title: Antiestrogens induce growth inhibition by sequential activation of p38 mitogen-activated protein kinase and transforming growth factor-beta pathways in human breast cancer cells.
abstract: Antiestrogens are successfully used in the treatment of breast cancer. The purpose of this study was to investigate the role of different signal transduction pathways in antiestrogen-induced growth inhibition to gain insights into mechanisms of antiestrogen resistance. We used specific MAPK inhibitors and MCF-7 carcinoma cells as a model to demonstrate that p38 MAPK is an important mediator of antiestrogen growth inhibition in breast cancer. A kinase assay showed that antiestrogens (4-hydroxytamoxifen and ICI 182.780) rapidly induce p38 activity. Overexpression of kinase-deficient mutants of p38 reduced the antiestrogen suppression of Cyclin A transcription. TGFbeta, a negative regulator of breast cancer cell growth, is induced by antiestrogens; therefore, activation of p38 could have been mediated by TGFbeta. We used a TGFbeta and antiestrogen-sensitive reporter gene assay to show that p38 activation precedes TGFbeta activation. These results were further confirmed by quantitative RT-PCR analysis of the antiestrogen-induced transcription of TGFbeta2 and TGFbeta receptor II. Inhibition of p38 reduced the induction of both genes. Finally, Western blot analysis shows that antiestrogens induce phosphorylation of Smad (mothers against decapentaplegic homolog) 2 via p38. Promoter assays with the Smad-dependent reporter p6SBE confirm participation of Smad3 and Smad4 in antiestrogen action. Taken together, our data delineate an antiestrogen signal transduction pathway involving sequential activation of p38 and TGFbeta pathways to mediate growth inhibition.
authors.affiliation: Dr. Margarete Fischer-Bosch Institute of Clinical Pharmacology, 70376 Stuttgart, Germany.
authors.forename: Miriam B
authors.initials: MB
authors.lastname: Buck
authors.forename: Klaus
authors.initials: K
authors.lastname: Pfizenmaier
authors.forename: Cornelius
authors.initials: C
authors.lastname: Knabbe
mesh_terms: D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D049109:Cell Proliferation / Q000187:drug effects; D019925:Cyclin A / Q000037:antagonists & inhibitors / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000187:drug effects / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004958:Estradiol / Q000031:analogs & derivatives* / Q000494:pharmacology; D020847:Estrogen Receptor Modulators / Q000494:pharmacology*; D000077267:Fulvestrant; D006801:Humans; D009154:Mutation; D017346:Protein Serine-Threonine Kinases; D000077294:Receptor, Transforming Growth Factor-beta Type II; D018125:Receptors, Transforming Growth Factor beta / Q000187:drug effects / Q000378:metabolism; D051899:Smad2 Protein; D051900:Smad3 Protein; D051901:Smad4 Protein; D013629:Tamoxifen / Q000031:analogs & derivatives* / Q000494:pharmacology; D015534:Trans-Activators / Q000187:drug effects / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000187:drug effects / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D048051:p38 Mitogen-Activated Protein Kinases / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*
chemical_list: D019925:Cyclin A; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D020847:Estrogen Receptor Modulators; D018125:Receptors, Transforming Growth Factor beta; C497782:SMAD2 protein, human; C497790:SMAD3 protein, human; C497796:SMAD4 protein, human; D051899:Smad2 Protein; D051900:Smad3 Protein; D051901:Smad4 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D013629:Tamoxifen; C016601:afimoxifene; D000077267:Fulvestrant; D004958:Estradiol; D017346:Protein Serine-Threonine Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D000077294:Receptor, Transforming Growth Factor-beta Type II