Effects of hypoxia on expression of HIF-1alpha,P53, and cyclin D1 in human lung adenocarcinoma cell line A549

Objective: Many studies showed that hypoxia inducible factor-1 alpha (HIF-1alpha)was an essential component for hypoxia- induced cell cycle arrest, but the definite mechanism and the degree of HIF-1alpha affecting cell cycle arrest were unknown yet. This study was to explore the probable mechanism of hypoxia-induced tumor cell cycle arrest.

Methods: Human lung adenocarcinoma cell line A549 were divided into 3 groups: 12-h hypoxia group, 24-h hypoxia group, and control group. The hypoxia groups were exposed to hypoxic conditions (37degrees C, 5% CO2, and 2.0% O2) for 12 h, and 24 h, respectively, while control group was exposed to normal oxygen conditions (37 degrees C, 5% CO2, and 21% O2) for 24 h. Flow cytometry was used to measure the distribution of cell cycles and the expression of cyclin D1. The expression of HIF-1alpha, and p53 was detected using immunohistochemistry.

Results: (1) The ratio of G(0)/G(1) in 12-h hypoxia group was (70.20+/-3.33)%, and in 24-h hypoxia group was (82.85+/-1.75)%, significantly higher than that in control group [(50.36+/-4.09) %] (F=202.34, P< 0.01).(2) There was significant difference in cyclin D1 expression among 12-h hypoxia group [(80.22+/-1.55)%], 24-h hypoxia group [(73.65+/-2.10)%], and control group [(90.35+/-2.68)%] (F=100.45, P< 0.01). (3) HIF-1alpha expression in 12-hypoxia group, 24-hypoxia group, and control group was 0.16 +/- 0.02, 0.26 +/- 0.05, and 0.01 +/- 0.00, respectively, with significant difference among the 3 groups (F=105.28, P< 0.01). (4) In hypoxia groups, cyclin D1 expression was negatively correlated with G(0)/G(1) arrest (r=-0.91, P< 0.01), HIF-1alpha expression was positively correlated with p53 expression (r=0.84, P< 0.01), and negatively correlated with cyclin D1 expression (r=-0.90, P< 0.01), and p53 expression was negatively correlated with cyclin D1 expression (r=-0.78,P< 0.01).

Conclusions: Hypoxia can cause G(0)/G(1) cell cycle arrest in human lung adenocarcinoma cell line A549. HIF-1alpha-p53-cyclin D1 pathway might play an important role in the hypoxia-induced G(0)/G(1) cell cycle arrest of human lung adenocarcinoma cell line A549.