In vitro and in vivo suppression of osteoclast function by adenovirus vector-induced csk gene

The proto-oncogene c-src, which encodes a non-receptor-type tyrosine kinase c-Src, has been shown to be essential for osteoclastic bone resorption by the finding that the targeted disruption of the c-src gene induced osteopet rosis in mice, The csk (C-terminal Src family kinase) gene encodes a cytopl asmic protein-tyrosine kinase that specifically phosphorylates the negative regulatory site of c-Src (Tyr-527), thereby inhibiting its kinase activity . To regulate osteoclast function by modulating the kinase activity of c-Sr c, we constructed an adenovirus vector that carries this gene. The recombin ant adenovirus vector carrying csk cDNA induced Csk expression in mouse ost eoclast-like cells formed in vitro and clearly reduced c-Src kinase activit y in a dose-dependent manner. The expression of Csk caused cytoskeletal dis organization of osteoclast-like cells and strongly suppressed pit-forming a ctivity of the cells in vitro. In addition, the viral vector carrying csk g ene dramatically suppressed interleukin-1 alpha-induced bone resorption in vivo. Conversely, kinase-inactive Csk caused an increase in c-Src kinase ac tivity and bone resorbing activity of the cells both in vitro and in vivo, acting as a dominant negative molecule against intrinsic Csk, These finding s indicate that the inhibition of c-Src activity by adenovirus vector-media ted csk expression offers an efficient means for inhibiting pathological bo ne resorption by suppressing osteoclast function.