title: Progesterone-independent effects of human progesterone receptors (PRs) in estrogen receptor-positive breast cancer: PR isoform-specific gene regulation and tumor biology.
abstract: Progesterone receptors (PRs) are prognostic markers in breast cancers irrespective of the patient's progestational status. However, there are two PR isoforms, PR-A and PR-B, that are equimolar in the normal breast but dysregulated in advanced disease. Postmenopausal, tamoxifen-treated patients with estrogen receptor (ER)-positive, PR-A-rich tumors have much faster disease recurrence than patients with PR-B-rich tumors. To study the mechanisms we engineered ER+ breast cancer cells that express each PR isoform under control of an inducible promoter. We identified 79 genes regulated by progesterone (P), mainly by PR-B, and 51 genes regulated without progesterone, mainly by PR-A. Only nine genes were regulated with and without ligand, leading to definition of three classes: I) genes regulated only by liganded PR; II) genes regulated only by unliganded PR; III) genes regulated by both. Unliganded PR-A and PR-B differentially regulate genes that coordinate extracellular signaling pathways and influence tumor cell biology. Indeed, in the absence of P, compared with ER+/PR-B+ or PR- cells, ER+, PR-A+ cells exhibit an aggressive phenotype, are more adhesive to an extracellular matrix, and are more migratory. Additionally, unliganded PR-A and PR-B both inhibit cell growth and provoke resistance to Taxol-induced apoptosis. We propose that PR-A:PR-B ratios, even in the absence of P, influence the biology and treatment response of ER+ tumors, that PR-A isoforms are functionally dominant in P-deficient states, and that PR-A rich tumors are especially aggressive.
authors.affiliation: Department of Medicine, University of Colorado Health Sciences Center, Aurora, Colorado 80045, USA. Britta.Jacobsen@uchsc.edu
authors.forename: Britta M
authors.initials: BM
authors.lastname: Jacobsen
authors.forename: Stephanie A
authors.initials: SA
authors.lastname: Schittone
authors.forename: Jennifer K
authors.initials: JK
authors.lastname: Richer
authors.forename: Kathryn B
authors.initials: KB
authors.lastname: Horwitz
mesh_terms: D017209:Apoptosis; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology; D002448:Cell Adhesion; D045744:Cell Line, Tumor; D002465:Cell Movement; D005260:Female; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D008024:Ligands; D018613:Microscopy, Confocal; D009362:Neoplasm Metastasis; D009369:Neoplasms / Q000378:metabolism; D017239:Paclitaxel / Q000494:pharmacology; D011374:Progesterone / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D020033:Protein Isoforms; D012333:RNA, Messenger / Q000378:metabolism; D011960:Receptors, Estrogen / Q000378:metabolism*; D011980:Receptors, Progesterone / Q000737:chemistry / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013997:Time Factors; D014158:Transcription, Genetic
chemical_list: D008024:Ligands; D020033:Protein Isoforms; D012333:RNA, Messenger; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; C101118:progesterone receptor A; C097314:progesterone receptor B; D011374:Progesterone; D017239:Paclitaxel