AXL Promotes Metformin-Induced Apoptosis Through Mediation of Autophagy by Activating ROS-AMPK-ULK1 Signaling in Human Esophageal Adenocarcinoma

Abstract

AXL receptor tyrosine kinase promotes an invasive phenotype and chemotherapy resistance in esophageal adenocarcinoma (EAC). AXL has been implicated in the regulation of autophagy, but the underlying molecular mechanism remains poorly understood. Herein, we investigate the mechanistic role of AXL in autophagy as well as metformin-induced effects on the growth and survival of EAC. We demonstrate that AXL mediates autophagic flux through activation of AMPK-ULK1 signaling in a reactive oxygen species (ROS)-dependent mechanism by glucose starvation. AXL positively regulates basal cellular ROS levels without significantly affecting mitochondrial ROS production in EAC cells. Pharmacological inhibition of cellular ROS using Trolox abrogates glucose starvation-induced AMPK signaling and autophagy. We demonstrate that AXL expression is required for metformin-induced apoptosis in EAC cells in vitro. The apoptosis induction by metformin is markedly attenuated by inhibition of autophagy through genetic silencing of Beclin1 or ATG7 autophagy mediators, thereby confirming the requirement of intact autophagy for enhancing metformin-induced apoptosis in EAC cells. Our data indicate that metformin-induced autophagy displays a pro-apoptotic function in EAC cells. We show that the metformin-induced suppression of tumor growth in vivo is highly dependent on AXL expression in a tumor xenograft mouse model of EAC. We demonstrate that AXL promotes metformin-induced apoptosis through activation of autophagy in EAC. AXL may be a valuable biomarker to identify tumors that are sensitive to metformin. Therefore, AXL expression could inform the selection of patients for future clinical trials to evaluate the therapeutic efficacy of metformin in EAC.

Metformin in Esophageal Carcinoma: Exploring Molecular Mechanisms and Therapeutic Insights

“…The data from their study indicate that metformin-induced autophagy serves a pro-apoptotic function in EAC cells. Additionally, they substantiated the conclusion that the metformin-induced suppression of tumor growth in vivo is highly contingent on AXL expression, as demonstrated in a tumor xenograft mouse model of EAC [60]. The above are presented concisely in Table 5.…”

“…Numerous studies have delved into the in vitro and in vivo consequences of metformin on ESCC and EAC cells, with predominant emphasis on two pathways: the signal transducer and activator of transcription 3 (Stat3)/Bcl-2 pathway [ 54 , 55 , 56 ] and the phosphoinositide 3-kinase (PI3K)/AKT/mTOR pathway [ 57 ]. Additionally, more recent studies have explored the anti-tumor activity of metformin through the modulation of redox homeostasis [ 58 , 59 , 60 ]. In relation to the former mechanism, studies have revealed that metformin demonstrates a selective inhibition of cell growth in ESCC tumor cells while sparing immortalized noncancerous esophageal epithelial cells.…”

“…Recent research has revealed that the anti-diabetic medication metformin demonstrates anti-tumor activity through the modulation of redox homeostasis [ 55 , 59 , 60 ]. Peng et al conducted a comparative analysis of the molecular mechanisms of metformin in the ESCC cell line, EC109, and the normal esophageal epithelial cell line, HEEC [ 55 ].…”

“…Consequently, the Stat3/Bcl-2 pathway-mediated apoptosis underscores the cell type-specific sensitivity to the drug, suggesting that metformin possesses therapeutic efficacy and selectivity in the context of esophageal cancer [ 55 ]. Concentrating on EAC cells, Hong et al conducted an investigation into the mechanistic role of the tyrosine kinase receptor AXL in autophagy, as well as the effects induced by metformin on the growth and survival of EAC [ 60 ]. They revealed that AXL orchestrates autophagic flux through the activation of AMPK-ULK1 signaling in an ROS-dependent manner induced by glucose starvation.…”