Colony-stimulating factor-1 stimulates the formation of multimeric cytosolic complexes of signaling proteins and cytoskeletal components in macrophages

Stimulation of macrophages with colony-stimulating factor-1 (CSF-1) results in the protein tyrosine phosphorylation of the CSF-1 receptor (CSF- 1R) and many other, primarily cytosolic, proteins. Stimulation by CSF-1 at 4 °C was used to facilitate the purification and identification of the proteins of the cytosolic anti-phosphotyrosine (PY)-reactive fraction (αPY- RF) involved in downstream signaling pathways. Confocal microscopy revealed that the PY proteins are in close proximity to the CSF-1R at the plasma membrane. The αPY-RF contained pre-existing complexes of PY proteins and non-PY proteins which generally increased in size and PY protein content following CSF-1 stimulation. PY proteins identified by microsequencing and Western blotting include Cbl, STAT3, STAT5a, STAT5b, SHP-1, Shc, and two novel proteins pp57 and pp37. Other proteins included cytoskeletal/contractile proteins (paxillin, vimentin, elongation factor- 1α, F-actin, tropomyosin, and myosin regulatory light chain), Ras family signaling proteins (p85 (phosphoinositide 3-kinase), Vav, Ras-GTPase- activating protein SH3 domain-binding protein, and Grb2), DnaJ-like protein, and glyceraldehyde-3-phosphate dehydrogenase. CSF-1 induced the de novo recruitment of Cbl, STAT3, STAT5a, STAT5b, p85, SHP-1, Shc, vimentin, and Grb2 to complexes and caused preexisting complexes involving Vav, elongation factor-1α, and F-actin to increase in size. These studies indicate that CSF- l-induced protein tyrosine phosphorylation is associated with the reorganization of complexes of cytoskeletal, signaling, and other proteins that mediate CSF-l-regulated motility and growth.