MicroRNA-495-3p inhibits multidrug resistance by modulating autophagy through GRP78/mTOR axis in gastric cancer

Sheng Chen,Daiming Fan,Kai Jiao,Jianqin Kang,Guohong Zhao,Yongquan Shi,Jian Wu,Jiaojiao Ma,Di Chen,Qiong Wu,Guodong Zhao

doi:10.1038/s41419-018-0950-x

Abstract

Multidrug resistance (MDR) accounts for poor prognosis in gastric cancer (GC). MicroRNAs (miRNAs) are critical regulators of MDR via modulation of the target genes. The present study revealed that miR-495-3p could act via a target gene, GRP78, to regulate the process of autophagy and inhibit MDR. Based on the in vitro and in vivo gain-of-function or loss-of-function experiments, overexpression of miR-495-3p was sufficient to reverse the MDR to four chemotherapeutics in vitro and inhibit the tumor growth in vivo. Moreover, GRP78 was positively associated with the occurrence of autophagy. Thus, reducing the expression of GRP78 by siRNA resulted in autophagy-suppressive activity similar to that of miR-495-3p on mammalian target of rapamycin (mTOR) and its substrates activation and autophagy inhibition, while restoring GRP78 attenuated the anti-autophagy effects caused by miR-495-3p. Clinically, either miR-495-3p downregulation or GRP78 upregulation was associated with malignant phenotypes in patients with GC. In conclusion, these findings demonstrate that miR-495-3p is an important regulator of autophagy balance and MDR by modulating the GRP78/mTOR axis. In addition, miR-495-3p and GRP78 could be used as prognostic factors for overall survival in GC, which implicates miR-495-3p as a therapeutic target in cancer.

Highlights

Multidrug resistance (MDR) is a significant clinical issue with respect to chemotherapy in cancer, especially gastric cancer (GC)[1]
We found that ectopic expression of miR-495-3p can sensitize the GC cells to chemotherapy, which resulted from the inhibition of autophagy induced by miR-495-3p
MiR-495-3p inhibits autophagy in GC MDR cells As autophagy exerts a dual role that contributes to the anti-cancer efficacy of chemotherapy drugs as well as drug resistance on cancer cells[7], we investigated whether miR495-3p can regulate the process of autophagy in GC MDR cells

Summary

Result

MiR-495-3p is downregulated in GC and inhibits MDR and proliferation of GC MDR cells miR-495 was previously reported to sensitize MDR cancer cells and downregulated in various cancers[14,15]. MDR cells expressed a high level of autophagy-associated protein and gene (Supplementary Fig. 1B and 1C) as assessed by western blotting and real-time PCR. Western blotting demonstrated that overexpression of miR-495-3p significantly suppressed GRP78 expression in GC MDR cells cells and that silencing of miR-495-3p increased the expression of GRP78 in SGC7901 cells (Fig. 3c). MiR-495-3p depletion in SGC7901 decreased the levels of phospho-mTOR, phospho-S6K, and phospho-S6 These data suggested that miR-495-3p regulated the activity of mTOR in MDR cells. The mTOR pathway was markedly activated in MDR cells wherein the expression of GRP78 was suppressed, as demonstrated by the increased phosphorylation levels of mTOR, S6K, and p-4E-BP1 (Fig. 6b).

Discussion

Findings

Materials and methods