Crosstalk between Smad2/3 and specific isoforms of ERK in TGF‐β1‐induced TIMP‐3 expression in rat chondrocytes

This study investigated the roles of ERK1 and ERK2 in transforming growth factor-β1 (TGF-β1)-induced tissue inhibitor of metalloproteinases-3 (TIMP-3) expression in rat chondrocytes, and the specific roles of ERK1 and ERK2 in crosstalk with Smad2/3 were investigated to demonstrate the molecular mechanism of ERK1/2 regulation of TGF-β1 signalling. To examine the interaction of specific isoforms of ERK and the Smad2/3 signalling pathway, chondrocytes were infected with LV expressing either ERK1 or ERK2 siRNA and stimulated with or without TGF-β1. At indicated time-points, TIMP-3 expression was determined by real-time PCR and Western blotting; p-Smad3, nuclear p-Smad3, Smad2/3, p-ERK1/2 and ERK1/2 levels were assessed. And then, aggrecan, type II collagen and the intensity of matrix were examined. TGF-β1-induced TIMP-3 expression was significantly inhibited by ERK1 knock-down, and the decrease in TIMP-3 expression was accompanied by a reduction of p-Smad3 in ERK1 knock-down cells. Knock-down of ERK2 had no effect on neither TGF-β1-induced TIMP-3 expression nor the quantity of p-Smad3. Moreover, aggrecan, type II collagen expression and the intensity of matrix were significantly suppressed by ERK1 knock-down instead of ERK2 knock-down. Taken together, ERK1 and ERK2 have different roles in TGF-β1-induced TIMP-3 expression in rat chondrocytes. ERK1 instead of ERK2 can regulate TGF-β/Smad signalling, which may be the mechanism through which ERK1 regulates TGF-β1-induced TIMP-3 expression.