Effects of lentivirus-mediated HIF-1α knockdown on hypoxia-related cisplatin resistance and their dependence on p53 status in fibrosarcoma cells

Therapy targeting hypoxia-inducible factor-1 (HIF-1) to reverse the hypoxia-related drug resistance has received much interest. Despite a close interaction between HIF-1 and p53 and that p53 mutation is seen in > 50% of tumors, whether HIF-1 silencing by targeted therapy depends on tumor p53 status remains unknown. Two isogenic fibrosarcoma cells HT1080 (wild-type p53) and HT1080-6TG (mutant p53) were transduced with HIF-1 alpha-specific RNAi lentiviral vectors and selected with blasticidin. Real-time PCR and western blot analysis of HIF-1 alpha mRNA and protein respectively validated the silencing effects. Cells were first preconditioned under hypoxia (0.5% O-2) for 4 h and then co-treated with cisplatin for another 24 h. MTT was used for assessment of chemosensitivity to cisplatin. Moreover, annexin V and propidium iodide staining was detected on flow cytometry for analysis of cisplatin-induced apoptosis. Furthermore, changes of some Bcl-2 family members were detected on western blotting. Exposure to hypoxia significantly increased resistance to cisplatin than exposure to normoxia. HIF-1 alpha knockdown could reverse hypoxia-related resistance to cisplatin and apoptotic resistance only in HT1080 cells, but had little effect on HT1080-6TG cells. With HIF-1 alpha knockdown, Bid expression was higher in HT1080 than in HT1080-6TG under hypoxia. In summary, HIF-1 targeted therapy to reverse hypoxia-related cisplatin resistance depends on normal p53 status. Changes of Bid expression levels under hypoxia might contribute in part to the differential response to HIF-1 alpha silencing in cells with different p53 status.