EFFECTS OF HYPOXIA ON THE EXPRESSIONS OF HIF SUBUNITS HIF-1α,HIF-2α and HIF-β IN HUMAN LUNG CANCER CELL LINES AND THEIR CORRELATIONS

Objective To explore the effects of hypoxia on the expressions of hypoxia inducible factor-1α(HIF-1α),hypoxia inducible factor-2α(HIF-2α) and hypoxia inducible factor-β(HIF-β) in human lung cancer cell lines and their correlations.Methods Six lung cancer cell lines(SPCA1,A549,H446,SH77,H520 and 95D) were incubated under 0.5% O_2 for 4 to 24 hours.Western blotting and real-time RT-PCR were used for protein and mRNA analysis of HIF-1α,HIF-2α and HIF-β.Results Both HIF-1α and HIF-2α mRNAs were at very low levels or almost undectable under normoxia,as well as their proteins.HIF-1α mRNA experienced a decrease after transcient hypoxia,while the level of HIF-2α mRNA increased.By contrast,under chronic hypoxia,the levels of both HIF-1α and HIF-2α mRNA increased steadily.HIF-1α and HIF-2α proteins were accumulated and changed differently under prolonged hypoxia.HIF-1α was expressed in all the cell lines at various levels,but HIF-2α protein was absent in some cell lines.While both the levels of HIF-β mRNA and HIF-β protein were insensitive to changes of O_2 concentration.Besides,the level of HIF-2α mRNA under hypoxia was closely related to its protein level(r=0.989,P=0.011),while HIF-1α and HIF-β showed no such correlation.Conclusion HIF-1α,HIF-2α and HIF-1β revealed different responses to hypoxia and their expressions were cell specific.Hypoxia may regulate HIF-1α and HIF-2α at the translational level and the transcriptional level respectively,whereas it has no effect on HIF-β expression.