Ginsenoside Rh2 represses autophagy to promote cervical cancer cell apoptosis during starvation

Jiawen Wang,Wanying Zhang,Song Yang,Siming Wang,Shuai Bian,Xueyuan Bai,Daqing Zhao,Meichen Liu

doi:10.1186/s13020-020-00396-w

Abstract

BackgroundCancer cells through autophagy-mediated recycling to meet the metabolic demands of growth and proliferation. The steroidal saponin 20(S)-ginsenoside Rh2 effectively inhibits the growth and survival of a variety of tumor cell lines and animal models, but the effects of Rh2 on autophagy remain elusive.MethodsCell viability was measured by CCK-8 (cell counting kit-8) assays. Apoptosis, ROS generation and mitochondrial membrane potential were analyzed by flow cytometry. Western blot analyses were used to determine changes in protein levels. Morphology of apoptotic cells and autophagosome accumulation were analyzed by DAPI staining and transmission electron microscopy. Autophagy induction was monitored by acidic vesicular organelle staining, EGFP-LC3 and mRFP-GFP-LC3 transfection. Atg7 siRNA and autophagy regulator was used to assess the effect of autophagy on apoptosis induced by G-Rh2.ResultsIn this study, we found that low concentration G-Rh2 attenuated cancer cell growth and induced apoptosis upon serum-free starvation. Caspase 3 inhibitors failed to block apoptosis in G-Rh2-treated cells, indicating a caspase-independent mechanism. G-Rh2-treated cells in serum-deprived conditions showed impaired mitochondrial function, increased release and nuclear translocation of apoptosis-inducing factor, but little changes in the mitochondrial and cytoplasmic distributions of cytochrome C. Annexin A2 overexpression in 293T cells inhibited G-Rh2-induced apoptosis under serum-starved conditions. Meanwhile, G-Rh2 reduced lysosomal activity and inhibited the fusion of autophagosome and lysosome, leading to a block of autophagic flux. Knockdown Atg7 significantly inhibited autophagy and triggered AIF-induced apoptosis in serm free condition. The autophagy inducer significantly decreased the apoptosis levels of G-Rh2-treated cells in serum-free conditions.ConclusionsUnder nutrient deficient conditions, G-Rh2 represses autophagy in cervical cancer cells and enhanced apoptosis through an apoptosis-inducing factor mediated pathway.

Highlights

Cancer cells through autophagy-mediated recycling to meet the metabolic demands of growth and proliferation
20(S)-Ginsenoside Rh2 (G-Rh2) enhanced susceptibility to serum deprivation-induced apoptosis via inhibiting autophagy. These results demonstrated a novel activity of G-Rh2, autophagy suppression, which enhanced apoptosis in HeLa cells under starvation conditions
Serum deprivation is often used as a means of emulating the tumor microenvironment

Summary

Introduction

Cancer cells through autophagy-mediated recycling to meet the metabolic demands of growth and proliferation. The steroidal saponin 20(S)-ginsenoside Rh2 effectively inhibits the growth and survival of a variety of tumor cell lines and animal models, but the effects of Rh2 on autophagy remain elusive. Ginsenosides extracted from ginseng display a wide range of pharmacological activities and several of these have been shown to inhibit cancer cell proliferation [2, 3]. Wang et al Chin Med (2020) 15:118 ginsenoside 20 (S)-Rh2 exerts antitumor effects in several cancer models [4,5,6]. Several ginsenosides exert cytotoxic activity in cervical cancer cells [9,10,11,12]

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