title: TM9SF4 is a novel V-ATPase-interacting protein that modulates tumor pH alterations associated with drug resistance and invasiveness of colon cancer cells.
abstract: 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.
authors: Therapeutic Research and Medicines Evaluation Department, Istituto Superiore di Sanità, Rome, Italy.
authors: F
authors: F
authors: Lozupone
authors: Infectious, Parasitic and Immune-Mediated Diseases Department, Istituto Superiore di Sanità, Rome, Italy.
authors: M
authors: M
authors: Borghi
authors: Therapeutic Research and Medicines Evaluation Department, Istituto Superiore di Sanità, Rome, Italy.
authors: F
authors: F
authors: Marzoli
authors: Therapeutic Research and Medicines Evaluation Department, Istituto Superiore di Sanità, Rome, Italy.
authors: T
authors: T
authors: Azzarito
authors: Therapeutic Research and Medicines Evaluation Department, Istituto Superiore di Sanità, Rome, Italy.
authors: P
authors: P
authors: Matarrese
authors: Therapeutic Research and Medicines Evaluation Department, Istituto Superiore di Sanità, Rome, Italy.
authors: E
authors: E
authors: Iessi
authors: Therapeutic Research and Medicines Evaluation Department, Istituto Superiore di Sanità, Rome, Italy.
authors: G
authors: G
authors: Venturi
authors: Technology and Health Department, Istituto Superiore di Sanità, Rome, Italy.
authors: S
authors: S
authors: Meschini
authors: Therapeutic Research and Medicines Evaluation Department, Istituto Superiore di Sanità, Rome, Italy.
authors: A
authors: A
authors: Canitano
authors: Therapeutic Research and Medicines Evaluation Department, Istituto Superiore di Sanità, Rome, Italy.
authors: R
authors: R
authors: Bona
authors: Therapeutic Research and Medicines Evaluation Department, Istituto Superiore di Sanità, Rome, Italy.
authors: A
authors: A
authors: Cara
authors: Therapeutic Research and Medicines Evaluation Department, Istituto Superiore di Sanità, Rome, Italy.
authors: S
authors: S
authors: Fais
mesh_terms: D015153:Blotting, Western; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000378:metabolism / Q000473:pathology*; D019008:Drug Resistance, Neoplasm / Q000502:physiology*; D031541:Fluorescence Resonance Energy Transfer; D006801:Humans; D006863:Hydrogen-Ion Concentration; D047468:Immunoprecipitation; D008565:Membrane Proteins / Q000378:metabolism*; D018613:Microscopy, Confocal; D009361:Neoplasm Invasiveness / Q000473:pathology*; D016133:Polymerase Chain Reaction; D014162:Transfection; D025262:Vacuolar Proton-Translocating ATPases / Q000378:metabolism*
chemical_list: D008565:Membrane Proteins; C547837:TM9SF4 protein, human; D025262:Vacuolar Proton-Translocating ATPases