Expression and function of voltage gated proton channels (H V 1) in MDA-MB-231 cells

Abstract

Expression of the voltage gated proton channel (HV1) as identified by immunocytochemistry has been previously reported in breast cancer tissue. Increased expression of HV1 was correlated with poor prognosis and decreases overall and disease-free survival but the mechanism of its involvement in the disease is unknown. Here we present electrophysiological recordings of HV1 channel activity thus, demonstrating their presence and functional properties in the plasma membrane of a breast cancer cell line, MDA-MB-231. With western blotting we also identify significant levels of HV1 expression in 3 out of 8 "triple negative" breast cancer cell lines (estrogen, progesterone, and HER2 receptor expression negative). We examine the function of HV1 in breast cancer using MDA-MB-231 cells as a model by suppressing the expression of HV1 using shRNA ("knock-down; "KD") and by eliminating HV1 using CRISPR/Cas9 gene editing ("knock-out"; "KO"). However, these two approaches produced different effects. Knock-down of HV1 using shRNA resulted in slower cell migration in a scratch assay and a significant reduction in H2O2 release. In contrast, HV1 KO cells do not show reduction in migration or H2O2 release. HV1 KO but not knock-down cells showed an increased glycolytic rate with an accompanied increase in p-AKT (Phospho-AKT, Ser473) activity. The expression of CD171/LCAM-1, an adhesion molecule and prognostic indicator for breast cancer, was reduced in the absence of HV1 expression. When we compared MDA-MB-231 xenograft growth rates in immunocompromised mice, tumors from HV1 KO cells grew less in mass with lower staining for the Ki-67 maker for cell proliferation rate. Therefore, deletion of HV1 expression in MDA-MB-231 cells limits tumor growth rate. The limited growth thus, appears to be independent of oxidant production by NADPH oxidase molecules and be determined through cell adhesion activity. While HV1 KO results in cell mechanisms different from KD, both implicate HV1-mediated pathways for control of tumor growth in the MDA-MB-231 cell line.