Hypoxia induces S phase entry and E2F1 activation in chicken PASMCs. Chicken PASMCs were cultured under normoxic (21% oxygen) or hypoxic (2% oxygen) conditions for 24 h. (A) Cell cycle profile was determined using the method as described in materials and methods. (B) Cells were treated as in (A), and the protein level of E2F1, CCNE1, and β-actin were analyzed. (C) The relative expression levels of E2F1 and CCNE1 were determined from the immunoblots by densitometric analysis. Values are mean ± SEM (n=5). *P<0.05 compared with normoxic control.