Hic-5 is a CAKβ-binding protein localized at focal adhesions. Here we show that overexpression of CAKβ or Fyn, but not FAK, enhanced the tyrosine phosphorylation of coexpressed Hic-5 in COS-7 cells. These phosphorylations were further augmented by stimulating cells with osmotic stress. The Y60F mutant of Hic-5 was not phosphorylated, and Hic-5 phosphorylated on tyrosine 60 was bound specifically to the SH2 domain of Csk. Coexpression experiments revealed that the phosphorylation of Hic-5 by CAKβ required the kinase activation of CAKβ and binding of Hic-5 by CAKβ. Specific phosphorylation of Hic-5 by CAKβ and Fyn may activate a signaling pathway mediated by Hic-5.
