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A new family of nuclear receptor coregulators that integrate nuclear receptor signaling through CREB-binding protein.

ABSTRACT: We describe the cloning and characterization of a new family of nuclear receptor coregulators (NRCs) which modulate the function of nuclear hormone receptors in a ligand-dependent manner. NRCs are expressed as alternatively spliced isoforms which may exhibit different intrinsic activities and receptor specificities. The NRCs are organized into several modular structures and contain a single functional LXXLL motif which associates with members of the steroid hormone and thyroid hormone/retinoid receptor subfamilies with high affinity. Human NRC (hNRC) harbors a potent N-terminal activation domain (AD1), which is as active as the herpesvirus VP16 activation domain, and a second activation domain (AD2) which overlaps with the receptor-interacting LXXLL region. The C-terminal region of hNRC appears to function as an inhibitory domain which influences the overall transcriptional activity of the protein. Our results suggest that NRC binds to liganded receptors as a dimer and this association leads to a structural change in NRC resulting in activation. hNRC binds CREB-binding protein (CBP) with high affinity in vivo, suggesting that hNRC may be an important functional component of a CBP complex involved in mediating the transcriptional effects of nuclear hormone receptors.

SUBMITTER: Mahajan MA

PROVIDER: S-EPMC85955 | biostudies-literature | 2000 Jul

REPOSITORIES: biostudies-literature

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A new family of nuclear receptor coregulators that integrate nuclear receptor signaling through CREB-binding protein.

Mahajan M A MA Samuels H H HH

Molecular and cellular biology 20000701 14

We describe the cloning and characterization of a new family of nuclear receptor coregulators (NRCs) which modulate the function of nuclear hormone receptors in a ligand-dependent manner. NRCs are expressed as alternatively spliced isoforms which may exhibit different intrinsic activities and receptor specificities. The NRCs are organized into several modular structures and contain a single functional LXXLL motif which associates with members of the steroid hormone and thyroid hormone/retinoid r ...[more]

PMID: 10866662

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Project description:Endometriosis is defined as the colonization and growth of endometrial tissue at anatomic sites outside the uterine cavity. Up to 15% of reproductive-aged women in the USA suffer from painful symptoms of endometriosis, such as infertility, pelvic pain, menstrual cycle abnormalities and increased risk of certain cancers. However, many of the current clinical treatments for endometriosis are not sufficiently effective and yield unacceptable side effects. There is clearly an urgent need to identify new molecular mechanisms that critically underpin the initiation and progression of endometriosis in order to develop more specific and effective therapeutics which lack the side effects of current therapies. The aim of this review is to discuss how nuclear receptors (NRs) and their coregulators promote the progression of endometriosis. Understanding the pathogenic molecular mechanisms for the genesis and maintenance of endometriosis as modulated by NRs and coregulators can reveal new therapeutic targets for alternative endometriosis treatments.This review was prepared using published gene expression microarray data sets obtained from patients with endometriosis and published literature on NRs and their coregulators that deal with endometriosis progression. Using the above observations, our current understanding of how NRs and NR coregulators are involved in the progression of endometriosis is summarized.Aberrant levels of NRs and NR coregulators in ectopic endometriosis lesions are associated with the progression of endometriosis. As an example, endometriotic cell-specific alterations in gene expression are correlated with a differential methylation status of the genome compared with the normal endometrium. These differential epigenetic regulations can generate favorable cell-specific NR and coregulator milieus for endometriosis progression. Genetic alterations, such as single nucleotide polymorphisms and insertion/deletion polymorphisms of NR and coregulator genes, are frequently detected in ectopic lesions compared with the normal endometrium. These genetic variations impart new molecular properties to NRs and coregulators to increase their capacity to stimulate progression of endometriosis. Finally, post-translational modifications of NR coregulators, such as proteolytic processing, generate endometriosis-specific isoforms. Compared with the unmodified coregulators, these coregulator isoforms have unique functions that enhance the pathogenesis of endometriosis.Epigenetic/genetic variations and posttranslational modifications of NRs and coregulators alter their original function so that they become potent 'drivers' of endometriosis progression.

Project description:Estrogen receptor (ER) positive breast cancers exist in a complex environment of steroid hormones and their cognate receptors. Receptors for estrogens, progestogens (PR), androgens (AR), glucocorticoids (GR) and mineralocorticoids (MR) are variably expressed in these hormone- sensitive breast cancers. Clinical translation of crosstalk among these receptors has been limited by an incomplete understanding of ER reprogramming by PR, GR, AR and MR (NR3C receptors). This study reports that each of the NR3C receptors reprograms ER chromatin binding to sites enriched for NR3C binding motifs and that hormonal co-treatment increases the likelihood of ER binding to estrogen response elements. A major overlap is observed among ER conserved sites, but not among ER sites that are lost or gained due to reprogramming by each of the NR3C receptors. This stability of ER genomic binding is reflected in the resulting transcriptomes, as there is significant overlap among genes whose expression is unaltered in response to joint hormonal interventions but not among genes whose expression is enhanced or opposed by an individual NR3C receptor. The addition of NR3C ligands can enhance or oppose estrogen-mediated induction and repression of gene transcription, resulting in net agonism or antagonism of ER-mediated actions at gene loci and of cellular pathways of interest. In addition to differential modulation of chromatin binding, differences in cofactor associations for ER, PR and GR likely contribute to the divergent functions of these receptors in breast cancer. Among the NR3C receptors, MR activation differentially reprograms ER chromatin binding and, in contrast to ligands for PR, GR or AR, the MR ligand aldosterone does not inhibit estrogen-induced cell proliferation or potentiate the anti-proliferative effect of tamoxifen in ER+ MCF7 cells. PR, GR, AR and MR may be functionally relevant in ER+ breast cancer because higher expression of these NR3C receptors; or genes whose estrogen-regulated expression is altered by each of these receptors is significantly associated with better overall and relapse-free survival. In summary, this study highlights the diverse yet overlapping activities of NR3C receptors in reprogramming ER signaling.

Dataset Information

A new family of nuclear receptor coregulators that integrate nuclear receptor signaling through CREB-binding protein.

Publications

A new family of nuclear receptor coregulators that integrate nuclear receptor signaling through CREB-binding protein.

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