Objective: The Sox9 transcription factor has emerged as an important determinant of chondrocyte differentiation, including the regulation of type II collagen (Col2) and aggrecan gene expression. We sought to identify a human cell line model that conserves the Sox9 regulatory pathways identified in the mouse.
Design: The SW1353 chondrosarcoma cell line was considered to be a candidate for Sox9 studies. The activity of a Sox9 regulated Col2a1 enhancer reporter gene was analyzed in response to treating cells with known regulators of murine Sox9 expression/activity. The effect of treatment on expression of the endogenous Sox9 gene was analyzed by real-time PCR and Western blot.
Results: Col2 enhancer activity was stimulated by fibroblast growth factors (FGF-1 and -2) and repressed by inflammatory cytokines (IL-1beta and TNFalpha) in SW1353 cells. These effects correlated with changes in Sox9 mRNA and protein levels. In addition, FGF-9 was shown to stimulate enhancer activity and Sox9 expression. Cotreatment studies demonstrated that FGFs functionally antagonize the cytokine-mediated repression of Sox9 expression and Col2 enhancer activity.
Conclusions: SW1353 cells represent a useful human cell model as they conserve many Sox9 signaling pathways previously demonstrated in mouse chondrocytes. We identify FGF-9 as a particularly potent Sox9 agonist. The antagonism between FGFs and cytokines on Sox9 expression and Col2 enhancer activity suggests that Sox9 integrates the opposing activities of FGFs and cytokines. We also find that SW1353 cells respond to very low doses of IL-1 with Col2 enhancer activation, while increasing doses lead to repression.