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Hypoxia-induced carbonic anhydrase IX facilitates lactate flux in human breast cancer cells by non-catalytic function.

Jamali S, Klier M, Ames S, Barros LF, McKenna R, Deitmer JW, Becker HM - Sci Rep (2015)

Bottom Line: Our results show that CAIX augments MCT1 transport activity by a non-catalytic interaction.Mutation studies in Xenopus oocytes indicate that CAIX, via its intramolecular H(+)-shuttle His200, functions as a "proton-collecting/distributing antenna" to facilitate rapid lactate flux via MCT1.Knockdown of CAIX significantly reduced proliferation of cancer cells, suggesting that rapid efflux of lactate and H(+), as enhanced by CAIX, contributes to cancer cell survival under hypoxic conditions.

View Article: PubMed Central - PubMed

Affiliation: Division of Zoology/Membrane Transport, FB Biologie, TU Kaiserslautern, P.O. Box 3049, D-67653 Kaiserslautern, Germany.

ABSTRACT
The most aggressive tumour cells, which often reside in hypoxic environments, rely on glycolysis for energy production. Thereby they release vast amounts of lactate and protons via monocarboxylate transporters (MCTs), which exacerbates extracellular acidification and supports the formation of a hostile environment. We have studied the mechanisms of regulated lactate transport in MCF-7 human breast cancer cells. Under hypoxia, expression of MCT1 and MCT4 remained unchanged, while expression of carbonic anhydrase IX (CAIX) was greatly enhanced. Our results show that CAIX augments MCT1 transport activity by a non-catalytic interaction. Mutation studies in Xenopus oocytes indicate that CAIX, via its intramolecular H(+)-shuttle His200, functions as a "proton-collecting/distributing antenna" to facilitate rapid lactate flux via MCT1. Knockdown of CAIX significantly reduced proliferation of cancer cells, suggesting that rapid efflux of lactate and H(+), as enhanced by CAIX, contributes to cancer cell survival under hypoxic conditions.

No MeSH data available.


Related in: MedlinePlus

Schematic model of the CAIX-mediated increase in lactate transport in cancer cells under hypoxic conditions.Under normoxic conditions (upper scheme), cancer cells rely on glycolysis and oxidative energy production in the tricarboxylic acid cycle (TCA) to meet their metabolic requirements. Under hypoxic conditions, glycolysis becomes the prime energy source, which leads to vast production of lactate (produced from pyruvate by lactate dehydrogenase, LDH) and H+. Under these conditions (lower left scheme), hypoxia-regulated CAIX, which is directly bound to the complex of MCT and its chaperon CD147, could move protons between the transporter pore and extracellular protonatable residues (light brown circles). Thereby CAIX can function as a ‘H+-distributing antenna’ for the MCT to facilitate rapid extrusion of lactate and H+ from the cell. Knockdown of CAIX (lower right scheme) leads to loss of the ‘H+-distributing antenna’, which decreases MCT transport activity, leading to accumulation of lactate and H+ in the cytosol. A detailed description of the mechanism is given in the Discussion section.
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f7: Schematic model of the CAIX-mediated increase in lactate transport in cancer cells under hypoxic conditions.Under normoxic conditions (upper scheme), cancer cells rely on glycolysis and oxidative energy production in the tricarboxylic acid cycle (TCA) to meet their metabolic requirements. Under hypoxic conditions, glycolysis becomes the prime energy source, which leads to vast production of lactate (produced from pyruvate by lactate dehydrogenase, LDH) and H+. Under these conditions (lower left scheme), hypoxia-regulated CAIX, which is directly bound to the complex of MCT and its chaperon CD147, could move protons between the transporter pore and extracellular protonatable residues (light brown circles). Thereby CAIX can function as a ‘H+-distributing antenna’ for the MCT to facilitate rapid extrusion of lactate and H+ from the cell. Knockdown of CAIX (lower right scheme) leads to loss of the ‘H+-distributing antenna’, which decreases MCT transport activity, leading to accumulation of lactate and H+ in the cytosol. A detailed description of the mechanism is given in the Discussion section.

Mentions: The present study shows that lactate transport capacity in MCF-7 breast cancer cells is significantly increased under hypoxic conditions. The increase in lactate transport is mediated by a non-catalytic interaction between MCT1 and CAIX, expression of the latter is upregulated under hypoxia. Heterologous coexpression of MCT1 and CAIX in Xenopus oocytes identified the intramolecular H+-shuttle His200 in CAIX as a central component within this mechanism. Intracellular CAII, when directly bound to MCT1, can move protons between the transporter pore and surrounding protonatable residues at the plasma membrane, which dissipates local proton microdomains and facilitates H+/lactate cotransport when the proteins are heterologously expressed in Xenopus oocytes3338. Like in the cytoplasm, diffusion of ions in the extracellular space (ECS) is restricted. It has been shown, that extracellular diffusion of ions is hindered by tortuosity of the ECS, proteoglycans at the outer membrane surface, charges at the extracellular matrix, and also by extracellular buffers39. Therefore an effective co-transport of lactate and H+ across the cell membrane requires efficient proton handling on the extracellular side of the plasma membrane. Like CAII, CAIX facilitates a histidine residue (H200) as an intramolecular H+ shuttle to move protons between its catalytic centre and the surrounding aqueous solution40. Therefore it appears plausible that CAIX, which is directly bound to the complex of MCT1 and its chaperon CD147 at the extracellular face of the plasma membrane, could move protons between the transporter pore and extracellular protonatable residues (Fig. 7).


Hypoxia-induced carbonic anhydrase IX facilitates lactate flux in human breast cancer cells by non-catalytic function.

Jamali S, Klier M, Ames S, Barros LF, McKenna R, Deitmer JW, Becker HM - Sci Rep (2015)

Schematic model of the CAIX-mediated increase in lactate transport in cancer cells under hypoxic conditions.Under normoxic conditions (upper scheme), cancer cells rely on glycolysis and oxidative energy production in the tricarboxylic acid cycle (TCA) to meet their metabolic requirements. Under hypoxic conditions, glycolysis becomes the prime energy source, which leads to vast production of lactate (produced from pyruvate by lactate dehydrogenase, LDH) and H+. Under these conditions (lower left scheme), hypoxia-regulated CAIX, which is directly bound to the complex of MCT and its chaperon CD147, could move protons between the transporter pore and extracellular protonatable residues (light brown circles). Thereby CAIX can function as a ‘H+-distributing antenna’ for the MCT to facilitate rapid extrusion of lactate and H+ from the cell. Knockdown of CAIX (lower right scheme) leads to loss of the ‘H+-distributing antenna’, which decreases MCT transport activity, leading to accumulation of lactate and H+ in the cytosol. A detailed description of the mechanism is given in the Discussion section.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4559800&req=5

f7: Schematic model of the CAIX-mediated increase in lactate transport in cancer cells under hypoxic conditions.Under normoxic conditions (upper scheme), cancer cells rely on glycolysis and oxidative energy production in the tricarboxylic acid cycle (TCA) to meet their metabolic requirements. Under hypoxic conditions, glycolysis becomes the prime energy source, which leads to vast production of lactate (produced from pyruvate by lactate dehydrogenase, LDH) and H+. Under these conditions (lower left scheme), hypoxia-regulated CAIX, which is directly bound to the complex of MCT and its chaperon CD147, could move protons between the transporter pore and extracellular protonatable residues (light brown circles). Thereby CAIX can function as a ‘H+-distributing antenna’ for the MCT to facilitate rapid extrusion of lactate and H+ from the cell. Knockdown of CAIX (lower right scheme) leads to loss of the ‘H+-distributing antenna’, which decreases MCT transport activity, leading to accumulation of lactate and H+ in the cytosol. A detailed description of the mechanism is given in the Discussion section.
Mentions: The present study shows that lactate transport capacity in MCF-7 breast cancer cells is significantly increased under hypoxic conditions. The increase in lactate transport is mediated by a non-catalytic interaction between MCT1 and CAIX, expression of the latter is upregulated under hypoxia. Heterologous coexpression of MCT1 and CAIX in Xenopus oocytes identified the intramolecular H+-shuttle His200 in CAIX as a central component within this mechanism. Intracellular CAII, when directly bound to MCT1, can move protons between the transporter pore and surrounding protonatable residues at the plasma membrane, which dissipates local proton microdomains and facilitates H+/lactate cotransport when the proteins are heterologously expressed in Xenopus oocytes3338. Like in the cytoplasm, diffusion of ions in the extracellular space (ECS) is restricted. It has been shown, that extracellular diffusion of ions is hindered by tortuosity of the ECS, proteoglycans at the outer membrane surface, charges at the extracellular matrix, and also by extracellular buffers39. Therefore an effective co-transport of lactate and H+ across the cell membrane requires efficient proton handling on the extracellular side of the plasma membrane. Like CAII, CAIX facilitates a histidine residue (H200) as an intramolecular H+ shuttle to move protons between its catalytic centre and the surrounding aqueous solution40. Therefore it appears plausible that CAIX, which is directly bound to the complex of MCT1 and its chaperon CD147 at the extracellular face of the plasma membrane, could move protons between the transporter pore and extracellular protonatable residues (Fig. 7).

Bottom Line: Our results show that CAIX augments MCT1 transport activity by a non-catalytic interaction.Mutation studies in Xenopus oocytes indicate that CAIX, via its intramolecular H(+)-shuttle His200, functions as a "proton-collecting/distributing antenna" to facilitate rapid lactate flux via MCT1.Knockdown of CAIX significantly reduced proliferation of cancer cells, suggesting that rapid efflux of lactate and H(+), as enhanced by CAIX, contributes to cancer cell survival under hypoxic conditions.

View Article: PubMed Central - PubMed

Affiliation: Division of Zoology/Membrane Transport, FB Biologie, TU Kaiserslautern, P.O. Box 3049, D-67653 Kaiserslautern, Germany.

ABSTRACT
The most aggressive tumour cells, which often reside in hypoxic environments, rely on glycolysis for energy production. Thereby they release vast amounts of lactate and protons via monocarboxylate transporters (MCTs), which exacerbates extracellular acidification and supports the formation of a hostile environment. We have studied the mechanisms of regulated lactate transport in MCF-7 human breast cancer cells. Under hypoxia, expression of MCT1 and MCT4 remained unchanged, while expression of carbonic anhydrase IX (CAIX) was greatly enhanced. Our results show that CAIX augments MCT1 transport activity by a non-catalytic interaction. Mutation studies in Xenopus oocytes indicate that CAIX, via its intramolecular H(+)-shuttle His200, functions as a "proton-collecting/distributing antenna" to facilitate rapid lactate flux via MCT1. Knockdown of CAIX significantly reduced proliferation of cancer cells, suggesting that rapid efflux of lactate and H(+), as enhanced by CAIX, contributes to cancer cell survival under hypoxic conditions.

No MeSH data available.


Related in: MedlinePlus