SRY-Related HMG Box 9 Regulates the Expression of Col4a2 through Transactivating Its Enhancer Element in Mesangial Cells

Accumulation of α1(IV) and α2(IV) collagen is one of the characteristic pathological changes in glomerulosclerosis. Although the Col4a2 gene is known to have a 0.3-kb critical enhancer element with the GAACAAT motif, which transcription factor binds and transactivates this motif has not been identified. In this study, we found that SRY-related HMG box 9 (SOX9) was bound to the GAACAAT motif in the Col4a2 enhancer in vitro and in vivo in mesangial cells. SOX9 strongly activated this enhancer when cotransfected with Col4a2 enhancer-promoter construct in mesangial cells and Swiss/3T3 cells. Mutation in the GAACAAT motif eliminated the activation by SOX9. Furthermore, transforming growth factor-β (TGF-β) treatment induced the expression of SOX9 and Col4a2, and a small interfering RNA against SOX9 reduced Col4a2 expression induced by TGF-β treatment in mesangial cells. In vivo, we found that the expression of SOX9 was dramatically increased along with the expression of TGF-β and Col4a2 in mouse nephrotoxic nephritis. These results indicate that SOX9 is essential for Col4a2 expression in mesangial cells and might be involved in the accumulation of α2(IV) collagen in experimental nephritis.