A potential role for the Src‐like adapter protein SLAP‐2 in signaling by the colony stimulating factor‐1 receptor

Abstract

The development of macrophages from myeloid progenitor cells is primarily controlled by the growth factor colony stimulating factor-1 (CSF-1) and its cognate receptor, a transmembrane tyrosine kinase encoded by the c-Fms proto-oncogene. The CSF-1 receptor exerts its biological effects on cells via a range of signaling proteins including Erk1/2 and Akt. Here we have investigated the potential involvement of the Src-like adapter protein (SLAP-2) in signaling by the CSF-1 receptor in mouse bone marrow-derived macrophages. RT-PCR analysis revealed constitutive expression of the SLAP-2 gene in bone marrow macrophages. Surprisingly, co-immunoprecipitation and GST binding experiments demonstrated that the CSF-1 receptor could bind to SLAP-2 in a ligand-independent manner. Furthermore, the binding of SLAP-2 to the CSF-1 receptor involved multiple domains of SLAP-2. SLAP-2 also bound c-Cbl, with the interaction being mediated, at least in part, by the unique C-terminal domain of SLAP-2. Overexpression of SLAP-2 in bone marrow macrophages partially suppressed the CSF-1-induced tyrosine phosphorylation and/or expression level of a approximately 80 kDa protein without affecting CSF-1-induced global tyrosine phosphorylation, or activation of Akt or Erk1/2. Significantly, CSF-1 stimulation induced serine phosphorylation of SLAP-2. Pharmacologic inhibition of specific protein kinases revealed that CSF-1-induced phosphorylation of SLAP-2 was dependent on JNK activity. Taken together, our results suggest that SLAP-2 could potentially be involved in signaling by the CSF-1 receptor.