PNRC2 is a 16 kDa coactivator that interacts with nuclear receptors through an SH3-binding motif

PNRC2 (proline-rich nuclear receptor co-regulatory protein 2) was identified using mouse steroidogenic factor 1 (SF1) as bait in a yeast two-hybrid screening of a human mammary gland cDNA expression library. PNRC2 is an unusual coactivator in that it is the smallest coactivator identified so far, with a molecular weight of 16 kDa, and interacts with nuclear receptors using a proline-rich sequence. In yeast two-hybrid assays PNRC2 interacted with orphan receptors SF1 and estrogen receptor-related receptor α1 in a ligand-independent manner. PNRC2 was also found to interact with the ligand-binding domains of estrogen receptor, glucocorticoid receptor, progesterone receptor, thyroid receptor, retinoic acid receptor and retinoid X receptor in a ligand-dependent manner. A functional activation function 2 domain is required for nuclear receptors to interact with PNRC2. Using the yeast two-hybrid assay, the region amino acids 85–139 was found to be responsible for the interaction with nuclear receptors. This region contains an SH3 domain-binding motif (SEPPSPS) and an NR box-like sequence (LKTLL). A mutagenesis study has shown that the SH3 domain-binding motif is important for PNRC2 to interact with all the nuclear receptors tested. Our results reveal that PNRC2 has a structure and function similar to PNRC, a previously characterized coactivator. These two proteins represent a new type of nuclear receptor co-regulatory proteins.     

核受体辅活化子PNRC与孤儿核受体SF1的相互作用有赖于SF1的AF-2功能结构域

核受体辅活化子PNRC(proline richnuclearreceptorcoregulatoryprotein ,富含脯氨酸的核受体辅调节蛋白 )可通过含SH3结合模体的PNRC2 78 30 0区域与孤儿核受体类固醇生成因子 1(steroido genicfactor 1,SF1)相互作用 .激活功能 2 (activationfunction 2 ,AF 2 )结构域在核受体配体依赖性转录激活中发挥了重要作用 ,为探讨AF 2结构域在SF1转录激活中的作用机制 ,采用酵母双杂合分析、缺失突变技术和瞬时转染等研究方法考察了AF 2结构域对SF1反式激活功能及SF1与PNRC相互作用的影响 .SF1的反式激活功能有赖于AF 2结构域 ,其机制是SF1AF 2结构域的突变严重影响了SF1与PNRC的有效相互作用 ,并消除了PNRC对SF1反式激活功能的辅激活作用 .结果表明 ,SF1与PNRC的相互作用有赖于AF 2的功能结构域     

Bisphenol A derivatives act as novel coactivator-binding inhibitors for estrogen receptor β

Bisphenol A and its derivatives are recognized as endocrine disruptors based on their complex effects on estrogen receptor (ER) signaling. While the effects of bisphenol derivatives on ERα have been thoroughly evaluated, how these chemicals affect ERβ signaling is less well understood. Herein, we sought to identify novel ERβ ligands using a radioligand competitive binding assay to screen a chemical library of bisphenol derivatives. Many of the compounds identified showed intriguing dual activities as both ERα agonists and ERβ antagonists. Docking simulations of these compounds and ERβ suggested that they bound not only to the canonical binding site of ERβ but also to the coactivator binding site located on the surface of the receptor, suggesting that they act as coactivator-binding inhibitors (CBIs). Receptor–ligand binding experiments using WT and mutated ERβ support the presence of a second ligand-interaction position at the coactivator-binding site in ERβ, and direct binding experiments of ERβ and a coactivator peptide confirmed that these compounds act as CBIs. Our study is the first to propose that bisphenol derivatives act as CBIs, presenting critical insight for the future development of ER signaling–based drugs and their potential to function as endocrine disruptors.     

核受体辅活化子PNRC与孤儿核受体SF1相互作用位点的鉴定

为了阐明核受体辅活化子 (proline richnuclearreceptorcoactivatorprotein ,PNRC)在孤儿核受体类固醇生成因子 1(steroidogenicfactor1,SF1)基因表达调控中的作用 ,采用酵母双杂合分析、缺失突变技术和瞬时转染等研究方法鉴定了PNRC与SF1的相互作用位点 .结果显示 ,PNRC中氨基酸 2 78～ 30 0区域是与SF1相互作用的位点 .该区域富含脯氨酸 ,其中有 1个SH3结合模体 (motif) ,单独的SH3模体不足以与SF1产生有效的相互作用 .瞬时转染分析表明 ,PNRC 2 70 32 7对野生型PNRC的辅激活功能具有负显性抑制效应 .研究结果表明 ,含SH3结合模体的PNRC 2 78 30 0区域是与SF1相互作用的位点     

LKB1 Catalytic Activity Contributes to Estrogen Receptor α Signaling

The tumor suppressor serine-threonine kinase LKB1 is mutated in Peutz-Jeghers syndrome (PJS) and in epithelial cancers, including hormone-sensitive organs such as breast, ovaries, testes, and prostate. Clinical studies in breast cancer patients show low LKB1 expression is related to poor prognosis, whereas in PJS, the risk of breast cancer is similar to the risk from germline mutations in breast cancer (BRCA) 1/BRCA2. In this study, we investigate the role of LKB1 in estrogen receptor α (ERα) signaling. We demonstrate for the first time that LKB1 binds to ERα in the cell nucleus in which it is recruited to the promoter of ERα-responsive genes. Furthermore, LKB1 catalytic activity enhances ERα transactivation compared with LKB1 catalytically deficient mutants. The significance of our discovery is that we demonstrate for the first time a novel functional link between LKB1 and ERα. Our discovery places LKB1 in a coactivator role for ERα signaling, broadening the scientific scope of this tumor suppressor kinase and laying the groundwork for the use of LKB1 as a target for the development of new therapies against breast cancer.     

OTUD7B stabilizes estrogen receptor α and promotes breast cancer cell proliferation

Breast cancer is the most common malignancy in women worldwide. Estrogen receptor α (ERα) is expressed in ∼70% of breast cancer cases and promotes estrogen-dependent cancer progression. In the present study, we identified OTU domain-containing 7B (OTUD7B), a deubiquitylase belonging to A20 subgroup of ovarian tumor protein superfamily, as a bona fide deubiquitylase of ERα in breast cancer. OTUD7B expression was found to be positively correlated with ERα in breast cancer and associated with poor prognosis. OTUD7B could interact with, deubiquitylate, and stabilize ERα in a deubiquitylation activity-dependent manner. Depletion of OTUD7B decreased ERα protein level, the expression of ERα target genes, and the activity of estrogen response element in breast cancer cells. In addition, OTUD7B depletion significantly decreased ERα-positive breast cancer cell proliferation and migration. Finally, overexpression of ERα could rescue the suppressive effect induced by OTUD7B depletion, suggesting that the ERα status was essential to the function of OTUD7B in breast carcinogenesis. In conclusion, our study revealed an interesting post-translational mechanism between ERα and OTUD7B in ERα-positive breast cancer. Targeting the OTUD7B–ERα complex may prove to be a potential approach to treat patients with ERα-positive breast cancer.Subject terms: Breast cancer, Cell growth     

Tissue- and nuclear receptor-specific function of the C-terminal LXXLL motif of coactivator NCoA6/AIB3 in mice

Although the LXXLL motif of nuclear receptor (NR) coactivators is essential for interaction with NRs, its role has not been assessed in unbiased animal models. The nuclear receptor coactivator 6 (NCoA6; also AIB3, PRIP, ASC-2, TRBP, RAP250, or NRC) is a coactivator containing an N-terminal LXXLL-1 (L1) and a C-terminal L2. L1 interacts with many NRs, while L2 interacts with the liver X receptor α (LXRα) and the estrogen receptor α (ERα). We generated mice in which L2 was mutated into AXXAL (L2m) to disrupt its interaction with LXRα and ERα. NCoA6^L2m/L2m mice exhibited normal reproduction, mammary gland morphogenesis, and ERα target gene expression. In contrast, when treated with an LXRα agonist, lipogenesis and the LXRα target gene expression were significantly reduced in NCoA6^L2m/L2m mice. The induction of Cyp7A1 expression by a high-cholesterol diet was impaired in NCoA6^L2m/L2m mice, which reduced bile acid synthesis in the liver and excretion in the feces and resulted in cholesterol accumulation in the liver and blood. These results demonstrate that L2 plays a tissue- and NR-specific role: it is required for NCoA6 to mediate LXRα-regulated lipogenesis and cholesterol/bile acid homeostasis in the liver but not required for ERα function in the mammary gland.     

Unraveling the regulatory connections between two controllers of breast cancer cell fate

Estrogen receptor alpha (ERα) expression is critical for breast cancer classification, high ERα expression being associated with better prognosis. ERα levels strongly correlate with that of GATA binding protein 3 (GATA3), a major regulator of ERα expression. However, the mechanistic details of ERα–GATA3 regulation remain incompletely understood. Here we combine mathematical modeling with perturbation experiments to unravel the nature of regulatory connections in the ERα–GATA3 network. Through cell population-average, single-cell and single-nucleus measurements, we show that the cross-regulation between ERα and GATA3 amounts to overall negative feedback. Further, mathematical modeling reveals that GATA3 positively regulates its own expression and that ERα autoregulation is most likely absent. Lastly, we show that the two cross-regulatory connections in the ERα–GATA3 negative feedback network decrease the noise in ERα or GATA3 expression. This may ensure robust cell fate maintenance in the face of intracellular and environmental fluctuations, contributing to tissue homeostasis in normal conditions, but also to the maintenance of pathogenic states during cancer progression.