Bone Abstracts

CCN2/CTGF is known as a multi-functional growth factor for various mesenchymal cells including chondrocytes, osteoblasts, vascular endothelial cells and its function is suggested to be produced by its binding to other growth factors or membrane proteins. Therefore, finding out these binding partners are critically important in understanding the molecular function of the CCN2. As a result of screening, DCL-1/CD302 was found as a new candidate of CCN2-binding molecule. DCL-1/CD302 is one of C-type lectin receptors but the distribution and the function are mostly not clarified. Among a few reports on DCL-1/CD302, there is a report that it is express in macrophages but no report on expression and role of DCL-1/CD302 on pre-osteoclasts or osteoclasts that are the same lineage cells of macrophages. In the present study, we investigated significance of interaction between CCN2 and DCL-1/CD302 in osteoclastogenesis.

Gene expression of DCL-1/CD302 assayed by RT-PCR increased during in vitro osteoclastogenesis using mouse* bone marrow cells stimulated by M-CSF and RANKL. Westernblot analysis also confirmed increase in DCL-1/CD302 protein during osteoclastogenesis. Immunoprecipitation and western blotting assay using lysates of osteoclasts derived from muse bone marrow cells and recombinant CCN2 confirmed binding of DCL-1/CD302 to CCN2. Immunostaining revealed that DCL-1/CD302 localized with actin ring (together with CCN2) in mature osteoclasts. Suppression of DCL-1/CD302 by its siRNA inhibited maturation of osteoclasts and formation of bone resorption pits in vitro. The siRNA targeting DCL-1/CD302 also caused fragmentations of actin ring. Because we previously reported that CCN2 binds to action¹, these data suggest that DCL-1/CD302 has a critical role in actin ring formation and that CCN2 may play an important role in to this process.

Reference1. Yosimichi G. et al. BBRC, 2002 299 755–756. *Animal experiments were all approved by the Animal Committee of Okayama University.