Novel evidence for retinoic acid‐induced G (Rig‐G) as a tumor suppressor by activating p53 signaling pathway in lung cancer

Background: Lung cancer is one of most common malignancies worldwide. We have previously identified retinoic acid-induced gene G (Rig-G) as a tumor suppressor in not only acute promyelocytic leukemia, but as well in other solid tumors. However, the clinical significance of Rig-G and the underlying mechanism(s) for its biological function in lung cancer remain largely unexplored. Methods: We first compared the expression of Rig-G between lung cancer (n=138) and normal tissues (n=23), from public-available datasets and our patient cohort. We further analyzed the correlation of Rig-G expression with key clinico-pathological features and survival outcomes in a multi-site clinical cohort of 300 lung cancer patients. Functional studies for Rig-G were performed in cell lines, and an animal model to support clinical findings. Findings: We found that Rig-G was frequently downregulated in lung cancer tissues and celllines, and correlated with poor prognosis in lung cancer patients. Overexpression of Rig-G led to significantly reduced cell growth and suppressed migrationin A549 and NCI-H1944 cells, accompanied by reduced epithelial-mesenchymal transition. Likewise, restoration of Rig-G in Lewis lung carcinoma cells permitted development of fewer cancer metastases vs. controls in an animal model. Gene expression profiling results identified p53 pathway as a key downstream target of Rig-G, and p53 inhibition by pifithrin-α caused abrogation of tumor-suppressive effects of Rig-G in lung cancer. Interpretation: We for the first time have identified Rig-G as a novel and important tumor suppressor, which may serve as a potential therapeutic target for restoring p53 expression in lung cancer patients. Funding Statement: This work was supported by the National Cancer Institute, NIH (CA72851, CA184792, CA202797 and CA187956), the National Natural Science Foundation of China (81272603, 81472179 and 81873975), the Excellent Academic Leader Training Program of Shanghai Health System (2018BR31), the Clinical Research and Cultivation Project of Shanghai Tongji Hospital grant [ITJ(ZD)1803]. This work was also supported by the National Natural Science Foundation of China (81672826 and 81874179), the Municipal Human Resources Development Program for Outstanding Young Talents in Medical and Health Sciences in Shanghai (2017YQ044), the Shanghai Pujiang Talent Plan (18PJD047), the Natural Science Foundation of Shanghai (19ZR1448800), the Medical Guidance Science and Technology Support Project of Shanghai (9411964800) and the National Natural Science Foundation Training Program of Tongji Hospital (GJPY1804). Declaration of Interests: None of the authors have any potential conflicts to disclose. Ethics Approval Statement: A written informed consent was obtained from all patients and the study was approved by ethics committee of Shanghai Tongji Hospital. All animal experiments were approved by the Tongji Hospital of Tongji University Ethics Committee on the Use and Care of Animals.