Involvement of TOB1 on autophagy in gastric cancer AGS cells via decreasing the activation of AKT/mTOR signaling pathway

Abstract

Background We previously identified the tumor suppressor gene TOB1 as related to gastric cancer. The purpose of this study was to explore whether TOB1 induces autophagy through the AKT/mTOR signaling pathway in gastric cancer. Methods Western blotting was used to detect the protein levels of TOB1, LC3, AKT, mTOR, phosphorylated (p) AKT, and p-mTOR. A double fluorescent GFP-RFP-LC3 fusion protein was used to trace autophagy by laser confocal microscopy. Autophagosomes were observed by transmission electron microscopy. Results The conversion of LC3-I to LC3-II and the LC3-II/LC3-I ratio were significantly increased in AGS cells overexpressing TOB1 compared with control cells. Fluorescence imaging showed LC3 puncta at 48 h, and these puncta increased significantly at 72 h after TOB1 transfection compared with control tumor cells. The presence of autophagosomes in AGS cells was observed at 72 h after TOB1 transfection by transmission electron microscopy, and no autophagosomes were found in the control cells. Moreover, the levels of p-AKT and p -mTOR were lower in AGS cells than in control cancer cells. Conclusion Our results provide novel insight that TOB1 might suppress gastric cancer by inducing autophagy, possibly through decreasing phosphorylation and the subsequent activation of the AKT/mTOR signaling pathway.

The Overexpression of TOB1 Induces Autophagy in Gastric Cancer Cells by Secreting Exosomes

“…Subsequently, our group has successively demonstrated that TOB1 is downregulated and phosphorylated in gastric cancer tissues [ 20 ], and TOB1 plays an antiproliferative role in the nucleus [ 21 ] and a series of studies [ 22 – 24 ]. Furthermore, the latest study of our group confirmed that TOB1 can induce autophagy in gastric cancer cells via decreasing the activation of AKT/mTOR signaling pathway [ 25 ], and the present study also proved for the first time that gastric cancer cells overexpressing TOB1 can induce autophagy in tumor cells by secreting exosomes.…”

“…Many studies have shown that the abnormality of TOB1 gene is closely related to the occurrence and development of tumors [ 35 ]. TOB1 is the first gastric cancer-related tumor suppressor gene revealed by our research group [ 18 – 24 ], and our group also revealed in the previous study that overexpression of TOB1 in gastric cancer cells can induce autophagy in gastric cancer cells, and its molecular mechanism may be related to downregulation of AKT/mTOR signaling pathway [ 25 ]. Here, our study provides further evidence that exosomes secreted by gastric cancer cells overexpressing TOB1 can induce autophagy in gastric cancer cells.…”

“…The hallmark structure of autophagy is the formation of autophagosomes; so, the observation of autophagosome under TEM is the “gold standard” to detect autophagy [ 25 ]. Autophagosomes have a bilayer or multilayer membrane structure and contain cytoplasmic components or organelles (such as mitochondria or endoplasmic reticulum fragments) to be digested and degraded [ 39 – 41 ].…”

“…Regarding the relationship between TOB1 and PI3K/AKT/mTOR signaling, Zhang et al found that knocking out TOB1 gene in estrogen-dependent breast cancer cell MCF-7 can activate a downstream target of ERBB2 signaling, and ultimately, estrogen-independent cells are more sensitive to AKT and mTOR inhibitors [ 50 ]. The latest study of our group confirmed that TOB1 can induce autophagy in gastric cancer cells via decreasing the activation of AKT/mTOR signaling pathway [ 25 ].…”

A budding concept with certain microbiota, anti-proliferative family proteins, and engram theory for the innovative treatment of colon cancer

“…Regarding the relationship between Tob1 and PI3K/AKT/mTOR signaling, it has been found that Tob1 antagonizes the PI3K/AKT/mTOR survival signaling and induces cancer cell apoptosis [60]. Tob1 could induce autophagy in gastric cancer cells via decreasing the activation of the PI3K/AKT/mTOR signaling [61]. Interestingly, overexpression of Tob1 in gastric cancer cells can induce autophagy by secreting exosomes [62].…”