A miR-567-PIK3AP1- PI3K/AKT-c-Myc Feedback Loop Regulates Tumor Growth and Chemoresistance in Gastric Cancer

BACKGROUND: Gastric cancer (GC) ranks the fifth most common cancer and third for cancer death, chemotherapy is one of the most common treatments for GC. However, chemoresistance limits the effectiveness of chemotherapy and leads to treatment failure. This study aims to investigate the biological effect of miR-567 on gastric cancer and to reveal the possible mechanism. METHODS: We measured the expression of miR-567 in 37 paired normal and stomach tumor specimens, as well as GC cell lines by Real-time PCR. The functional effects of miR-567 were validated using in vitro and in vivo assays. Dual-luciferase report assays and Chromatin immunoprecipitation (ChIP) assay were conducted for target evaluation, western blot assay was used to confirm the relationships.   FINDINGS:  Our data showed that miR-567 was downregulated in gastric tissues and gastric cancer cells compared with normal tissues and gastric epithelial cells. In vitro, Gain- and lose-of-function assays showed miR-567 not only weakened cells proliferative ability, but also sensitized GC cells to 5-FU and oxaliplatin. In vivo, miR-567 overexpression significantly repressed the tumorigenesis of GC cells compared with the vector control. Mechanistic analyses showed that PIK3AP1 activated AKT phosphorylation in GC, miR-567 directly targeted PIK3AP1 to inactivate PI3K/AKT/c-Myc and regulated its own expression. This feedback loop further inhibited cells proliferation via PI3K/AKT pathway.   INTERPRETATION:  Our studies revealed that as a tumor suppressor, miR-567 repressed tumor growth, cells proliferation and increased drug sensitivity via a miR-567-PIK3AP1- PI3K/AKT-c-Myc feedback loop. These results suggest that miR-567 may serve as a target for chemoresistance and a potential prognostic biomarker for gastric cancer. FUNDING STATEMENT: This work was supported by the National Natural Science Foundation of China (Nos. 81572813, 81773082, 81702903, 81872423), Guangdong Natural Science Foundation (2017A030310038, 2018B030311036), Fork Ying Tung Education Foundation (161035), Higher Education Fund Project of Guangzhou (2012C070) and Special Funds for the Cultivation of Guangdong College Students' Scientific and Technological Innovation. (“Climbing Program” Special Funds) (pdjhb0102). DECLARATION OF INTERESTS: The authors have declared that no conflict of interest exists. ETHICS APPROVAL STATEMENT: All experiments performed are endorsed by the Ethics Committee of Southern Medical University and complied with the Declaration of Helsinki. No informed consent was required because data were going to be analyzed anonymously. All animal experiments were carried out with the approval of the Southern Medical University Animal Care and Use Committee in accordance with the guidelines for the ethical treatment of animals.