CAIX forms a transport metabolon with monocarboxylate transporters in human breast cancer cells.

Tumor cells rely on glycolysis to meet their elevated demand for energy. Thereby they produce significant amounts of lactate and protons, which are exported via monocarboxylate transporters (MCTs), supporting the formation of an acidic microenvironment. The present study demonstrates that carbonic anhydrase IX (CAIX), one of the major acid/base regulators in cancer cells, forms a protein complex with MCT1 and MCT4 in tissue samples from human breast cancer patients, but not healthy breast tissue.

Modeling of pH regulation in tumor cells: Direct interaction between proton-coupled lactate transporters and cancer-associated carbonic anhydrase.

The most aggressive tumor cells, which often reside in a hypoxic environment, can release vast amounts of lactate and protons via monocarboxylate transporters (MCTs). This additional proton efflux exacerbates extracellular acidification and supports the formation of a hostile environment. In the present study we propose a novel, data-based model for this proton-coupled lactate transport in cancer cells.

Membrane-anchored carbonic anhydrase IV interacts with monocarboxylate transporters via their chaperones CD147 and GP70.

Monocarboxylate transporters (MCTs) mediate the proton-coupled exchange of high-energy metabolites, including lactate and pyruvate, between cells and tissues. The transport activity of MCT1, MCT2, and MCT4 can be facilitated by the extracellular carbonic anhydrase IV (CAIV) via a noncatalytic mechanism. Combining physiological measurements in HEK-293 cells and oocytes with pulldown experiments, we analyzed the direct interaction between CAIV and the two MCT chaperones basigin (CD147) and embigin (GP70).

The proteoglycan-like domain of carbonic anhydrase IX mediates non-catalytic facilitation of lactate transport in cancer cells.

Highly glycolytic tumor cells release vast amounts of lactate and protons via monocarboxylate transporters (MCTs), which exacerbate extracellular acidification and support the formation of a hostile environment. Transport activity of MCTs can be facilitated by non-catalytic interaction with carbonic anhydrase IX (CAIX), the expression of which has been shown to be upregulated under hypoxia. We have now studied the mechanisms that enable CAIX-mediated facilitation of proton-coupled lactate transport in breast cancer cells and oocytes.

A surface proton antenna in carbonic anhydrase II supports lactate transport in cancer cells.

Many tumor cells produce vast amounts of lactate and acid, which have to be removed from the cell to prevent intracellular lactacidosis and suffocation of metabolism. In the present study, we show that proton-driven lactate flux is enhanced by the intracellular carbonic anhydrase CAII, which is colocalized with the monocarboxylate transporter MCT1 in MCF-7 breast cancer cells. Co-expression of MCTs with various CAII mutants in oocytes demonstrated that CAII facilitates MCT transport activity in a process involving CAII-Glu69 and CAII-Asp72, which could function as surface proton antennae for the enzyme.

Selective inhibition of human carbonic anhydrase IX in Xenopus oocytes and MDA-MB-231 breast cancer cells.

Human carbonic anhydrase IX (CA IX) is overexpressed in the most aggressive and invasive tumors. Therefore, CA IX has become the promising antitumor drug target. Three inhibitors have been shown to selectively and with picomolar affinity inhibit human recombinant CA IX.

Catalytic activity of human carbonic anhydrase isoform IX is displayed both extra- and intracellularly.

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.

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

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.