Nuclear processes such as transcription, DNA replication, and recombination are dynamically regulated by chromatin structure. Transcription is known to be regulated by chromatin-associated proteins containing conserved protein domains that specifically recognize distinct covalent posttranslational modifications on histones. However, it has been unclear whether similar mechanisms are involved in mammalian DNA recombination. Here, we show that RAG2 -an essential component of the RAG1/2 V(D)J recombinase, that mediates antigen receptor gene assembly 1 -contains a plant homeodomain (PHD) finger that specifically recognizes histone H3 trimethylated at lysine 4 (H3K4me3). The high-resolution crystal structure of the RAG2 PHD finger bound to H3K4me3 reveals the molecular basis of H3K4me3-recognition by RAG2. Mutations that abrogate RAG2's recognition of H3K4me3 severely impair V(D)J recombination in vivo. Reducing the level of H3K4me3 similarly leads to a decrease in V(D)J recombination in vivo. Notably, a conserved tryptophan residue (W453) that constitutes a key structural component of the K4me3-binding surface and is essential for RAG2's recognition of H3K4me3 is mutated in patients with immunodeficiency syndromes. Together our results identify a novel function for histone methylation in mammalian DNA recombination. Furthermore, our results provide the first evidence suggesting that disrupting the read-out of histone modifications can cause an inherited human disease. +To whom correspondence should be addressed: oettinger@frodo.mgh.harvard.edu; ogozani@stanford.edu. * These authors contributed equally to the work Note added in proof: While this work was under review, another study also reported that the RAG2 PHD finger binds to methylated H3K4 30 .Atomic coordinates and structure factors of the RAG2 PHD -H3K4me3 peptide complex have been deposited in the Protein Data Bank with the accession code of 2v89. Reprints and permissions information is available at npg.nature.com/reprintsandpermissions.Supplementary Information is linked to the online version of the paper at www.nature.com/nature. Since RAG2 contains a noncanonical plant homeodomain (PHD) finger 6,7 -a module that can mediate interactions with chromatin 8-10 -we asked whether a polypeptide encompassing the RAG2 PHD finger (RAG2 PHD : aa 414-527) can recognize modified histone proteins. In an in vitro screen of peptide microarrays containing ~70 distinct modified histone peptides, we found that RAG2 PHD specifically binds to histone H3 trimethylated at lysine 4 (H3K4me3) ( Fig. 1a ; Fig. S1; data not shown). The specificity of this interaction was confirmed by peptide pulldown assays ( Fig. 1b ; Fig. S2; Fig. S3). RAG2 has a C-terminal extension of 40 aa that is essential for phosphoinositide (PtdInsP)-binding 7 (aa 488-527), but this region is dispensable for H3K4me3-binding as the minimal PHD finger alone (aa 414-487) is sufficient for H3K4me3-recognition (Fig. 1c). In addition, the acidic hinge region of RAG2 (aa 388-412), previously implicated in...

SUMMARY The histone lysine methyltransferase NSD2 (MMSET/WHSC1) is implicated in diverse diseases and commonly overexpressed in multiple myeloma due to a recurrent t(4;14) chromosomal translocation. However, the precise catalytic activity of NSD2 is obscure, preventing progress in understanding how this enzyme influences chromatin biology and myeloma pathogenesis. Here we show that dimethylation of histone H3 at lysine 36 (H3K36me2) is the principal chromatin-regulatory activity of NSD2. Catalysis of H3K36me2 by NSD2 is sufficient for gene activation. In t(4;14)-positive myeloma cells, the normal genome-wide and gene-specific distribution of H3K36me2 is obliterated, creating a chromatin landscape that selects for a transcription profile favorable for myelomagenesis. Catalytically active NSD2 confers xenograft tumor formation upon t(4;14)-negative cells, and promotes oncogenic transformation of primary cells in an H3K36me2-dependent manner. Together our findings establish H3K36me2 as the primary product generated by NSD2, and demonstrate that genomic disorganization of this canonical chromatin mark by NSD2 initiates oncogenic programming.

COVID-19 is associated with a wide range of clinical manifestations, including autoimmune features and autoantibody production. Here we develop three protein arrays to measure IgG autoantibodies associated with connective tissue diseases, anti-cytokine antibodies, and anti-viral antibody responses in serum from 147 hospitalized COVID-19 patients. Autoantibodies are identified in approximately 50% of patients but in less than 15% of healthy controls. When present, autoantibodies largely target autoantigens associated with rare disorders such as myositis, systemic sclerosis and overlap syndromes. A subset of autoantibodies targeting traditional autoantigens or cytokines develop de novo following SARS-CoV-2 infection. Autoantibodies track with longitudinal development of IgG antibodies recognizing SARS-CoV-2 structural proteins and a subset of non-structural proteins, but not proteins from influenza, seasonal coronaviruses or other pathogenic viruses. We conclude that SARS-CoV-2 causes development of new-onset IgG autoantibodies in a significant proportion of hospitalized COVID-19 patients and are positively correlated with immune responses to SARS-CoV-2 proteins.

Recognition of distinctly modified histones by specialized “effector” proteins constitutes a key mechanism for transducing molecular events at chromatin to biological outcomes1. Effector proteins influence DNA-templated processes, including transcription, DNA recombination, and DNA repair; however, no effector functions have yet been identified within the mammalian machinery that regulates DNA replication. Here we show that ORC1 – a component of ORC (origin of replication complex), which mediates pre-DNA replication licensing2 – contains a BAH (bromo adjacent homology) domain that specifically recognizes histone H4 dimethylated at lysine 20 (H4K20me2). Recognition of H4K20me2 is a property common to BAH domains present within diverse metazoan ORC1 proteins. Structural studies reveal that the specificity of the BAH domain for H4K20me2 is mediated by a dynamic aromatic dimethyllysine-binding cage and multiple intermolecular contacts involving the bound peptide. H4K20me2 is enriched at replication origins and abrogating ORC1 recognition of H4K20me2 in cells impairs ORC1 occupancy at origins, ORC chromatin loading, and cell-cycle progression. Mutation of the ORC1 BAH domain has been implicated in the etiology of Meier-Gorlin syndrome (MGS)3,4, a form of primordial dwarfism5, and ORC1 depletion in zebrafish results in an MGS-like phenotype4. We find that wild-type human ORC1, but not ORC1 H4K20me2-binding mutants, rescues the growth retardation of orc1 morphants. Moreover, zebrafish depleted of H4K20me2 have diminished body size, mirroring the phenotype of orc1 morphants. Together, our results identify the BAH domain as a novel methyllysine-binding module, thereby establishing the first direct link between histone methylation and the metazoan DNA replication machinery, and defining a pivotal etiologic role for the canonical H4K20me2 mark, via ORC1, in primordial dwarfism.

The NSD (nuclear receptor SET domain-containing) family of histone lysine methyltransferases is a critical participant in chromatin integrity as evidenced by the number of human diseases associated with the aberrant expression of its family members. Yet, the specific targets of these enzymes are not clear, with marked discrepancies being reported in the literature. We demonstrate that NSD2 can exhibit disparate target preferences based on the nature of the substrate provided. The NSD2 complex purified from human cells and recombinant NSD2 both exhibit specific targeting of histone H3 lysine 36 (H3K36) when provided with nucleosome substrates, but histone H4 lysine 44 is the primary target in the case of octamer substrates, irrespective of the histones being native or recombinant. This disparity is negated when NSD2 is presented with octamer targets in conjunction with short single- or double-stranded DNA. Although the octamers cannot form nucleosomes, the target is nonetheless nucleosome-specific as is the product, dimethylated H3K36. This study clarifies in part the previous discrepancies reported with respect to NSD targets. We propose that DNA acts as an allosteric effector of NSD2 such that H3K36 becomes the preferred target.

Protein lysine methylation signaling is implicated in diverse biological and disease processes. Yet the catalytic activity and substrate specificity are unknown for many human protein lysine methyltransferases (PKMTs). We screened over forty candidate PKMTs and identified SETD6 as a methyltransferase that monomethylates chromatin-associated NF-κB RelA at lysine 310 (RelAK310me1). SETD6-mediated methylation rendered RelA inert and attenuated RelA-driven transcriptional programs, including inflammatory responses in primary immune cells. RelAK310me1 was recognized by the ankryin repeat of GLP, which under basal conditions, promoted a repressed chromatin state at RelA target genes through GLP-mediated H3K9 methylation. NF-κB activation-linked phosphorylation of RelA by PKCζ at serine 311 blocked GLP binding to RelAK310me1 and relieved target gene repression. Our findings establish a new mechanism by which chromatin signaling regulates inflammation programs.

Post-translational modifications of histone proteins and exchanges of histone variants of chromatin are central to the regulation of nearly all DNA-templated biological processes. However, the degree and variability of chromatin modifications in specific human immune cells remain largely unknown. Here, we employ a highly multiplexed mass cytometry analysis to profile the global levels of a broad array of chromatin modifications in primary human immune cells at the single-cell level. Our data reveal markedly different cell-type- and hematopoietic-lineage-specific chromatin modification patterns. Differential analysis between younger and older adults shows that aging is associated with increased heterogeneity between individuals and elevated cell-to-cell variability in chromatin modifications. Analysis of a twin cohort unveils heritability of chromatin modifications and demonstrates that aging-related chromatin alterations are predominantly driven by non-heritable influences. Together, we present a powerful platform for chromatin and immunology research. Our discoveries highlight the profound impacts of aging on chromatin modifications.

Recombination activating gene (RAG) 1 and RAG2 together catalyze V(D)J gene rearrangement in lymphocytes as the first step in the assembly and maturation of antigen receptors. RAG2 contains a plant homeodomain (PHD) near its C terminus (RAG2-PHD) that recognizes histone H3 methylated at lysine 4 (H3K4me) and influences V(D)J recombination. We report here crystal structures of RAG2-PHD alone and complexed with five modified H3 peptides. Two aspects of RAG2-PHD are unique. First, in the absence of the modified peptide, a peptide N-terminal to RAG2-PHD occupies the substrate-binding site, which may reflect an autoregulatory mechanism. Second, in contrast to other H3K4me3-binding PHD domains, RAG2-PHD substitutes a carboxylate that interacts with arginine 2 (R2) with a Tyr, resulting in binding to H3K4me3 that is enhanced rather than inhibited by dimethylation of R2. Five residues involved in histone H3 recognition were found mutated in severe combined immunodeficiency (SCID) patients. Disruption of the RAG2-PHD structure appears to lead to the absence of T and B lymphocytes, whereas failure to bind H3K4me3 is linked to Omenn Syndrome. This work provides a molecular basis for chromatindependent gene recombination and presents a single protein domain that simultaneously recognizes two distinct histone modifications, revealing added complexity in the read-out of combinatorial histone modifications.J recombination is the site-specific DNA rearrangement that assembles antigen receptor genes from dispersed arrays of V, D, and J gene segments. Recombination is initiated by the lymphoid-specific recombination activating gene (RAG) 1 and RAG2 recombinase, which recognizes and cleaves the recombination signal sequences (1). V(D)J recombination is tightly regulated, occurring in a preferred temporal order and only in specific cell types and developmental stages. Ig heavy chain rearrangement precedes light chain rearrangement and Ig heavy-chain D to J joining precedes V to DJ recombination. In addition, Ig genes are fully rearranged only in B cells (not T cells), and T cell receptor genes are assembled in T but not B cells (1). Overexpression of RAG1 and RAG2 in nonlymphoid cells is sufficient to induce recombination of an artificial extrachromosomal substrate but does not support V(D)J recombination of endogenous loci (2). Therefore, the accessibility of these loci to the recombinase must be regulated (3). A large body of evidence suggests that the regulation of chromatin structure is involved in the regulation of V(D)J recombination (4-6).