Role of dimerization and modification of the CSF-1 receptor in its activation and internalization during the CSF-1 response

We have used kinetic and cross-linking approaches to study CSF-I-induced changes in the structure and function of the CSF-1R. Addition of CSF-1 to cells stimulates or stabilizes non-covalent CSF-1R dimerization resulting inactivation 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 modified forms are selectively internalized. Pre-treatment of cells with the alkylating agent, iodoacetic acid (IAA), selectively inhibits covalent dimerization, modification and internalization but enhances protein tyrosine phosphorylation. It is proposed that ligand-induced non-covalent dimerization activates the CSF-1R kinase, whereas the covalent dimerization and subsequent modification lead to kinase inactivation, phosphotyrosine dephosphorylation and internalization of the receptor-ligand complex.