title: Progesterone receptor activation downregulates GATA3 by transcriptional repression and increased protein turnover promoting breast tumor growth.
abstract: BACKGROUND
  The transcription factor GATA3 is involved in mammary gland development and is crucial for the maintenance of the differentiated status of luminal epithelial cells. The role of GATA3 in breast cancer as a tumor suppressor has been established, although insights into the mechanism of GATA3 expression loss are still required.
  
  
  METHODS
  Chromatin immunoprecipitation assays were conducted to study progestin modulation of recruitment of transcription factors to GATA3 promoter. We performed western blot and reverse RT-qPCR experiments to explore progestin regulation of GATA3 protein and mRNA expression respectively. Confocal microscopy and in vitro phosphorylation studies were conducted to examine progestin capacity to induce GATA3 serine phosphorylation in its 308 residue. GATA3 participation in progestin-induced breast cancer growth was addressed in in vitro proliferation and in vivo tumor growth experiments.
  
  
  RESULTS
  In this study, we demonstrate that progestin-activated progesterone receptor (PR) reduces GATA3 expression through regulation at the transcriptional and post-translational levels in breast cancer cells. In the former mechanism, the histone methyltransferase enhancer of zeste homolog 2 is co-recruited with activated PR to a putative progesterone response element in the GATA3 proximal promoter, increasing H3K27me3 levels and inducing chromatin compaction, resulting in decreased GATA3 mRNA levels. This transcriptional regulation is coupled with increased GATA3 protein turnover through progestin-induced GATA3 phosphorylation at serine 308 followed by 26S proteasome-mediated degradation. Both molecular mechanisms converge to accomplish decreased GATA3 expression levels in breast cancer cells upon PR activation. In addition, we demonstrated that decreased GATA3 levels are required for progestin-induced upregulation of cyclin A2, which mediates the G1 to S phase transition of the cell cycle and was reported to be associated with poor prognosis in breast cancer. Finally, we showed that downregulation of GATA3 is required for progestin stimulation of both in vitro cell proliferation and in vivo tumor growth.
  
  
  CONCLUSIONS
  In the present study, we reveal that progestin-induced PR activation leads to loss of GATA3 expression in breast cancer cells through transcriptional and post-translational regulation. Importantly, we demonstrate that GATA3 downregulation is required for progestin-induced upregulation of cyclin A2 and for progestin-induced in vitro and in vivo breast cancer cell growth.
authors.affiliation: Instituto de Biología y Medicina Experimental (IBYME), CONICET, Vuelta de Obligado 2490, Buenos Aires, 1428 ADN, Argentina. fizzo13@gmail.com.
authors.forename: Franco
authors.initials: F
authors.lastname: Izzo
authors.affiliation: Instituto de Biología y Medicina Experimental (IBYME), CONICET, Vuelta de Obligado 2490, Buenos Aires, 1428 ADN, Argentina. florenciamercogliano@gmail.com.
authors.forename: Florencia
authors.initials: F
authors.lastname: Mercogliano
authors.affiliation: Instituto de Biología y Medicina Experimental (IBYME), CONICET, Vuelta de Obligado 2490, Buenos Aires, 1428 ADN, Argentina. leaventurutti@gmail.com.
authors.forename: Leandro
authors.initials: L
authors.lastname: Venturutti
authors.affiliation: Instituto de Biología y Medicina Experimental (IBYME), CONICET, Vuelta de Obligado 2490, Buenos Aires, 1428 ADN, Argentina. mercedestkach@gmail.com.
authors.forename: Mercedes
authors.initials: M
authors.lastname: Tkach
authors.affiliation: Sanatorio Mater Dei, Buenos Aires, Argentina. gloriainurri@yahoo.com.ar.
authors.forename: Gloria
authors.initials: G
authors.lastname: Inurrigarro
authors.affiliation: Instituto de Biología y Medicina Experimental (IBYME), CONICET, Vuelta de Obligado 2490, Buenos Aires, 1428 ADN, Argentina. rschillaci@ibyme.conicet.gov.ar.
authors.forename: Roxana
authors.initials: R
authors.lastname: Schillaci
authors.affiliation: Weill Cornell Medical College, New York, NY, 10021, USA. lec2010@med.cornell.edu.
authors.forename: Leandro
authors.initials: L
authors.lastname: Cerchietti
authors.affiliation: Instituto de Biología y Medicina Experimental (IBYME), CONICET, Vuelta de Obligado 2490, Buenos Aires, 1428 ADN, Argentina. patriciaelizalde@ibyme.conicet.gov.ar.
authors.forename: Patricia V
authors.initials: PV
authors.lastname: Elizalde
authors.affiliation: Instituto de Biología y Medicina Experimental (IBYME), CONICET, Vuelta de Obligado 2490, Buenos Aires, 1428 ADN, Argentina. cproietti@ibyme.conicet.gov.ar.
authors.forename: Cecilia J
authors.initials: CJ
authors.lastname: Proietti
mesh_terms: D000818:Animals; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism; D045744:Cell Line, Tumor; D056751:Cyclin A2 / Q000235:genetics* / Q000378:metabolism; D015536:Down-Regulation; D005260:Female; D050990:GATA3 Transcription Factor / Q000235:genetics* / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D015674:Mammary Neoplasms, Animal / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D010766:Phosphorylation; D011372:Progestins / Q000378:metabolism*; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone / Q000378:metabolism*
chemical_list: D056751:Cyclin A2; D050990:GATA3 Transcription Factor; C494749:GATA3 protein, human; C494748:Gata3 protein, mouse; D011372:Progestins; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone