title: Ser-884 adjacent to the LXXLL motif of coactivator TRBP defines selectivity for ERs and TRs.
abstract: Ligand-dependent interaction of nuclear receptors and coactivators is a critical step in nuclear receptor-mediated transcriptional regulation. TR-binding protein (TRBP) interacts with nuclear receptors through a single LXXLL motif. Evidence suggested that the sequences flanking the LXXLL motif in a number of coactivators determine receptor selectivity. We performed mutagenesis studies at residues adjacent to the TRBP LXXLL motif and identified S884 of TRBP at the -3 position of the LXXLL motif as a key residue for receptor selectivity. Analysis of in vitro and in vivo receptor interactions with TRBP suggested that S884 allowed selective interactions for ERbeta, TR, and RXR vs. ERalpha. Transient transfection studies further confirmed that the LXXLL-binding affinity correlates with TRBP transcriptional activity. Consistent with the structural modeling, an E380G substitution within ERalpha altered the binding to TRBP mutants, demonstrating the direct contact between TRBP S884 and ERalpha E380, which is a residue that distinguishes receptor subclasses. Furthermore, S884 can be phosphorylated by MAPK in vitro, an event that significantly altered the binding of TRBP to ER and suggests a potential mechanism for regulatory interaction. As the differential recruitment of TRBP to ERalpha and ERbeta may rely on S884, our finding provides insight into estrogen signaling and may lead to the development of therapeutic receptor-selective peptide antagonists.
authors.affiliation: Lilly Research Laboratories, Department of Gene Regulation, Bone and Inflammation Research, Eli Lilly & Co., Indianapolis, Indiana 46285, USA. kol@lilly.com
authors.forename: Lan
authors.initials: L
authors.lastname: Ko
authors.forename: Guemalli R
authors.initials: GR
authors.lastname: Cardona
authors.forename: Toshiharu
authors.initials: T
authors.lastname: Iwasaki
authors.forename: Kelli S
authors.initials: KS
authors.lastname: Bramlett
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Burris
authors.forename: William W
authors.initials: WW
authors.lastname: Chin
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010766:Phosphorylation; D011487:Protein Conformation; D011960:Receptors, Estrogen / Q000378:metabolism*; D018168:Receptors, Retinoic Acid / Q000378:metabolism; D011988:Receptors, Thyroid Hormone / Q000378:metabolism*; D047488:Retinoid X Receptors; D012694:Serine; D015534:Trans-Activators / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D011960:Receptors, Estrogen; D018168:Receptors, Retinoic Acid; D011988:Receptors, Thyroid Hormone; D047488:Retinoid X Receptors; D015534:Trans-Activators; D014157:Transcription Factors; D012694:Serine; D020928:Mitogen-Activated Protein Kinases