title: Growth factor regulation of estrogen receptor coregulator PELP1 functions via Protein Kinase A pathway.
abstract: PELP1 (proline-rich, glutamic acid-rich, and leucine-rich protein-1) is a potential proto-oncogene that functions as a coregulator of estrogen receptor (ER), and its expression is deregulated during breast cancer progression. Emerging evidence suggests growth factor signaling crosstalk with ER as one possible mechanism by which breast tumors acquire resistance to therapy. In this study, we examined mechanisms by which growth factors modulate PELP1 functions, leading to activation of ER. Using in vivo labeling assays, we have found that growth factors promote phosphorylation of PELP1. Utilizing a panel of substrate-specific phosphorylated antibodies, we discovered that growth factor stimulation promotes phosphorylation of PELP1 that is recognized by a protein kinase A (PKA) substrate-specific antibody. Accordingly, growth factor-mediated PELP1 phosphorylation was effectively blocked by PKA-specific inhibitor H89. Utilizing purified PKA enzyme and in vitro kinase assays, we obtained evidence of direct PELP1 phosphorylation by PKA. Using deletion and mutational analysis, we identified PELP1 domains that are phosphorylated by PKA. Interestingly, site-directed mutagenesis of the putative PKA site in PELP1 compromised growth factor-induced activation and subnuclear localization of PELP1 and also affected PELP1-mediated transactivation function. Utilizing MCF-7 cells expressing a PELP1 mutant that cannot be phosphorylated by PKA, we provide mechanistic insights by which growth factor signaling regulates ER transactivation in a PELP1-dependent manner. Collectively, these findings suggest that growth factor signals promote phosphorylation of ER coactivator PELP1 via PKA pathway, and such modification may have functional implications in breast tumors with deregulated growth factor signaling.
authors.affiliation: Department of Obstetrics and Gynecology, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, Mail Code 7836, San Antonio, TX 78229-3900, USA.
authors.forename: Jatin K
authors.initials: JK
authors.lastname: Nagpal
authors.forename: Sujit
authors.initials: S
authors.lastname: Nair
authors.forename: Dimple
authors.initials: D
authors.lastname: Chakravarty
authors.forename: Rajib
authors.initials: R
authors.lastname: Rajhans
authors.forename: Saikumar
authors.initials: S
authors.lastname: Pothana
authors.forename: Darrell W
authors.initials: DW
authors.lastname: Brann
authors.forename: Rajeshwar Rao
authors.initials: RR
authors.lastname: Tekmal
authors.forename: Ratna K
authors.initials: RK
authors.lastname: Vadlamudi
mesh_terms: D000818:Animals; D019556:COS Cells; D045744:Cell Line, Tumor; D002522:Chlorocebus aethiops; D056970:Co-Repressor Proteins; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D017353:Gene Deletion; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism; D007546:Isoquinolines / Q000494:pharmacology; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D000090063:Proto-Oncogene Mas; D011960:Receptors, Estrogen / Q000378:metabolism*; D015398:Signal Transduction; D013449:Sulfonamides / Q000494:pharmacology; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors
chemical_list: D056970:Co-Repressor Proteins; D036341:Intercellular Signaling Peptides and Proteins; D007546:Isoquinolines; C000715470:MAS1 protein, human; C438485:PELP1 protein, human; D000090063:Proto-Oncogene Mas; D011960:Receptors, Estrogen; D013449:Sulfonamides; D015534:Trans-Activators; D014157:Transcription Factors; D017868:Cyclic AMP-Dependent Protein Kinases; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide