Multifaceted Histone H3 Methylation and Phosphorylation Readout by the Plant Homeodomain Finger of Human Nuclear Antigen Sp100C

SP140 represses specific loci by recruiting polycomb repressive complex 2 and NuRD complex

SP140, a lymphocytic-restricted protein, is an epigenetic reader working as a corepressor of genes implicated in inflammation and orchestrating macrophage transcriptional programs to maintain cellular identity. Reduced SP140 expression is associated both to autoimmune diseases and blood cancers. However, the molecular mechanisms that link SP140 altered protein levels to detrimental effects on the immune response and cellular growth, as well as the interactors through which SP140 promotes gene silencing, remain elusive. In this work, we have applied a multi-omics approach (i.e. interactomics, ChIP-seq and proteomics) in two Burkitt lymphoma cell lines to identify both interactors and target genes of endogenous SP140. We found that SP140 interacts with the PRC2 and NuRD complexes, and we showed that these interactions are functional as SP140 directs H3K27me3 deposition and NuRD binding on a set of target genes implicated in cellular growth and leukemia progression.

Sp140L Is a Novel Herpesvirus Restriction Factor

Herpesviruses, including the oncogenic Epstein-Barr Virus (EBV), must bypass host DNA sensing mechanisms to establish infection. The first viral latency protein expressed, EBNA-LP, is essential for transformation of naïve B cells, yet its role in evading host defenses remains unclear. Using single-cell RNA sequencing of EBNA-LP-Knockout (LPKO)-infected B cells, we reveal an antiviral response landscape implicating the 'speckled proteins' as key restriction factors countered by EBNA-LP. Specifically, loss of SP100 or the primate-specific SP140L reverses the restriction of LPKO, suppresses a subset of canonically interferon-stimulated genes, and restores viral gene transcription and cellular proliferation. Notably, we also identify Sp140L as a restriction target of the herpesvirus saimiri ORF3 protein, implying a role in immunity to other DNA viruses. This study reveals Sp140L as a restriction factor that we propose links sensing and transcriptional suppression of viral DNA to an IFN-independent innate immune response, likely relevant to all nuclear DNA viruses.

Structural insights into an atypical histone binding mechanism by a PHD finger

Complex associating with SET1 (COMPASS) is a histone H3K4 tri-methyltransferase controlled by several regulatory subunits including CXXC zinc finger protein 1 (Cfp1). Prior studies established the structural underpinnings controlling H3K4me3 recognition by the PHD domain of Cfp1's yeast homolog (Spp1). However, metazoans Cfp1PHD lacks structural elements important for H3K4me3 stabilization in Spp1, suggesting that in metazoans, Cfp1PHD domain binds H3K4me3 differently. The structure of Cfp1PHD in complex with H3K4me3 shows unique features such as non-canonical coordination of the first zinc atom and a disulfide bond forcing the reorientation of Cfp1PHD N-terminus, thereby leading to an atypical H3K4me3 binding pocket. This configuration minimizes Cfp1PHD reliance on canonical residues important for histone binding functions of other PHD domains. Cancer-related mutations in Cfp1PHD impair H3K4me3 binding, implying a potential impact on epigenetic signaling. Our work highlights a potential diversification of PHD histone binding modes and the impact of cancer mutations on Cfp1 functions.

It Runs in the Bromodomain Family: Speckled Proteins (SP) Play a Role in the Antitumor Immune Response in Solid Tumors

Cells and immune cells in the extracellular matrix: Depending on the tumor type and variety of TAAs (tumor-associated antigens), immune infiltrates are composed of many different subpopulations of immune cells. Epigenetic changes are also considered to be characteristic of cancer. Epigenetic factors taking part in the regulation of gene expression include the VII group of bromodomain proteins (BrD)-SP-family proteins. Here, we used transcriptomic data from the TCGA database, as well as immunological evidence from ESTIMATE, TIP, and TIMER2.0 databases for various solid tumor types and harnessed several publicly available bioinformatic tools (such as GSEA and GSCA) to demonstrate mechanisms and interactions between BrD proteins and immune infiltrates in cancer. We present a consistently positive correlation between the SP-family genes and immune score regardless of the tumor type. The SP-family proteins correlate positively with T cells' trafficking and infiltration into tumor. Our results also show an association between the high expression of SP family genes and enriched transcriptome profiles of inflammatory response and TNF-α signaling via NF-κβ. We also show that the SP-family proteins could be considered good predictors of high immune infiltration phenotypes.

PML Body Component Sp100A Is a Cytosolic Responder to IFN and Activator of Antiviral ISGs

Promyelocytic leukemia protein (PML) bodies are implicated in one of the key pathways in the establishment of antiviral status in response to interferon (IFN), yet the molecular mechanisms bridging the cross talk remain elusive. Herein, we report that a major constitutive component of the PML body, Sp100A, is ubiquitously located in the cytosol of various cell types and is an immediate responder to multiple extracellular stimuli, including virus infection, IFN, epidermal growth factor (EGF), glial cell-derived nerve factor (GDNF), etc., signaling through the phosphatidylinositol 3-kinase (PI3K) pathway. IFN-β induces phosphorylation of Sp100A on Ser188, which fortifies the binding of Sp100A to pyruvate kinase 2 (PKM2) and facilitates its nuclear importation through the extracellular signal-regulated kinase 1/2 (ERK1/2)-PKM2-PIN1-importin axes. Blocking PI3K pathway signaling or interference with the ERK1/2-PKM2-PIN1-importin axes independently hampers nuclear translocation of Sp100A in response to IFN, reflecting a dual-regulation mechanism governing this event. In the nucleus, Sp100A is enriched in the promoter regions of essential antiviral interferon-stimulated genes (ISGs), such as those coding for IFI16, OAS2, and RIG-I, and activates their transcription. Importantly, nuclear importation of Sp100A, but not accumulation of a mutant Sp100A that failed to respond to IFN, during infection potently enhanced transcription of these antiviral ISGs and restricted virus propagation. These findings depict a novel IFN response mechanism by PML bodies in the cytosol and shed light on the complex sensing-regulatory network of PML bodies. IMPORTANCE PML bodies sit at the center stage of various important biological processes; however, the signal transduction networks of these macromolecular protein complexes remain enigmatic. The present study illustrates, in detail and for the first time, the course of signal receiving, processing, and implementation by PML bodies in response to IFN and virus infection. It shows that PML body constitutive component Sp100A was phosphorylated on Ser188 by IFN signaling through the PI3K pathway in the cytosol, cotranslocated into the nucleus with PKM2, enriched on the promoter regions of essential antiviral ISGs such as those coding for IFI16, RIG-I, OAS2, etc., and mediating their transcriptional activation.

Immune chromatin reader SP140 regulates microbiota and risk for inflammatory bowel disease

Inflammatory bowel disease (IBD) is driven by host genetics and environmental factors, including commensal microorganisms. Speckled Protein 140 (SP140) is an immune-restricted chromatin "reader" that is associated with Crohn's disease (CD), multiple sclerosis (MS), and chronic lymphocytic leukemia (CLL). However, the disease-causing mechanisms of SP140 remain undefined. Here, we identify an immune-intrinsic role for SP140 in regulating phagocytic defense responses to prevent the expansion of inflammatory bacteria. Mice harboring altered microbiota due to hematopoietic Sp140 deficiency exhibited severe colitis that was transmissible upon cohousing and ameliorated with antibiotics. Loss of SP140 results in blooms of Proteobacteria, including Helicobacter in Sp140-/- mice and Enterobacteriaceae in humans bearing the CD-associated SP140 loss-of-function variant. Phagocytes from patients with the SP140 loss-of-function variant and Sp140-/- mice exhibited altered antimicrobial defense programs required for control of pathobionts. Thus, mutations within this epigenetic reader may constitute a predisposing event in human diseases provoked by microbiota.

PML Body Component Sp100A Restricts Wild-Type Herpes Simplex Virus 1 Infection

Sp100 (speckled protein 100 kDa) is a constituent component of nuclear structure PML (promyelocytic leukemia) bodies, playing important roles in mediating intrinsic and innate immunity. The Sp100 gene encodes four isoforms with distinct roles in the transcriptional regulation of both cellular and viral genes. Since Sp100 is a primary intranuclear target of infected-cell protein 0 (ICP0), an immediate early E3 ligase encoded by herpes simplex virus 1 (HSV-1), previous investigations attempting to analyze the functions of individual Sp100 variants during HSV-1 infection mostly avoided using a wild-type virus. Therefore, the role of Sp100 under natural infection by HSV-1 remains to be clarified. Here, we reappraised the antiviral capacity of four Sp100 isoforms during infection by a nonmutated HSV-1, examined the molecular behavior of the Sp100 protein in detail, and revealed the following intriguing observations. First, Sp100 isoform A (Sp100A) inhibited wild-type HSV-1 propagation in HEp-2, Sp100-/-, and PML-/- cells. Second, endogenous Sp100 is located in both the nucleus and the cytoplasm. During HSV-1 infection, the nuclear Sp100 level decreased drastically upon the detection of ICP0 in the same subcellular compartment, but cytosolic Sp100 remained stable. Third, transfected Sp100A showed subcellular localizations similar to those of endogenous Sp100 and matched the protein size of endogenous cytosolic Sp100. Fourth, HSV-1 infection induced increased secretion of endogenous Sp100 and ectopically expressed Sp100A, which copurified with extracellular vesicles (EVs) but not infectious virions. Fifth, the Sp100A level in secreting cells positively correlated with its level in EVs, and EV-associated Sp100A restricted HSV-1 in recipient cells. IMPORTANCE Previous studies show that the PML body component Sp100 protein is immediately targeted by ICP0 of HSV-1 in the nucleus during productive infection. Therefore, extensive studies investigating the interplay of Sp100 isoforms with HSV-1 were conducted using a mutant virus lacking ICP0 or in the absence of infection. The role of Sp100 variants during natural HSV-1 infection remains blurry. Here, we report that Sp100A potently and independently inhibited wild-type HSV-1 and that during HSV-1 infection, cytosolic Sp100 remained stable and was increasingly secreted into the extracellular space, in association with EVs. Furthermore, the Sp100A level in secreting cells positively correlated with its level in EVs and the anti-HSV-1 potency of these EVs in recipient cells. In summary, this study implies an active antiviral role of Sp100A during wild-type HSV-1 infection and reveals a novel mechanism of Sp100A to restrict HSV-1 through extracellular communications.

Functional Roles of Bromodomain Proteins in Cancer

Histone acetylation is generally associated with an open chromatin configuration that facilitates many cellular processes including gene transcription, DNA repair, and DNA replication. Aberrant levels of histone lysine acetylation are associated with the development of cancer. Bromodomains represent a family of structurally well-characterized effector domains that recognize acetylated lysines in chromatin. As part of their fundamental reader activity, bromodomain-containing proteins play versatile roles in epigenetic regulation, and additional functional modules are often present in the same protein, or through the assembly of larger enzymatic complexes. Dysregulated gene expression, chromosomal translocations, and/or mutations in bromodomain-containing proteins have been correlated with poor patient outcomes in cancer. Thus, bromodomains have emerged as a highly tractable class of epigenetic targets due to their well-defined structural domains, and the increasing ease of designing or screening for molecules that modulate the reading process. Recent developments in pharmacological agents that target specific bromodomains has helped to understand the diverse mechanisms that bromodomains play with their interaction partners in a variety of chromatin processes, and provide the promise of applying bromodomain inhibitors into the clinical field of cancer treatment. In this review, we explore the expression and protein interactome profiles of bromodomain-containing proteins and discuss them in terms of functional groups. Furthermore, we highlight our current understanding of the roles of bromodomain-containing proteins in cancer, as well as emerging strategies to specifically target bromodomains, including combination therapies using bromodomain inhibitors alongside traditional therapeutic approaches designed to re-program tumorigenesis and metastasis.

The Fate of Speckled Protein 100 (Sp100) During Herpesviruses Infection

The constitutive expression of Speckled-100 (Sp100) is known to restrict the replication of many clinically important DNA viruses. This pre-existing (intrinsic) immune defense to virus infection can be further upregulated upon interferon (IFN) stimulation as a component of the innate immune response. In humans, Sp100 is encoded by a single gene locus, which can produce alternatively spliced isoforms. The widely studied Sp100A, Sp100B, Sp100C and Sp100HMG have functions associated with the transcriptional regulation of viral and cellular chromatin, either directly through their characteristic DNA-binding domains, or indirectly through post-translational modification (PTM) and associated protein interaction networks. Sp100 isoforms are resident component proteins of promyelocytic leukemia-nuclear bodies (PML-NBs), dynamic nuclear sub-structures which regulate host immune defenses against many pathogens. In the case of human herpesviruses, multiple protein antagonists are expressed to relieve viral DNA genome transcriptional silencing imposed by PML-NB and Sp100-derived proteinaceous structures, thereby stimulating viral propagation, pathogenesis, and transmission to new hosts. This review details how different Sp100 isoforms are manipulated during herpesviruses HSV1, VZV, HCMV, EBV, and KSHV infection, identifying gaps in our current knowledge, and highlighting future areas of research.

Optimization of Alchemical Pathways Using Extended Thermodynamic Integration

Thermodynamic integration (TI) is a commonly used method to determine free-energy differences. One of its disadvantages is that many intermediate λ-states need to be sampled in order to be able to integrate accurately over ⟨∂H/∂λ⟩. Here, we use the recently introduced extended TI to study alternative parameterizations of H(λ) and its influence on the smoothness of the ⟨∂H/∂λ⟩ curves as well as the efficiency of the simulations. We find that the extended TI approach can be used to select curves of low curvature. An optimal parameterization is suggested for the calculation of hydration free energies. For calculations of relative binding free energies, we show that optimized parameterizations of the Hamiltonian in the unbound state also effectively lower the curvature in the bound state of the ligand.

The Speckled Protein (SP) Family: Immunity's Chromatin Readers

Chromatin 'readers' are central interpreters of the epigenome that facilitate cell-specific transcriptional programs and are therapeutic targets in cancer and inflammation. The Speckled Protein (SP) family of chromatin 'readers' in humans consists of SP100, SP110, SP140, and SP140L. SPs possess functional domains (SAND, PHD, bromodomain) that dock to DNA or post-translationally modified histones and a caspase activation and recruitment domain (CARD) to promote multimerization. Mutations within immune expressed SPs associate with numerous immunological diseases including Crohn's disease, multiple sclerosis, chronic lymphocytic leukemia, veno-occlusive disease with immunodeficiency, as well as Mycobacterium tuberculosis infection, underscoring their importance in immune regulation. In this review, we posit that SPs are central chromatin regulators of gene silencing that establish immune cell identity and function.

Characterization of the plant homeodomain (PHD) reader family for their histone tail interactions

BACKGROUND

Plant homeodomain (PHD) fingers are central "readers" of histone post-translational modifications (PTMs) with > 100 PHD finger-containing proteins encoded by the human genome. Many of the PHDs studied to date bind to unmodified or methylated states of histone H3 lysine 4 (H3K4). Additionally, many of these domains, and the proteins they are contained in, have crucial roles in the regulation of gene expression and cancer development. Despite this, the majority of PHD fingers have gone uncharacterized; thus, our understanding of how these domains contribute to chromatin biology remains incomplete.

RESULTS

We expressed and screened 123 of the annotated human PHD fingers for their histone binding preferences using reader domain microarrays. A subset (31) of these domains showed strong preference for the H3 N-terminal tail either unmodified or methylated at H3K4. These H3 readers were further characterized by histone peptide microarrays and/or AlphaScreen to comprehensively define their H3 preferences and PTM cross-talk.

CONCLUSIONS

The high-throughput approaches utilized in this study establish a compendium of binding information for the PHD reader family with regard to how they engage histone PTMs and uncover several novel reader domain-histone PTM interactions (i.e., PHRF1 and TRIM66). This study highlights the usefulness of high-throughput analyses of histone reader proteins as a means of understanding how chromatin engagement occurs biochemically.

Correcting electrostatic artifacts due to net-charge changes in the calculation of ligand binding free energies

Alchemically derived free energies are artifacted when the perturbed moiety has a nonzero net charge. The source of the artifacts lies in the effective treatment of the electrostatic interactions within and between the perturbed atoms and remaining (partial) charges in the simulated system. To treat the electrostatic interactions effectively, lattice-summation (LS) methods or cutoff schemes in combination with a reaction-field contribution are usually employed. Both methods render the charging component of the calculated free energies sensitive to essential parameters of the system like the cutoff radius or the box side lengths. Here, we discuss the results of three previously published studies of ligand binding. These studies presented estimates of binding free energies that were artifacted due to the charged nature of the ligands. We show that the size of the artifacts can be efficiently calculated and raw simulation data can be corrected. We compare the corrected results with experimental estimates and nonartifacted estimates from path-sampling methods. Although the employed correction scheme involves computationally demanding continuum-electrostatics calculations, we show that the correction estimate can be deduced from a small sample of configurations rather than from the entire ensemble. This observation makes the calculations of correction terms feasible for complex biological systems. To show the general applicability of the proposed procedure, we also present results where the correction scheme was used to correct independent free energies obtained from simulations employing a cutoff scheme or LS electrostatics. In this work, we give practical guidelines on how to apply the appropriate corrections easily.

SP140 regulates the expression of immune-related genes associated with multiple sclerosis and other autoimmune diseases by NF-κB inhibition

SP140 locus has been associated with multiple sclerosis (MS) as well as other autoimmune diseases by genome-wide association studies (GWAS). The causal variant of these associations (rs28445040-T) alters the splicing of the SP140 gene transcripts reducing the protein expression. We aimed to understand why the reduction of SP140 expression produced by the risk variant can increase the susceptibility to MS. To this end, we determined by RNA sequencing (RNA-seq) analysis the differentially expressed genes after SP140 silencing in lymphoblastoid cell lines (LCLs). We analyzed these genes by gene ontology (GO), comparative transcriptome profiles, enrichment of transcription factors (TFs) in the promoters of these genes and colocalization with GWAS risk variants. We also monitored the activity of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) in SP140-silenced cells by luciferase reporter system. We identified 100 genes that were up-regulated and 22 genes down-regulated in SP140-silenced LCLs. GO analysis revealed that genes affected by SP140 were involved in regulation of cytokine production, inflammatory response and cell-cell adhesion. We observed enrichment of NF-κB TF in the promoter of up-regulated genes and NF-κB-increased activity in SP140-silenced cell lines. We showed enrichment of genes regulated by SP140 in GWAS-detected risk loci for MS (14.63 folds), Crohn's disease (4.82 folds) and inflammatory bowel disease (4.47 folds), not observed in other unrelated immune diseases. Our findings showed that SP140 is an important repressor of genes implicated in inflammation, suggesting that decreased expression of SP140, promoted by the rs28445040-T risk variant, may lead to up-regulation of these genes by means of NF-κB inhibition in B cells.

Sp140 is a multi-SUMO-1 target and its PHD finger promotes SUMOylation of the adjacent Bromodomain

BACKGROUND

Human Sp140 protein is a leukocyte-specific member of the speckled protein (Sp) family (Sp100, Sp110, Sp140, Sp140L), a class of multi-domain nuclear proteins involved in intrinsic immunity and transcriptional regulation. Sp140 regulates macrophage transcriptional program and is implicated in several haematologic malignancies. Little is known about Sp140 structural domains and its post-translational modifications.

METHODS

We used mass spectrometry and biochemical experiments to investigate endogenous Sp140 SUMOylation in Burkitt's Lymphoma cells and Sp140 SUMOylation sites in HEK293T cells, FLAG-Sp140 transfected and His₆-SUMO-1^T95K infected. NMR spectroscopy and in vitro SUMOylation reactions were applied to investigate the role of Sp140 PHD finger in the SUMOylation of the adjacent BRD.

RESULTS

Endogenous Sp140 is a SUMO-1 target, whereby FLAG-Sp140 harbors at least 13 SUMOylation sites distributed along the protein sequence, including the BRD. NMR experiments prove direct binding of the SUMO E2 ligase Ubc9 and SUMO-1 to PHD-BRD_Sp140. In vitro SUMOylation reactions show that the PHD_Sp140 behaves as SUMO E3 ligase, assisting intramolecular SUMOylation of the adjacent BRD.

CONCLUSIONS

Sp140 is multi-SUMOylated and its PHD finger works as versatile protein-protein interaction platform promoting intramolecular SUMOylation of the adjacent BRD. Thus, combinatorial association of Sp140 chromatin binding domains generates a multifaceted interaction scaffold, whose function goes beyond the canonical histone recognition.

GENERAL SIGNIFICANCE

The addition of Sp140 to the increasing lists of multi-SUMOylated proteins opens new perspectives for molecular studies on Sp140 transcriptional activity, where SUMOylation could represent a regulatory route and a docking surface for the recruitment and assembly of leukocyte-specific transcription regulators.

Integrative analysis reveals functional and regulatory roles of H3K79me2 in mediating alternative splicing

Background

Accumulating evidence suggests alternative splicing (AS) is a co-transcriptional splicing process not only controlled by RNA-binding splicing factors, but also mediated by epigenetic regulators, such as chromatin structure, nucleosome density, and histone modification. Aberrant AS plays an important role in regulating various diseases, including cancers.

Methods

In this study, we integrated AS events derived from RNA-seq with H3K79me2 ChIP-seq data across 34 different normal and cancer cell types and found the higher enrichment of H3K79me2 in two AS types, skipping exon (SE) and alternative 3′ splice site (A3SS).

Results

Interestingly, by applying self-organizing map (SOM) clustering, we unveiled two clusters mainly comprised of blood cancer cell types with a strong correlation between H3K79me2 and SE. Remarkably, the expression of transcripts associated with SE was not significantly different from that of those not associated with SE, indicating the involvement of H3K79me2 in splicing has little impact on full mRNA transcription. We further showed that the deletion of DOT1L1, the sole H3K79 methyltransferase, impeded leukemia cell proliferation as well as switched exon skipping to the inclusion isoform in two MLL-rearranged acute myeloid leukemia cell lines. Our data demonstrate H3K79me2 was involved in mediating SE processing, which might in turn influence transformation and disease progression in leukemias.

Conclusions

Collectively, our work for the first time reveals that H3K79me2 plays functional and regulatory roles through a co-transcriptional splicing mechanism.

Electronic supplementary material

The online version of this article (10.1186/s13073-018-0538-1) contains supplementary material, which is available to authorized users.

A systems medicine approach reveals disordered immune system and lipid metabolism in multiple sclerosis patients

Identification of autoimmune processes and introduction of new autoantigens involved in the pathogenesis of multiple sclerosis (MS) can be helpful in the design of new drugs to prevent unresponsiveness and side effects in patients. To find significant changes, we evaluated the autoantibody repertoires in newly diagnosed relapsing-remitting MS patients (NDP) and those receiving disease-modifying therapy (RP). Through a random peptide phage library, a panel of NDP- and RP-specific peptides was identified, producing two protein data sets visualized using Gephi, based on protein--protein interactions in the STRING database. The top modules of NDP and RP networks were assessed using Enrichr. Based on the findings, a set of proteins, including ATP binding cassette subfamily C member 1 (ABCC1), neurogenic locus notch homologue protein 1 (NOTCH1), hepatocyte growth factor receptor (MET), RAF proto-oncogene serine/threonine-protein kinase (RAF1) and proto-oncogene vav (VAV1) was found in NDP and was involved in over-represented terms correlated with cell-mediated immunity and cancer. In contrast, transcription factor RelB (RELB), histone acetyltransferase p300 (EP300), acetyl-CoA carboxylase 2 (ACACB), adiponectin (ADIPOQ) and phosphoenolpyruvate carboxykinase 2 mitochondrial (PCK2) had major contributions to viral infections and lipid metabolism as significant events in RP. According to these findings, further research is required to demonstrate the pathogenic roles of such proteins and autoantibodies targeting them in MS and to develop therapeutic agents which can ameliorate disease severity.

Sp100 colocalizes with HPV replication foci and restricts the productive stage of the infectious cycle

We have shown previously that Sp100 (a component of the ND10 nuclear body) represses transcription, replication and establishment of incoming human papillomavirus (HPV) DNA in the early stages of infection. In this follow up study, we show that Sp100 does not substantially regulate viral infection in the maintenance phase, however at late stages of infection Sp100 interacts with amplifying viral genomes to repress viral processes. We find that Sp100 localizes to HPV16 replication foci generated in primary keratinocytes, to HPV31 replication foci that form in differentiated cells, and to HPV16 replication foci in CIN 1 cervical biopsies. To analyze this further, Sp100 was down regulated by siRNA treatment of differentiating HPV31 containing cells and levels of viral transcription and replication were assessed. This revealed that Sp100 represses viral transcription and replication in differentiated cells. Analysis of Sp100 binding to viral chromatin showed that Sp100 bound across the viral genome, and that binding increased at late stages of infection. Therefore, Sp100 represses the HPV life cycle at both early and late stages of infection.

Understanding the Phosphorylation Mechanism by Using Quantum Chemical Calculations and Molecular Dynamics Simulations

Phosphorylation is one of the most frequent post-translational modifications on proteins. It regulates many cellular processes by modulation of phosphorylation on protein structure and dynamics. However, the mechanism of phosphorylation-induced conformational changes of proteins is still poorly understood. Here, we report a computational study of three representative groups of tyrosine in ADP-ribosylhydrolase 1, serine in BTG2, and serine in Sp100C by using six molecular dynamics (MD) simulations and quantum chemical calculations. Added phosphorylation was found to disrupt hydrogen bond, and increase new weak interactions (hydrogen bond and hydrophobic interaction) during MD simulations, leading to conformational changes. Quantum chemical calculations further indicate that the phosphorylation on tyrosine, threonine, and serine could decrease the optical band gap energy (Egap), which can trigger electronic transitions to form or disrupt interactions easily. Our results provide an atomic and electronic description of how phosphorylation facilitates conformational and dynamic changes in proteins, which may be useful for studying protein function and protein design.

Maintenance of macrophage transcriptional programs and intestinal homeostasis by epigenetic reader SP140

Epigenetic "readers" that recognize defined posttranslational modifications on histones have become desirable therapeutic targets for cancer and inflammation. SP140 is one such bromodomain- and plant homeodomain (PHD)-containing reader with immune-restricted expression, and single-nucleotide polymorphisms (SNPs) within SP140 associate with Crohn's disease (CD). However, the function of SP140 and the consequences of disease-associated SP140 SNPs have remained unclear. We show that SP140 is critical for transcriptional programs that uphold the macrophage state. SP140 preferentially occupies promoters of silenced, lineage-inappropriate genes bearing the histone modification H3K27me3, such as the HOXA cluster in human macrophages, and ensures their repression. Depletion of SP140 in mouse or human macrophages resulted in severely compromised microbe-induced activation. We reveal that peripheral blood mononuclear cells (PBMCs) or B cells from individuals carrying CD-associated SNPs within SP140 have defective SP140 messenger RNA splicing and diminished SP140 protein levels. Moreover, CD patients carrying SP140 SNPs displayed suppressed innate immune gene signatures in a mixed population of PBMCs that stratified them from other CD patients. Hematopoietic-specific knockdown of Sp140 in mice resulted in exacerbated dextran sulfate sodium (DSS)-induced colitis, and low SP140 levels in human CD intestinal biopsies correlated with relatively lower intestinal innate cytokine levels and improved response to anti-tumor necrosis factor (TNF) therapy. Thus, the epigenetic reader SP140 is a key regulator of macrophage transcriptional programs for cellular state, and a loss of SP140 due to genetic variation contributes to a molecularly defined subset of CD characterized by ineffective innate immunity, normally critical for intestinal homeostasis.