title: RAS/ERK modulates TGFbeta-regulated PTEN expression in human pancreatic adenocarcinoma cells.
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.
authors.affiliation: Division of Gastroenterology, Department of Medicine, University of California, San Diego, MC 0063, 9500 Gilman Drive, La Jolla, CA 92093-0063, USA.
authors.forename: Jimmy Y C
authors.initials: JY
authors.lastname: Chow
authors.forename: Khai T
authors.initials: KT
authors.lastname: Quach
authors.forename: Betty L
authors.initials: BL
authors.lastname: Cabrera
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Cabral
authors.forename: Stayce E
authors.initials: SE
authors.lastname: Beck
authors.forename: John M
authors.initials: JM
authors.lastname: Carethers
mesh_terms: D015153:Blotting, Western; D002460:Cell Line; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D051059:PTEN Phosphohydrolase / Q000235:genetics*; D010190:Pancreatic Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D016283:Proto-Oncogene Proteins p21(ras) / Q000502:physiology*; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051901:Smad4 Protein / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000502:physiology*
chemical_list: D005419:Flavonoids; D047428:Protein Kinase Inhibitors; D012333:RNA, Messenger; D051901:Smad4 Protein; D016212:Transforming Growth Factor beta; D020928:Mitogen-Activated Protein Kinases; D051059:PTEN Phosphohydrolase; C494929:PTEN protein, human; D016283:Proto-Oncogene Proteins p21(ras); C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one