Protein tyrosine phosphatase phi regulates paxillin tyrosine phosphorylation and mediates colony-stimulating factor 1-induced morphological changes in macrophages

Removal of colony-stimulating factor 1 (CSF-1) causes macrophages to round up and to increase their expression of protein tyrosine phosphatase phi (PT P phi). This is accompanied by the disruption of focal complexes and the fo rmation of ruffles. Here,ve have overexpressed wild-type (WT) PTP phi and a phosphatase-inactive (C325S) mutant in a macrophage cell line in the prese nce and absence of CSF-1. In the presence of CSF-1, WT PTP phi induces cell rounding and ruffle formation, while C325S PTP phi has no effect. In contr ast, in CSF-l-starved cells, C325S PTP phi behaves in a dominant negative f ashion, preventing rounding and ruffling. Furthermore, C325S PTP phi increa ses adhesion in cycling cells, while WT PTP phi enhances motility. In WT PT P phi -overexpressing cells, the focal contact protein paxillin is selectiv ely depleted from focal complexes and specifically dephosphorylated on tyro sine. In contrast, paxillin is hyperphosphorylated in C325S PTP phi -expres sing cells. Moreover, a complex containing PTP phi, paxillin, and a paxilli n-associated tyrosine kinase, Pyk2, can be immunoprecipitated from macropha ge lysates, and the catalytic domain of PTP phi selectively binds paxillin and Pyk2 in vitro. Although PTP phi and Pyk2 do not colocalize with paxilli n in focal complexes, all three proteins are colocalized in dorsal ruffles. The results suggest that paxillin is dephosphorylated by PTP phi in dorsal ruffles, using Pyk2 as a bridging molecule, resulting in a reduced pool of tyrosine-phosphorylated paxillin available for incorporation into focal co mplexes, thereby mediating CSF-1 regulation of macrophage morphology, adhes ion, and motility.