title: Inhibition of transforming growth factor-beta/Smad signaling by phosphatidylinositol 3-kinase pathway.
abstract: Gastrin-releasing peptide (GRP) activates phosphatidylinositol 3-kinase (PI3-K)/Akt, an important cell survival signaling pathway, to stimulate growth of various cell types. Transforming growth factor (TGF) superfamily ligands activate intracellular Smad signaling to regulate cell growth, differentiation and apoptosis; dysregulation of the TGF-beta/Smad pathway has been noted in cancer cells. Therefore, we sought to determine whether a potential cross-talk exists between the TGF-beta/Smad and PI3-K pathways in the regulation of neuroblastoma cell growth. Increased Smad DNA binding was noted in SK-N-SH human neuroblastoma cells when treated with LY294002, an inhibitor of PI3-K, by transcription factor/DNA array analysis and electrophoretic mobility shift assay. LY294002 treatment resulted in Smad2 accumulation in the nuclei and an increased Smad binding element (SBE)-luciferase activity. These findings were corroborated by co-transfection with pCGNN-Deltap85 plasmid, which expresses a PI3-K mutant p85 subunit. In contrast, GRP treatment decreased Smad binding activity in neuroblastoma cells. Our findings demonstrate that the PI3-K pathway negatively regulates TGF-beta/Smad signaling in neuroblastoma cells. GRP-induced activation of PI3-K, resulting in neuroblastoma cell growth promotion, is potentiated by down-regulation of TGF-beta/Smad signaling.
authors.affiliation: Department of Surgery, The University of Texas Medical Branch, 301 University Boulevard, Galveston, TX 77555-0353, USA.
authors.forename: Jingbo
authors.initials: J
authors.lastname: Qiao
authors.forename: Junghee
authors.initials: J
authors.lastname: Kang
authors.forename: Tien C
authors.initials: TC
authors.lastname: Ko
authors.forename: B Mark
authors.initials: BM
authors.lastname: Evers
authors.forename: Dai H
authors.initials: DH
authors.lastname: Chung
mesh_terms: D049109:Cell Proliferation; D002867:Chromones / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008024:Ligands; D009025:Morpholines / Q000494:pharmacology; D009154:Mutation; D009447:Neuroblastoma / Q000188:drug therapy / Q000201:enzymology*; D020411:Oligonucleotide Array Sequence Analysis; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D051785:Smad Proteins / Q000378:metabolism*; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000378:metabolism*
chemical_list: D002867:Chromones; D004791:Enzyme Inhibitors; D008024:Ligands; D009025:Morpholines; D051785:Smad Proteins; D016212:Transforming Growth Factor beta; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D019869:Phosphatidylinositol 3-Kinases