ERK1/2 pathway involvement in the Res-induced repression of YKL-40 expression. A. YKL-40 protein expression after treatment with 20 nM PD98059 alone, 20 nM PD98059 along with 100 μM Res, or with 100 μM Res alone for 48 h by western blotting. B. Phospho-ERK1/2 expression after treatment with 100 μM Res for 24, 48, and 72 h determined by western blotting. Asterisks indicate statistically significant changes (P < 0.01). Bars indicate SE.