title: Progesterone receptor rapid signaling mediates serine 345 phosphorylation and tethering to specificity protein 1 transcription factors.
abstract: Human progesterone receptors (PR) rapidly activate cytosolic signaling pathways, in addition to their classical function as ligand-activated transcription factors. Using ER+/PR-B+ T47D breast cancer cells, we probed the role of progestin-stimulated rapid PR signaling in the transcriptional regulation of target genes involved in breast cancer cell proliferation. Epidermal growth factor receptor (EGFR) was rapidly activated after a 10-min treatment with R5020. Progestin induced EGFR-, c-Src-, and MAPK-dependent phosphorylation of PR-B on the MAPK consensus site, Ser345. Ser345-phosphorylated PR-B receptors strongly associated with specificity protein 1 (Sp1) transcription factors to regulate PR cell cycle (p21) and growth-promoting (EGFR) target genes whose promoters lack canonical progesterone response element sequences. Inhibitors of EGFR, c-Src, or MAPK activities blocked PR tethering to Sp1 and progestin-stimulated S-phase entry. Mutant PR-B receptors defective for c-Src binding (mPro) were not phosphorylated on Ser345 in response to progestin and failed to interact with Sp1. Hormone-induced complexes containing Sp1 and wild-type PR-B, but not S345A or mPro PR-B, were recruited to Sp1 sites within the endogenous p21 promoter. Progestin-induced S-phase entry was attenuated in T47D cells containing wild-type PR-B and treated with EGFR, c-Src, or MAPK kinase inhibitors or in T47D cells stably expressing mPro or mutant DNA-binding domain PR-B. In sum, rapid progestin-activated PR signaling leads to PR Ser345 phosphorylation and tethering to Sp1. These events are critical for progestin-stimulated regulation of Sp1 target genes and breast cancer cell proliferation. Our data demonstrate the therapeutic potential for PR-targeted breast cancer treatment by exploiting multiple nodes along the PR signaling pathway, including PR-B, EGFR, c-Src, MAPK, or Sp1.
authors.affiliation: Department of Medicine, Division of Hematology, Oncology, and Transplantation, University of Minnesota Cancer Center, Minneapolis, Minnesota 55455, USA.
authors.forename: Emily J
authors.initials: EJ
authors.lastname: Faivre
authors.forename: Andrea R
authors.initials: AR
authors.lastname: Daniel
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Hillard
authors.forename: Carol A
authors.initials: CA
authors.lastname: Lange
mesh_terms: D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D047369:Chromatin Immunoprecipitation; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000378:metabolism; D005434:Flow Cytometry; D006801:Humans; D015151:Immunoblotting; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D008954:Models, Biological; D010766:Phosphorylation / Q000187:drug effects; D011372:Progestins / Q000494:pharmacology; D011397:Promegestone / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism; D011980:Receptors, Progesterone / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012694:Serine / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D016329:Sp1 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D011372:Progestins; D011980:Receptors, Progesterone; D016329:Sp1 Transcription Factor; D012694:Serine; D011397:Promegestone; C512478:EGFR protein, human; D066246:ErbB Receptors; D016392:Proto-Oncogene Proteins pp60(c-src); D020928:Mitogen-Activated Protein Kinases