Signal-dependent Transcription Factors Research Articles

Interplay of Transcriptional Factors In Beta Cells Development and Maturation

Diabetes is a group of metabolic disorders resulting from defects in insulin secretion, insulin action, or both. It is characterized by high blood sugar levels over a prolonged period of time with disturbances of carbohydrate, protein, and fat metabolism. It is a global disorder affecting about half a billion or 536.6 million people worldwide, which is said to rise to 783.2 million by 2045. To maintain normoglycemia, pancreatic β-cells release insulin in proportion to the amounts of nutrients in the blood. Through a process of postnatal development, β-cells learn to connect insulin release to food cues. The insulin secretory response in mature β-cells adjusts to alterations in nutritional status. The interaction between transcriptional programs specific to each cell type and external stimuli is necessary for both β-cell maturation and functional adaptation. In this review, we examine the growing data that suggests lineage-determining and signal-dependent transcription factors (LDTFs and SDTFs, respectively) work together to regulate β-cell activity during development and homeostasis. In-depth knowledge of β-cell SDTFs and their corresponding signals would clarify the processes involved in β-cell maturation and functional adaptation, directly affecting diabetes treatments and the production of mature β-cells from stem cells.

Lhx3/4 initiates a cardiopharyngeal-specific transcriptional program in response to widespread FGF signaling.

Individual signaling pathways, such as fibroblast growth factors (FGFs), can regulate a plethora of inductive events. According to current paradigms, signal-dependent transcription factors (TFs), such as FGF/MapK-activated Ets family factors, partner with lineage-determining factors to achieve regulatory specificity. However, many aspects of this model have not been rigorously investigated. One key question relates to whether lineage-determining factors dictate lineage-specific responses to inductive signals or facilitate these responses in collaboration with other inputs. We utilize the chordate model Ciona robusta to investigate mechanisms generating lineage-specific induction. Previous studies in C. robusta have shown that cardiopharyngeal progenitor cells are specified through the combined activity of FGF-activated Ets1/2.b and an inferred ATTA-binding transcriptional cofactor. Here, we show that the homeobox TF Lhx3/4 serves as the lineage-determining TF that dictates cardiopharyngeal-specific transcription in response to pleiotropic FGF signaling. Targeted knockdown of Lhx3/4 leads to loss of cardiopharyngeal gene expression. Strikingly, ectopic expression of Lhx3/4 in a neuroectodermal lineage subject to FGF-dependent specification leads to ectopic cardiopharyngeal gene expression in this lineage. Furthermore, ectopic Lhx3/4 expression disrupts neural plate morphogenesis, generating aberrant cell behaviors associated with execution of incompatible morphogenetic programs. Based on these findings, we propose that combinatorial regulation by signal-dependent and lineage-determinant factors represents a generalizable, previously uncategorized regulatory subcircuit we term "cofactor-dependent induction." Integration of this subcircuit into theoretical models will facilitate accurate predictions regarding the impact of gene regulatory network rewiring on evolutionary diversification and disease ontogeny.

SinCMat: A single-cell-based method for predicting functional maturation transcription factors

A major goal of regenerative medicine is to generate tissue-specific mature and functional cells. However, current cell engineering protocols are still unable to systematically produce fully mature functional cells. While existing computational approaches aim at predicting transcription factors (TFs) for cell differentiation/reprogramming, no method currently exists that specifically considers functional cell maturation processes. To address this challenge, here, we develop SinCMat, a single-cell RNA sequencing (RNA-seq)-based computational method for predicting cell maturation TFs. Based on a model of cell maturation, SinCMat identifies pairs of identity TFs and signal-dependent TFs that co-target genes driving functional maturation. A large-scale application of SinCMat to the Mouse Cell Atlas and Tabula Sapiens accurately recapitulates known maturation TFs and predicts novel candidates. We expect SinCMat to be an important resource, complementary to preexisting computational methods, for studies aiming at producing functionally mature cells.

Genomic Determinants of Hematopoietic Progenitor Sensitivity to Innate Immune Signaling

Innate immune processes impact diverse hematopoietic stem and progenitor cell (HSPC) functions, yet how innate immune signaling networks are sensed by HSPC genomes and how HSPC genomic activity alters cell responsiveness to innate immune regulators are not fully understood. We demonstrated that E14.5 primary (-77 -/-) and immortalized (hi-77 -/-) GATA2-deficient fetal progenitors from Gata2 -77 enhancer deletion mice upregulate Interferon-gamma (IFNγ) and Toll-like receptor (TLR) signaling components (Johnson et al. JEM 2020) and are hypersensitive to IFNγ and TLR signaling (Tran et al. iScience 2023). Combinatorial signaling involving both pathways regulates genes that are not regulated by individual pathways and amplifies responses beyond that induced by single pathways. Innate immune-activated genes harbor motifs for signal-dependent transcription factors, including the ETS factor PU.1, and GATA2 deficiency elevates PU.1 activity to upregulate B-lineage and myeloid genes (Jung et al. JCI 2023). We hypothesize that PU.1 links innate immune signaling networks and HSPC genome control. In new multi-omic studies, we asked if PU.1 is required to sense exclusively IFNγ or TLR signaling, both pathways independently or combinatorially, or is not essential. We used hi-77 -/- progenitors lacking a PU.1 enhancer ( Spi1URE-/-) with ~2-fold lower PU.1 vs. control hi-77 -/- progenitors. RNA-seq was conducted with hi-77 -/- and hi-77 -/-; Spi1URE-/- progenitors, with or without IFNγ, TLR1/2 agonist Pam 3CSK 4, or both agents for 4 h. hi-77 -/-; Spi1URE-/- progenitors lost the responsiveness of 27 TLR-activated genes and retained the responsiveness of 6 TLR-activated genes. 80% of IFNγ-activated genes (115 of 144) retained IFNγ-responsiveness when PU.1 was reduced. In hi-77 -/-; Spi1URE-/- progenitors, 68.2% (148 of 217 genes) retained their responsiveness to combinatorial signaling. These studies revealed the disproportionate importance of PU.1 for TLR- vs. IFNγ-mediated transcriptional control and a PU.1 requirement for combinatorial signaling at the majority of loci. Elevated IFNγ and TLR1/2 signaling in GATA2-deficient fetal progenitors is associated with increased monocytic and reduced granulocytic progenitors (Johnson et al. JEM 2020; Blood Adv 2022). Ablation of Irf8, encoding an IFNγ pathway component, partially normalizes the granulocytic progenitor deficit (Johnson et al. Blood Adv. 2022). Since GATA2 deficiency creates crosstalk between IFNγ and TLR1/2 pathways to elevate cytokine/chemokine production (Tran et al . iScience 2023), we asked if attenuating TLR signaling reverses the differentiation defect. As MYD88 Innate Immune Signal Transduction Adaptor (MYD88) is crucial for TLR1/2 signaling, we generated -77 +/-; Myd88-/- mice. Timed matings were conducted to obtain -77 +/+, -77 -/-, Myd88-/-, and -77 -/-; Myd88-/- E14.5 embryos. Myd88 ablation in -77 -/- embryos did not reverse the skewed granulocytic vs. monocytic progenitor ratio. To determine if MYD88 loss impacts -77 -/- progenitor function, we analyzed CMP and GMP populations from E14.5 embryos with CFU assays. In comparison with -77 +/+, -77 -/- CMP and Myd88-/- CMP produced fewer CFU-G colonies (1.9-fold decrease, P = 0.0097 and 2.0-fold decrease, P = 0.007, respectively). Surprisingly, -77 -/-; Myd88-/- CMP exhibited a further reduction in CFU-G colonies (5.2-fold decrease, P < 0.0001). The CFU-G colonies produced by -77 +/-; Myd88-/- CMP resembled that of -77 +/+ CMP. Thus, GATA2 and MYD88 synergistically promote CFU-G production from CMP, and a single -77 allele maintains CMP activity to produce CFU-G without Myd88. Myd88 deletion did not affect the reduced CFU-G nor the increased CFU-M with -77 -/- GMP. We are testing if TLR1/2 signaling is not required to maintain balanced fetal liver progenitor populations or if another signaling adapter nullifies the impact of MYD88 loss. Our studies revealed a mechanism underlying the hypersensitivity of GATA2-deficient fetal progenitors to innate immune signaling, and MYD88 loss further decreases the reduced CFU-G generated from -77 -/- CMP. We are testing the hypothesis that GATA2 restricts assembly of PU.1-containing chromatin complexes and analyzing models to unveil functional ramifications of elevated innate immune signaling in single HSPCs.

Discrimination of cell-intrinsic and environment-dependent effects of natural genetic variation on Kupffer cell epigenomes and transcriptomes

Noncoding genetic variation drives phenotypic diversity, but underlying mechanisms and affected cell types are incompletely understood. Here, investigation of effects of natural genetic variation on the epigenomes and transcriptomes of Kupffer cells derived from inbred mouse strains identified strain-specific environmental factors influencing Kupffer cell phenotypes, including leptin signaling in Kupffer cells from a steatohepatitis-resistant strain. Cell-autonomous and non-cell-autonomous effects of genetic variation were resolved by analysis of F1 hybrid mice and cells engrafted into an immunodeficient host. During homeostasis, non-cell-autonomous trans effects of genetic variation dominated control of Kupffer cells, while strain-specific responses to acute lipopolysaccharide injection were dominated by actions of cis-acting effects modifying response elements for lineage-determining and signal-dependent transcription factors. These findings demonstrate that epigenetic landscapes report on trans effects of genetic variation and serve as a resource for deeper analyses into genetic control of transcription in Kupffer cells and macrophages in vitro.

Restricting genomic actions of innate immune mediators on fetal hematopoietic progenitor cells

Innate immune signaling protects against pathogens, controls hematopoietic development, and functions in oncogenesis, yet the relationship between these mechanisms is undefined. Downregulating the GATA2 transcription factor in fetal hematopoietic progenitor cells upregulates genes encoding innate immune regulators, increases Interferon-γ (IFNγ) signaling, and disrupts differentiation. We demonstrate that deletion of an enhancer that confers GATA2 expression in fetal progenitors elevated Toll-like receptor (TLR) TLR1/2 and TLR2/6 expression and signaling. Rescue by expressing GATA2 downregulated elevated TLR signaling. IFNγ amplified TLR1/2 and TLR2/6 signaling in GATA2-deficient progenitors, synergistically activating cytokine/chemokine genes and elevating cytokine/chemokine production in myeloid cell progeny. Genomic analysis of how innate immune signaling remodels the GATA2-deficient progenitor transcriptome revealed hypersensitive responses at innate immune genes harboring motifs for signal-dependent transcription factors and factors not linked to these mechanisms. As GATA2 establishes a transcriptome that constrains innate immune signaling, insufficient GATA2 renders fetal progenitor cells hypersensitive to innate immune signaling.

Stochastic models of nucleosome dynamics reveal regulatory rules of stimulus-induced epigenome remodeling.

The genomic positions of nucleosomes are a defining feature of the cell's epigenomic state, but signal-dependent transcription factors (SDTFs), upon activation, bind to specific genomic locations and modify nucleosome positioning. Here we leverage SDTFs as perturbation probes to learn about nucleosome dynamics in living cells. We develop Markov models of nucleosome dynamics and fit them to time course sequencing data of DNA accessibility. We find that (1) the dynamics of DNA unwrapping are significantly slower in cells than reported from cell-free experiments, (2) only models with cooperativity in wrapping and unwrapping fit the available data, (3) SDTF activity produces the highest eviction probability when its binding site is adjacent to but not on the nucleosome dyad, and (4) oscillatory SDTF activity results in high location variability. Our work uncovers the regulatory rules governing SDTF-induced nucleosome dynamics in live cells, which can predict chromatin accessibility alterations during inflammation at single-nucleosome resolution.

Abstract 5732: p53 deficiency causes Myc dysregulation through a novel TGFβ-facilitated promoter switching mechanism to instigate osteosarcoma development

Abstract p53 deficiency and Myc dysregulation, driven by genetic and epigenetic alterations, respectively, are frequently associated with cancer. Previously, we reported that the combination of p53 inactivation and Myc overexpression, mediated by Runx transcription factors (TFs), leads to osteosarcoma (OS), the most common primary bone cancer. However, the mechanisms leading to Myc upregulation by Runx in a p53-deficient microenvironment remain unclear. TGFβ is a main driver of the epithelial-to-mesenchymal transition and its signal-dependent TFs, Smads, are known to associate with lineage-determining TFs including Runx. As TGFβ paracrine signalling is reportedly increased during human OS development, we immunodetected increased co-expression of TGFβ and phospho-Smad2 in the bone marrow of osteoprogenitor-specific p53 knockout mice, Osterix (Osx)/Sp7-Cre; p53fl/fl mice, which are widely used as an animal model of human OS. Heterozygous deletion of the type II TGFβ receptor in those mice weakened their susceptibility to OS, phenocopying the overall life-extending effect of Myc depletion in the same model. p53 disruption caused TGFβ to aberrantly induce Myc in osteoprogenitors, rendering the cells tumorigenic upon transplantation into immunocompromised mice. Within the 3-Mb Myc regulatory region, we identified a TGFβ-responsive element dubbed m340, which contains binding sites for multiple TFs including Runx. The m340 enhancer caused Myc upregulation upon p53 disruption by switching its associated promoter from the lncRNA Pvt1 to Myc. In support of this promoter switching mechanism, a specific disruption of the evolutionarily conserved p53 site within the Pvt1 promoter recapitulated TGFβ-induced Myc overexpression. At m340, TGFβ promoted its occupancy by a transcriptional complex consisting of Runx, its cooperative factors Smads and AP1, and CBP, further activating the enhancer by increasing H3K27ac deposition. Runx inhibition not only repressed the aberrant upregulation of Myc by reducing Smad occupancy at m340, but also suppressed OS development in vivo. These results suggest that p53 deficiency causes Myc dysregulation through a novel promoter switching programme that is facilitated by TGFβ signalling and reveals a novel epigenetic mechanism underlying the interaction between cancer-predisposing genetic alterations (p53 deficiency) and environmental cues (TGFβ) in tumorigenesis. Considering the mediating role Runx plays in m340 activation, our study may provide a clinical rationale for targeting Runx in p53-deficient malignancies. Citation Format: Yuki Date, Tomoya Ueno, Kosei Ito. p53 deficiency causes Myc dysregulation through a novel TGFβ-facilitated promoter switching mechanism to instigate osteosarcoma development [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5732.

ZMIZ proteins: partners in transcriptional regulation and risk factors for human disease.

Coregulator proteins interact with signal-dependent transcription factors to modify their transcriptional activity. ZMIZ1 and ZMIZ2 (zinc finger MIZ-type containing 1 and 2) are coregulators with nonredundant functions that share unique structural characteristics. Among other interacting domains, they possess a MIZ (Msx-interacting zinc finger) that relates them to members of the protein inhibitor of activated STAT (PIAS) family and provides them the capacity to function as SUMO E3 ligases. The ZMIZ proteins stimulate the activity of various signaling pathways, including the androgen receptor (AR), P53, SMAD3/4, WNT/β-catenin, and NOTCH1 pathways, and interact with the BAF chromatin remodeling complex. Due to their molecular versatility, ZMIZ proteins have pleiotropic effects and thus are important for embryonic development and for human diseases. Both have been widely associated with cancer, and ZMIZ1 has been very frequently identified as a risk allele for several autoimmune conditions and other disorders. Moreover, mutations in the coding region of the ZMIZ1 gene are responsible for a severe syndromic neurodevelopmental disability. Because the actions of coregulators are highly gene-specific, a better knowledge of the associations that exist between the function of the ZMIZ coregulators and human pathologies is expected to potentiate the use of ZMIZ1 and ZMIZ2 as new drug targets for diseases such as hormone-dependent cancers.

Identifying the combinatorial control of signal-dependent transcription factors.

The effectiveness of immune responses depends on the precision of stimulus-responsive gene expression programs. Cells specify which genes to express by activating stimulus-specific combinations of stimulus-induced transcription factors (TFs). Their activities are decoded by a gene regulatory strategy (GRS) associated with each response gene. Here, we examined whether the GRSs of target genes may be inferred from stimulus-response (input-output) datasets, which remains an unresolved model-identifiability challenge. We developed a mechanistic modeling framework and computational workflow to determine the identifiability of all possible combinations of synergistic (AND) or non-synergistic (OR) GRSs involving three transcription factors. Considering different sets of perturbations for stimulus-response studies, we found that two thirds of GRSs are easily distinguishable but that substantially more quantitative data is required to distinguish the remaining third. To enhance the accuracy of the inference with timecourse experimental data, we developed an advanced error model that avoids error overestimates by distinguishing between value and temporal error. Incorporating this error model into a Bayesian framework, we show that GRS models can be identified for individual genes by considering multiple datasets. Our analysis rationalizes the allocation of experimental resources by identifying most informative TF stimulation conditions. Applying this computational workflow to experimental data of immune response genes in macrophages, we found that a much greater fraction of genes are combinatorially controlled than previously reported by considering compensation among transcription factors. Specifically, we revealed that a group of known NFκB target genes may also be regulated by IRF3, which is supported by chromatin immuno-precipitation analysis. Our study provides a computational workflow for designing and interpreting stimulus-response gene expression studies to identify underlying gene regulatory strategies and further a mechanistic understanding.

Genome-wide crosstalk between steroid receptors in breast and prostate cancers

Steroid receptors (SRs) constitute an important class of signal-dependent transcription factors (TFs). They regulate a variety of key biological processes and are crucial drug targets in many disease states. In particular, estrogen (ER) and androgen receptors (AR) drive the development and progression of breast and prostate cancer, respectively. Thus, they represent the main specific drug targets in these diseases. Recent evidence has suggested that the crosstalk between signal-dependent TFs is an important step in the reprogramming of chromatin sites; a signal-activated TF can expand or restrict the chromatin binding of another TF. This crosstalk can rewire gene programs and thus alter biological processes and influence the progression of disease. Lately, it has been postulated that there may be an important crosstalk between the AR and the ER with other SRs. Especially, progesterone (PR) and glucocorticoid receptor (GR) can reprogram chromatin binding of ER and gene programs in breast cancer cells. Furthermore, GR can take the place of AR in antiandrogen-resistant prostate cancer cells. Here, we review the current knowledge of the crosstalk between SRs in breast and prostate cancers. We emphasize how the activity of ER and AR on chromatin can be modulated by other SRs on a genome-wide scale. We also highlight the knowledge gaps in the interplay of SRs and their complex interactions with other signaling pathways and suggest how to experimentally fill in these gaps.

Transcriptional Regulation of Inflammasomes.

Inflammasomes are multimolecular complexes with potent inflammatory activity. As such, their activity is tightly regulated at the transcriptional and post-transcriptional levels. In this review, we present the transcriptional regulation of inflammasome genes from sensors (e.g., NLRP3) to substrates (e.g., IL-1β). Lineage-determining transcription factors shape inflammasome responses in different cell types with profound consequences on the responsiveness to inflammasome-activating stimuli. Pro-inflammatory signals (sterile or microbial) have a key transcriptional impact on inflammasome genes, which is largely mediated by NF-κB and that translates into higher antimicrobial immune responses. Furthermore, diverse intrinsic (e.g., circadian clock, metabolites) or extrinsic (e.g., xenobiotics) signals are integrated by signal-dependent transcription factors and chromatin structure changes to modulate transcriptionally inflammasome responses. Finally, anti-inflammatory signals (e.g., IL-10) counterbalance inflammasome genes induction to limit deleterious inflammation. Transcriptional regulations thus appear as the first line of inflammasome regulation to raise the defense level in front of stress and infections but also to limit excessive or chronic inflammation.

The transcription factor PU.1 mediates enhancer-promoter looping that is required for IL-1β eRNA and mRNA transcription in mouse melanoma and macrophage cell lines

The DNA-binding protein PU.1 is a myeloid lineage-determining and pioneering transcription factor due to its ability to bind "closed" genomic sites and maintain "open" chromatin state for myeloid lineage-specific genes. The precise mechanism of PU.1 in cell type-specific programming is yet to be elucidated. The melanoma cell line B16BL6, although it is nonmyeloid lineage, expressed Toll-like receptors and activated the transcription factor NF-κB upon stimulation by the bacterial cell wall component lipopolysaccharide. However, it did not produce cytokines, such as IL-1β mRNA. Ectopic PU.1 expression induced remodeling of a novel distal enhancer (located ∼10 kbp upstream of the IL-1β transcription start site), marked by nucleosome depletion, enhancer-promoter looping, and histone H3 lysine 27 acetylation (H3K27ac). PU.1 induced enhancer-promoter looping and H3K27ac through two distinct PU.1 regions. These PU.1-dependent events were independently required for subsequent signal-dependent and co-dependent events: NF-κB recruitment and further H3K27ac, both of which were required for enhancer RNA (eRNA) transcription. In murine macrophage RAW264.7 cells, these PU.1-dependent events were constitutively established and readily expressed eRNA and subsequently IL-1β mRNA by lipopolysaccharide stimulation. In summary, this study showed a sequence of epigenetic events in programming IL-1β transcription by the distal enhancer priming and eRNA production mediated by PU.1 and the signal-dependent transcription factor NF-κB.

Transcriptional and epigenetic regulation of macrophages in atherosclerosis.

Monocytes and macrophages provide defence against pathogens and danger signals. These cells respond to stimulation in a fast and stimulus-specific manner by utilizing complex cascaded activation by lineage-determining and signal-dependent transcription factors. The complexity of the functional response is determined by interactions between triggered transcription factors and depends on the microenvironment and interdependent signalling cascades. Dysregulation of macrophage phenotypes is a major driver of various diseases such as atherosclerosis, rheumatoid arthritis and type 2 diabetes mellitus. Furthermore, exposure of monocytes, which are macrophage precursor cells, to certain stimuli can lead to a hypo-inflammatory tolerized phenotype or a hyper-inflammatory trained phenotype in a macrophage. In atherosclerosis, macrophages and monocytes are exposed to inflammatory cytokines, oxidized lipids, cholesterol crystals and other factors. All these stimuli induce not only a specific transcriptional response but also interact extensively, leading to transcriptional and epigenetic heterogeneity of macrophages in atherosclerotic plaques. Targeting the epigenetic landscape of plaque macrophages can be a powerful therapeutic tool to modulate pro-atherogenic phenotypes and reduce the rate of plaque formation. In this Review, we discuss the emerging role of transcription factors and epigenetic remodelling in macrophages in the context of atherosclerosis and inflammation, and provide a comprehensive overview of epigenetic enzymes and transcription factors that are involved in macrophage activation.

Off the Clock: From Circadian Disruption to Metabolic Disease.

Circadian timekeeping allows appropriate temporal regulation of an organism’s internal metabolism to anticipate and respond to recurrent daily changes in the environment. Evidence from animal genetic models and from humans under circadian misalignment (such as shift work or jet lag) shows that disruption of circadian rhythms contributes to the development of obesity and metabolic disease. Inappropriate timing of food intake and high-fat feeding also lead to disruptions of the temporal coordination of metabolism and physiology and subsequently promote its pathogenesis. This review illustrates the impact of genetically or environmentally induced molecular clock disruption (at the level of the brain and peripheral tissues) and the interplay between the circadian system and metabolic processes. Here, we discuss some mechanisms responsible for diet-induced circadian desynchrony and consider the impact of nutritional cues in inter-organ communication, with a particular focus on the communication between peripheral organs and brain. Finally, we discuss the relay of environmental information by signal-dependent transcription factors to adjust the timing of gene oscillations. Collectively, a better knowledge of the mechanisms by which the circadian clock function can be compromised will lead to novel preventive and therapeutic strategies for obesity and other metabolic disorders arising from circadian desynchrony.

Labelled regulatory elements are pervasive features of the macrophage genome and are dynamically utilized by classical and alternative polarization signals.

The concept of tissue-specific gene expression posits that lineage-determining transcription factors (LDTFs) determine the open chromatin profile of a cell via collaborative binding, providing molecular beacons to signal-dependent transcription factors (SDTFs). However, the guiding principles of LDTF binding, chromatin accessibility and enhancer activity have not yet been systematically evaluated. We sought to study these features of the macrophage genome by the combination of experimental (ChIP-seq, ATAC-seq and GRO-seq) and computational approaches. We show that Random Forest and Support Vector Regression machine learning methods can accurately predict chromatin accessibility using the binding patterns of the LDTF PU.1 and four other key TFs of macrophages (IRF8, JUNB, CEBPA and RUNX1). Any of these TFs alone were not sufficient to predict open chromatin, indicating that TF binding is widespread at closed or weakly opened chromatin regions. Analysis of the PU.1 cistrome revealed that two-thirds of PU.1 binding occurs at low accessible chromatin. We termed these sites labelled regulatory elements (LREs), which may represent a dormant state of a future enhancer and contribute to macrophage cellular plasticity. Collectively, our work demonstrates the existence of LREs occupied by various key TFs, regulating specific gene expression programs triggered by divergent macrophage polarizing stimuli.

Regulation of cardiac transcription by thyroid hormone and Med13

Thyroid hormone (TH) is a key regulator of transcriptional homeostasis in the heart. While hypothyroidism is known to result in adverse cardiac effects, the molecular mechanisms that modulate TH signaling are not completely understood. Mediator is a multiprotein complex that coordinates signal-dependent transcription factors with the basal transcriptional machinery to regulate gene expression. Mediator complex protein, Med13, represses numerous thyroid receptor (TR) response genes in the heart. Further, cardiac-specific overexpression of Med13 in mice that were treated with propylthiouracil (PTU), an inhibitor of the biosynthesis of the active TH, triiodothyronine (T3), resulted in resistance to PTU-dependent decreases in cardiac contractility. Therefore, these studies aimed to determine if Med13 is necessary for the cardiac response to hypothyroidism. Here we demonstrate that Med13 expression is induced in the hearts of mice with hypothyroidism. To elucidate the role of Med13 in regulating gene transcription in response to TH signaling in cardiac tissue, we utilized an unbiased RNA sequencing approach to define the TH-dependent alterations in gene expression in wild-type mice or those with a cardiac-specific deletion in Med13 (Med13cKO). Mice were fed a diet of PTU to induce a hypothyroid state or normal chow for either 4 or 16 weeks, and an additional group of mice on a PTU diet were treated acutely with T3 to re-establish a euthyroid state. Echocardiography revealed that wild-type mice had a decreased heart rate in response to PTU with a trend toward a reduced cardiac ejection fraction. Notably, cardiomyocyte-specific deletion of Med13 exacerbated cardiac dysfunction. Collectively, these studies reveal cardiac transcriptional pathways regulated in response to hypothyroidism and re-establishment of a euthyroid state and define molecular pathways that are regulated by Med13 in response to TH signaling.

JAK/STAT signaling in regulation of innate lymphoid cells: The gods before the guardians.

Immunity to pathogens is ensured through integration of early responses mediated by innate cells and late effector functions taking place after terminal differentiation of adaptive lymphocytes. In this context, innate lymphoid cells (ILCs) and adaptive T cells represent a clear example of how prototypical effector functions, including polarized expression of cytokines and/or cytotoxic activity, can occur with overlapping modalities but different timing. The ability of ILCs to provide early protection relies on their poised epigenetic state, which determines their propensity to quickly respond to cytokines and to activate specific patterns of signal-dependent transcription factors. Cytokines activating the Janus kinases (JAKs) and members of the signal transducer and activator of transcription (STAT) pathway are key regulators of lymphoid development and sustain the processes underlying T-cell activation and differentiation. The role of the JAK/STAT pathway has been recently extended to several aspects of ILC biology. Here, we discuss how JAK/STAT signals affect ILC development and effector functions in the context of immune responses, highlighting the molecular mechanisms involved in regulation of gene expression as well as the potential of targeting the JAK/STAT pathway in inflammatory pathologies.

Abstract 585: CDK8 Activity-dependent Regulation of Heart Disease

Pathological cardiac hypertrophy represents a major risk factor for heart failure (HF). The hypertrophic response is orchestrated in part through transcriptional alterations that ultimately modify cardiac function. Mediator is a multiprotein complex that coordinates signal dependent transcription factors with basal transcriptional machinery including RNA polymerase II and general transcription factors. Transcriptional regulation by Mediator complex can be modified by the association of the Mediator complex kinase submodule with the core complex. Cyclin-dependent kinase 8 (CDK8) is a kinase present in the submodule that has been demonstrated to have a complex role in transcriptional regulation through a number of mechanisms involving both transcriptional activation and inhibition. Our lab has demonstrated that CDK8 expression is upregulated in murine HF models as well as in failing human hearts. In addition, cardiac CDK8 over-expression promotes transcriptional remodeling that results in dilated cardiomyopathy suggesting that CDK8 inhibition may represent a novel pharmacological target. This study utilizes CDK8 kinase inhibitor, Senexin A, which is being evaluated as an anti-cancer chemotherapeutic agent. Here, we demonstrate that Senexin A inhibits kinase activity in an in vitro neonatal rat cardiomyocyte (NRCM) model resulting in reduced cardiomyocyte hypertrophy as well as a reduction in expression of specific cardiomyocyte hypertrophy markers. These studies demonstrate a role for CDK8 activity in transcriptional regulation of genes associated with pathological cardiac remodeling that drives cardiac hypertrophy and ultimately HF.

NCR+ ILC3 maintain larger STAT4 reservoir via T-BET to regulate type 1 features upon IL-23 stimulation in mice.

Innate lymphoid cells (ILCs) producing IL-22 and/or IL-17, designated as ILC3, comprise a heterogeneous subset of cells involved in regulation of gut barrier homeostasis and inflammation. Exogenous environmental cues in conjunction with regulated expression of endogenous factors are key determinants of plasticity of ILC3 toward the type 1 fate. Herein, by using mouse models and transcriptomic approaches, we defined at the molecular level, initial events driving ILC3 expressing natural cytotoxicity receptors (NCR+ ILC3) to acquire type 1 features. We observed that NCR+ ILC3 exhibited high basal expression of the signal-dependent transcription factor STAT4 due to T-BET, leading to predisposed potential for the type 1 response. We found that the prototypical inducer of type 3 response, IL-23, played a predominant role over IL-12 by accessing STAT4 and preferentially inducing its phosphorylation in ILC3 expressing T-BET. The early effector program driven by IL-23 was characterized by the expression of IL-22, followed by a production of IFN-γ, which relies on STAT4, T-BET and required chromatin remodeling of the Ifng locus. Altogether, our findings shed light on a feed-forward mechanism involving STAT4 and T-BET that modulates the outcome of IL-23 signaling in ILC3.