FUNCTIONAL SPECIFICITY OF CYTOPLASMIC AND TRANSMEMBRANE TYROSINE KINASES - IDENTIFICATION OF 130-KILODALTON AND 75-KILODALTON SUBSTRATES OFC-FPS FES TYROSINE KINASE IN MACROPHAGES/

c-fps/fes encodes a 92-kDa protein-tyrosine kinase (NCP92) that is exp ressed at the highest levels in macrophages. To determine if c-fps/fes can mediate the action of the colony-stimulating factor 1 (CSF-1) rec eptor (CSF-1R) and to identify potential targets of c-fps/fes in macro phages, we have overexpressed c-fps/fes in a CSF-1-dependent macrophag e cell line. A 30- to 50-fold overexpression of c-fps/fes partially re leased these cells from their factor dependence by a nonautocrine mech anism, and this correlated,vith the tyrosine phosphorylation of two pr oteins of 130 and 75 kDa (P130 and P75). c-fps/fes did not cause tyros ine phosphorylation or activation of CSF-1-dependent targets, includin g CSF-1R, She, a nd phosphatidyl inositol 3-kinase, and conversely, CS F-1 did not induce tyrosine phosphorylation of P130 and P75. P75 appea rs to be a novel phosphotyrosyl protein, whereas P130 cross-reacts wit h a known substrate of v-src. P130 and P75 may be direct substrates of c-fps/fes: P130 was tightly associated with NCP92, and the src homolo gy 2 domain of NCP92 specifically bound phosphorylated P130 and P75 bu t not the CSF-1-induced phosphotyrosyl proteins, consistent with the p ossibility that P130 and P75 are physiological targets of c-fps/fes. W e conclude that although c-fps/fes can functionally substitute for CSF -1R to a certain extent, these tyrosine kinases act largely independen tly of each other and that P130 and P75 are novel targets whose mechan isms of action may be unrelated to the signalling pathways utilized by receptor tyrosine kinases.