Nuclear Receptor Cofactor Research Articles

Mechanisms of epigenomic and functional convergence between glucocorticoid- and IL4-driven macrophage programming

Macrophages adopt distinct phenotypes in response to environmental cues, with type-2 cytokine interleukin-4 promoting a tissue-repair homeostatic state (M2IL4). Glucocorticoids (GC), widely used anti-inflammatory therapeutics, reportedly impart a similar phenotype (M2GC), but how such disparate pathways may functionally converge is unknown. We show using integrative functional genomics that M2IL4 and M2GC transcriptomes share a striking overlap mirrored by a shift in chromatin landscape in both common and signal-specific gene subsets. This core homeostatic program is enacted by transcriptional effectors KLF4 and the glucocorticoid receptor, whose genome-wide occupancy and actions are integrated in a stimulus-specific manner by the nuclear receptor cofactor GRIP1. Indeed, many of the M2IL4:M2GC-shared transcriptomic changes were GRIP1-dependent. Consistently, GRIP1 loss attenuated phagocytic activity of both populations in vitro and macrophage tissue-repair properties in the murine colitis model in vivo. These findings provide a mechanistic framework for homeostatic macrophage programming by distinct signals, to better inform anti-inflammatory drug design.

UHRF1 poly-auto-ubiquitination induced by the anti-cancer drug, thymoquinone, is involved in the DNA repair machinery recruitment.

DNA methylation is one of the most important epigenetic mark involved in many physiologic cellular processes and pathologies. During mitosis, the transmission of DNA methylation patterns from a mother to the daughter cells is ensured through the action of the Ubiquitin-like, containing PHD and RING domains, 1/DNA methyltransferase 1 (UHRF1/DNMT1) tandem. UHRF1 is involved in the silencing of many tumor suppressor genes (TSGs) via mechanisms that remain largely to be deciphered. The present study investigated the role and the regulation of UHRF1 poly-ubiquitination induced by thymoquinone, a natural anti-cancer drug, known to enhance or re-activate the expression of TSGs. We found that the auto-ubiquitination of UHRF1, induced by TQ, is mediated by reactive oxygen species, and occurs following DNA damage. We demonstrated that the poly-ubiquitinated form of UHRF1 is K63-linked and can still silence the tumor suppressor gene p16INK4A/CDKN2A. We further showed that TQ-induced auto-ubiquitination is mediated via the activity of Tip60. Since this latter is known as a nuclear receptor co-factor, we investigated if the glucocorticoid receptor (GR) might be involved in the regulation of UHRF1 ubiquitination. Activation of the GR, with dexamethasone, did not influence auto-ubiquitination of UHRF1. However, we could observe that TQ induced a K48-linked poly-ubiquitination of GR, probably involved in the proteosomal degradation pathway. Mass-spectrometry analysis of FLAG-HA-tagged UHRF1 identified UHRF1 partners involved in DNA repair and showed that TQ increased their association with UHRF1, suggesting that poly-ubiquitination of UHRF1 is involved in the DNA repair process. We propose that poly-ubiquitination of UHRF1 serves as a scaffold to recruit the DNA repair machinery at DNA damage sites.

Abstract PO-011: Analysis of nuclear receptor expression in head and neck cancer

Abstract Background: The nuclear receptor (NR) superfamily contains a wide array of transcription factors responsible for cellular metabolism, inflammation, differentiation, and hormonal functions. For 45 years these receptors have been of interest in head and neck squamous cell carcinoma (HNSCC) treatment and prevention, especially retinoic acid receptor (RAR), peroxisome proliferator-activated receptor (PPAR), and vitamin D receptor (VDR) families. In the current study we examined expression patterns of these receptors in The Cancer Genome Atlas (TCGA). Methods: TCGA RNA-Seq data within the cBioportal platform comparing HNSCC samples (n=515 patients/samples) to normal tissue (n=82 patients/samples) was interrogated for significant differences in nuclear receptor expression. Genes with a z-score relative to normal samples (log RNA-Seq V2 RSEM normalized) greater than +2 or less than -2 in ≥50% of cases were considered significant. Unpaired, two-tailed t-tests were used to analyze comparisons in nuclear receptor genes’ z-scores across multiple clinical and pathologic parameters, p<0.05 was deemed significant. Statistical stringency for differential gene expression conformed to cBioportal and the University of Alabama at Birmingham’s Cancer Data Analysis Portal (UALCAN). Results: Of the 46 NR genes and 19 NR cofactors examined, ninety nine percent of tumor samples in the TCGA had some form of NR gene ‘alteration’ compared to normal tissue. These alterations predominantly encompass expression up- or down-regulation. NR genes Peroxisome Proliferator Activated Receptor Gamma (PPARγ) and Retinoic Acid Receptor Related Orphan Receptor C (RORC) (both in the thyroid hormone receptor-like family), and the NR cofactor, Nuclear Receptor Coactivator 1 (NCOA1), were differentially expressed and downregulated in tumors compared to normal tissue. Differences in specific NR expression varied significantly with HPV status (30 NRs), organ site (oral cavity vs hypopharynx & larynx; 20 NRs), tumor size (T1/2 vs. T3/4; 21 NRs), gender (male vs. female; 7 NRs); tumor staging (stage I/II vs. stage III/IV; 6 NRs); lymph node status (N0 vs. N+; 5 NRs), smoking history (smokers vs. non-smokers; 3 NRs), and patient race (White vs. Black/African American; 2 NRs). Conclusions: In prior studies of nuclear receptors in aerodigestive cancer, the retinoid receptor axis was downregulated, and a subsequent goal was stimulation and restoration of activity with natural or synthetic retinoids as a rationale for treatment. Presently, we have discovered significant decreases in PPARγ expression and are targeting this receptor with thiazolidinediones in a series of preclinical and human trials in a similar rationale to promote restoration of normal signaling and events like maturation. Here, we observed significant differences in a variety of parameters of several receptors associated with risk factors, stage, race, and gender that are observed and may become the focus of interest in future targeting efforts. Citation Format: Lindsey Mortensen, Beverly R. Wuertz, Frank G. Ondrey. Analysis of nuclear receptor expression in head and neck cancer [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Innovating through Basic, Clinical, and Translational Research; 2023 Jul 7-8; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2023;29(18_Suppl):Abstract nr PO-011.

Estrogen receptor α K303R mutation reorganizes its binding to forkhead box protein A1 regions and induces chromatin opening

BackgroundEstrogen receptor alpha (ERα) is a frequently mutated gene in breast cancer (BC). While many studies have investigated molecular dysregulation by hotspot mutations at Y537 and D538, which exhibit an estrogen-independent constitutively active phenotype, the functional abnormalities of other mutations remain obscure. The K303R mutation in primary invasive BC has been implicated with endocrine resistance, tumor size, and lymph node positivity. However, the impact of the K303R mutation on the cell epigenome is yet unknown.Methods and resultsWe introduced the K303R ERα mutant in ERα-negative MDA-MB-453 cells to monitor ERα-dependent transactivation and to perform epigenomic analyses. ATAC-seq and ChIP-Seq analyses indicated that both wild-type (WT) and the K303R mutant associated with Forkhead box (Fox) protein family motif regions at similar rates, even without an ERα-binding sequence, but only the K303R mutant induced chromatin opening at those regions. Biochemical analyses demonstrated that the WT and the K303R mutant can be tethered on DNA by FoxA1 indirectly, but only the K303R/FoxA1/DNA complex can induce associations with the nuclear receptor cofactor 2 (NCOA2).ConclusionsThese findings suggest that the K303R mutant induces chromatin opening at the Fox binding region through the FoxA1-dependent associations of the K303R mutant to NCOA2 and then probably disrupts the regulation of Fox-target genes, resulting in K303R-related BC events.

OR26-6 | LBMON298 The Role Of Nuclear Receptor Coregulator Grip1 In Homeostatic Programming Of Macrophages

Abstract Aberrant macrophage function is implicated in acute and chronic inflammatory settings, and central to diseases such as obesity, atherosclerosis and cancer. However, the transcriptional and epigenomic programs driving macrophage polarization toward distinct phenotypic states are not well understood. Macrophage phenotypes exist on a spectrum, with pro-inflammatory (M1-like) and homeostatic, tissue repair (M2-like) states viewed as polar opposites and relatively stable. The main driver of the M2-like program is a type-2 cytokine, IL4 which signals to STAT6 followed by the Krüppel-like factor 4 (KLF4), a master regulator for numerous M2-specific genes. Reportedly, glucocorticoid (GC) hormones also promote the M2-like state, although the extent to which the phenotypes elicited by such disparate signals overlap is unknown. Interestingly, we discovered that GRIP1, a well-known cofactor for nuclear receptors including GR, serves as a KLF4 coactivator, suggesting that GRIP1 could mediate transcriptional and phenotypic convergence of the IL4- and GC-driven pathways. Gene expression profiling on differentially polarized macrophages revealed a highly significant overlap between M2IL4 and M2GC transcriptomes which was mirrored by the H3K27ac de novo enhancer landscape. Notably, loss of GRIP1 blunted both up-regulation of M2- and downregulation of M1-associated genes irrespective of the signal driving M2 polarization. At the cellular level, polarization with either IL4 or GCs enhanced macrophage phagocytosis relative to non-polarized M0, and did so in a GRIP1-dependent manner. Finally, in the dextran sulphate sodium (DSS)-induced colitis model of intestinal inflammation and tissue damage, GRIP1-cKO mice lacking GRIP1 in myeloid cells, including macrophages, displayed more severe destruction of the colonic mucosa and greater immune cell infiltration into the mucosa and submucosa. Moreover, in total colon RNA, the abundance of many characteristic M2 transcripts was reduced in the cKO mice. Surprisingly, the expression of proinflammatory mediators such as TNF, IL1b and IL23 was unaffected by GRIP1 deletion, suggesting that the more severe disease in the cKO stems primarily from the failure of M2-like resolving macrophage to efficiently mitigate tissue destruction and repair the damage. Together, these findings point to GRIP1 as a crucial regulator of macrophage polarization to the homeostatic state in vitro and in vivo. Presentation: Monday, June 13, 2022 12:15 p.m. - 12:30 p.m., Monday, June 13, 2022 12:30 p.m. - 2:30 p.m.

Single-Cell Transcriptome Analysis Defines Expression of Kabuki Syndrome-Associated KMT2D Targets and Interacting Partners.

Objectives. Kabuki syndrome (KS) is a rare genetic disorder characterized by developmental delay, retarded growth, and cardiac, gastrointestinal, neurocognitive, renal, craniofacial, dental, and skeletal defects. KS is caused by mutations in the genes encoding histone H3 lysine 4 methyltransferase (KMT2D) and histone H3 lysine 27 demethylase (KDM6A), which are core components of the complex of proteins associated with histone H3 lysine 4 methyltransferase SET1 (SET1/COMPASS). Using single-cell RNA data, we examined the expression profiles of Kmt2d and Kdm6a in the mouse dental pulp. In the incisor pulp, Kmt2d and Kdm6a colocalize with other genes of the SET1/COMPASS complex comprised of the WD-repeat protein 5 gene (Wdr5), the retinoblastoma-binding protein 5 gene (Rbbp5), absent, small, and homeotic 2-like protein-encoding gene (Ash2l), nuclear receptor cofactor 6 gene (Ncoa6), and Pax-interacting protein 1 gene (Ptip1). In addition, we found that Kmt2d and Kdm6a coexpress with the downstream target genes of the Wingless and Integrated (WNT) and sonic hedgehog signaling pathways in mesenchymal stem/stromal cells (MSCs) at different stages of osteogenic differentiation. Taken together, our results suggest an essential role of KMT2D and KDK6A in directing lineage-specific gene expression during differentiation of MSCs.

P1941The nuclear receptor corepressor 1 blocks CD36-mediated foam cell formation in atherogenesis

Abstract Background Nuclear receptors and their cofactors regulate the expression of various target genes in different tissue and organs to orchestrate downstream (patho)physiological processes. Although the function of several nuclear receptors in atherosclerosis has been studied, very little is known about the role of nuclear receptor cofactors in atherosclerosis. Given its important role to suppress inflammatory processes, we speculated that macrophage nuclear receptor corepressor 1 (NCOR1) plays a protective function in atherosclerosis development. Purpose To evaluate the contribution of macrophage NCOR1 in atherosclerosis we used myeloid cell-specific Ncor1 knockout mice on an atherosclerosis-prone background. Methods and results 8-week-old male and female mice were exposed to a high high-cholesterol diet for 12 weeks. Our findings demonstrate that the lack of macrophage Ncor1 leads to a severe atherosclerotic phenotype in both sexes. These mice show a higher content of plaques along the thoraco-abdominal aortae as well as at the aortic sinus, which were characterized by larger necrotic cores and thinner fibrous caps, a typical signature of unstable plaques. Moreover, we found that the pro-atherogenic effects of the Ncor1 deletion are mediated via derepression of peroxisome proliferator-activated receptor gamma (PPARγ) target genes in mouse and human macrophages, especially the enhanced expression of the CD36 scavenger receptor and the subsequent rise in oxLDL uptake. Interestingly, while the expression of NCOR1 is reduced, the PPARγ signature is increased in human atherosclerotic plaques, and this signature is further pronounced in ruptured compared to stable carotid plaques. Conclusion Our findings suggest that macrophage NCOR1 blocks the pro-atherogenic functions of PPARγ in atherosclerosis and prevents the disease development. Acknowledgement/Funding The Swiss National Science Foundation, the Novartis Foundation, Olga-Mayenfisch Foundation, the OPO foundation

Phenotypic variation reveals sites of evolutionary constraint in the androgenic signaling pathway

Steroid hormone systems play an important role in shaping the evolution of vertebrate sexual traits, but several aspects of this relationship remain unclear. For example, we currently know little about how steroid signaling complexes are adapted to accommodate the emergence of behavior in response to sexual selection. We use downy woodpeckers (Dryobates pubescens) to evaluate how the machinery underlying androgen action can evolve to accommodate this bird's main territorial signal, the drum. We focus specifically on modifications to androgenic mechanisms in the primary neck muscle that actuates the hammering movements underlying this signal. Of the signaling components we examine, we find that levels of circulating testosterone (T) and androgen receptor (AR) expression are consistently increased in a way that likely enhances androgenic regulation of drumming. By contrast, the expression of nuclear receptor co-factors—the ‘molecular rheostats’ of steroid action—show no such relationship in our analyses. If anything, co-factors are expressed in directions that would presumably hinder androgenic regulation of the drum. These findings therefore collectively point to T levels and AR as the more evolutionarily labile components of the androgenic system, in that they are likely more apt to change over time to support sexual selection for territorial signaling in woodpeckers. Yet the signaling elements that fine-tune AR's functional effects on the genome—namely the receptor's transcriptional co-factors—do not change in such a manner, and thus may be under tighter evolutionary constraint.

Abstract 3605: The role of androgen receptor in invasive lobular breast carcinoma

Abstract The leading problem for women with estrogen receptor α (ER) breast cancer – approximately 70% of all breast cancers – is that while the majority of tumors initially respond to anti-estrogen treatment including Tamoxifen and aromatase inhibitors, they will develop endocrine resistance. A histological subset of breast cancer called invasive lobular carcinoma (ILC) accounts for 15% of all breast cancer cases and approximately 90% of ILC are ER-positive. Despite clinical markers suggesting a better prognosis for ILC compared to the more common invasive ductal carcinoma (IDC), recent data suggests women with ILC develop Tamoxifen resistance at a higher rate than IDC. New strategies for treating hormone refractory tumors are needed that not only overcome anti-estrogen resistance, but also present a more tolerable side effect profile and have fewer dose-limiting toxicities than adjuvant chemotherapy. The majority of ER-positive breast cancers also express androgen receptor (AR) and while AR presence in breast cancer is controversial, increased expression of AR leads to Tamoxifen resistance in IDC cell lines. Since ILC has more AR expression than IDC, the role of AR in ILC was studied by treating cells with the non-aromatizable androgen dihydrotestosterone (DHT) and the synthetic androgen R1881 as well as the anti-androgen Enzalutamide. We have previously begun to characterize a Tamoxifen resistant variant of the ILC cell line Sum44PE termed LCCTam cells. In both Sum44PE and LCCTam cells, AR protein expression increases in response to androgens, an action that is blocked by Enzalutamide. Interestingly, androgens do not promote growth in ILC cells, but Enzalutamide is still able to inhibit growth. These results suggest Enzalutamide may be an effective alternative therapy for women with ILC. Future studies will focus on whether regulation of nuclear receptor co-factors influences differences in AR signaling in ILC. Citation Format: Hillary Stires, Rebecca B. Riggins. The role of androgen receptor in invasive lobular breast carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3605. doi:10.1158/1538-7445.AM2017-3605

The nuclear cofactor receptor interacting protein-140 (RIP140) regulates the expression of genes involved in Aβ generation

The receptor interacting protein-140 (RIP140) is a cofactor for several nuclear receptors and has been involved in the regulation of metabolic and inflammatory genes. We hypothesize that RIP140 may also affect Aβ generation because it modulates the activity of transcription factors previously implicated in amyloid precursor protein (APP) processing, such as peroxisome proliferator-activated receptor-γ (PPARγ). We found that the levels of RIP140 are reduced in Alzheimer's disease (AD) postmortem brains compared with healthy controls. In addition, in situ hybridization experiments revealed that RIP140 expression is enriched in the same brain areas involved in AD pathology, such as cortex and hippocampus. Furthermore, we provide evidence using cell lines and genetically modified mice that RIP140 is able to modulate the transcription of certain genes involved in AD pathology, such as β-APP cleaving enzyme (BACE1) and GSK3. Consequently, we found that RIP140 overexpression reduced the generation of Aβ in a neuroblastoma cell line by decreasing the transcription of β-APP cleaving enzyme via a PPARγ–dependent mechanism. The results of this study therefore provide molecular insights into common signaling pathways linking metabolic disease with AD.

The transcriptional coregulator GRIP1 controls macrophage polarization and metabolic homeostasis.

Diet-induced obesity causes chronic macrophage-driven inflammation in white adipose tissue (WAT) leading to insulin resistance. WAT macrophages, however, differ in their origin, gene expression and activities: unlike infiltrating monocyte-derived inflammatory macrophages, WAT-resident macrophages counteract inflammation and insulin resistance, yet, the mechanisms underlying their transcriptional programming remain poorly understood. We recently reported that a nuclear receptor cofactor—glucocorticoid receptor (GR)-interacting protein (GRIP)1—cooperates with GR to repress inflammatory genes. Here, we show that GRIP1 facilitates macrophage programming in response to IL4 via a GR-independent pathway by serving as a coactivator for Kruppel-like factor (KLF)4—a driver of tissue-resident macrophage differentiation. Moreover, obese mice conditionally lacking GRIP1 in macrophages develop massive macrophage infiltration and inflammation in metabolic tissues, fatty livers, hyperglycaemia and insulin resistance recapitulating metabolic disease. Thus, GRIP1 is a critical regulator of immunometabolism, which engages distinct transcriptional mechanisms to coordinate the balance between macrophage populations and ultimately promote metabolic homeostasis.

The Proteomic Profile of Deleted in Breast Cancer 1 (DBC1) Interactions Points to a Multifaceted Regulation of Gene Expression

Deleted in breast cancer 1 (DBC1) has emerged as an important regulator of multiple cellular processes, ranging from gene expression to cell cycle progression. DBC1 has been linked to tumorigenesis both as an inhibitor of histone deacetylases, HDAC3 and sirtuin 1, and as a transcriptional cofactor for nuclear hormone receptors. However, despite mounting interest in DBC1, relatively little is known about the range of its interacting partners and the scope of its functions. Here, we carried out a functional proteomics-based investigation of DBC1 interactions in two relevant cell types, T cells and kidney cells. Microscopy, molecular biology, biochemistry, and mass spectrometry studies allowed us to assess DBC1 mRNA and protein levels, localization, phosphorylation status, and protein interaction networks. The comparison of DBC1 interactions in these cell types revealed conserved regulatory roles for DBC1 in gene expression, chromatin organization and modification, and cell cycle progression. Interestingly, we observe previously unrecognized DBC1 interactions with proteins encoded by cancer-associated genes. Among these interactions are five components of the SWI/SNF complex, the most frequently mutated chromatin remodeling complex in human cancers. Additionally, we identified a DBC1 interaction with TBL1XR1, a component of the NCoR complex, which we validated by reciprocal isolation. Strikingly, we discovered that DBC1 associates with proteins that regulate the circadian cycle, including DDX5, DHX9, and SFPQ. We validated this interaction by colocalization and reciprocal isolation. Functional assessment of this association demonstrated that DBC1 protein levels are important for regulating CLOCK and BMAL1 protein oscillations in synchronized T cells. Our results suggest that DBC1 is integral to the maintenance of the circadian molecular clock. Furthermore, the identified interactions provide a valuable resource for the exploration of pathways involved in DBC1-associated tumorigenesis.

Identification of a naturally occurring retinoid X receptor agonist from Brazilian green propolis

BackgroundBrazilian green propolis (BGP), a resinous substance produced from Baccharis dracunculifolia by Africanized honey bees (Apis mellifera), is used as a folk medicine. Our present study explores the retinoid X receptor (RXR) agonistic activity of BGP and the identification of an RXR agonist in its extract. MethodsRXRα agonistic activity was evaluated using a luciferase reporter gene assay. Isolation of the RXRα agonist from the ethanolic extract of BGP was performed using successive silica gel and a reversed phase column chromatography. The interaction between the isolated RXRα agonist and RXRα protein was predicted by a receptor–ligand docking simulation. The nuclear receptor (NR) cofactor assay was used to estimate whether the isolated RXRα agonist bound to various NRs, including RXRs and peroxisome proliferator-activated receptors (PPARs). We further examined its effect on adipogenesis in 3T3-L1 fibroblasts. ResultsWe identified drupanin as an RXRα agonist with an EC50 value of 4.8±1.0μM. Drupanin activated three RXR subtypes by a similar amount and activated PPARγ moderately. Additionally, drupanin induced adipogenesis and elevated aP2 mRNA levels in 3T3-L1 fibroblasts. ConclusionsDrupanin, a component of BGP, is a novel RXR agonist with slight PPARγ agonistic activity. General significanceThis study revealed for the first time that BGP activates RXR and drupanin is an RXR agonist in its extract.

Modulation of the Glucocorticoid Receptor Activity by Post-Translational Modifications

Glucocorticoids (GCs) regulate numerous physiologic processes in order to maintain homeostasis. Most of their actions are mediated by an intracellular GC receptor (GR). The dysregulation of the GR function has been associated with different pathologies such as stress-related disorders and inflammatory and autoimmune diseases. The final outcome of GC actions is regulated at multiple levels and has been extensively reported. Nowadays, novel insights into the modulation of the GR activity arise from the study of the multiprotein chaperone/cochaperone machinery, the nuclear receptor cofactors (coactivators and corepressors), and chromatin regulation and their concomitant impact on GR-mediated gene transcription. Nevertheless, the complexity of GR-mediated gene regulation cannot be explained by a finite number of chaperones and cofactors. A further level in the regulation of GR activity is achieved by posttranslational modifications (PTMs) in response to external stimuli. PTMs can regulate protein stability, structure, function, activity, intracellular localization, and interaction with other proteins during cellular processes. Therefore, dynamic regulation of the molecular properties of these proteins by PTMs allows for further understanding the complexity of GR-dependent gene expression and its impact on GR-mediated pathophysiological processes.

Down-regulation of Zac1 gene expression in rat white adipose tissue by androgens

ZAC1 is a zinc-finger protein transcription factor, a transcriptional cofactor for nuclear receptors, and a co-activator of nuclear receptors, which interacts with multiple signaling pathways affecting apoptosis, cell cycle arrest, and metabolism. Some data suggest that ZAC1 regulates the expression of genes associated with function of adipose tissue. Since there is no information about the levels of Zac1 gene expression in white adipose tissue (WAT), and the expression of several genes associated with metabolic function of WAT is significantly lower in male than female animals, we have examined: (a) the relative ZAC1 mRNA levels in some organs/tissues, including three main depots of WAT, in 3-month-old male rats; (b) the relative ZAC1 mRNA levels in WAT of male and female rats; (c) the effect of orchidectomy and orchidectomy with concomitant testosterone treatment on ZAC1 mRNA and protein levels; (d) the effect of ovariectomy and ovariectomy with concomitant 17β-estradiol treatment on ZAC1 mRNA levels; (e) the effect of dihydrotestosterone on ZAC1 mRNA levels in isolated adipocytes.Our results indicate that: (a) ZAC1 mRNA levels are relatively high in WAT in comparison with other organs/tissues; (b) ZAC1 mRNA levels in subcutaneous WAT are approximately 2-fold lower than in epididymal and retroperitoneal adipose tissue; (c) ZAC1 mRNA levels in WAT of adult female rats are approximately 2-fold higher than in male rats; (d) testosterone is inversely related to ZAC1 mRNA and protein levels in WAT of male rats; and (e) dihydrotestosterone decreases the ZAC1 mRNA levels in adipocytes in dose dependent manner.In conclusion, Zac1 gene is highly expressed in white adipose tissue of adult rats. Androgens could play an important role in down-regulation of the ZAC1 mRNA and protein levels in rats.

Elevated expression of coactivator-associated arginine methyltransferase 1 is associated with early hepatocarcinogenesis

Aberrant expression of regulators for epigenetics is involved in tumorigenesis. There is an urgent need to identify and characterize regulators concerned with epigenetics in the early stages of hepatocarcinogenesis. In the present study, we found that the expression of coactivator-associated arginine methyltransferase 1 (CARM1), a histone methyltransferase that functions as a cofactor for nuclear hormone receptors and several transcription factors, was elevated in adenomas and aberrant in carcinomas during hepatocellular carcinogenesis. In addition to RNA expression, immunohistochemical staining of liver sections revealed that CARM1 was highly expressed in the nucleus of tumor marker glutathione S-transferase placental form (GST-P)-positive foci. Neoplastic transformation of GST-P-positive foci guides the formation of hepatocellular carcinomas. CARM1 expression was not elevated in GST-P-negative regions. Furthermore, a luciferase reporter analysis revealed that CARM1 activated the Gst-p promoter in H4IIE, a hepatocellular carcinoma cell line. This activation was mediated by the enhancer element responsible for the carcinogenic-specific expression of Gst-p and nuclear factor E2-related factor2. Knockdown of Carm1 by shRNA in H4IIE cells inhibited cell proliferation. These findings suggest that aberrantly expressed CARM1 in tumor marker-positive cells promotes tumorigenesis in the early stages of hepatocarcinogenesis.

DNA Homologous Recombination Factor SFR1 Physically and Functionally Interacts with Estrogen Receptor Alpha

Estrogen receptor alpha (ERα), a ligand-dependent transcription factor, mediates the expression of its target genes by interacting with corepressors and coactivators. Since the first cloning of SRC1, more than 280 nuclear receptor cofactors have been identified, which orchestrate target gene transcription. Aberrant activity of ER or its accessory proteins results in a number of diseases including breast cancer. Here we identified SFR1, a protein involved in DNA homologous recombination, as a novel binding partner of ERα. Initially isolated in a yeast two-hybrid screen, the interaction of SFR1 and ERα was confirmed in vivo by immunoprecipitation and mammalian one-hybrid assays. SFR1 co-localized with ERα in the nucleus, potentiated ER’s ligand-dependent and ligand-independent transcriptional activity, and occupied the ER binding sites of its target gene promoters. Knockdown of SFR1 diminished ER’s transcriptional activity. Manipulating SFR1 expression by knockdown and overexpression revealed a role for SFR1 in ER-dependent and -independent cancer cell proliferation. SFR1 differs from SRC1 by the lack of an intrinsic activation function. Taken together, we propose that SFR1 is a novel transcriptional modulator for ERα and a potential target in breast cancer therapy.

Spatial Profiling of Nuclear Receptor Transcription Patterns over the Course ofDrosophilaDevelopment

Previous work has shown that many of the 18 family members of Drosophila nuclear receptor transcription factors function in a temporal hierarchy to coordinate developmental progression and growth with the rate limiting process of metabolism. To gain further insight into these interactions and processes, we have undertaken a whole-family analysis of nuclear receptor mRNA spatial expression patterns over the entire process of embryogenesis, as well as the 3rd instar wandering larva stage, by using high-resolution fluorescence in situ hybridization. Overall, the patterns of expression are remarkably consistent with previously mapped spatial activity profiles documented during the same time points, with similar hot spots and temporal profiles in endocrine and metabolically important tissues. Among the more remarkable of the findings is that the majority of mRNA expression patterns observed show striking subcellular distributions, indicating potentially critical roles in the control of protein synthesis and subsequent subcellular distributions. These patterns will serve as a useful reference for future studies on the tissue-specific roles and interactions of nuclear receptor proteins, partners, cofactors and ligands.

Adipogenic effects of piperlonguminine in 3T3-L1 cells and plasma concentrations of several amide constituents from Piper chaba extracts after treatment of mice

In our previous study, piperlonguminine from the fruit of Piper chaba was reported to promote adipogenesis in 3T3-L1 cells like the peroxisome proliferator-activated receptor-γ (PPARγ) agonist, troglitazone. In the present study, the mode of action of piperlonguminine in cells was examined. Piperlonguminine increased mRNA levels of adiponectin, glucose transporter 4, and fatty acid-binding protein (aP2). It also increased mRNA levels of PPARγ2 but, unlike troglitazone, piperlonguminine did not activate PPARγ directly in a nuclear receptor cofactor assay. Analyses of plasma from mice treated with piperlonguminine, piperine, and retrofractamide A, and an extract of the fruit, showed that concentrations of piperlonguminine were higher than those of piperine and retrofractamide A, and that the "area-under-the-curve" of piperine increased following in vivo administration of the extract.

Interaction of silencing mediator for retinoid and thyroid receptors with steroid and xenobiotic receptor on multidrug resistance 1 promoter

AimsThe steroid and xenobiotic receptor (SXR) regulates the transcription of its target genes by interacting with various nuclear receptor cofactors. We have previously shown that silencing mediator for retinoid and thyroid receptors (SMRT) interacts with SXR even in the presence of rifampicin on cytochrome P450 monooxygenase 3A4 (CYP3A4) promoter in HepG2 cells. To examine the specificity of such interaction, the involvement of SMRT on SXR-mediated transcription through multidrug resistance (MDR) 1 gene promoter was examined using LS174T intestine-derived clonal cells. Main methodsTransient transfection-based reporter gene assay was carried out to examine the effect of SMRT or nuclear receptor corepressor (NCoR) on SXR-mediated transcription in LS174T cells. Semi-quantitative RT-PCR was performed to confirm the expression of MDR1 mRNA in LS174T cells. To examine the interaction of SMRT with SXR, we carried out mammalian one-hybrid assay in CV-1 cells and immunoprecipitation study in HEK-293 cells. Key findingsSMRT, but not NCoR suppressed rifampicin-induced SXR-mediated transcription. The SXR-mediated MDR1 mRNA expression was augmented in the presence of rifampicin, whereas it suppressed the expression following the overexpression of SMRT. In mammalian one-hybrid assay, only SMRT but not NCoR interacted with SXR on MDR1 promoter in the presence of rifampicin. In immunoprecipitation study, SMRT bound to SXR regardless of the presence or absence of rifampicin. SignificanceSMRT may be recruited in the SXR-cofactor complex even in the presence of ligand. SMRT may be involved not only in SXR-mediated suppression without ligand, but also in ligand-activated transcription to suppress the overactivation of transcription.