NHE5 regulates growth factor signaling, integrin trafficking, and degradation in glioma cells

Toru Kurata,Sachio Fushida,Vinotheni Rajendran,Steven Fan,Masayuki Numata,Tetsuo Ohta

doi:10.1007/s10585-019-10001-6

Toru Kurata, Sachio Fushida + Show 4 more

Open Access

https://doi.org/10.1007/s10585-019-10001-6

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Abstract

Na+/H+ exchanger 5 (NHE5) is enriched in neurons and cycles between recycling endosomes and plasma membranes and transports protons to the endosomal lumen as well as to the extracellular space. Although NHE5 expression is undetectable in normal astrocytes, C6 glioma cells express NHE5 at an elevated level. Using C6 cells as a model, here we demonstrate that NHE5 has an important role in tumor growth and tumor cell proliferation and invasion. Glioma xenografts originating from NHE5-knockdown cells exhibited significantly slower growth than those from NHE1-knockdown cells and control cells. Histological characterization of the migration front of NHE5-knockdown tumors revealed a less invasive and less proliferative appearance than NHE1-knockdown and control tumors. NHE5-knockdown but not NHE1-knockdown led to downregulation of fetal bovine serum (FBS)-induced MET and EGFR signaling. Moreover, depletion of NHE5 but not NHE1 reduced the ability of cells to spread on collagen. We found that NHE5 depletion greatly abrogated endocytic recycling and the protein stability of β1-integrin, which in part accounted for the defective cell adhesion, spreading, and invasion of NHE5-knockdown cells.

Highlights

Acidic extracellular pH is a hallmark of the tumor microenvironment, where proton-pumping activity in malignant tumor cells has a critical role in establishing extracellular acidity by exporting protons produced by tumor metabolism [1]. Na+/H+ exchanger NHE1 is one of the most extensively studied pH-regulating ion transporters [2, 3]
NHE1 knockdown resulted in a slight reduction in the phosphorylation of AKT and ERK1/2, whereas there was no effect on MET and EGFR phosphorylation
NHE1 inhibitors are known to effectively retard cell proliferation of different malignant tumor cells [8,9,10,11], we have shown that Na+/H+ exchanger 5 (NHE5) knockdown by short hairpin RNA (shRNA) markedly diminishes the proliferation and invasion of C6 glioma cells, and demonstrate that NHE5 knockdown has a significantly different effect on tumor growth and invasion in mouse xenografts compared to the impact caused by NHE1 knockdown

Summary

Introduction

Acidic extracellular pH is a hallmark of the tumor microenvironment, where proton-pumping activity in malignant tumor cells has a critical role in establishing extracellular acidity by exporting protons produced by tumor metabolism [1]. Na+/H+ exchanger NHE1 is one of the most extensively studied pH-regulating ion transporters [2, 3]. Previous studies showed the importance of NHE1 in cell proliferation [7,8,9,10], little is known about the involvement of other NHE isoforms that may be expressed in malignant tumor cells. NHE5 cycles between recycling endosomes and the plasma membrane [15], and acidifies the lumen of recycling endosomes [16], thereby playing a critical role in regulating the cell-surface availability of the high-affinity nerve growth factor receptor TrkA in PC12 pheochromocytoma cells of adrenal gland origin [17] and the hepatocyte growth factor/scatter factor (HGF) receptor MET in C6 glioma cells [14]. We have investigated the involvement of NHE5 and NHE1 in glioma cell signaling, proliferation, and tumor growth through characterization of C6 glioma-based knockdown cell lines

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