title: TGF-beta inhibits prolactin-induced expression of beta-casein by a Smad3-dependent mechanism.
abstract: Transforming growth factor-beta (TGF-beta) is a multifunctional growth factor, affecting cell proliferation, apoptosis, and extracellular matrix homeostasis. It also plays critical roles in mammary gland development, one of which involves inhibition of the expression of milk proteins, such as beta-casein, during pregnancy. Here we further explore the underlying signaling mechanism for it. Our results show that TGF-beta suppresses prolactin-induced expression of beta-casein mRNA and protein in primary mouse mammary epithelial cells, but its effect on protein expression is more evident. We also find out that this inhibition is not due to the effect of TGF-beta on cell apoptosis. Furthermore, inhibition of TGF-beta type I receptor kinase activity by a pharmacological inhibitor SB431542 or overexpression of dominant negative Smad3 substantially restores beta-casein expression. By contrast, inhibition of p38 and Erk that are known to be activated by TGF-beta does not alleviate the inhibitory effect of TGF-beta. These results are consistent with our other observation that Smad but not MAPK pathway is activated by TGF-beta in mammary epithelial cells. Lastly, we show that prolactin-induced tyrosine phosphorylation of Jak2 and Stat5 as well as serine/threonine phosphorylation of p70S6K and S6 ribosomal protein are downregulated by TGF-beta, although the former event requires considerably long exposure to TGF-beta. We speculate that these events might be involved in repressing transcription and translation of beta-casein gene, respectively. Taken together, our results demonstrate that TGF-beta abrogates prolactin-stimulated beta-casein gene expression in mammary epithelial cells through, at least in part, a Smad3-dependent mechanism.
authors.affiliation: Institute of Medical and Molecular Toxicology, Chung Shan Medical University, Taichung, Taiwan, ROC.
authors.forename: Wen-Jun
authors.initials: WJ
authors.lastname: Wu
authors.forename: Chin-Feng
authors.initials: CF
authors.lastname: Lee
authors.forename: Chung-Han
authors.initials: CH
authors.lastname: Hsin
authors.forename: Jyun-Yi
authors.initials: JY
authors.lastname: Du
authors.forename: Tsai-Ching
authors.initials: TC
authors.lastname: Hsu
authors.forename: Ting-Hui
authors.initials: TH
authors.lastname: Lin
authors.forename: Tsung-You
authors.initials: TY
authors.lastname: Yao
authors.forename: Cheng-Hsieh
authors.initials: CH
authors.lastname: Huang
authors.forename: Yi-Ju
authors.initials: YJ
authors.lastname: Lee
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001549:Benzamides / Q000494:pharmacology; D002364:Caseins / Q000235:genetics* / Q000378:metabolism; D002478:Cells, Cultured; D004149:Dioxoles / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects / Q000201:enzymology; D005786:Gene Expression Regulation / Q000187:drug effects; D005799:Genes, Dominant; D006801:Humans; D053614:Janus Kinase 2 / Q000378:metabolism; D008321:Mammary Glands, Animal / Q000166:cytology / Q000201:enzymology; D010768:Phosphoserine / Q000378:metabolism; D010769:Phosphothreonine / Q000378:metabolism; D019000:Phosphotyrosine / Q000378:metabolism; D011388:Prolactin / Q000494:pharmacology*; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000037:antagonists & inhibitors; D038601:Ribosomal Protein S6 / Q000378:metabolism; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D050799:STAT5 Transcription Factor / Q000378:metabolism; D051900:Smad3 Protein / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
chemical_list: C459179:4-(5-benzo(1,3)dioxol-5-yl-4-pyridin-2-yl-1H-imidazol-2-yl)benzamide; D001549:Benzamides; D002364:Caseins; D004149:Dioxoles; D012333:RNA, Messenger; D018125:Receptors, Transforming Growth Factor beta; D038601:Ribosomal Protein S6; D050799:STAT5 Transcription Factor; D051900:Smad3 Protein; D016212:Transforming Growth Factor beta; D010769:Phosphothreonine; D010768:Phosphoserine; D019000:Phosphotyrosine; D011388:Prolactin; C507926:Jak2 protein, mouse; D053614:Janus Kinase 2; D017346:Protein Serine-Threonine Kinases; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D000077293:Receptor, Transforming Growth Factor-beta Type I