Expression and tyrosine phosphorylation of Cbl regulates macrophage chemokinetic and chemotactic movement

Primary macrophages isolated from hck^-/-fgr^-/- mice display altered morphology and F-actin cytoskeletal structures and reduced migration. The ability of phorbol myristyl acetate (PMA), a protein kinase C activator that has been reported to increase macrophage spreading and carcinoma cell motility, to rescue these hck^-/- fgr^-/- defects was tested. Although PMA-treated wild-type and hck^-/-fgr^-/- macrophages exhibited a similar flattened, spread phenotype, PMA did not rescue the hck^-/-fgr^-/- macrophage migration defect. Instead, both PMA-treated wild type and hck^-/-fgr^-/- macrophages were defective in spontaneous and chemotactic migration and tyrosine phosphorylation of the Cbl protooncoprotein was decreased in both. Moreover, c-cbl^-/- macrophages displayed the same impairment of motility as hck^-/-fgr^-/- macrophages and a similar morphology with less polarization and more dorsal ruffling than wild-type macrophages. As Hck and Fgr expression and activity were not decreased in c-cbl^-/- macrophages, these results suggest that Cbl is likely to be an important downstream mediator of the Src family kinase-regulated macrophage motility pathway.