c-Src-Dependent and -Independent Functions of Matk in Osteoclasts and Osteoblasts.

The non-receptor tyrosine kinase c-Src participates in bone metabolism by regulating the activities of both the bone-resorbing osteoclasts and bone-forming osteoblasts. In this study, we investigated whether megakaryocyte-associated tyrosine kinase (Matk), a potent inhibitor of c-Src, affects the functions of murine osteoclasts and osteoblasts. Results revealed that the formation of osteoclasts with actin rings was attenuated by Matk overexpression in osteoclast precursor cells but was enhanced by Matk knockdown. The inhibitory effect of Matk on osteoclasts was closely related with the inhibition of c-Src activity. Intriguingly, Matk overexpression in osteoblasts reduced bone nodule formation. Conversely, Matk knockdown increased osteoblast function. Most importantly, binding of Matk to Runx2 resulted in the inhibition of Runx2 translocation into the nucleus and downregulation of Runx2 target genes. Taken together, our findings demonstrated that Matk plays a critical role in bone metabolism by impairing the functions of osteoclasts and osteoblasts via distinct mechanisms involving inhibition of c-Src-dependent and -independent signaling pathways.