title: Signaling through the Smad pathway by insulin-like growth factor-binding protein-3 in breast cancer cells. Relationship to transforming growth factor-beta 1 signaling.
abstract: We previously demonstrated in T47D cells transfected to express the transforming growth factor-beta receptor type II (TGF-betaRII) that insulin-like growth factor binding protein-3 (IGFBP-3) could stimulate Smad2 and Smad3 phosphorylation, potentiate TGF-beta1-stimulated Smad phosphorylation, and cooperate with exogenous TGF-beta1 in cell growth inhibition (Fanayan, S., Firth, S. M., Butt, A. J., and Baxter, R. C. (2000) J. Biol. Chem. 275, 39146-39151). This study further explores IGFBP-3 signaling through the Smad pathway. Like TGF-beta1, natural and recombinant IGFBP-3 stimulated the time- and dose-dependent phosphorylation of TGF-betaR1 as well as Smad2 and Smad3. This effect required the presence of TGF-betaRII. IGFBP-3 mutated in carboxyl-terminal nuclear localization signal residues retained activity in TGF-betaR1 and Smad phosphorylation, whereas IGFBP-5 was inactive. Immunoneutralization of endogenous TGF-beta1 suggested that TGF-beta1 was not essential for IGFBP-3 stimulation of this pathway, but it increased the effect of IGFBP-3. IGFBP-3, like TGF-beta1, elicited a rapid decline in immunodetectable Smad4 and Smad4.Smad2 complexes. IGFBP-3 and nuclear localization signal mutant IGFBP-3 stimulated the activation of the plasminogen activator inhibitor-1 promoter but was not additive with TGF-beta, suggesting that this end point is not a direct marker of the IGFBP-3 effect on cell proliferation. This study defines a signaling pathway for IGFBP-3 from a cell surface receptor to nuclear transcriptional activity, requiring TGF-betaRII but not dependent on the nuclear translocation of IGFBP-3. The precise mechanism by which IGFBP-3 interacts with the TGF-beta receptor system remains to be established.
authors.affiliation: Kolling Institute of Medical Research, University of Sydney, Royal North Shore Hospital, St. Leonards 2065, New South Wales, Australia.
authors.forename: Susan
authors.initials: S
authors.lastname: Fanayan
authors.forename: Sue M
authors.initials: SM
authors.lastname: Firth
authors.forename: Robert C
authors.initials: RC
authors.lastname: Baxter
mesh_terms: D030201:Activin Receptors, Type I / Q000378:metabolism; D001943:Breast Neoplasms / Q000378:metabolism*; D002455:Cell Division; D002467:Cell Nucleus / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006801:Humans; D015151:Immunoblotting; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000378:metabolism*; D009154:Mutation; D010766:Phosphorylation; D011233:Precipitin Tests; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases; D000077293:Receptor, Transforming Growth Factor-beta Type I; D000077294:Receptor, Transforming Growth Factor-beta Type II; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D051901:Smad4 Protein; D013997:Time Factors; D015534:Trans-Activators / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D053773:Transforming Growth Factor beta1; D014407:Tumor Cells, Cultured
chemical_list: D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D018972:Insulin-Like Growth Factor Binding Protein 3; D018125:Receptors, Transforming Growth Factor beta; D011994:Recombinant Proteins; C497796:SMAD4 protein, human; D051901:Smad4 Protein; C508960:TGFB1 protein, human; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D017346:Protein Serine-Threonine Kinases; D030201:Activin Receptors, Type I; D000077293:Receptor, Transforming Growth Factor-beta Type I; D000077294:Receptor, Transforming Growth Factor-beta Type II