The retinoic acid-related orphan receptor gamma (RORgamma) has important roles in development and metabolic homeostasis. Although the biological functions of RORgamma have been studied extensively, no ligands for RORgamma have been identified, and no structure of RORgamma has been reported. In this study, we showed that hydroxycholesterols promote the recruitment of coactivators by RORgamma using biochemical assays. We also report the crystal structures of the RORgamma ligand-binding domain bound with hydroxycholesterols. The structures reveal the binding modes of various hydroxycholesterols in the RORgamma pocket, with the receptors all adopting the canonical active conformation. Mutations that disrupt the binding of hydroxycholesterols abolish the constitutive activity of RORgamma. Our observations suggest an important role for the endogenous hydroxycholesterols in modulating RORgamma-dependent biological processes.

Vertical sleeve gastrectomy (VSG) is one of the most commonly performed clinical bariatric surgeries used for the remission of obesity and diabetes. However, the precise molecular mechanism by which VSG exerts its beneficial effects remains elusive. Here we report that the membrane-bound G protein-coupled bile acid receptor, GPBAR-1 (also known as TGR5), is required to mediate the effects of anti-obesity, anti-hyperglycemia, and improvements of fatty liver of VSG in mice. In the absence of TGR5, the beneficial metabolic effects of VSG in mice are lost. Moreover, we found that expression of TGR5 was significantly increased after VSG, and VSG alters both BA levels and composition in mice, resulting in enhancement of TGR5 signaling in the ileum and brown adipose tissues, concomitant with improved glucose control and increased energy expenditure. Conclusion Our study elucidates a novel underlying mechanism by which VSG achieves its postoperative therapeutic effects through enhanced TGR5 signaling.

Farnesoid X receptor (FXR) has important roles in maintaining bile acid and cholesterol homeostasis. Here we report that the antiparasitic drug ivermectin is a ligand for nuclear FXR. We identify ivermectin using a high-throughput compound library screening and show that it induces the transcriptional activity of the FXR with distinctive properties in modulating coregulator recruitment. The crystal structure of ivermectin complexed with the ligand-binding domain of FXR reveals a unique binding mode of ivermectin in the FXR ligand-binding pocket, including the highly dynamic AF-2 helix and an expanded ligand-binding pocket. Treatment of wild-type mice, but not of FXR-null mice, with ivermectin decreases serum glucose and cholesterol levels, suggesting that ivermectin regulates metabolism through FXR. Our results establish FXR as the first mammalian protein targeted by ivermectin with high selectivity. Considering that ivermectin is a widely used clinical drug, our findings reveal a safe template for the design of novel FXR ligands.

Axin is a multidomain protein that plays a critical role in Wnt signaling, serving as a scaffold for down-regulation of ␤-catenin. It also activates the JNK mitogenactivated protein kinase by binding to MEKK1. However, it is intriguing that Axin requires several additional elements for JNK activation, including a requirement for homodimerization, sumoylation at the extreme C-terminal sites, and a region in the protein phosphatase 2A-binding domain. In our present study, we have shown that another MEKK family member, MEKK4, also binds to Axin in vivo and mediates Axininduced JNK activation. Surprisingly MEKK4 binds to a region distinct from the MEKK1-binding site.

Nuclear receptors are important transcriptional factors that share high sequence identity and conserved domains, including a DNA-binding domain (DBD) and a ligand-binding domain (LBD). The LBD plays a crucial role in ligand-mediated nuclear receptor activity. Hundreds of different crystal structures of nuclear receptors have revealed a general mechanism for the molecular basis of ligand binding and ligand-mediated regulation of nuclear receptors. Despite the conserved fold of nuclear receptor LBDs, the ligand-binding pocket is the least conserved region among different nuclear receptor LBDs. Structural comparison and analysis show that several features of the pocket, like the size and also the shape, have contributed to the ligand binding affinity and specificity. In addition, the plastic nature of the ligand-binding pockets in many nuclear receptors provides greater flexibility to further accommodate specific ligands with a variety of conformations. Nuclear receptor coactivators usually contain multiple LXXLL motifs that are used to interact with nuclear receptors. The nuclear receptors respond differently to distinct ligands and readily exchange their ligands in different environments. The conformational flexibility of the AF-2 helix allows the nuclear receptor to sense the presence of the bound ligands, either an agonist or an antagonist, and to recruit the coactivators or corepressors that ultimately determine the transcriptional activation or repression of nuclear receptors. Keywords nuclear receptor; crystal structure; ligand binding domain; ligand recognition; cofactor recruitment 1, Introduction on functional domains of nuclear receptorsNuclear receptors are important transcriptional factors essential for a broad aspect of human physiology, ranging from development and differentiation to metabolic homeostasis [1]. The complete human genome contains 48 nuclear receptors that include classic receptors, adopted orphan receptors and orphan receptors (Table 1). Classic receptors are regulated by endocrine ligands that have been extensively studied, such as steroid hormones, retinoic acids, vitamin D and thyroid hormone. The human nuclear receptors also include a class of orphan receptors for which no ligand was known when the receptor was cloned [2;3]. Since nuclear receptors are critical in physiology, there has been enormous interest in pursuing the © 2010 Elsevier B.V. All rights reserved * Corresponding author, Department of Pharmaceutical Sciences, Center for Pharmacogenetics, University of Pittsburgh, 709 Salk Hall, Pittsburgh, PA 15261, USA. Tel.: +1412 648 1982 fax: +1412 648 1664.edu (Y. Li). Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered whi...

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In principle, the technique of gene delivery involves taking complete or parts of genes that can code specific messages and delivering them to selected cells in the body. Such a transfer of plasmid DNA into mammalian cells has posed major challenges for gene therapy. A series of gelatin-siloxane nanoparticles (GS NPs) with controlled size and surface charge were synthesized through a two-step sol-gel process. In order to increase the efficiency of cellular uptake, HIV-derived Tat peptide was further grafted to GS NPs. In vitro co-location and endocytosis inhibition experiments suggested that the as-synthesized TG NPs may enter HeLa cells via a combined pathway of lipid-raft- and receptor-dependent endocytosis, and only cause little cell damage. Moreover, this study shows the encapsulation of a plasmid DNA in TG NPs to be obtained as a non-viral gene vector. This kind of encapsulation provides complete protection to the plasmid DNA from the external DNase and serum environment, and generates the hope that the resulting formulation can be developed into a potential vector for effective gene delivery. In order to check this potential, the reporter gene pSVβ-gal was encapsulated, and in vitro transfection efficiency of this system was found to be nearly 130% compared to the commercially available transfection reagent Lipofectamine™.

Axin is a recently identified tumor suppressor that plays an important role in liver and colon cancers. To gain further insights into the structure and function of Axin in controlling cell growth, we analyzed 54 colorectal cancer tissues for mutations in AXIN1 gene. We employed PCR amplification with 23 sets of primers against introns that encompassed the whole coding region of AXIN1 followed by single-strand conformation polymorphism (SSCP) analysis. After subcloning and sequencing analysis of the reamplified DNA from the aberrant bands, we found, in addition to 3 silent mutations, 6 misssense point mutations in different functionally important regions. The missense mutation rate is hence 11%, suggesting that Axin deficiency may contribute to the onset of colorectal tumorigenesis.