Ligand reduces galectin-1 sensitivity to oxidative inactivation by enhancing dimer formation

J Biol Chem. 2009 Feb 20;284(8):4989-99. doi: 10.1074/jbc.M808925200. Epub 2008 Dec 22.

Abstract

Galectin-1 (Gal-1) regulates leukocyte turnover by inducing the cell surface exposure of phosphatidylserine (PS), a ligand that targets cells for phagocytic removal, in the absence of apoptosis. Gal-1 monomer-dimer equilibrium appears to modulate Gal-1-induced PS exposure, although the mechanism underlying this regulation remains unclear. Here we show that monomer-dimer equilibrium regulates Gal-1 sensitivity to oxidation. A mutant form of Gal-1, containing C2S and V5D mutations (mGal-1), exhibits impaired dimerization and fails to induce cell surface PS exposure while retaining the ability to recognize carbohydrates and signal Ca(2+) flux in leukocytes. mGal-1 also displayed enhanced sensitivity to oxidation, whereas ligand, which partially protected Gal-1 from oxidation, enhanced Gal-1 dimerization. Continual incubation of leukocytes with Gal-1 resulted in gradual oxidative inactivation with concomitant loss of cell surface PS, whereas rapid oxidation prevented mGal-1 from inducing PS exposure. Stabilization of Gal-1 or mGal-1 with iodoacetamide fully protected Gal-1 and mGal-1 from oxidation. Alkylation-induced stabilization allowed Gal-1 to signal sustained PS exposure in leukocytes and mGal-1 to signal both Ca(2+) flux and PS exposure. Taken together, these results demonstrate that monomer-dimer equilibrium regulates Gal-1 sensitivity to oxidative inactivation and provides a mechanism whereby ligand partially protects Gal-1 from oxidation.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alkylation / drug effects
  • Amino Acid Substitution
  • Animals
  • Calcium / metabolism*
  • Dimerization
  • Galectin 1 / genetics
  • Galectin 1 / metabolism*
  • HL-60 Cells
  • Humans
  • Iodoacetamide / pharmacology
  • Leukocytes / metabolism*
  • Ligands
  • Mice
  • Mutation, Missense
  • Oxidation-Reduction / drug effects
  • Phagocytosis / drug effects
  • Phagocytosis / physiology*
  • Phosphatidylserines / metabolism*
  • Phosphatidylserines / pharmacology
  • Signal Transduction / drug effects
  • Signal Transduction / physiology*

Substances

  • Galectin 1
  • Ligands
  • Phosphatidylserines
  • Calcium
  • Iodoacetamide