Na+,HCO3 −-cotransport is functionally upregulated during human breast carcinogenesis and required for the inverted pH gradient across the plasma membrane

Abstract

Metabolic and biochemical changes during breast carcinogenesis enhance cellular acid production. Extrusion of the acid load from the cancer cells raises intracellular pH, while it decreases extracellular pH creating an inverted pH gradient across the plasma membrane compared to normal cells and promoting cancer cell metabolism, proliferation, migration, and invasion. We investigated the effects of breast carcinogenesis on the mechanisms of cellular pH control using multicellular epithelial organoids freshly isolated from human primary breast carcinomas and matched normal breast tissue. Intracellular pH was measured by fluorescence microscopy, while protein expression was investigated by immunofluorescence imaging and immunoblotting. We found that cellular net acid extrusion increased during human breast carcinogenesis due to enhanced Na(+),HCO3 (-)-cotransport, which created an alkaline shift (~0.3 units of magnitude) in steady-state intracellular pH of human primary breast carcinomas compared to normal breast tissue. Na(+)/H(+)-exchange activity and steady-state intracellular pH in the absence of CO2/HCO3 (-) were practically unaffected by breast carcinogenesis. These effects were evident under both acidic (pH 6.8, representative of the tumor microenvironment) and physiological (pH 7.4) extracellular conditions. Protein expression of the Na(+),HCO3 (-)-cotransporter NBCn1 (SLC4A7), which has been linked to breast cancer susceptibility in multiple genome-wide association studies, was twofold higher in human breast carcinomas compared to matched normal breast tissue. Protein expression of the Na(+)/H(+)-exchanger NHE1 (SLC9A1) was markedly less affected. We propose that upregulated NBCn1 during human breast carcinogenesis contributes to the characteristic acid distribution within human breast carcinomas and thereby plays a pathophysiological role for breast cancer development and progression.

Expressional and Functional Characterization of Intracellular pH Regulators and Effects of Ethanol in Human Oral Epidermoid Carcinoma Cells

“…Moreover, some isoforms of NBC might play a vital role on the development of oral carcinogenesis. Indeed, it has been found that the enhancement of NBC activity is the main reason for an alkaline shift (~0.3 units of magnitude) in steady-state intracellular pH of human primary breast carcinomas compared to normal breast tissue [54]. Furthermore, upregulated NBCn1 during human breast carcinogenesis contributes to the characteristic acid distribution within human breast carcinomas [54].…”

“…Indeed, it has been found that the enhancement of NBC activity is the main reason for an alkaline shift (~0.3 units of magnitude) in steady-state intracellular pH of human primary breast carcinomas compared to normal breast tissue [54]. Furthermore, upregulated NBCn1 during human breast carcinogenesis contributes to the characteristic acid distribution within human breast carcinomas [54]. Therefore, our present study has provided a new strategy of potential role of inhibitors/ activators of isoforms of NHE and NBC in clinical setting.…”

Enhanced Reactive Oxygen Species Production, Acidic Cytosolic pH and Upregulated Na+/H+ Exchanger (NHE) in Dicer Deficient CD4+ T Cells

“…Na + /H + exchanger Nhe1 contributes to regulatory cell volume increase, which is in part accomplished by parallel activity of Na + /H + and Cl - /HCO 3 - exchanger [55, 56]. Increase of cell volume is a precondition for cell proliferation and stimulation of cell proliferation is paralleled by a shift of Na + /H + exchanger cell volume regulatory set point to larger volumes [57-59].…”

Ion channels and transporters in metastasis

“…NHE1 does not always play an exclusive, predominant role in the pHregulation of cancer cells. In human breast cancer carcinomas, for instance, the expression of NBCn1 is twofold higher compared to normal breast cancer tissue obtained from the same patient [118,121]. This is accompanied by an increase in the clearly NBCn1-mediated cellular net-acid extrusion (=HCO 3 -import) leading to an alkaline shift in the steady-state pH i by ~0.3 pH units.…”