TM9SF4 is a novel V-ATPase-interacting protein that modulates tumor pH alterations associated with drug resistance and invasiveness of colon cancer cells

• Published in: Oncogene 2015-10, Vol.34 (40), p.5163-5174
• Main Authors: Lozupone, F, Borghi, M, Marzoli, F, Azzarito, T, Matarrese, P, Iessi, E, Venturi, G, Meschini, S, Canitano, A, Bona, R, Cara, A, Fais, S
• Format: Article
• Language: English
• Subjects: 13/89; 14/63; 5-Fluorouracil; 631/67/2327; 96; 96/109; 96/2; Acidity; Acidosis; Adenosine triphosphatase; Apoptosis; Blotting, Western; Cancer; Cell Biology; Cell Line, Tumor; Cell membranes; Cells; Colon; Colon cancer; Colonic Neoplasms - metabolism; Colonic Neoplasms - pathology; Colorectal cancer; Cytosol; Cytotoxicity; Development and progression; Drug resistance; Drug Resistance, Neoplasm - physiology; Fluorescence Resonance Energy Transfer; Genetic aspects; H+-transporting ATPase; Health aspects; Human Genetics; Humans; Hydrogen-Ion Concentration; Immunoprecipitation; Innovations; Internal Medicine; Invasiveness; Ion channels; Medicine; Medicine & Public Health; Melanoma; Membrane proteins; Membrane Proteins - metabolism; Metastases; Microscopy, Confocal; Molecular targeted therapy; Neoplasm Invasiveness - pathology; Observations; Oncology; original-article; pH effects; Phenotypes; Polymerase Chain Reaction; Proteins; Solid tumors; Temperature effects; Transfection; Tumor cell lines; Tumors; Vacuolar Proton-Translocating ATPases - metabolism
• ISSN: 0950-9232; 1476-5594
• DOI: 10.1038/onc.2014.437

An inverted pH gradient across the cell membranes is a typical feature of malignant cancer cells that are characterized by extracellular acidosis and cytosol alkalization. These dysregulations are able to create a unique milieu that favors tumor progression, metastasis and chemo/immune-resistance traits of solid tumors. A key event mediating tumor cell pH alterations is an aberrant activation of ion channels and proton pumps such as (H+)-vacuolar-ATPase (V-ATPase). TM9SF4 is a poorly characterized transmembrane protein that we have recently shown to be related to cannibal behavior of metastatic melanoma cells. Here, we demonstrate that TM9SF4 represents a novel V-ATPase-associated protein involved in V-ATPase activation. We have observed in HCT116 and SW480 colon cancer cell lines that TM9SF4 interacts with the ATP6V1H subunit of the V-ATPase V1 sector. Suppression of TM9SF4 with small interfering RNAs strongly reduces assembly of V-ATPase V0/V1 sectors, thus reversing tumor pH gradient with a decrease of cytosolic pH, alkalization of intracellular vesicles and a reduction of extracellular acidity. Such effects are associated with a significant inhibition of the invasive behavior of colon cancer cells and with an increased sensitivity to the cytotoxic effects of 5-fluorouracil. Our study shows for the first time the important role of TM9SF4 in the aberrant constitutive activation of the V-ATPase, and the development of a malignant phenotype, supporting the potential use of TM9SF4 as a target for future anticancer therapies.