Prognostic significance and function of the vacuolar H+-ATPase subunit V1E1 in esophageal squamous cell carcinoma

Sung Wook Son,Sung Hee Um,Eun-Yi Moon,Suhkneung Pyo,Seok-Hyung Kim,Dong-Hoon Kim

doi:10.18632/oncotarget.10340

Abstract

Vacuolar H+-ATPase (V-ATPase), a hetero-multimeric ATP-driven proton pump has recently emerged as a critical regulator of mTOR-induced amino acid sensing for cell growth. Although dysregulated activity of cell growth regulators is often associated with cancer, the prognostic significance and metabolic roles of V-ATPase in esophageal cancer progression remain unclear. Here, we show that high levels of V-ATPase subunit V1E1 (V-ATPase V1E1) were significantly associated with shortened disease-free survival in patients with esophageal squamous cell carcinoma (ESCC). Multivariate analysis identified the V-ATPase V1E1 as an independent adverse prognostic factor (hazard ratio;1.748, P = 0.018). In addition, depletion of V-ATPase V1E1 resulted in reduced cell motility, decreased glucose uptake, diminished levels of lactate, and decreased ATP production, as well as inhibition of glycolytic enzyme expression in TE8 esophageal cancer cells. Consistent with these results, the Cancer Genome Atlas (TCGA) data and Gene Set Enrichment Analysis (GSEA) showed a high frequency of copy number alterations of the V-ATPase V1E1 gene, and identified a correlation between levels of V-ATPase V1E1 mRNA and Pyruvate Kinase M2 (PKM2) in ESCC. High expression levels of both V-ATPase V1E1 and phosphorylated PKM2 (p-PKM2), a key player in cancer metabolism, were associated with poorer prognosis in ESCC. Collectively, our findings suggest that expression of the V-ATPase V1E1 has prognostic significance in ESCC, and is closely linked to migration, invasion, and aerobic glycolysis in esophageal cancer cells.

Highlights

esophageal squamous cell carcinoma (ESCC) is an aggressive malignant tumor with a high mortality rate [1]
Between each round of staining, each slide was image-captured to generate a virtual microscope file, and antibodies were stripped from the slide, and staining with the antibody was performed. With this novel multiplex immunohistochemistry, we found that there was significant overlap among expression of these proteins in esophageal cancer tissues. These results indicate that V-ATPase V1E1 is critical for aerobic glycolysis, and that its presence is required for regulation of the levels of ATP, lactate synthesis, expression of glycolytic enzymes, and signaling related to glucose metabolism in TE8 esophageal cancer cells
V-ATPase assembly is regulated by glucose [7], and is required for the activation of Rag GTPases and mTOR, which are critical for amino acid sensing

Summary

Introduction

ESCC is an aggressive malignant tumor with a high mortality rate [1]. The 5-year survival rate of ESCC patients after surgery is 30% to 45% [2]. Esophageal cancer cells preferentially metabolize glucose, and express high levels of glycolytic enzymes such as PKM2 and Lactate dehydrogenase A (LDHA), which contribute to the invasion, metastasis, and poor outcome [3, 4]. Expression of Hexokinase-1 (HK1), another glycolytic enzyme, is associated with disease progression, invasion, and poor survival of patients with ESCC [5]. These studies suggest that cancer metabolism is critical to the development and prognosis of ESCC

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Conclusion