Autophagy related 4B, upregulated by HIF-1alpha, attenuates the sensitivity to cisplatin in nasopharyngeal carcinoma cells.

OBJECTIVE: Increasing evidence has shown that autophagy related proteins and hypoxia-inducible factor-1alpha (HIF-1alpha) are both involved in the malignant progress of nasopharyngeal carcinoma (NPC), and HIF-1alpha plays an emerging role in the chemosensitivity of NPC cells. However, it is still unknown whether autophagy related proteins are associated with HIF-1alpha in regulating the chemosensitivity of NPC cells. MATERIALS AND METHODS: Quantitative Real-time PCR (qPCR) was applied to determine mRNA levels of HIF-1alpha and the autophagy related proteins, such as ATG3, ATG4B, ATG5, Beclin1, ATG7, ATG10, ATG12 and ATG16L1. Western blot was applied to determine protein levels of HIF-1alpha, ATG4B and cleaved Caspase-3. Cell viability and death were investigated by cell counting kit-8 and trypan blue exclusion assay. In addition, Caspase-3 activity was detected to reflect apoptosis. Furthermore, Luciferase reporter assay was applied to explore the mechanism by which HIF-1alpha transcriptionally upregulated ATG4B expression. RESULTS: Our study reveals that HIF-1alpha increased ATG4B expression in NPC cells, and in turn upregulated the cisplatin (DDP)-induced protective autophagy, resulting in enhanced killing effect of DDP to NPC cells. In mechanism, reporter assay showed that HIF-1alpha upregulated ATG4B expression by activating its gene promoter region. The binding site (-225 to -216) was required for HIF-1alpha-induced increase of ATG4B gene promoter activity. CONCLUSIONS: These results indicate that HIF-1alpha elevates ATG4B via promoting its transcription, which alleviates the sensitivity of DDP in NPC cells through enhancing protective autophagy, suggesting that ATG4B, upregulated by HIF-1alpha, may be a novel target for DDP sensitization in the treatment of NPC in clinic.