TGF-Beta suppresses VEGFA-mediated angiogenesis in colon cancer metastasis

PLoS One. 2013;8(3):e59918. doi: 10.1371/journal.pone.0059918. Epub 2013 Mar 25.

Abstract

The FET cell line, derived from an early stage colon carcinoma, is non-tumorigenic in athymic nude mice. Engineered FET cells that express TGF-α (FETα) display constitutively active EGFR/ErbB signaling. These cells readily formed xenograft tumors in athymic nude mice. Importantly, FETα cells retained their response to TGF-beta-mediated growth inhibition, and, like the parental FET cells, expression of a dominant negative TGF-beta type II receptor (DNRII) in FETα cells (FETα/DNRII) abrogated responsiveness to TGF-beta-induced growth inhibition and apoptosis under stress conditions in vitro and increased metastatic potential in an orthotopic model in vivo, which indicates metastasis suppressor activity of TGF-beta signaling in this model. Cancer angiogenesis is widely regarded as a key attribute for tumor formation and progression. Here we show that TGF-beta signaling inhibits expression of vascular endothelial growth factor A (VEGFA) and that loss of autocrine TGF-beta in FETα/DNRII cells resulted in increased expression of VEGFA. Regulation of VEGFA expression by TGF-beta is not at the transcriptional level but at the post-transcriptional level. Our results indicate that TGF-beta decreases VEGFA protein stability through ubiquitination and degradation in a PKA- and Smad3-dependent and Smad2-independent pathway. Immunohistochemical (IHC) analyses of orthotopic tumors showed significantly reduced TGF-beta signaling, increased CD31 and VEGFA staining in tumors of FETα/DNRII cells as compared to those of vector control cells. These results indicate that inhibition of TGF-beta signaling increases VEGFA expression and angiogenesis, which could potentially contribute to enhanced metastasis of those cells in vivo. IHC studies performed on human colon adenocarcinoma specimens showed that TGF-beta signaling is inversely correlated with VEGFA expression, indicating that TGF-beta-mediated suppression of VEGFA expression exists in colon cancer patients.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Adenocarcinoma / genetics
  • Adenocarcinoma / metabolism
  • Adenocarcinoma / pathology
  • Cell Line, Tumor
  • Colonic Neoplasms / genetics*
  • Colonic Neoplasms / metabolism
  • Colonic Neoplasms / pathology*
  • Gene Expression Regulation, Neoplastic
  • Humans
  • Neoplasm Metastasis
  • Neovascularization, Pathologic / genetics*
  • RNA Processing, Post-Transcriptional / drug effects
  • Signal Transduction / drug effects
  • Transforming Growth Factor beta / genetics*
  • Transforming Growth Factor beta / metabolism
  • Transforming Growth Factor beta / pharmacology
  • Vascular Endothelial Growth Factor A / genetics*
  • Vascular Endothelial Growth Factor A / metabolism

Substances

  • Transforming Growth Factor beta
  • Vascular Endothelial Growth Factor A