Mutations in the AF-2 region abolish ligand-induced intranuclear immobilization of the liver X receptor alpha

Identifying new liver X receptor alpha modulators and distinguishing between agonists and antagonists by crystal ligand pocket screening

Background: Modulators of LXRα are of high pharmacological interest as LXRα regulates fatty acid metabolism, inflammatory processes and cancer. We aim to identify new LXRα modulators and to recognize a distinguishable feature of agonists. Results&methodology: The ligand self-dock and largest-cavity-size searching purposely located two appropriate ligand-binding sites to reach the two aims. One is identifying the new modulators from Maybridge library. 20 new compounds are confirmed by the in vitro reporter gene assay. The other is denoting an agonist by at least one best docking pose having one hydrogen bond to LXRα Helix12 His421. Conclusion: Based on the quality x-ray binding pocket, we can identify new LXRα modulators and distinguish between agonists and antagonists by molecular docking.

Flow cytometry detection of vitamin D receptor changes during vitamin D treatment in Crohn's disease

Crohn's disease (CD) is a chronic inflammatory disease associated with a dysregulated T cell response towards intestinal microflora. Vitamin D has immune modulatory effects on T cells through the nuclear vitamin D receptor (VDR) in vitro. It is unclear how oral vitamin D treatment affects VDR expression. The aim of this study was to establish a flow cytometry protocol, including nuclear and cytoplasmic VDR expression, and to investigate the effects of vitamin D treatment on T cell VDR expression in CD patients. The flow cytometry protocol for VDR staining was developed using the human acute monocytic leukaemia cell line (THP-1). The protocol was evaluated in anti-CD3/CD28-stimulated peripheral blood mononuclear cells (PBMCs) from vitamin D3- (n = 9) and placebo-treated (n = 9) CD patients. Anti-VDR-stained PBMCs were examined by flow cytometry, and their cytokine production was determined by cytokine bead array. VDR, CYP27B1 and RXRα mRNA expression levels in CD4(+) T cells were measured by quantitative reverse transcriptase polymerase chain reaction. The flow cytometry protocol enabled detection of cytoplasmic and nuclear VDR expression. The results were confirmed by confocal microscopy and supported by correlation with VDR mRNA expression. VDR expression in CD4(+) T cells increased following stimulation. This VDR up-regulation was inhibited with 30% by vitamin D treatment compared to placebo in CD patients (P = 0027). VDR expression was correlated with in-vitro interferon-γ production in stimulated PBMCs (P = 0.01). Flow cytometry is a useful method with which to measure intracellular VDR expression. Vitamin D treatment in CD patients reduces T cell receptor-mediated VDR up-regulation.

Estrogen-related Receptor β Reduces the Subnuclear Mobility of Estrogen Receptor α and Suppresses Estrogen-dependent Cellular Function

Estrogen-related receptor (ERR) is a member of the nuclear receptor superfamily that has strong homology with estrogen receptor (ER) α. ERR has three subtypes (α, β, and γ) expressed in estrogen-sensitive organs, including ovary, breast, and brain. No endogenous ligands of ERRs have been identified, but these receptors share a common DNA element with ERα and control estrogen-mediated gene transcription. Recent evidence suggests a role of ERRs in estrogen-related pathophysiology, but the detailed mechanisms of ERR functions in estrogen-related tissues are unclear. Using live-cell imaging with fluorescent protein labeling, we found that only ERRβ among the ERRs exhibits a punctate intranuclear pattern overlapping with ERα following 17β-estradiol (E2)-stimulation. Fluorescence recovery after photobleaching showed significant reduction of the mobility of ligand-activated ERα with co-expression of ERRβ. Fluorescence resonance energy transfer revealed that ERRβ directly interacts with ERα. The N-terminal domain of ERRβ was identified as the region that interacts with ERα. We also found a correlation between punctate cluster formation of ERα and interaction between the receptors. Expression of ERRβ significantly repressed ERα-mediated transactivity, whereas that of other ERR subtypes had no effect on the transactivity of ERα. Consistent with this finding, E2-stimulated proliferation of MCF-7 breast carcinoma cells and bcl-2 expression was significantly inhibited by expression of ERRβ. These results provide strong evidence for a suppressive effect of ERRβ on estrogen signaling through reduction of the intranuclear mobility of ERα. The findings further suggest a unique inhibitory role for ERRβ in estrogen-dependent cellular function such as cancer cell proliferation.

Heterodimerization with different Jun proteins controls c-Fos intranuclear dynamics and distribution

The c-Fos proto-oncogenic transcription factor defines a multigene family controlling many processes both at the cell and the whole organism level. To bind to its target AP-1/12-O-tetradecanoylphorbol-13-acetate-responsive element or cAMP-responsive element DNA sequences in gene promoters and exert its transcriptional part, c-Fos must heterodimerize with other bZip proteins, its best studied partners being the Jun proteins (c-Jun, JunB, and JunD). c-Fos expression is regulated at many transcriptional and post-transcriptional levels, yet little is known on how its localization is dynamically regulated in the cell. Here we have investigated its intranuclear mobility using fluorescence recovery after photobleaching, genetic, and biochemical approaches. Whereas monomeric c-Fos is highly mobile and distributed evenly with nucleolar exclusion in the nucleus, heterodimerization with c-Jun entails intranuclear redistribution and dramatic reduction in mobility of c-Fos caused by predominant association with the nuclear matrix independently of any binding to AP-1/12-O-tetradecanoylphorbol-13-acetate-responsive element or cAMP-responsive element sequences. In contrast to c-Jun, dimerization with JunB does not detectably affect c-Fos mobility. However, dimerization with JunB affects intranuclear distribution with significant differences in the localization of c-Fos.c-Jun and c-Fos.JunB dimers. Moreover, c-Jun and JunB exert comparable effects on another Fos family member, Fra-1. Thus, we report a novel regulation, i.e. differentially regulated intranuclear mobility and distribution of Fos proteins by their Jun partners, and suggest the existence of intranuclear storage sites for latent c-Fos.c-Jun AP-1 complexes. This may affect the numerous physiopathological functions these transcription factors control.