the growth factors. Phosphoamino acid analyses indicated that the 57-kDa proteins from the various cell lines were all phosphorylated on both serine and tyrosine residues. V8 protease peptide mapping of ({dollar}\sp{lcub}35{rcub}{dollar}S) -methionine-labeled 57-kDa proteins from CSF-1 stimulated BAC1.2F5, PDGF-stimulated NIH 3T3 and NIH 3T3 (c-fms) incubated with CSF-1 indicated that they are closely related. The tyrosine phosphorylation of the 57-kDa protein was constitutive in v-fms and c-fms (F969, S301)-transformed NIH 3T3 cells but not in untransformed NIH 3T3 (c-fms) and NIH 3T3 (c-fms, F969) cells. The effect of the growth factors on the tyrosine phosphorylation of the 57-kDa protein can be mimicked by treating the cells with vanadate, a PTPase inhibitor, in the absence of the receptor kinase activation. These data suggest that the 57-kDa is a common target for growth factor stimulated tyrosine phosphorylation and that the regulation of the 57-kDa protein tyrosine phosphorylation could be mediated by either activation of tyrosine kinases or inhibition of PTPases.