Targeting GABARAPL1/HIF-2a axis to induce tumor cell apoptosis in nasopharyngeal carcinoma.

Objectives: The primary gene mutations associated with nasopharyngeal carcinoma (NPC) are located within the phosphoinositide 3-kinase-mammalian target of rapamycin signaling pathways, which have inhibitory effects on autophagy. Compounds that target autophagy could potentially be used to treat NPC. However, autophagy-related molecular targets in NPC remain to be elucidated. We aimed to examine levels of autophagy-related genes, including autophagy-related 4B cysteine peptidase (ATG4B) and gamma-aminobutyric acid (GABA) type A receptor-associated protein-like 1 (GABARAPL1), in NPC cells and explored their potential role as novel targets for the treatment of NPC. Materials and Methods: The mRNA and protein expression of autophagy-related genes were detected in several NPC cells. Levels of GABARAPL1 were modified by either overexpression or knockdown, followed by examining downstream targets using RT-qPCR and western blotting. The role of GABARAPL1 in NPC proliferation and apoptosis was examined by flow cytometry. Furthermore, the role of GABARAPL1 was assessed in vivo using a nude mouse xenograft tumor model. The underlying mechanism by which GABARAPL1 regulated nasopharyngeal tumor growth was investigated. Results: Autophagy-related 4B cysteine peptidase (ATG4B), GABARAPL1, and Unc-51-like kinase 1 (ULK1) were significantly down-regulated in multiple NPC cell lines. Overexpression of GABARAPL1 up-regulated the expression of autophagy-related proteins, decreased the level of hypoxia-inducible factor (HIF)-2α, and induced apoptosis in NPC cells. Importantly, overexpression of GABARAPL1 slowed tumor growth. Western blotting showed that autophagy was activated, and HIF-2α was down-regulated in tumor tissues. Conclusion: HIF-2α, as a substrate for autophagic degradation, may play an interesting role during NPC progression.