(A) GSNO (100µM) supplementation prevented DHFR reduction induced by CHX (30µg/ml) treatment. DHFR degradation induced by eNOS silencing (B) or PTIO (150µM) (C) could be inhibited by proteasome inhibitor, MG132 (1µM). (D) PTIO- (150µM) induced DHFR poly-ubiquitination, which could be suppressed by GSNO (100µM). (n=3; *p<0.05 vs. control in A, C and D, or p<0.05 vs. Scr siRNA in B; #p<0.05 vs. eNOS siRNA in B, or p<0.05 vs. PTIO in C and D)