In Vitro and In Vivo Suppression of Osteoclast Function by Adenovirus Vector–Induced csk Gene

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Abstract
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 osteopetrosis in mice. The csk (C‐terminal Src family kinase) gene encodes a cytoplasmic 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‐Src, we constructed an adenovirus vector that carries this gene. The recombinant adenovirus vector carrying csk cDNA induced Csk expression in mouse osteoclast‐like cells formed in vitro and clearly reduced c‐Src kinase activity in a dose‐dependent manner. The expression of Csk caused cytoskeletal disorganization of osteoclast‐like cells and strongly suppressed pit‐forming activity of the cells in vitro. In addition, the viral vector carrying csk gene dramatically suppressed interleukin‐1α–induced bone resorption in vivo. Conversely, kinase‐inactive Csk caused an increase in c‐Src kinase activity and bone resorbing activity of the cells both in vitro and in vivo, acting as a dominant negative molecule against intrinsic Csk. These findings indicate that the inhibition of c‐Src activity by adenovirus vector‐mediated csk expression offers an efficient means for inhibiting pathological bone resorption by suppressing osteoclast function.