siRNA knockdown of STAT1 confers resistance to STAT3 inhibition-induced cell death. (A) SupM2 cells were exposed to various doses of Stattic for 4 hours, and western blots showed the decrease of pSTAT3 in a dose-dependent manner. (B) SupM2 cells transfected with two species of STAT1 siRNA showed significantly higher half maximal inhibitory concentration (IC₅₀) to Stattic compared with cells transfected with scrambled siRNA. Western blot studies showed the siRNA knockdown efficiency, which was higher with species 1 compared with species 2. The densitometry values shown were normalized to the band of γ-tubulin. (C) Transfection of STAT1 siRNA significantly reduced the suppression of cell growth induced by STAT3 siRNA in SupM2 cells. The western blots results showed the efficiency of siRNA knockdowns. Image J software was used to analyze the densitometry value of western blots bands. Statistical significance was calculated by Student t test. *P < .05; **P < .01.