title: Intracellular carbonic anhydrase activity sensitizes cancer cell pH signaling to dynamic changes in CO2 partial pressure.
abstract: Carbonic anhydrase (CA) enzymes catalyze the chemical equilibration among CO2, HCO3(-) and H(+). Intracellular CA (CAi) isoforms are present in certain types of cancer, and growing evidence suggests that low levels correlate with disease severity. However, their physiological role remains unclear. Cancer cell CAi activity, measured as cytoplasmic CO2 hydration rate (kf), ranged from high in colorectal HCT116 (∼2 s(-1)), bladder RT112 and colorectal HT29, moderate in fibrosarcoma HT1080 to negligible (i.e. spontaneous kf = 0.18 s(-1)) in cervical HeLa and breast MDA-MB-468 cells. CAi activity in cells correlated with CAII immunoreactivity and enzymatic activity in membrane-free lysates, suggesting that soluble CAII is an important intracellular isoform. CAi catalysis was not obligatory for supporting acid extrusion by H(+) efflux or HCO3(-) influx, nor for maintaining intracellular pH (pHi) uniformity. However, in the absence of CAi activity, acid loading from a highly alkaline pHi was rate-limited by HCO3(-) supply from spontaneous CO2 hydration. In solid tumors, time-dependence of blood flow can result in fluctuations of CO2 partial pressure (pCO2) that disturb cytoplasmic CO2-HCO3(-)-H(+) equilibrium. In cancer cells with high CAi activity, extracellular pCO2 fluctuations evoked faster and larger pHi oscillations. Functionally, these resulted in larger pH-dependent intracellular [Ca(2+)] oscillations and stronger inhibition of the mTORC1 pathway reported by S6 kinase phosphorylation. In contrast, the pHi of cells with low CAi activity was less responsive to pCO2 fluctuations. Such low pass filtering would "buffer" cancer cell pHi from non-steady-state extracellular pCO2. Thus, CAi activity determines the coupling between pCO2 (a function of tumor perfusion) and pHi (a potent modulator of cancer cell physiology).
authors: From the Department of Physiology, Anatomy and Genetics, Oxford University, Parks Road, Oxford OX1 3PT, United Kingdom and.
authors: Alzbeta
authors: A
authors: Hulikova
authors: From the Department of Physiology, Anatomy and Genetics, Oxford University, Parks Road, Oxford OX1 3PT, United Kingdom and.
authors: Nicholas
authors: N
authors: Aveyard
authors: Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Oxford University, Oxford OX3 9DS, United Kingdom.
authors: Adrian L
authors: AL
authors: Harris
authors: From the Department of Physiology, Anatomy and Genetics, Oxford University, Parks Road, Oxford OX1 3PT, United Kingdom and.
authors: Richard D
authors: RD
authors: Vaughan-Jones
authors: From the Department of Physiology, Anatomy and Genetics, Oxford University, Parks Road, Oxford OX1 3PT, United Kingdom and pawel.swietach@dpag.ox.ac.uk.
authors: Pawel
authors: P
authors: Swietach
mesh_terms: D001639:Bicarbonates / Q000737:chemistry / Q000378:metabolism*; D002245:Carbon Dioxide / Q000737:chemistry / Q000378:metabolism*; D002256:Carbonic Anhydrases / Q000737:chemistry / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism / Q000473:pathology; D045325:HCT116 Cells; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009369:Neoplasms / Q000473:pathology; D010313:Partial Pressure; D011522:Protons; D015398:Signal Transduction
chemical_list: D001639:Bicarbonates; D011522:Protons; D002245:Carbon Dioxide; D002256:Carbonic Anhydrases
keywords: Calcium; Cancer Biology; Metabolism; Perfusion; Proton Transport; Signal Transduction; Signaling; pH Regulation