Expression of a Y559F mutant CSF-1 receptor in M1 myeloid cells: a role for Src kinases in CSF-1 receptor-mediated differentiation.

We have established two M1 myeloid cell lines, M1/WT cells overexpressing the wild-type CSF-1 receptor and M1/Y559F cells expressing a specific tyrosine mutant. M1/WT cells differentiated in response to CSF-1, with a reduction in their proliferative capacity. CSF-1-mediated differentiation was partially abrogated in the M1/Y559F cells, with a less marked reduction in proliferative capacity. The Src tyrosine kinases c-Src, c-Yes, c-Fyn, and c-Hck were tyrosine phosphorylated in the M1/WT cells in response to CSF-1 and bound to the WT CSF-1R through their SH2 domains. Binding of the Src kinases to the CSF-1 receptor was greatly reduced in the M1/Y559F cells. CSF-1-mediated activation of STAT3 was also abrogated in the M1/Y559F cell line. Treatment of M1/WT cells with the Src family inhibitor PP2 resulted in an inhibition of CSF-1-mediated differentiation, equivalent to that observed in the M1/Y559F cells. These data suggest that the reduced Src binding observed in the M1/Y559F cells may contribute to their reduced ability to differentiate.