Abstract 5573: Loss of glutathione S-transferase omega 2 promotes immunosuppressive tumor microenvironment by the induction of PD-L1 expression in lung adenocarcinoma
Authors: Sumiya Ryusuke , Hatano Hiroto , Hagiwara Teruki , Nagasaka Satoshi , Yamada Kazuhiko , Kokudo Norihiro , Suzuki Hiromu , Kawamura Yuki I. 
Published: March 2024

Abstract
Glutathione S-transferase omega 2 (GSTO2) is known as one of important regulators for the glutathione redox balance. We recently reported that GSTO2 is 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 completely lost in lung squamous cell carcinoma (LSCC) (Cancer Science, 2022). In this study, we examined the expression of GSTO2 in lung adenocarcinoma (LAC), another type of lung cancer, and analyzed the relationship between GSTO2 expression and clinicopathological features. We enrolled 139 patients who were diagnosed with LAC and underwent surgery, and immunohistochemically evaluated the expression of GSTO2 using formalin-fixed, paraffin-embedded sections of surgical specimens. Fifty eight of 139 lung adenocarcinoma samples exhibited GSTO2 expression, while remaining 81 cases did not. The expression of GSTO2 in LAC samples was significantly associated with never or light (Brinkman Index &lt; 400) smoking history (P=0.0027) and histological subtypes (lepidic 77%; acinar 44%; papillary 22%; micropapillary 16.7%; solid 9.6%; P&lt;0.0001). There were no significant differences between the groups with respect to pN, pM, EGFR mutation, ALK fusion, and ROS-1 fusion. However, GSTO2 expression in LAC significantly associated with pT1 (P&lt;0.0001), early stage (P&lt;0.0001), and absence of PD-L1 expression (P=0.0027). Moreover, patients with GSTO2-negative LAC had a significantly lower disease-free survival rate than those with GSTO2-positve LAC (P=0.028). To examine whether GSTO2 expression affects PD-L1 expression, we prepared GSTO2-transfected and mock-transfected lung adenocarcinoma cell lines (A549 and PC-9). In both cell lines, mRNA level of PD-L1 was significantly reduced in GSTO2-transfectants. Because Jang RH et al reported that vimentin, reflecting to acquire mesenchymal traits in epithelial-mesenchymal transition (EMT), regulates the PD-L1 expression, we next examined whether GSTO2 overexpression affects the expression of EMT related molecules. There was no difference in a mRNA level of E-cadherin, while the mRNA expression of vimentin and SLUG, a transcriptional inducer of EMT, were significantly suppressed in GSTO2-transfected PC-9. In both cell lines, protein expression of vimentin was also significantly reduced in GSTO2-transfectants. The present study shed light on a novel function of GSTO2 as a PD-L1 regulator, which may contribute to prevention of tumor immune escape.
Citation Format: Ryusuke Sumiya, Hiroto Hatano, Teruki Hagiwara, Satoshi Nagasaka, Kazuhiko Yamada, Norihiro Kokudo, Hiromu Suzuki, Yuki I. Kawamura. Loss of glutathione S-transferase omega 2 promotes immunosuppressive tumor microenvironment by the induction of PD-L1 expression in lung adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5573.