title: Modulation of testicular receptor 4 activity by mitogen-activated protein kinase-mediated phosphorylation.
abstract: Testicular receptor 4 (TR4) is an orphan member of the nuclear receptor superfamily. Despite the lack of identified ligands, its functional role has been demonstrated both in animals and cell cultures. However, it remains unclear how the biological activity of TR4 is regulated without specific ligands. In this study, we showed that in the absence of specific ligands the activity of TR4 could be modulated by mitogen-activated protein kinase (MAPK)-mediated phosphorylation of its activation function 1 (AF-1) domain. A mass spectrometry-based proteome analysis of TR4 expressed in insect cells revealed three phosphorylation sites in its AF-1 domain, specifically on Ser(19), Ser(55), and Ser(68). Site-directed mutagenesis studies demonstrated the functionality of phosphorylation on Ser(19) and Ser(68) but not Ser(55). We also demonstrated that MAPK-mediated phosphorylation of the AF-1 domain rendered TR4 a repressor, mediated through the preferential recruitment of corepressor RIP140. Dephosphorylation of its AF-1 made TR4 an activator due to its selective recruitment of coactivator, P300/cyclic AMP-responsive element binding protein-binding protein-associated factor (PCAF). The biological effects were validated by using the wild type TR4 and its constitutive negative (dephosphorylated) and constitutive positive (phosphorylated) mutants in the studies of regulation of its natural target gene, apoE. This study uncovered, for the first time, a ligand-independent mechanism underlying the biological activity of TR4 that was mediated by MAPK-mediated receptor phosphorylation of AF-1 domain.
authors.affiliation: Department of Pharmacology, University of Minnesota Medical School, Minneapolis, Minnesota 55455, USA.
authors.forename: M D Mostaqul
authors.initials: MD
authors.lastname: Huq
authors.forename: Pawan
authors.initials: P
authors.lastname: Gupta
authors.forename: Nien-Pei
authors.initials: NP
authors.lastname: Tsai
authors.forename: Li-Na
authors.initials: LN
authors.lastname: Wei
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D007313:Insecta / Q000166:cytology; D008297:Male; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008969:Molecular Sequence Data; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D020543:Proteome / Q000378:metabolism*; D011987:Receptors, Steroid / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011988:Receptors, Thyroid Hormone / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020218:Response Elements; D013737:Testis / Q000378:metabolism; D015534:Trans-Activators / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: C490514:Nr2c2 protein, mouse; D020543:Proteome; D011987:Receptors, Steroid; D011988:Receptors, Thyroid Hormone; D012097:Repressor Proteins; D015534:Trans-Activators; D020928:Mitogen-Activated Protein Kinases