RAS/ERK modulates TGFbeta-regulated PTEN expression in human pancreatic adenocarcinoma cells

Carcinogenesis. 2007 Nov;28(11):2321-7. doi: 10.1093/carcin/bgm159. Epub 2007 Jul 17.

Abstract

Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is rarely mutated in pancreatic cancers, but its regulation by transforming growth factor (TGF)-beta might mediate growth suppression and other oncogenic actions. Here, we examined the role of TGFbeta and the effects of oncogenic K-RAS/ERK upon PTEN expression in the absence of SMAD4. We utilized two SMAD4-null pancreatic cell lines, CAPAN-1 (K-RAS mutant) and BxPc-3 (WT-K-RAS), both of which express TGFbeta surface receptors. Cells were treated with TGFbeta1 and separated into cytosolic/nuclear fractions for western blotting with phospho-SMAD2, SMAD 2, 4 phospho-ATP-dependent tyrosine kinases (Akt), Akt and PTEN antibodies. PTEN mRNA levels were assessed by reverse transcriptase-polymerase chain reaction. The MEK1 inhibitor, PD98059, was used to block the downstream action of oncogenic K-RAS/ERK, as was a dominant-negative (DN) K-RAS construct. TGFbeta increased phospho-SMAD2 in both cytosolic and nuclear fractions. PD98059 treatment further increased phospho-SMAD2 in the nucleus of both pancreatic cell lines, and DN-K-RAS further improved SMAD translocation in K-RAS mutant CAPAN cells. TGFbeta treatment significantly suppressed PTEN protein levels concomitant with activation of Akt by 48 h through transcriptional reduction of PTEN mRNA that was evident by 6 h. TGFbeta-induced PTEN suppression was reversed by PD98059 and DN-K-RAS compared with treatments without TGFbeta. TGFbeta-induced PTEN expression was inversely related to cellular proliferation. Thus, oncogenic K-RAS/ERK in pancreatic adenocarcinoma facilitates TGFbeta-induced transcriptional down-regulation of the tumor suppressor PTEN in a SMAD4-independent manner and could constitute a signaling switch mechanism from growth suppression to growth promotion in pancreatic cancers.

Publication types

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

MeSH terms

  • Blotting, Western
  • Cell Line
  • Flavonoids / pharmacology
  • Humans
  • Mitogen-Activated Protein Kinases / metabolism*
  • PTEN Phosphohydrolase / genetics*
  • Pancreatic Neoplasms / genetics
  • Pancreatic Neoplasms / metabolism*
  • Pancreatic Neoplasms / pathology
  • Protein Kinase Inhibitors / pharmacology
  • Proto-Oncogene Proteins p21(ras) / physiology*
  • RNA, Messenger / genetics
  • Reverse Transcriptase Polymerase Chain Reaction
  • Smad4 Protein / metabolism
  • Transforming Growth Factor beta / physiology*

Substances

  • Flavonoids
  • Protein Kinase Inhibitors
  • RNA, Messenger
  • Smad4 Protein
  • Transforming Growth Factor beta
  • Mitogen-Activated Protein Kinases
  • PTEN Phosphohydrolase
  • PTEN protein, human
  • Proto-Oncogene Proteins p21(ras)
  • 2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one