Intracellular galectin-7 expression in cancer cells results from an autocrine transcriptional mechanism and endocytosis of extracellular galectin-7

PLoS One. 2017 Nov 8;12(11):e0187194. doi: 10.1371/journal.pone.0187194. eCollection 2017.

Abstract

The β-galactoside binding protein galectin-7 (gal-7) is constitutively expressed at abnormally high levels in the outside milieu and intracellular compartments of many types of epithelial cancer cells, most notably in aggressive forms of ovarian and breast cancer. It is thus of utmost importance to understand how gal-7 traffics between both intracellular and extracellular compartments to develop novel drugs that target the protumorigenic functions of galectin-7. In the present work, we report that extracellular gal-7 plays a central role in controlling intracellular gal-7 in cells. It does so via two distinct yet complementary mechanisms: firstly by increasing the transcriptional activation of lgals7 gene transcription, and secondly via re-entry into the cells. Increased mRNA levels were dose- and time-dependent and occur in all cell lines tested, including ovarian and breast cancer cell lines. Addition of recombinant gal-7 to MDA-MB-231 transfected with a luciferase reporter vector containing response elements of the lgals7 promoter indicated that increased mRNA level of lgals7 occurs via de novo gene transcription. Re-entry of extracellular gal-7 inside cells was rapid, and reached cytosolic and mitochondrial compartments. Taken together, these findings reveal the existence of a positive self-amplification pathway that regulates intracellular gal-7 expression in breast and ovarian cancer cells.

MeSH terms

  • Autocrine Communication / drug effects
  • Autocrine Communication / genetics*
  • Blotting, Western
  • Cell Line, Tumor
  • Endocytosis* / drug effects
  • Extracellular Space / metabolism*
  • Female
  • Fluorescein-5-isothiocyanate / metabolism
  • Galectins / chemistry
  • Galectins / genetics*
  • Galectins / metabolism
  • Gene Expression Regulation, Neoplastic / drug effects
  • Humans
  • Intracellular Space / metabolism*
  • Microscopy, Confocal
  • Mitochondria / drug effects
  • Mitochondria / metabolism
  • Neoplasms / genetics*
  • Neoplasms / pathology*
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Recombinant Proteins / pharmacology
  • Transcription, Genetic* / drug effects

Substances

  • Galectins
  • LGALS7 protein, human
  • RNA, Messenger
  • Recombinant Proteins
  • Fluorescein-5-isothiocyanate

Grants and funding

This study was supported by the National Science and Engineering Research Council of Canada (Grant No. 298215-2013 to YSP) (http://www.nserc-crsng.gc.ca). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.