CTGF/Hcs24 induces chondrocyte differentiation through a p38 mitogen-activated protein kinase (p38MAPK), and proliferation through a p44/42 MAPK/extracellular-signal regulated kinase (ERK)

Connective tissue growth factor/hypertrophic chondrocyte specific gene prod uct 24 (CTGF/Hcs24) promotes proliferation and differentiation of chondrocy tes in culture. We investigated the roles of two major types of mitogen act ivated protein kinase (MAPK) in the promotion of proliferation and differen tiation by CTGF/Hcs24. Here we report the effects of the MAPKK/MEK 1/2 inhi bitor, PD098059, and p38 MAPK inhibitor, SB203580, in a human chondrosarcom a-derived chondrocytic cell line (HCS-2/8) and rabbit growth cartilage (RGC ) cells treated with CTGF/Hcs24. In the proliferation phase, CTGF/Hcs24 ind uced a approximate to fivefold increase in the phosphorylation of p44/42 MA PK/ERK and a approximate to twofold increase in that of p38 MAPK in an in v ivo kinase assay. These inhibitors of MAPKK and MAPK suppressed phosphoryla tion of ets-like gene-1 (Elk-1) and nuclear activating transcription factor -2 (Atf-2) induced by CTGF/Hcs24 in a dose-dependent manner, respectively. Western blot analysis showed that phosphorylation of ERK was induced from 3 0 to 60 min and phosphorylation of p38 MAPK from 10 to 15 min after the add ition of CTGF/Hcs24 in confluence HCS-2/8 cells. PD098059 suppressed the DN A synthesis of HCS-2/8 cells and RGC cells, while SB203580 did not. On the other hand, the p38 MAPK inhibitor, SB203580, completely inhibited the CTGF /Hcs24-induced synthesis of proteoglycans in HCS-2/8 cells and RGC cells bu t the MEK1/2 inhibitor, PD098059, did not. These results suggest that ERK m ediates the CTGF/Hcs24-induced proliferation of chondrocytes, and that p38 MAPK mediates the CTGF/Hcs24-induced differentiation of chondrocytes.