Yangsik Jeong

Anatomical Profiling of Nuclear Receptor Expression Reveals a Hierarchical Transcriptional Network

In multicellular organisms, the ability to regulate reproduction, development, and nutrient utilization coincided with the evolution of nuclear receptors (NRs), transcription factors that utilize lipophilic ligands to mediate their function. Studying the expression profile of NRs offers a simple, powerful way to obtain highly relational information about their physiologic functions as individual proteins and as a superfamily. We surveyed the expression of all 49 mouse NR mRNAs in 39 tissues, representing diverse anatomical systems. The resulting data set uncovers several NR clades whose patterns of expression indicate their ability to coordinate the transcriptional programs necessary to affect distinct physiologic pathways. Remarkably, this regulatory network divides along the following two physiologic paradigms: (1) reproduction, development, and growth and (2) nutrient uptake, metabolism, and excretion. These data reveal a hierarchical transcriptional circuitry that extends beyond individual tissues to form a meganetwork governing physiology on an organismal scale.

Expression profiling of nuclear receptors in human and mouse embryonic stem cells

Nuclear receptors (NRs) regulate gene expression in essential biological processes including differentiation and development. Here we report the systematic profiling of NRs in human and mouse embryonic stem cell (ESC) lines and during their early differentiation into embryoid bodies. Expression of the 48 human and mouse NRs was assessed by quantitative real-time PCR. In general, expression of NRs between the two human cell lines was highly concordant, whereas in contrast, expression of NRs between human and mouse ESCs differed significantly. In particular, a number of NRs that have been implicated previously as crucial regulators of mouse ESC biology, including ERRbeta, DAX-1, and LRH-1, exhibited diametric patterns of expression, suggesting they may have distinct species-specific functions. Taken together, these results highlight the complexity of the transcriptional hierarchy that exists between species and governs early development. These data should provide a unique resource for further exploration of the species-specific roles of NRs in ESC self-renewal and differentiation.

Nuclear receptor regulation of stemness and stem cell differentiation

Stem cells include a diverse number of toti-, pluri-, and multi-potent cells that play important roles in cellular genesis and differentiation, tissue development, and organogenesis. Genetic regulation involving various transcription factors results in the self-renewal and differentiation properties of stem cells. The nuclear receptor (NR) superfamily is composed of 48 ligand-activated transcription factors involved in diverse physiological functions such as metabolism, development, and reproduction. Increasing evidence shows that certain NRs function in regulating stemness or differentiation of embryonic stem (ES) cells and tissue-specific adult stem cells. Here, we review the role of the NR superfamily in various aspects of stem cell biology, including their regulation of stemness, forward- and trans-differentiation events; reprogramming of terminally differentiated cells; and interspecies differences. These studies provide insights into the therapeutic potential of the NR superfamily in stem cell therapy and in treating stem cell-associated diseases (e.g., cancer stem cell).

Suppression of β-catenin signaling by liver X receptor ligands

The nuclear receptors liver X receptor (LXR) alpha and LXRbeta serve as oxysterol receptors and play an important role in the regulation of lipid metabolism. We investigated the potential effects of LXRs on pathways of colon carcinogenesis and found that LXR activation suppresses the transactivation activity of beta-catenin, a key molecule in Wnt signaling. LXRalpha and LXRbeta inhibited beta-catenin transactivation of T cell factor-mediated transcription in a ligand-dependent manner. LXR activation suppressed an oncogenic beta-catenin, which has phosphorylation site mutations, and did not change beta-catenin protein expression in cells. In contrast, beta-catenin enhanced LXR transactivation activity. Nuclear LXRs and beta-catenin were coimmunoprecipitated in colon cancer HCT116 cells, and in vitro experiments showed that LXRs bind directly to the Armadillo repeat region of beta-catenin in a ligand-independent manner. LXR ligand decreased mRNA expression of beta-catenin targets, MYC, MMP7 and BMP4, and recruited LXRs to MYC and MMP7 promoters. Transfection of a dominant negative LXR to HCT116 cells and experiments using LXR-null cells showed the involvement of cellular LXRs in beta-catenin suppression and proliferation inhibition. The results show lipid-sensing receptor LXRs regulate the beta-catenin activity and cellular proliferation.

Nuclear Receptor Expression Defines a Set of Prognostic Biomarkers for Lung Cancer

David Mangelsdorf and colleagues show that nuclear receptor expression is strongly associated with clinical outcomes of lung cancer patients, and this expression profile is a potential prognostic signature for lung cancer patient survival time, particularly for individuals with early stage disease.

Gallic Acid Regulates Body Weight and Glucose Homeostasis Through AMPK Activation

Gallic acid [3,4,5-trihydroxybenzoic acid (GA)], a natural phytochemical, is known to have a variety of cellular functions including beneficial effects on metabolic syndromes. However, the molecular mechanism by which GA exerts its beneficial effects is not known. Here we report that GA plays its role through the activation of AMP-activated protein kinase (AMPK) and by regulating mitochondrial function via the activation of peroxisome proliferator-activated receptor-γ coactivator1α (PGC1α). Sirtuin 1 (Sirt1) knockdown significantly blunted GAs effect on PGC1α activation and downstream genes, suggesting a critical role of the AMPK/Sirt1/PGC1α pathway in GAs action. Moreover, diet-induced obese mice treated with GA showed significantly improved glucose and insulin homeostasis. In addition, the administration of GA protected diet-induced body weight gain without a change in food intake. Biochemical analyses revealed a marked activation of AMPK in the liver, muscle, and interscapular brown adipose tissue of the GA-treated mice. Moreover, uncoupling protein 1 together with other genes related to energy expenditure was significantly elevated in the interscapular brown adipose tissue. Taken together, these results indicate that GA plays its beneficial metabolic roles by activating the AMPK/Sirt1/PGC1α pathway and by changing the interscapular brown adipose tissue genes related to thermogenesis. Our study points out that targeting the activation of the AMPK/Sirt1/PGC1α pathway by GA or its derivatives might be a potential therapeutic intervention for insulin resistance in metabolic diseases.

Research Resource: Diagnostic and Therapeutic Potential of Nuclear Receptor Expression in Lung Cancer

Lung cancer is the leading cause of cancer-related death. Despite a number of studies that have provided prognostic biomarkers for lung cancer, a paucity of reliable markers and therapeutic targets exist to diagnose and treat this aggressive disease. In this study we investigated the potential of nuclear receptors (NRs), many of which are well-established drug targets, as therapeutic markers in lung cancer. Using quantitative real-time PCR, we analyzed the expression of the 48 members of the NR superfamily in a human panel of 55 normal and lung cancer cell lines. Unsupervised cluster analysis of the NR expression profile segregated normal from tumor cell lines and grouped lung cancers according to type (i.e. small vs. non-small cell lung cancers). Moreover, we found that the NR signature was 79% accurate in diagnosing lung cancer incidence in smokers (n = 129). Finally, the evaluation of a subset of NRs (androgen receptor, estrogen receptor, vitamin D receptor, and peroxisome proliferator-activated receptor-γ) demonstrated the therapeutic potential of using NR expression to predict ligand-dependent growth responses in individual lung cancer cells. Preclinical evaluation of one of these receptors (peroxisome proliferator activated receptor-γ) in mouse xenografts confirmed that ligand-dependent inhibitory growth responses in lung cancer can be predicted based on a tumors receptor expression status. Taken together, this study establishes NRs as theragnostic markers for predicting lung cancer incidence and further strengthens their potential as therapeutic targets for individualized treatment.

Differential expression and function of alternative splicing variants of human liver X receptor α.

The liver X receptor α (LXRα) is a nuclear receptor that is involved in regulation of lipid metabolism, cellular proliferation and apoptosis, and immunity. In this report, we characterize three human LXRα isoforms with variation in the ligand-binding domain (LBD). While examining the expression of LXRα3, which lacks 60 amino acids within the LBD, we identified two novel transcripts that encode LXRα-LBD variants (LXRα4 and LXRα5). LXRα4 has an insertion of 64 amino acids in helix 4/5, and LXRα5 lacks the C-terminal helices 7 to 12 due to a termination codon in an additional exon that encodes an intron in the LXRα1 mRNA. LXRα3, LXRα4, and LXRα5 were expressed at lower levels compared with LXRα1 in many human tissues and cell lines. We also observed weak expression of LXRα3 and LXRα4 in several tissues of mice. LXR ligand treatment induced differential regulation of LXRα isoform mRNA expression in a cell type-dependent manner. Whereas LXRα3 had no effect, LXRα4 has weak transactivation, retinoid X receptor (RXR) heterodimerization, and coactivator recruitment activities. LXRα5 interacted with a corepressor in a ligand-independent manner and inhibited LXRα1 transactivation and target gene expression when overexpressed. Combination of LXRα5 cotransfection and LXRα antagonist treatment produced additive effects on the inhibition of ligand-dependent LXRα1 activation. We constructed structural models of the LXRα4-LBD and its complexes with ligand, RXR-LBD, and coactivator peptide. The models showed that the insertion in the LBD can be predicted to disrupt RXR heterodimerization. Regulation of LXRα pre-mRNA splicing may be involved in the pathogenesis of LXRα-related diseases.

Sterol-dependent nuclear import of ORP1S promotes LXR regulated trans-activation of apoE

Oxysterol binding protein related protein 1S (ORP1S) is a member of a family of sterol transport proteins. Here we present evidence that ORP1S translocates from the cytoplasm to the nucleus in response to sterol binding. The sterols that best promote nuclear import of ORP1S also activate the liver X receptor (LXR) transcription factors and we show that ORP1S binds to LXRs, promotes binding of LXRs to LXR response elements (LXREs) and specifically enhances LXR-dependent transcription via the ME.1 and ME.2 enhancer elements of the apoE gene. We propose that ORP1S is a cytoplasmic sterol sensor, which transports sterols to the nucleus and promotes LXR-dependent gene transcription through select enhancer elements.

Nuclear receptor gene alteration in human induced pluripotent stem cells with hepatic differentiation propensity

Human induced pluripotent stem (hiPS) cells are an alternative cell source of regenerative medicine for liver disease. Because variations in hepatic differentiation efficacy among hiPS cells exist, it is important to select a hiPS cell line with hepatic differentiation propensity. In addition, nuclear receptors (NR) regulate essential biological processes including differentiation and development. In this study, we identified the hiPS cell line with hepatic differentiation propensity and examined expression levels of 48 NR during this process.