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

Elife. 2018 May 29;7:e35176. doi: 10.7554/eLife.35176.

Abstract

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 Xenopus 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. CAII-Glu69 and CAII-Asp72 seem to mediate proton transfer between enzyme and transporter, but CAII-His64, the central residue of the enzyme's intramolecular proton shuttle, is not involved in proton shuttling between the two proteins. Instead, this residue mediates binding between MCT and CAII. Taken together, the results suggest that CAII features a moiety that exclusively mediates proton exchange with the MCT to facilitate transport activity.

Keywords: biochemistry; breast cancer cells; chemical biology; human; hypoxia; monocarboxylate transporter; pH imaging; proton antenna; proton-sensitive micro electrodes; xenopus.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Biological Transport
  • Breast Neoplasms / genetics
  • Breast Neoplasms / metabolism*
  • Breast Neoplasms / pathology
  • Carbonic Anhydrase II / chemistry
  • Carbonic Anhydrase II / genetics
  • Carbonic Anhydrase II / metabolism*
  • Female
  • Humans
  • Lactic Acid / metabolism*
  • Monocarboxylic Acid Transporters / genetics
  • Monocarboxylic Acid Transporters / metabolism*
  • Oocytes / cytology
  • Oocytes / metabolism
  • Protein Conformation
  • Protons
  • Surface Properties
  • Symporters / genetics
  • Symporters / metabolism*
  • Tumor Cells, Cultured
  • Xenopus laevis / metabolism*

Substances

  • Monocarboxylic Acid Transporters
  • Protons
  • Symporters
  • monocarboxylate transport protein 1
  • Lactic Acid
  • Carbonic Anhydrase II

Grant support

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.