Circular RNA AKT3 upregulates PIK3R1 to enhance cisplatin resistance in gastric cancer via miR-198 suppression

Xiaoxu Huang,Weizhi Wang,Bowen Li,Qiang Li,Zhongyuan He,Xuan Zhang,Zhipeng Xu,Sen Wang,Qing Li,Linjun Wang,Zheng Li,Hao Xu,Xing Zhang,Zekuan Xu,Ailiang Zeng,Lu Zhang,Qiang Zhang,Lu Wang,Guangli Sun

doi:10.1186/s12943-019-0969-3

Abstract

BackgroundCisplatin (CDDP) treatment is one of the most predominant chemotherapeutic strategies for patients with gastric cancer (GC). A better understanding of the mechanisms of CDDP resistance can greatly improve therapeutic efficacy in patients with GC. Circular RNAs (circRNAs) are a class of noncoding RNAs whose functions are related to the pathogenesis of cancer, but, in CDDP resistance of GC remains unknown.MethodscircAKT3 (hsa_circ_0000199, a circRNA originating from exons 8, 9, 10, and 11 of the AKT3 gene) was identified by RNA sequencing and verified by quantitative reverse transcription PCR. The role of circAKT3 in CDDP resistance in GC was assessed both in vitro and in vivo. Luciferase reporter assay, biotin-coupled RNA pull-down and fluorescence in situ hybridization (FISH) were conducted to evaluate the interaction between circAKT3 and miR-198. Functional experiments were measured by western blotting, a cytotoxicity assay, clonogenic assay and flow cytometry.ResultsThe expression of circAKT3 was higher in CDDP-resistant GC tissues and cells than in CDDP-sensitive samples. The upregulation of circAKT3 in GC patients receiving CDDP therapy was significantly associated with aggressive characteristics and was an independent risk factor for disease-free survival (DFS). Our data indicated that circAKT3 promotes DNA damage repair and inhibits the apoptosis of GC cells in vivo and in vitro. Mechanistically, we verified that circAKT3 could promote PIK3R1 expression by sponging miR-198.ConclusionscircAKT3 plays an important role in the resistance of GC to CDDP. Thus, our results highlight the potential of circAKT3 as a therapeutic target for GC patients receiving CDDP therapy.

Highlights

Cisplatin (CDDP) treatment is one of the most predominant chemotherapeutic strategies for patients with gastric cancer (GC)
Ectopic circAKT3 expression levels are observed in CDDPresistant GC cells and tissues and are correlated with poor prognosis in GC patients receiving CDDP therapy To characterize circular RNA transcripts, we conducted RNA sequencing (RNA-Seq) analysis of CDDP-resistant SGC7901 and BGC823 cells (i.e., SGC7901CDDP and BGC823CDDP) and their corresponding parental strains (i.e., SGC7901 and BGC823), which are sensitive to CDDP
(See figure on previous page.) Fig. 5 circAKT3 exerts its function by sponging miR-198. a & b Schematic illustration showing the overlap of the target miRNAs of circAKT3 predicted by miRanda, PITA and RNAhybrid. c & d Lysates prepared from SGC7901CDDP and BGC823CDDP cells stably transfected with circAKT3 or vector were subjected to RNA pull-down and tested by real-time PCR (RT-PCR) (C) and Quantitative reverse transcription PCR (RT-qPCR) (D)

Summary

Introduction

Cisplatin (CDDP) treatment is one of the most predominant chemotherapeutic strategies for patients with gastric cancer (GC). Circular RNAs (circRNAs) are a class of noncoding RNAs whose functions are related to the pathogenesis of cancer, but, in CDDP resistance of GC remains unknown. The cytotoxicity of CDDP is mediated by its interaction with DNA to form DNA adducts. Intracellular CDDP primarily binds to nuclear DNA with high affinity and can physically interact with mitochondrial DNA. Studies have shown that the PI3K/AKT signaling pathway could suppress cell apoptosis and facilitate cell survival. This PI3K/AKT signaling function is crucial in the regulation of chemotherapy resistance of cancer cells [10, 11]. Activated PI3K/AKT signaling promotes the phosphorylation of caspase-3 and prevents the activation of caspase-3 and the inhibition of apoptosis [12]

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