Targeting GABARAPL۱/HIF-۲a axis to induce tumor cell apoptosis in nasopharyngeal carcinoma

Objective(s): The primary gene mutations associated with nasopharyngeal carcinoma (NPC) are located within the phosphoinositide ۳-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 ۴B cysteine peptidase (ATG۴B) and gamma-aminobutyric acid (GABA) type A receptor-associated protein-like ۱ (GABARAPL۱), 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 GABARAPL۱ were modified by either overexpression or knockdown, followed by examining downstream targets using RT-qPCR and western blotting. The role of GABARAPL۱ in NPC proliferation and apoptosis was examined by flow cytometry. Furthermore, the role of GABARAPL۱ was assessed in vivo using a nude mouse xenograft tumor model. The underlying mechanism by which GABARAPL۱ regulated nasopharyngeal tumor growth was investigated.Results: Autophagy-related ۴B cysteine peptidase (ATG۴B), GABARAPL۱, and Unc-۵۱-like kinase ۱ (ULK۱) were significantly down-regulated in multiple NPC cell lines. Overexpression of GABARAPL۱ up-regulated the expression of autophagy-related proteins, decreased the level of hypoxia-inducible factor (HIF)-۲α, and induced apoptosis in NPC cells. Importantly, overexpression of GABARAPL۱ slowed tumor growth. Western blotting showed that autophagy was activated, and HIF-۲α was down-regulated in tumor tissues.Conclusion: HIF-۲α, as a substrate for autophagic degradation, may play an interesting role during NPC progression.

Keywords:

ATG۴B , Autophagy , GABARAPL۱ , Hypoxia inducible factor , Nasopharyngeal carcinoma