TBL1XR1 Mutations Drive Extranodal Lymphoma by Inducing a Pro-tumorigenic Memory Fate.

The most aggressive B cell lymphomas frequently manifest extranodal distribution and carry somatic mutations in the poorly characterized gene TBL1XR1. Here, we show that TBL1XR1 mutations skew the humoral immune response toward generating abnormal immature memory B cells (MB), while impairing plasma cell differentiation. At the molecular level, TBL1XR1 mutants co-opt SMRT/HDAC3 repressor complexes toward binding the MB cell transcription factor (TF) BACH2 at the expense of the germinal center (GC) TF BCL6, leading to pre-memory transcriptional reprogramming and cell-fate bias. Upon antigen recall, TBL1XR1 mutant MB cells fail to differentiate into plasma cells and instead preferentially reenter new GC reactions, providing evidence for a cyclic reentry lymphomagenesis mechanism. Ultimately, TBL1XR1 alterations lead to a striking extranodal immunoblastic lymphoma phenotype that mimics the human disease. Both human and murine lymphomas feature expanded MB-like cell populations, consistent with a MB-cell origin and delineating an unforeseen pathway for malignant transformation of the immune system.

Nuclear corepressors NCOR1/NCOR2 regulate B cell development, maintain genomic integrity and prevent transformation.

The nuclear corepressors NCOR1 and NCOR2 interact with transcription factors involved in B cell development and potentially link these factors to alterations in chromatin structure and gene expression. Herein, we demonstrate that Ncor1/2 deletion limits B cell differentiation via impaired recombination, attenuates pre-BCR signaling and enhances STAT5-dependent transcription. Furthermore, NCOR1/2-deficient B cells exhibited derepression of EZH2-repressed gene modules, including the p53 pathway. These alterations resulted in aberrant Rag1 and Rag2 expression and accessibility. Whole-genome sequencing of Ncor1/2 DKO B cells identified increased number of structural variants with cryptic recombination signal sequences. Finally, deletion of Ncor1 alleles in mice facilitated leukemic transformation, whereas human leukemias with less NCOR1 correlated with worse survival. NCOR1/2 mutations in human leukemia correlated with increased RAG expression and number of structural variants. These studies illuminate how the corepressors NCOR1/2 regulate B cell differentiation and provide insights into how NCOR1/2 mutations may promote B cell transformation.

The corepressors GPS2 and SMRT control enhancer and silencer remodeling via eRNA transcription during inflammatory activation of macrophages.

While the role of transcription factors and coactivators in controlling enhancer activity and chromatin structure linked to gene expression is well established, the involvement of corepressors is not. Using inflammatory macrophage activation as a model, we investigate here a corepressor complex containing GPS2 and SMRT both genome-wide and at the Ccl2 locus, encoding the chemokine CCL2 (MCP-1). We report that corepressors co-occupy candidate enhancers along with the coactivators CBP (H3K27 acetylase) and MED1 (mediator) but act antagonistically by repressing eRNA transcription-coupled H3K27 acetylation. Genome editing, transcriptional interference, and cistrome analysis reveals that apparently related enhancer and silencer elements control Ccl2 transcription in opposite ways. 4C-seq indicates that corepressor depletion or inflammatory signaling functions mechanistically similarly to trigger enhancer activation. In ob/ob mice, adipose tissue macrophage-selective depletion of the Ccl2 enhancer-transcribed eRNA reduces metaflammation. Thus, the identified corepressor-eRNA-chemokine pathway operates in vivo and suggests therapeutic opportunities by targeting eRNAs in immuno-metabolic diseases.

HDAC3 ensures stepwise epidermal stratification via NCoR/SMRT-reliant mechanisms independent of its histone deacetylase activity.

Chromatin modifiers play critical roles in epidermal development, but the functions of histone deacetylases in this context are poorly understood. The class I HDAC, HDAC3, is of particular interest because it plays divergent roles in different tissues by partnering with tissue-specific transcription factors. We found that HDAC3 is expressed broadly in embryonic epidermis and is required for its orderly stepwise stratification. HDAC3 protein stability in vivo relies on NCoR and SMRT, which function redundantly in epidermal development. However, point mutations in the NCoR and SMRT deacetylase-activating domains, which are required for HDAC3's enzymatic function, permit normal stratification, indicating that HDAC3's roles in this context are largely independent of its histone deacetylase activity. HDAC3-bound sites are significantly enriched for predicted binding motifs for critical epidermal transcription factors including AP1, GRHL, and KLF family members. Our results suggest that among these, HDAC3 operates in conjunction with KLF4 to repress inappropriate expression of Tgm1, Krt16, and Aqp3 In parallel, HDAC3 suppresses expression of inflammatory cytokines through a Rela-dependent mechanism. These data identify HDAC3 as a hub coordinating multiple aspects of epidermal barrier acquisition.

Class IIa HDAC4 and HDAC7 cooperatively regulate gene transcription in Th17 cell differentiation.

Class II histone deacetylases (HDACs) are important in regulation of gene transcription during T cell development. However, our understanding of their cell-specific functions is limited. In this study, we reveal that class IIa Hdac4 and Hdac7 (Hdac4/7) are selectively induced in transcription, guiding the lineage-specific differentiation of mouse T-helper 17 (Th17) cells from naive CD4+ T cells. Importantly, Hdac4/7 are functionally dispensable in other Th subtypes. Mechanistically, Hdac4 interacts with the transcription factor (TF) JunB, facilitating the transcriptional activation of Th17 signature genes such as Il17a/f. Conversely, Hdac7 collaborates with the TF Aiolos and Smrt/Ncor1-Hdac3 corepressors to repress transcription of Th17 negative regulators, including Il2, in Th17 cell differentiation. Inhibiting Hdac4/7 through pharmacological or genetic methods effectively mitigates Th17 cell-mediated intestinal inflammation in a colitis mouse model. Our study uncovers molecular mechanisms where HDAC4 and HDAC7 function distinctively yet cooperatively in regulating ordered gene transcription during Th17 cell differentiation. These findings suggest a potential therapeutic strategy of targeting HDAC4/7 for treating Th17-related inflammatory diseases, such as ulcerative colitis.

Targeting nuclear receptor corepressors for reversible male contraception.

Despite numerous female contraceptive options, nearly half of all pregnancies are unintended. Family planning choices for men are currently limited to unreliable condoms and invasive vasectomies with questionable reversibility. Here, we report the development of an oral contraceptive approach based on transcriptional disruption of cyclical gene expression patterns during spermatogenesis. Spermatogenesis involves a continuous series of self-renewal and differentiation programs of spermatogonial stem cells (SSCs) that is regulated by retinoic acid (RA)-dependent activation of receptors (RARs), which control target gene expression through association with corepressor proteins. We have found that the interaction between RAR and the corepressor silencing mediator of retinoid and thyroid hormone receptors (SMRT) is essential for spermatogenesis. In a genetically engineered mouse model that negates SMRT-RAR binding (SMRTmRID mice), the synchronized, cyclic expression of RAR-dependent genes along the seminiferous tubules is disrupted. Notably, the presence of an RA-resistant SSC population that survives RAR de-repression suggests that the infertility attributed to the loss of SMRT-mediated repression is reversible. Supporting this notion, we show that inhibiting the action of the SMRT complex with chronic, low-dose oral administration of a histone deacetylase inhibitor reversibly blocks spermatogenesis and fertility without affecting libido. This demonstration validates pharmacologic targeting of the SMRT repressor complex for non-hormonal male contraception.

Cellular Differentiation of Human Monocytes Is Regulated by Time-Dependent Interleukin-4 Signaling and the Transcriptional Regulator NCOR2.

Human in vitro generated monocyte-derived dendritic cells (moDCs) and macrophages are used clinically, e.g., to induce immunity against cancer. However, their physiological counterparts, ontogeny, transcriptional regulation, and heterogeneity remains largely unknown, hampering their clinical use. High-dimensional techniques were used to elucidate transcriptional, phenotypic, and functional differences between human in vivo and in vitro generated mononuclear phagocytes to facilitate their full potential in the clinic. We demonstrate that monocytes differentiated by macrophage colony-stimulating factor (M-CSF) or granulocyte macrophage colony-stimulating factor (GM-CSF) resembled in vivo inflammatory macrophages, while moDCs resembled in vivo inflammatory DCs. Moreover, differentiated monocytes presented with profound transcriptomic, phenotypic, and functional differences. Monocytes integrated GM-CSF and IL-4 stimulation combinatorically and temporally, resulting in a mode- and time-dependent differentiation relying on NCOR2. Finally, moDCs are phenotypically heterogeneous and therefore necessitate the use of high-dimensional phenotyping to open new possibilities for better clinical tailoring of these cellular therapies.

Dichotomous engagement of HDAC3 activity governs inflammatory responses.

The histone deacetylases (HDACs) are a superfamily of chromatin-modifying enzymes that silence transcription through the modification of histones. Among them, HDAC3 is unique in that interaction with nuclear receptor corepressors 1 and 2 (NCoR1/2) is required to engage its catalytic activity1-3. However, global loss of HDAC3 also results in the repression of transcription, the mechanism of which is currently unclear4-8. Here we report that, during the activation of macrophages by lipopolysaccharides, HDAC3 is recruited to activating transcription factor 2 (ATF2)-bound sites without NCoR1/2 and activates the expression of inflammatory genes through a non-canonical mechanism. By contrast, the deacetylase activity of HDAC3 is selectively engaged at ATF3-bound sites that suppress Toll-like receptor signalling. Loss of HDAC3 in macrophages safeguards mice from lethal exposure to lipopolysaccharides, but this protection is not conferred upon genetic or pharmacological abolition of the catalytic activity of HDAC3. Our findings show that HDAC3 is a dichotomous transcriptional activator and repressor, with a non-canonical deacetylase-independent function that is vital for the innate immune system.

DUB3 Promotes BET Inhibitor Resistance and Cancer Progression by Deubiquitinating BRD4.

The bromodomain and extra-terminal domain (BET) protein BRD4 is emerging as a promising anticancer therapeutic target. However, resistance to BET inhibitors often occurs, and it has been linked to aberrant degradation of BRD4 protein in cancer. Here, we demonstrate that the deubiquitinase DUB3 binds to BRD4 and promotes its deubiquitination and stabilization. Expression of DUB3 is transcriptionally repressed by the NCOR2-HDAC10 complex. The NCOR2 gene is frequently deleted in castration-resistant prostate cancer patient specimens, and loss of NCOR2 induces elevation of DUB3 and BRD4 proteins in cancer cells. DUB3-proficient prostate cancer cells are resistant to the BET inhibitor JQ1 in vitro and in mice, but this effect is diminished by DUB3 inhibitory agents such as CDK4/6 inhibitor in a RB-independent manner. Our findings identify a previously unrecognized mechanism causing BRD4 upregulation and drug resistance, suggesting that DUB3 is a viable therapeutic target to overcome BET inhibitor resistance in cancer.

Toxicity of overexpressed MeCP2 is independent of HDAC3 activity.

Duplication of the X-linked MECP2 gene causes a severe neurological syndrome whose molecular basis is poorly understood. To determine the contribution of known functional domains to overexpression toxicity, we engineered a mouse model that expresses wild-type or mutated MeCP2 from the Mapt (Tau) locus in addition to the endogenous protein. Animals that expressed approximately four times the wild-type level of MeCP2 failed to survive to weaning. Strikingly, a single amino acid substitution that prevents MeCP2 from binding to the TBL1X(R1) subunit of nuclear receptor corepressor 1/2 (NCoR1/2) complexes, when expressed at equivalent high levels, was phenotypically indistinguishable from wild type, suggesting that excessive corepressor recruitment underlies toxicity. In contrast, mutations affecting the DNA-binding domain were toxic when overexpressed. As the NCoR1/2 corepressors are thought to act through histone deacetylation by histone deacetylase 3 (HDAC3), we asked whether mutations in NCoR1 and NCoR2 that drastically reduced their ability to activate this enzyme would relieve the MeCP2 overexpression phenotype. Surprisingly, severity was unaffected, indicating that the catalytic activity of HDAC3 is not the mediator of toxicity. Our findings shed light on the molecular mechanisms underlying MECP2 duplication syndrome and call for a re-evaluation of the precise biological role played by corepressor recruitment.

Glucocorticoid Receptor:MegaTrans Switching Mediates the Repression of an ERα-Regulated Transcriptional Program.

The molecular mechanisms underlying the opposing functions of glucocorticoid receptors (GRs) and estrogen receptor α (ERα) in breast cancer development remain poorly understood. Here we report that, in breast cancer cells, liganded GR represses a large ERα-activated transcriptional program by binding, in trans, to ERα-occupied enhancers. This abolishes effective activation of these enhancers and their cognate target genes, and it leads to the inhibition of ERα-dependent binding of components of the MegaTrans complex. Consistent with the effects of SUMOylation on other classes of nuclear receptors, dexamethasone (Dex)-induced trans-repression of the estrogen E2 program appears to depend on GR SUMOylation, which leads to stable trans-recruitment of the GR-N-CoR/SMRT-HDAC3 corepressor complex on these enhancers. Together, these results uncover a mechanism by which competitive recruitment of DNA-binding nuclear receptors/transcription factors in trans to hot spot enhancers serves as an effective biological strategy for trans-repression, with clear implications for breast cancer and other diseases.

Balanced control of thermogenesis by nuclear receptor corepressors in brown adipose tissue.

Brown adipose tissue (BAT) is a key thermogenic organ whose expression of uncoupling protein 1 (UCP1) and ability to maintain body temperature in response to acute cold exposure require histone deacetylase 3 (HDAC3). HDAC3 exists in tight association with nuclear receptor corepressors (NCoRs) NCoR1 and NCoR2 (also known as silencing mediator of retinoid and thyroid receptors [SMRT]), but the functions of NCoR1/2 in BAT have not been established. Here we report that as expected, genetic loss of NCoR1/2 in BAT (NCoR1/2 BAT-dKO) leads to loss of HDAC3 activity. In addition, HDAC3 is no longer bound at its physiological genomic sites in the absence of NCoR1/2, leading to a shared deregulation of BAT lipid metabolism between NCoR1/2 BAT-dKO and HDAC3 BAT-KO mice. Despite these commonalities, loss of NCoR1/2 in BAT does not phenocopy the cold sensitivity observed in HDAC3 BAT-KO, nor does loss of either corepressor alone. Instead, BAT lacking NCoR1/2 is inflamed, particularly with respect to the interleukin-17 axis that increases thermogenic capacity by enhancing innervation. Integration of BAT RNA sequencing and chromatin immunoprecipitation sequencing data revealed that NCoR1/2 directly regulate Mmp9, which integrates extracellular matrix remodeling and inflammation. These findings reveal pleiotropic functions of the NCoR/HDAC3 corepressor complex in BAT, such that HDAC3-independent suppression of BAT inflammation counterbalances stimulation of HDAC3 activity in the control of thermogenesis.

TGF-ß and retinoic acid induce the microRNA miR-10a, which targets Bcl-6 and constrains the plasticity of helper T cells.

Distinct CD4(+) T cell subsets are critical for host defense and immunoregulation. Although these subsets can act as terminally differentiated lineages, they have been increasingly noted to demonstrated plasticity. MicroRNAs are factors that control T cell stability and plasticity. Here we report that naturally occurring regulatory T cells (T(reg) cells) had high expression of the microRNA miR-10a and that miR-10a was induced by retinoic acid and transforming growth factor-ß (TGF-ß) in inducible T(reg) cells. By simultaneously targeting the transcriptional repressor Bcl-6 and the corepressor Ncor2, miR-10a attenuated the phenotypic conversion of inducible T(reg) cells into follicular helper T cells. We also found that miR-10a limited differentiation into the T(H)17 subset of helper T cells and therefore represents a factor that can fine-tune the plasticity and fate of helper T cells.

Design and synthesis of peptides as stabilizers of histone deacetylase 4.

Histone deacetylase 4 (HDAC4) contributes to gene repression by complex formation with HDAC3 and the corepressor silencing mediator for retinoid or thyroid hormone receptors (SMRT). We hypothesized that peptides derived from the class IIa specific binding site of SMRT would stabilize a specific conformation of its target protein and modulate its activity. Based on the SMRT-motif 1 (SM1) involved in the interaction of SMRT with HDAC4, we systematically developed cyclic peptides that exhibit Ki values that are 9 to 56 times lower than that of the linear SMRT peptide. The peptide macrocycles stabilize the wildtype of the catalytic domain of HDAC4 (cHDAC4) considerably better than its thermally more stable 'gain-of-function' (GOF) variant, cHDAC4-H976Y. Molecular docking and mutagenesis studies indicated that the cyclic peptides bind in a similar but not identical manner as the linear SMRT peptide to a discontinuous binding site. Ion mobility mass spectrometry showed no major changes in the protein fold upon peptide binding. Consistent with these results, preliminary hydrogen-deuterium exchange mass spectrometry measurements indicated only minor conformational changes. Taken together, the cyclic SMRT peptides most likely stabilize the apo form of cHDAC4.

Keratin-positive giant cell-rich tumors of soft tissue with HMGA2::NCOR2 fusions.

BACKGROUND: Giant cell tumor of soft tissue (GCT-ST) is a rare soft tissue neoplasm that is morphologically similar to but genetically distinct from giant cell tumor of bone. A novel keratin-positive GCT-ST (KPGCT-ST) harboring HMGA2::NCOR2 fusions was recently discovered. Fewer than 30 cases have been described; herein is reported an additional seven. METHODS: Cases diagnosed as GCT-ST were retrieved from institutional archives and consultation files. The histopathologic characteristics were assessed, and the electronic medical record was reviewed. RESULTS: Seven tumors were identified in six women and one man with a median age of 23 years. All patients underwent excision; no recurrences or metastases were noted during a median follow-up period of 7 months. Histopathologically, the tumors were characterized by a multinodular proliferation of keratin-positive mononuclear cells with evenly admixed osteoclast-like giant cells and absent neoplastic bone. A fibrous capsule with lymphoid cuffing was frequently seen. Foamy macrophages, inflammation, hemorrhage, and hemosiderin were variably present. The HMGA2::NCOR2 fusion was detected in all cases. CONCLUSIONS: Our findings support previously reported hypotheses that KPGCT-ST is a spectrum of the same entity as the recently described xanthogranulomatous epithelial tumor. Although follow-up data are limited, to date, KPGCT-ST appears to follow an indolent course.

Xanthogranulomatous epithelial tumors and keratin-positive giant cell-rich soft tissue tumors: two aspects of a single entity with frequent HMGA2-NCOR2 fusions.

Xanthogranulomatous epithelial tumor (XGET) and keratin-positive giant cell-rich soft tissue tumor with HMGA2-NCOR2 fusion (KPGCT) are two recently described neoplasms with both distinct and overlapping clinical and histopathologic features. We hypothesized that XGET and KPGCT may be related and represent a histologic spectrum of a single entity. To test this, we sought to characterize the clinical, radiographic, immunohistochemical, ultrastructural and molecular features of additional tumors with features of XGET and/or KPGCT, which we refer to descriptively as keratin-positive xanthogranulomatous/giant cell-rich tumors (KPXG/GCT). The archives were searched for potential cases of KPXG/GCT. Clinical and imaging features were noted. Slides were assessed for histologic and immunohistochemical findings. Ultrastructural and next generation RNA sequencing-based analysis were also performed. Nine cases were identified arising in seven women and two men [median age of 33 years (range: 12-87)]. Median tumor size was 4 cm (range: 2.4-14.0 cm) and tumors presented in the thigh (2), buttock (1), forearm (2), groin (1), cranial fossa (1), ilium (1), and tibia (1). Morphologically, tumors were most frequently characterized by a fibrous capsule, with associated lymphoid reaction, enclosing a polymorphous proliferation of histiocytes, giant cells (Touton and osteoclast-types), mixed inflammatory infiltrate, hemorrhage and hemosiderin deposition, which imparted a variably xanthogranulomatous to giant cell tumor-like appearance. One case clearly showed mononuclear cells with eosinophilic cytoplasm characteristic of XGET. All cases expressed keratin and 7 of 9 were found to harbor HMGA2-NCOR2 fusions including cases with xanthogranulomatous appearance. One patient developed local recurrence and multifocal pulmonary lesions, which were radiographically suspicious for metastases. Shared clinical, histologic and immunohistochemical features, and the shared presence of HMGA2-NCOR2 fusions supports interpretation of KPXG/GCT as a single entity which includes XGET and KPGCT. Given limited clinical follow-up to date and rare cases with apparently aggressive findings, we provisionally regard these tumors as having uncertain biologic potential.

NCOR2 is a novel candidate gene for migraine-epilepsy phenotype.

HYPOTHESIS: To identify genetic factors predisposing to migraine-epilepsy phenotype utilizing a multi-generational family with known linkage to chr12q24.2-q24.3. METHODS: We used single nucleotide polymorphism (SNP) genotyping and next-generation sequencing technologies to perform linkage, haplotype, and variant analyses in an extended Finnish migraine-epilepsy family (n = 120). In addition, we used a large genome-wide association study (GWAS) dataset of migraine and two biobank studies, UK Biobank and FinnGen, to test whether variants within the susceptibility region associate with migraine or epilepsy related phenotypes in a population setting. RESULTS: The family showed the highest evidence of linkage (LOD 3.42) between rs7966411 and epilepsy. The haplotype shared among 12 out of 13 epilepsy patients in the family covers almost the entire NCOR2 and co-localizes with one of the risk loci of the recent GWAS on migraine. The haplotype harbors nine low-frequency variants with potential regulatory functions. Three of them, in addition to two common variants, show nominal associations with neurological disorders in either UK Biobank or FinnGen. CONCLUSION: We provide several independent lines of evidence supporting association between migraine-epilepsy phenotype and NCOR2. Our study suggests that NCOR2 may have a role in both migraine and epilepsy and thus would provide evidence for shared pathophysiology underlying these two diseases.

ChREBP downregulates SNAT2 amino acid transporter expression through interactions with SMRT in response to a high-carbohydrate diet.

Carbohydrate responsive element-binding protein (ChREBP) has been identified as a primary transcription factor that maintains energy homeostasis through transcriptional regulation of glycolytic, lipogenic, and gluconeogenic enzymes in response to a high-carbohydrate diet. Amino acids are important substrates for gluconeogenesis, but nevertheless, knowledge is lacking about whether this transcription factor regulates genes involved in the transport or use of these metabolites. Here, we demonstrate that ChREBP represses the expression of the amino acid transporter sodium-coupled neutral amino acid transporter 2 (SNAT2) in response to a high-sucrose diet in rats by binding to a carbohydrate response element (ChoRE) site located -160 bp upstream of the transcriptional start site in the SNAT2 promoter region. Additionally, immunoprecipitation assays revealed that ChREBP and silencing mediator of retinoic acid and thyroid hormone receptor (SMRT) interact with each other, as part of the complex that repress SNAT2 expression. The interaction between these proteins was confirmed by an in vivo chromatin immunoprecipitation assay. These findings suggest that glucogenic amino acid uptake by the liver is controlled by ChREBP through the repression of SNAT2 expression in rats consuming a high-carbohydrate diet.NEW & NOTEWORTHY This study highlights the key role of carbohydrate responsive element-binding protein (ChREBP) in the fine-tuned regulation between glucose and amino acid metabolism in the liver via regulation of the amino acid transporter sodium-coupled neutral amino acid transporter 2 (SNAT2) expression after the consumption of a high-carbohydrate diet. ChREBP binds to a carbohydrate response element (ChoRE) site in the SNAT2 promoter region and recruits silencing mediator of retinoic acid and thyroid hormone receptor (SMRT) corepressor to reduce SNAT2 transcription. This study revealed that ChREBP prevents the uptake of glucogenic amino acids upon the consumption of a high-carbohydrate diet.

Recurrent novel HMGA2-NCOR2 fusions characterize a subset of keratin-positive giant cell-rich soft tissue tumors.

Giant cell tumors of soft tissue (GCT-ST) are rare low-grade neoplasms that were at one time thought to represent the soft tissue counterparts of GCT of bone (GCT-B) but are now known to lack the H3F3 mutations characteristic of osseous GCT. We present six distinctive giant cell-rich soft tissue neoplasms that expressed keratins and carried a recurrent HMGA2-NCOR2 gene fusion. Patients were five females and one male aged 14-60 years (median, 29). All presented with superficial (subcutaneous) masses that were removed by conservative marginal (3) or wide (2) local excision. The tumors originated in the upper extremity (2), lower extremity (2), head/neck (1), and trunk (1). Five patients with follow-up (median, 21 months; range, 14-168) remained disease-free. Grossly, all tumors were well-demarcated but not encapsulated with variable lobulation. Histologically, they were composed of bland plump epithelioid or ovoid to spindled mononuclear cells admixed with evenly distributed multinucleated osteoclast-type giant cells. Foci of stromal hemorrhage and hemosiderin were seen in all cases. The mitotic activity ranged from 2 to 14/10 high power fields (median: 10). Foci of necrosis and vascular invasion were seen in one case each. The mononuclear cells were immunoreactive with the AE1/AE3 keratin cocktail and less frequently/less diffusely for K7 and K19 but lacked expression of other lineage-associated markers. RNA-based next-generation sequencing revealed an HMGA2-NCOR2 fusion in all tumors. None of the keratin-negative conventional GCT-ST showed the HMGA2-NCOR2 fusion (0/7). Metaplastic bone (4/9) and SATB2 expression (3/4) were frequent in keratin-negative conventional GCT-ST but were lacking in keratin-positive HMGA2-NCOR2 fusion-positive tumors. The distinctive immunophenotype and genotype of these tumors strongly suggest that they represent a discrete entity, differing from conventional GCT-ST and other osteoclast-rich morphologic mimics. Their natural history appears favorable, although a study of additional cases and longer follow-up are warranted.

PPARα and NCOR/SMRT corepressor network in liver metabolic regulation.

Peroxisome proliferator-activated receptor alpha (PPARα, NR1C1) belongs to a large family of ligand-dependent nuclear receptors (NRs). It is one of the best studied NRs which controls the lipid metabolism (mainly fatty acid oxidation) and inflammation, and has been a promising target for treating metabolic disorders such as fatty liver and cardiometabolic diseases. The function of PPARα relies on its interaction with various coregulators upon different stimulating contexts, and, thereby, activates or represses its transcription targets in a gene-selective manner. Understanding the transcription factor and coregulator network underlying the PPARα regulation is prerequisite to decipher its gene- and context-selectivity for designing better therapeutic ligands. In this review, we will summarize current knowledge of PPARα coregulator network, with major focus on a relatively well-studied corepressor complex containing core subunits of nuclear receptor corepressor (NCOR or NCOR1), silencing mediator of retinoic acid and thyroid hormone receptor (SMRT or NCOR2), G-protein suppressor 2 (GPS2), transducin ß-like protein 1 (TBL1 or TBL1X), TBL-related 1 (TBLR1 or TBL1XR1), and the catalytic core of histone deacetylase 3 (HDAC3). We will mainly review the molecular events of the complex and sub-complexes in controlling the liver metabolism. We will also discuss the potential perturbation of the subunit expression in human livers during liver metabolic disorder progression which potentially defines the patient disease susceptibility and drug responses.