A genome-wide CRISPR screen reconciles the role of N-linked glycosylation in galectin-3 transport to the cell surface

J Cell Sci. 2017 Oct 1;130(19):3234-3247. doi: 10.1242/jcs.206425. Epub 2017 Aug 3.

Abstract

Galectins are a family of lectin binding proteins expressed both intracellularly and extracellularly. Galectin-3 (Gal-3, also known as LGALS3) is expressed at the cell surface; however, Gal-3 lacks a signal sequence, and the mechanism of Gal-3 transport to the cell surface remains poorly understood. Here, using a genome-wide CRISPR/Cas9 forward genetic screen for regulators of Gal-3 cell surface localization, we identified genes encoding glycoproteins, enzymes involved in N-linked glycosylation, regulators of ER-Golgi trafficking and proteins involved in immunity. The results of this screening approach led us to address the controversial role of N-linked glycosylation in the transport of Gal-3 to the cell surface. We find that N-linked glycoprotein maturation is not required for Gal-3 transport from the cytosol to the extracellular space, but is important for cell surface binding. Additionally, secreted Gal-3 is predominantly free and not packaged into extracellular vesicles. These data support a secretion pathway independent of N-linked glycoproteins and extracellular vesicles.

Keywords: Galectin; Glycosylation; Unconventional secretion.

MeSH terms

  • Blood Proteins
  • CRISPR-Cas Systems
  • Endoplasmic Reticulum / genetics
  • Endoplasmic Reticulum / metabolism*
  • Galectin 3 / genetics
  • Galectin 3 / metabolism*
  • Galectins
  • Genome-Wide Association Study
  • Glycosylation
  • Golgi Apparatus / genetics
  • Golgi Apparatus / metabolism*
  • HeLa Cells
  • Humans
  • Protein Transport / physiology

Substances

  • Blood Proteins
  • Galectin 3
  • Galectins
  • LGALS3 protein, human