CD97 overexpression in tumor cells at the invasion front in colorectal cancer (CC) is independently regulated of the canonical Wnt pathway

Mol Carcinog. 2006 Nov;45(11):881-6. doi: 10.1002/mc.20262.

Abstract

Invasion of colorectal carcinomas (CC) is characterized by nuclear accumulation of beta-catenin, a key component of the Wnt pathway, in scattered tumor cells. beta-catenin acts in cooperation with T-cell factor (Tcf) HMG-box transcription factors as a transcriptional activator of genes involved in tumor progression. Overexpression of CD97, a molecule that correlates with dedifferentiation and tumor stage in CC, parallels to nuclear translocation of beta-catenin. Here, we investigated whether CD97 is a direct beta-catenin/Tcf target gene. SW480 CC cells were used to mimic the phenotypical switch between central and invasive tumor areas. We demonstrate two-fold higher CD97 expression and nuclear beta-catenin accumulation in cells grown at low density compared to cells cultured at high density, showing membrane-associated beta-catenin. This suggests that CD97 expression correlates with the cellular localization of beta-catenin. However, CD97 mRNA expression levels were not affected by Tcf-1 or Tcf-4 as determined in inducible dominant-negative (dn) Tcf CC cell lines. Furthermore, co-expression of wildtype (wt) or S33A mutated beta-catenin with Tcf-4 did not influence CD97 promoter activity. Inhibition of glycogen synthase kinase (GSK)-3beta, a negative regulator of the canonical Wnt pathway, had no influence on CD97 expression levels. In summary, enhanced CD97 expression in CC cells is regulated independent of beta-catenin/Tcf-4, and is thus not a direct target of the canonical Wnt pathway.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antigens, CD / metabolism*
  • Colorectal Neoplasms / immunology*
  • Colorectal Neoplasms / metabolism
  • Flow Cytometry
  • Humans
  • Membrane Glycoproteins / metabolism*
  • Microscopy, Confocal
  • Neoplasm Invasiveness
  • Polymerase Chain Reaction
  • Promoter Regions, Genetic
  • Receptors, G-Protein-Coupled
  • Wnt Proteins / physiology*
  • beta Catenin / metabolism

Substances

  • ADGRE5 protein, human
  • Antigens, CD
  • Membrane Glycoproteins
  • Receptors, G-Protein-Coupled
  • Wnt Proteins
  • beta Catenin