Abstract 3783: GSTO2, a novel tumor suppressor gene of lung squamous cell carcinoma, regulates mitochondria function via the p38/β-catenin signaling pathway

Abstract

Abstract Glutathione S-transferase omega 2 (GSTO2) is one of regulators of GSH/GSSG balance, and its polymorphism showed strong associations with lung functions as well as the risk of chronic obstructive pulmonary disease. Recently, we found that GSTO2 was exclusively expressed in airway basal cells, Clara cells and type II alveolar cells, which have self-renewal capacity in the lungs; however, its expression was lost in lung squamous cell carcinoma (LSCC). In the present study, we restored GSTO2 expression in LSCC cell lines (LK-2 and H520) to clarify the significance of GSTO2 loss in LSCC. In both LSCC cell lines used, GSTO2 overexpression significantly inhibited cell growth and colony formation in vitro. In a subcutaneous xenograft model, GSTO2-transfected LK-2 cells formed smaller tumors in nude mice than mock-transfected cells. Upon intravenous injection into nude mice, the incidence of liver metastasis was lower in mice injected with GSTO2-transfected LK-2 cells than in those injected with mock-transfected cells. Metabolomic analyses using the XF96 extracellular flux analyzer revealed that GSTO2 overexpression suppressed mitochondrial oxidative phosphorylation but did not affect glycolysis. Upon JC-1 dye staining, GSTO2-transfected cells showed decreased mitochondrial membrane potential compared with mock-transfected cells. Since β-catenin has been reported as a novel regulator of the OXPHOS in hepatocytes, we next examined the effect of GSTO2 expression on β-catenin expression in LSCC and found that GSTO2 overexpression suppressed the expression of β-catenin. Because p38 phosphorylation was accelerated in both GSTO2-transfected cells, we examined the involvement of the p38 signaling pathway in the GSTO2-mediated downregulation of β-catenin as well as mitochondrial membrane potential in LSCC.When GSTO2-transfected cells were treated with SB203580, a specific inhibitor of p38 MAPK, β-catenin expression and mitochondrial membrane potentialwere restored. Finally, we examine whether DNA methylation of the GSTO2 could explain the loss of GSTO2 expression in LSCC. When human LSCC cell lines were treated with 5-aza-2′-deoxycytidine, a DNA-methyltransferase inhibitor, GSTO2 transcription was induced. Bisulfite sequencing showed that the promoter region of the GSTO2 was frequently methylated in LSCC tissues than that of normal tissue. Our study indicated that the loss of GSTO2 via DNA hypermethylation contributes to the cell growth and progression of LSCC, probably by modulating oxidative phosphorylation in mitochondria via the p38/β-catenin signaling pathway. Citation Format: Ryusuke Sumiya, Masayoshi Terayama, Teruki Hagiwara, Kazuaki Nakata, Satoshi Nagasaka, Kazuhiko Yamada, Norihiro Kokudo, Hiromu Suzuki, Kawamura I. Yuki. GSTO2, a novel tumor suppressor gene of lung squamous cell carcinoma, regulates mitochondria function via the p38/β-catenin signaling pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3783.