Effects of hypoxia and BPS on BrdU incorporation in cells transfected with p27kip1siRNA. HPASMC were transfected with control or p27kip1 siRNA, then exposed to 21% and 2% oxygen with or without 10 μM BPS for 24 h. Western blot analysis showed that p27kip1 protein expression in cells transfected with p27kip1 siRNA was significantly suppressed under all conditions. Photomicrographs are representative of 4 similar experiments. Transfection with p27kip1 siRNA significantly prevented BPS-induced inhibition of DNA synthesis. Bar graphs show BrdU incorporation relative to 21% oxygen control. Open and solid bars, 21% and 2% oxygen, respectively. Data are expressed as means ± SE (n = 6). *P < 0.05 versus with 21% oxygen; †P < 0.05 versus without BPS.