title: Differential expression of and responsiveness to transforming growth factor-beta (TGF-beta) isoforms in hormone-dependent and independent lines of mouse mammary tumors.
abstract: Transforming growth factor-beta2 (TGF-beta2) and -beta3 mRNA expressions were studied in ductal hormone-dependent (HD) and -independent (HI) in vivo lines of the medroxyprogesterone acetate (MPA)-induced mammary tumor model in Balb/c mice. MPA treatment of HD tumors induced a significant decrease in TGF-beta2 and -beta3 mRNA levels. Progression to an HI phenotype of ductal tumors was associated with reduced TGF-beta2 and -beta3 expressions, as compared with their HD counterparts. Exogenously added TGF-beta1, -beta2, and -beta3 (1 ng/ml) inhibited the proliferation of primary cultures of epithelial cells from ductal HD and HI tumors. In addition, TGF-beta expression and effects were studied in the other type of MPA-induced mammary tumors, which are of lobular origin and lack steroid hormone receptors and evidence an HI behavior. These lobular HI lines showed TGF-beta2 levels similar to those found in HD lines growing in MPA-treated mice. In contrast, TGF-beta3 mRNA levels were 12- to 20-fold higher than in HD tumors. Primary cultures of lobular HI epithelial cells required either TGF-beta concentrations of 10 ng/ml to show an inhibitory response, or were completely resistant to TGF-beta inhibition. Studies of the molecular mechanisms involved in reduction or loss of TGF-beta responsiveness in lobular HI tumors showed that cell surface type II TGF-beta receptor levels were lower in these tumors than those present in HD tumors. Our results support the hypothesis that TGF-beta could play a role as an autocrine growth inhibitor in HD and HI ductal tumors. Autonomous growth of lobular HI tumors could be favored by undetectable or low TGF-beta1 and -beta2 expressions and by reduced or lost sensitivity of epithelial cells to TGF-beta's antiproliferative effects. However, the extremely high levels of TGF-beta3 expression in lobular HI tumors, in spite of reduced sensitivity to TGF-beta3 inhibitory growth effect in tumor epithelial cells, suggest a net positive role for TGF-beta3 in these tumors.
authors.affiliation: Instituto de Biología y Medicina Experimental, Buenos Aires, Argentina.
authors.forename: M H
authors.initials: MH
authors.lastname: Viegas
authors.forename: M
authors.initials: M
authors.lastname: Salatino
authors.forename: M
authors.initials: M
authors.lastname: Goin
authors.forename: G
authors.initials: G
authors.lastname: Peters
authors.forename: L
authors.initials: L
authors.lastname: Labriola
authors.forename: J
authors.initials: J
authors.lastname: Costa da cunha
authors.forename: C
authors.initials: C
authors.lastname: Lanari
authors.forename: E H
authors.initials: EH
authors.lastname: Charreau
authors.forename: P V
authors.initials: PV
authors.lastname: Elizalde
mesh_terms: D000345:Affinity Labels / Q000378:metabolism; D000818:Animals; D015152:Blotting, Northern; D019938:Cyclin D1 / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D008325:Mammary Neoplasms, Experimental / Q000378:metabolism*; D051379:Mice; D008807:Mice, Inbred BALB C; D009376:Neoplasms, Hormone-Dependent / Q000378:metabolism*; D020033:Protein Isoforms; D012333:RNA, Messenger / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
chemical_list: D000345:Affinity Labels; D020033:Protein Isoforms; D012333:RNA, Messenger; D016212:Transforming Growth Factor beta; D019938:Cyclin D1