Involvement of Rac1 GTPase in regulation of MMP13 in C28/I2 chondrocyte cells. (A) Effects of silencing Rac1 on the phosphorylation level of p38 (p-p38) and NFκB (p-NFκB). The level of p-p38 was reduced, while the level of p-NFκB was unchanged. Note that NC is the non-specific control siRNA. (B) Decrease in the level of MMP13 mRNA in response to transfection of siRNA specific to Rac1 GTPase. (C) MMP13 activity in the cells transfected with the Rac1 dominant negative (DN) or constitutively active (CA) mutant. MMP13 activity was reduced by the DN mutant, which it was elevated by the CA mutant. n = 3 per group (A-C).