Publication Date:
2012-09-05
Description:
Acid-extrusion by active transport is important in metabolically-active cancer cells, where it removes excess intracellular acid and sets the intracellular resting pH. Hypoxia is a major trigger of adaptive responses in cancer, but its effect on acid-extrusion remains unclear. We studied pH-regulation under normoxia and hypoxia in eight cancer cell-lines (HCT116, RT112, MDA-MB-468, MCF10A, HT29, HT1080, MiaPaca2, HeLa) using the pH-sensitive fluorophore, cSNARF-1. Hypoxia-responses were triggered by pre-incubation in low O 2 or with the 2-oxoglutarate-dependent dioxygenase inhibitor dimethyloxalylglycine (DMOG). By selective pharmacological inhibition or transport-substrate removal, acid-extrusion flux was dissected into components due to Na + /H + exchange (NHE) and Na + -dependent HCO 3 − -transport. In half of the cell-lines (HCT116, RT112, MDA-MB-468, MCF10A), acid-extrusion on NHE was the dominant flux during an acid-load, and in all of these, bar one (MDA-MB-468), NHE-flux was reduced following hypoxic incubation. Further studies in HCT116 cells showed that 〈4-hour hypoxic incubation reduced NHE-flux reversibly with a time-constant of 1-2 hours. This was not associated with a change in expression of NHE1, the principal NHE isoform. Following 48-hour hypoxia, inhibition of NHE-flux persisted but became slowly reversible and associated with reduced expression of the glycosylated form of NHE1. Acid-extrusion by Na + -dependent HCO 3 − -transport was hypoxia-insensitive and comparable in all cell-lines. This constitutive and stable element of pH-regulation was found to be important for setting and stabilizing resting pH at a mildly alkaline level (conducive for growth), irrespective of oxygenation status. In contrast, the more variable flux on NHE underlies cell-specific differences in their dynamic response to larger acid-loads. J. Cell. Physiol. © 2012 Wiley Periodicals, Inc.
Electronic ISSN:
1097-4652
Topics:
Biology
,
Medicine
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