title: Progestin drives breast cancer growth by inducing p21(CIP1) expression through the assembly of a transcriptional complex among Stat3, progesterone receptor and ErbB-2.
abstract: Cell cycle regulator p21(CIP1) has controversial biological effects in breast cancer since in spite of its role as cell cycle inhibitor and promoter of cellular senescence, it also induces cell proliferation and chemoteraphy resistance. We here explored the molecular mechanisms involved in progestin regulation of p21(CIP1) expression. We also investigated the biological effects of p21(CIP1) in breast cancer cells. We found that the synthetic progestin medroxyprogesterone acetate (MPA) upregulates p21(CIP1) protein expression via c-Src, signal transducer and activator of transcription 3 (Stat3) and ErbB-2 phosphorylation. Notably, we also found that ErbB-2 nuclear function plays a key role in MPA-induction of p21(CIP1) expression. Interestingly, we determined that progestin drives p21(CIP1) transcriptional activation via a novel nonclassical transcriptional mechanism in which progesterone receptor is recruited along with Stat3 and ErbB-2 to a Stat3 binding site at p21(CIP1) promoter. Our findings revealed that ErbB-2 functions as a coactivator of Stat3 in progestin induction of p21(CIP1) transcriptional activation. Furthermore, we demonstrated that blockage of p21(CIP1) expression strongly inhibited in vitro and in vivo progestin-induced breast cancer cell proliferation. These results further support the hypothesis that according to cell context and type of stimulus, p21(CIP1) is capable of inducing cell cycle progression. Moreover, we provided evidence that Stat3 and nuclear ErbB-2 are key players in progestin-induced p21(CIP1) regulation.
authors.affiliation: Instituto de Biología y Medicina Experimental (IBYME), CONICET, Vuelta de Obligado 2490, Buenos Aires C1428ADN, Argentina.
authors.forename: María C
authors.initials: MC
authors.lastname: Diaz Flaqué
authors.forename: Rocío
authors.initials: R
authors.lastname: Vicario
authors.forename: Cecilia J
authors.initials: CJ
authors.lastname: Proietti
authors.forename: Franco
authors.initials: F
authors.lastname: Izzo
authors.forename: Roxana
authors.initials: R
authors.lastname: Schillaci
authors.forename: Patricia V
authors.initials: PV
authors.lastname: Elizalde
mesh_terms: D000818:Animals; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000096:biosynthesis / Q000235:genetics*; D005260:Female; D051379:Mice; D008807:Mice, Inbred BALB C; D011372:Progestins / Q000494:pharmacology*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism*; D011980:Receptors, Progesterone / Q000378:metabolism*; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects* / Q000235:genetics; D014407:Tumor Cells, Cultured
chemical_list: D050759:Cyclin-Dependent Kinase Inhibitor p21; D011372:Progestins; D018719:Erb-b2 Receptor Tyrosine Kinases; D011980:Receptors, Progesterone; D050796:STAT3 Transcription Factor; C494087:Stat3 protein, mouse