Kif1c regulates osteoclastic bone resorption as a downstream molecule of p130Cas

Podosome formation in osteoclasts is an important initial step in osteoclastic bone resorption. Mice lacking c-Src (c-Src^−/−) exhibited osteopetrosis due to a lack of podosome formation in osteoclasts. We previously identified p130Cas (Crk-associated substrate [Cas]) as one of c-Src downstream molecule and osteoclast-specific p130Cas-deficient (p130Cas^ΔOCL−/−) mice also exhibited a similar phenotype to c-Src^−/− mice, indicating that the c-Src/p130Cas plays an important role for bone resorption by osteoclasts. In this study, we performed a cDNA microarray and compared the gene profiles of osteoclasts from c-Src^−/− or p130Cas^ΔOCL−/− mice with wild-type (WT) osteoclasts to identify downstream molecules of c-Src/p130Cas involved in bone resorption. Among several genes that were commonly downregulated in both c-Src^−/− and p130Cas^ΔOCL−/− osteoclasts, we identified kinesin family protein 1c (Kif1c), which regulates the cytoskeletal organization. Reduced Kif1c expression was observed in both c-Src^−/− and p130Cas^ΔOCL−/− osteoclasts compared with WT osteoclasts. Kif1c exhibited a broad tissue distribution, including osteoclasts. Knockdown of Kif1c expression using shRNAs in WT osteoclasts suppressed actin ring formation. Kif1c overexpression restored bone resorption subsequent to actin ring formation in p130Cas^ΔOCL−/− osteoclasts but not c-Src^−/− osteoclasts, suggesting that Kif1c regulates osteoclastic bone resorption in the downstream of p130Cas (191 words). Significance of the study: We previously showed that the c-Src/p130Cas (Cas) plays an important role for bone resorption by osteoclasts. In this study, we identified kinesin family protein 1c (Kif1c), which regulates the cytoskeletal organization, as a downstream molecule of c-Src/p130Cas axis, using cDNA microarray. Knockdown of Kif1c expression using shRNAs in wild-type osteoclasts suppressed actin ring formation. Kif1c overexpression restored bone resorption subsequent to actin ring formation in osteoclast-specific p130Cas-deficient (p130Cas^ΔOCL−/−) osteoclasts but not c-Src^−/− osteoclasts, suggesting that Kif1c regulates osteoclastic bone resorption in the downstream of p130Cas.