Effect of BPS and 8-Br-cAMP on p27kip1mRNA stability during hypoxia. Cultured HPASMC were exposed to 21% or 2% oxygen concentrations with or without 10 μM of BPS or 1 mM 8-Br-cAMP for indicated periods. The p27kip1 mRNA stability was measured after adding 400 nM of Act D using Real-time RT-PCR using LightCycler™. Degradation of p27kip1 mRNA was significantly suppressed by BPS and 8-Br-cAMP under both normoxic and moderately hypoxic conditions, and mRNA stability was slightly decreased by moderate hypoxia. Graphs show % maximal p27kip1 mRNA expression. Line with solid circles, 21% oxygen; dotted line with open circles, 2% oxygen; line with solid squares, 21% oxygen and BPS; line with solid triangles, 21% oxygen and 8-Br-cAMP; dotted line with open squares, 2% oxygen and BPS; dotted line with open triangle, 2% oxygen and 8-Br-cAMP. Data are expressed as means ± SE (n = 6). *P < 0.05 versus 21% oxygen. †P < 0.05 versus oxygen controls.