p38 mitogen-activated protein kinase functionally contributes to chondrogenesis induced by growth/differentiation factor-5 in ATDC5 cells

Recent studies of intracellular signal transduction mechanisms for the tran sforming growth factor-beta (TG;F-P) superfamily have focused on Smad prote ins, but have paid little attention to mitogen-activated protein (MAP) kina se cascades, Here we demonstrate that growth/differentiation factor-5 (GDF- 5), but neither bone morphogenetic protein-2 (BMP-2) nor TGF-beta 1, fully promotes the early phase of the chondrogenic response by inducing cellular condensation followed by cartilage nodule formation in a mouse chondrogenic cell line, ATDC5. We investigated which, if any, of the three major types of MAP kinase plays a functional role in the promotion of chondrogenesis in duced by GDF-5, GDF-5 induced phosphorylation of p38 MAP kinase and extrace llular signal-regulated kinase (ERK) but not that of c-Jun N-terminal kinas e (JNK). The phosphorylation of p38 MAP kinase was also induced by BMP-2 an d TGF-beta 1. An inhibitor of p38 and p38 beta MAP kinase, SB202190, showed complete inhibition of cartilage nodule formation but failed to affect alk aline phosphatase (ALP) activity induced by GDF-5, Expression of the type I I collagen gene, a hallmark of chondrogenesis in vertebrates, was also indu ced by GDF-5 treatment and strongly suppressed by SB202190, On the other ha nd, although an inhibitor of MAP/ERK kinase, PD98059, inhibited the rapid p hosphorylation of ERK by GDF-5, it inhibited neither ALP activity nor carti lage nodule formation induced by GDF-5. These results strongly suggest that the p38 MAP kinase cascade is involved in GDF-5 signaling pathways and tha t a role of the p38 MAP kinase pathway is necessary over a longer period to promote chondrogenesis in ATDC5 cells, (C) 1999 Academic Press.