title: Catalytic activity of human carbonic anhydrase isoform IX is displayed both extra- and intracellularly.
abstract: Most carbonic anhydrases catalyse the reversible conversion of carbon dioxide to protons and bicarbonate, either as soluble cytosolic enzymes, in or at intracellular organelles, or at the extracellular face of the cell membrane as membrane-anchored proteins. Carbonic anhydrase isoform IX (CA IX), a membrane-bound enzyme with catalytic activity at the extracellular membrane surface, has come to prominence in recent years because of its association with hypoxic tissue, particularly tumours, often indicating poor prognosis. We have evaluated the catalytic activity of CA IX heterologously expressed in Xenopus laevis oocytes by measuring the amplitude and rate of cytosolic pH changes as well as pH changes at the outer membrane surface (pHs ) during addition and removal of 5% CO2 /25 mm HCO3-, and by mass spectrometry. Our results indicate both extracellular and intracellular catalytic activity of CA IX. Reduced rates of CO2 -dependent intracellular pH changes after knockdown of CA IX confirmed these findings in two breast cancer cell lines: MCF-7 and MDA-MB-231. Our results demonstrate a new function of CA IX that may be important in the search for therapeutic cancer drugs targeting CA IX.
authors.affiliation: Abteilung für Allgemeine Zoologie, FB Biologie, University of Kaiserslautern, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Klier
authors.affiliation: Abteilung für Allgemeine Zoologie, FB Biologie, University of Kaiserslautern, Germany.
authors.forename: Somayeh
authors.initials: S
authors.lastname: Jamali
authors.affiliation: Abteilung für Allgemeine Zoologie, FB Biologie, University of Kaiserslautern, Germany.
authors.forename: Samantha
authors.initials: S
authors.lastname: Ames
authors.affiliation: Abteilung für Allgemeine Zoologie, FB Biologie, University of Kaiserslautern, Germany.
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Schneider
authors.affiliation: Abteilung für Allgemeine Zoologie, FB Biologie, University of Kaiserslautern, Germany.
authors.forename: Holger M
authors.initials: HM
authors.lastname: Becker
authors.affiliation: Abteilung für Allgemeine Zoologie, FB Biologie, University of Kaiserslautern, Germany.
authors.forename: Joachim W
authors.initials: JW
authors.lastname: Deitmer
mesh_terms: D000818:Animals; D000951:Antigens, Neoplasm / Q000378:metabolism*; D001639:Bicarbonates / Q000737:chemistry; D055162:Biocatalysis; D002245:Carbon Dioxide / Q000737:chemistry; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases / Q000378:metabolism*; D045744:Cell Line, Tumor; D005016:Ethoxzolamide / Q000494:pharmacology; D005110:Extracellular Space / Q000201:enzymology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D042541:Intracellular Space / Q000201:enzymology*; D007527:Isoenzymes / Q000378:metabolism; D061986:MCF-7 Cells; D009865:Oocytes / Q000166:cytology / Q000201:enzymology; D014982:Xenopus laevis
chemical_list: D000951:Antigens, Neoplasm; D001639:Bicarbonates; D007527:Isoenzymes; D002245:Carbon Dioxide; C089226:CA9 protein, human; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases; D005016:Ethoxzolamide
keywords: MCF-7; MDA-MB-231; Xenopus oocytes; breast cancer cells; pH