Epigenetic balance ensures mechanistic control of MLL amplification and rearrangement.

MLL/KMT2A amplifications and translocations are prevalent in infant, adult, and therapy-induced leukemia. However, the molecular contributor(s) to these alterations are unclear. Here, we demonstrate that histone H3 lysine 9 mono- and di-methylation (H3K9me1/2) balance at the MLL/KMT2A locus regulates these amplifications and rearrangements. This balance is controlled by the crosstalk between lysine demethylase KDM3B and methyltransferase G9a/EHMT2. KDM3B depletion increases H3K9me1/2 levels and reduces CTCF occupancy at the MLL/KMT2A locus, in turn promoting amplification and rearrangements. Depleting CTCF is also sufficient to generate these focal alterations. Furthermore, the chemotherapy doxorubicin (Dox), which associates with therapy-induced leukemia and promotes MLL/KMT2A amplifications and rearrangements, suppresses KDM3B and CTCF protein levels. KDM3B and CTCF overexpression rescues Dox-induced MLL/KMT2A alterations. G9a inhibition in human cells or mice also suppresses MLL/KMT2A events accompanying Dox treatment. Therefore, MLL/KMT2A amplifications and rearrangements are controlled by epigenetic regulators that are tractable drug targets, which has clinical implications.

METTL13 Methylation of eEF1A Increases Translational Output to Promote Tumorigenesis.

Increased protein synthesis plays an etiologic role in diverse cancers. Here, we demonstrate that METTL13 (methyltransferase-like 13) dimethylation of eEF1A (eukaryotic elongation factor 1A) lysine 55 (eEF1AK55me2) is utilized by Ras-driven cancers to increase translational output and promote tumorigenesis in vivo. METTL13-catalyzed eEF1A methylation increases eEF1A's intrinsic GTPase activity in vitro and protein production in cells. METTL13 and eEF1AK55me2 levels are upregulated in cancer and negatively correlate with pancreatic and lung cancer patient survival. METTL13 deletion and eEF1AK55me2 loss dramatically reduce Ras-driven neoplastic growth in mouse models and in patient-derived xenografts (PDXs) from primary pancreatic and lung tumors. Finally, METTL13 depletion renders PDX tumors hypersensitive to drugs that target growth-signaling pathways. Together, our work uncovers a mechanism by which lethal cancers become dependent on the METTL13-eEF1AK55me2 axis to meet their elevated protein synthesis requirement and suggests that METTL13 inhibition may constitute a targetable vulnerability of tumors driven by aberrant Ras signaling.

Repression of CTSG, ELANE and PRTN3-mediated histone H3 proteolytic cleavage promotes monocyte-to-macrophage differentiation.

Chromatin undergoes extensive reprogramming during immune cell differentiation. Here we report the repression of controlled histone H3 amino terminus proteolytic cleavage (H3ΔN) during monocyte-to-macrophage development. This abundant histone mark in human peripheral blood monocytes is catalyzed by neutrophil serine proteases (NSPs) cathepsin G, neutrophil elastase and proteinase 3. NSPs are repressed as monocytes mature into macrophages. Integrative epigenomic analysis reveals widespread H3ΔN distribution across the genome in a monocytic cell line and primary monocytes, which becomes largely undetectable in fully differentiated macrophages. H3ΔN is enriched at permissive chromatin and actively transcribed genes. Simultaneous NSP depletion in monocytic cells results in H3ΔN loss and further increase in chromatin accessibility, which likely primes the chromatin for gene expression reprogramming. Importantly, H3ΔN is reduced in monocytes from patients with systemic juvenile idiopathic arthritis, an autoinflammatory disease with prominent macrophage involvement. Overall, we uncover an epigenetic mechanism that primes the chromatin to facilitate macrophage development.

FAM86A methylation of eEF2 links mRNA translation elongation to tumorigenesis.

eEF2 post-translational modifications (PTMs) can profoundly affect mRNA translation dynamics. However, the physiologic function of eEF2K525 trimethylation (eEF2K525me3), a PTM catalyzed by the enzyme FAM86A, is unknown. Here, we find that FAM86A methylation of eEF2 regulates nascent elongation to promote protein synthesis and lung adenocarcinoma (LUAD) pathogenesis. The principal physiologic substrate of FAM86A is eEF2, with K525me3 modeled to facilitate productive eEF2-ribosome engagement during translocation. FAM86A depletion in LUAD cells causes 80S monosome accumulation and mRNA translation inhibition. FAM86A is overexpressed in LUAD and eEF2K525me3 levels increase through advancing LUAD disease stages. FAM86A knockdown attenuates LUAD cell proliferation and suppression of the FAM86A-eEF2K525me3 axis inhibits cancer cell and patient-derived LUAD xenograft growth in vivo. Finally, FAM86A ablation strongly attenuates tumor growth and extends survival in KRASG12C-driven LUAD mouse models. Thus, our work uncovers an eEF2 methylation-mediated mRNA translation elongation regulatory node and nominates FAM86A as an etiologic agent in LUAD.

SMYD5 methylation of rpL40 links ribosomal output to gastric cancer.

Dysregulated transcription due to disruption in histone lysine methylation dynamics is an established contributor to tumorigenesis1,2. However, whether analogous pathologic epigenetic mechanisms act directly on the ribosome to advance oncogenesis is unclear. Here we find that trimethylation of the core ribosomal protein L40 (rpL40) at lysine 22 (rpL40K22me3) by the lysine methyltransferase SMYD5 regulates mRNA translation output to promote malignant progression of gastric adenocarcinoma (GAC) with lethal peritoneal ascites. A biochemical-proteomics strategy identifies the monoubiquitin fusion protein partner rpL40 (ref. 3) as the principal physiological substrate of SMYD5 across diverse samples. Inhibiting the SMYD5-rpL40K22me3 axis in GAC cell lines reprogrammes protein synthesis to attenuate oncogenic gene expression signatures. SMYD5 and rpL40K22me3 are upregulated in samples from patients with GAC and negatively correlate with clinical outcomes. SMYD5 ablation in vivo in familial and sporadic mouse models of malignant GAC blocks metastatic disease, including peritoneal carcinomatosis. Suppressing SMYD5 methylation of rpL40 inhibits human cancer cell and patient-derived GAC xenograft growth and renders them hypersensitive to inhibitors of PI3K and mTOR. Finally, combining SMYD5 depletion with PI3K-mTOR inhibition and chimeric antigen receptor T cell administration cures an otherwise lethal in vivo mouse model of aggressive GAC-derived peritoneal carcinomatosis. Together, our work uncovers a ribosome-based epigenetic mechanism that facilitates the evolution of malignant GAC and proposes SMYD5 targeting as part of a potential combination therapy to treat this cancer.

Tip60-mediated H2A.Z acetylation promotes neuronal fate specification and bivalent gene activation.

Cell lineage specification is accomplished by a concerted action of chromatin remodeling and tissue-specific transcription factors. However, the mechanisms that induce and maintain appropriate lineage-specific gene expression remain elusive. Here, we used an unbiased proteomics approach to characterize chromatin regulators that mediate the induction of neuronal cell fate. We found that Tip60 acetyltransferase is essential to establish neuronal cell identity partly via acetylation of the histone variant H2A.Z. Despite its tight correlation with gene expression and active chromatin, loss of H2A.Z acetylation had little effect on chromatin accessibility or transcription. Instead, loss of Tip60 and acetyl-H2A.Z interfered with H3K4me3 deposition and activation of a unique subset of silent, lineage-restricted genes characterized by a bivalent chromatin configuration at their promoters. Altogether, our results illuminate the mechanisms underlying bivalent chromatin activation and reveal that H2A.Z acetylation regulates neuronal fate specification by establishing epigenetic competence for bivalent gene activation and cell lineage transition.

Chemical linguistics: Reading the modified proteome.

In this issue of Molecular Cell, Lin et al. (2021) develop a tri-functional amino acid probe for the discovery and characterization of protein domains that sense or "read" protein post-translational modifications, a chemical tool that can facilitate our understanding of how signaling networks act at the molecular level.

NSD2 dimethylation at H3K36 promotes lung adenocarcinoma pathogenesis.

The etiological role of NSD2 enzymatic activity in solid tumors is unclear. Here we show that NSD2, via H3K36me2 catalysis, cooperates with oncogenic KRAS signaling to drive lung adenocarcinoma (LUAD) pathogenesis. In vivo expression of NSD2E1099K, a hyperactive variant detected in individuals with LUAD, rapidly accelerates malignant tumor progression while decreasing survival in KRAS-driven LUAD mouse models. Pathologic H3K36me2 generation by NSD2 amplifies transcriptional output of KRAS and several complementary oncogenic gene expression programs. We establish a versatile in vivo CRISPRi-based system to test gene functions in LUAD and find that NSD2 loss strongly attenuates tumor progression. NSD2 knockdown also blocks neoplastic growth of PDXs (patient-dervived xenografts) from primary LUAD. Finally, a treatment regimen combining NSD2 depletion with MEK1/2 inhibition causes nearly complete regression of LUAD tumors. Our work identifies NSD2 as a bona fide LUAD therapeutic target and suggests a pivotal epigenetic role of the NSD2-H3K36me2 axis in sustaining oncogenic signaling.

Molecular basis of nucleosomal H3K36 methylation by NSD methyltransferases.

Histone methyltransferases of the nuclear receptor-binding SET domain protein (NSD) family, including NSD1, NSD2 and NSD3, have crucial roles in chromatin regulation and are implicated in oncogenesis1,2. NSD enzymes exhibit an autoinhibitory state that is relieved by binding to nucleosomes, enabling dimethylation of histone H3 at Lys36 (H3K36)3-7. However, the molecular basis that underlies this mechanism is largely unknown. Here we solve the cryo-electron microscopy structures of NSD2 and NSD3 bound to mononucleosomes. We find that binding of NSD2 and NSD3 to mononucleosomes causes DNA near the linker region to unwrap, which facilitates insertion of the catalytic core between the histone octamer and the unwrapped segment of DNA. A network of DNA- and histone-specific contacts between NSD2 or NSD3 and the nucleosome precisely defines the position of the enzyme on the nucleosome, explaining the specificity of methylation to H3K36. Intermolecular contacts between NSD proteins and nucleosomes are altered by several recurrent cancer-associated mutations in NSD2 and NSD3. NSDs that contain these mutations are catalytically hyperactive in vitro and in cells, and their ectopic expression promotes the proliferation of cancer cells and the growth of xenograft tumours. Together, our research provides molecular insights into the nucleosome-based recognition and histone-modification mechanisms of NSD2 and NSD3, which could lead to strategies for therapeutic targeting of proteins of the NSD family.

Elevated NSD3 histone methylation activity drives squamous cell lung cancer.

Amplification of chromosomal region 8p11-12 is a common genetic alteration that has been implicated in the aetiology of lung squamous cell carcinoma (LUSC)1-3. The FGFR1 gene is the main candidate driver of tumorigenesis within this region4. However, clinical trials evaluating FGFR1 inhibition as a targeted therapy have been unsuccessful5. Here we identify the histone H3 lysine 36 (H3K36) methyltransferase NSD3, the gene for which is located in the 8p11-12 amplicon, as a key regulator of LUSC tumorigenesis. In contrast to other 8p11-12 candidate LUSC drivers, increased expression of NSD3 correlated strongly with its gene amplification. Ablation of NSD3, but not of FGFR1, attenuated tumour growth and extended survival in a mouse model of LUSC. We identify an LUSC-associated variant NSD3(T1232A) that shows increased catalytic activity for dimethylation of H3K36 (H3K36me2) in vitro and in vivo. Structural dynamic analyses revealed that the T1232A substitution elicited localized mobility changes throughout the catalytic domain of NSD3 to relieve auto-inhibition and to increase accessibility of the H3 substrate. Expression of NSD3(T1232A) in vivo accelerated tumorigenesis and decreased overall survival in mouse models of LUSC. Pathological generation of H3K36me2 by NSD3(T1232A) reprograms the chromatin landscape to promote oncogenic gene expression signatures. Furthermore, NSD3, in a manner dependent on its catalytic activity, promoted transformation in human tracheobronchial cells and growth of xenografted human LUSC cell lines with amplification of 8p11-12. Depletion of NSD3 in patient-derived xenografts from primary LUSCs containing NSD3 amplification or the NSD3(T1232A)-encoding variant attenuated neoplastic growth in mice. Finally, NSD3-regulated LUSC-derived xenografts were hypersensitive to bromodomain inhibition. Thus, our work identifies NSD3 as a principal 8p11-12 amplicon-associated oncogenic driver in LUSC, and suggests that NSD3-dependency renders LUSC therapeutically vulnerable to bromodomain inhibition.

Decoding chromatin goes high tech.

Identifying proteins that recognize histone methylation is critical for understanding chromatin function. Vermeulen et al. (2010) now describe a cutting-edge strategy to identify and characterize several nuclear proteins and complexes that recognize five major histone trimethyl marks.

SETD3 is an actin histidine methyltransferase that prevents primary dystocia.

For more than 50 years, the methylation of mammalian actin at histidine 73 has been known to occur1. Despite the pervasiveness of His73 methylation, which we find is conserved in several model animals and plants, its function remains unclear and the enzyme that generates this modification is unknown. Here we identify SET domain protein 3 (SETD3) as the physiological actin His73 methyltransferase. Structural studies reveal that an extensive network of interactions clamps the actin peptide onto the surface of SETD3 to orient His73 correctly within the catalytic pocket and to facilitate methyl transfer. His73 methylation reduces the nucleotide-exchange rate on actin monomers and modestly accelerates the assembly of actin filaments. Mice that lack SETD3 show complete loss of actin His73 methylation in several tissues, and quantitative proteomics analysis shows that actin His73 methylation is the only detectable physiological substrate of SETD3. SETD3-deficient female mice have severely decreased litter sizes owing to primary maternal dystocia that is refractory to ecbolic induction agents. Furthermore, depletion of SETD3 impairs signal-induced contraction in primary human uterine smooth muscle cells. Together, our results identify a mammalian histidine methyltransferase and uncover a pivotal role for SETD3 and actin His73 methylation in the regulation of smooth muscle contractility. Our data also support the broader hypothesis that protein histidine methylation acts as a common regulatory mechanism.

The FAM86 domain of FAM86A confers substrate specificity to promote EEF2-Lys525 methylation.

FAM86A is a class I lysine methyltransferase (KMT) that generates trimethylation on the eukaryotic translation elongation factor 2 (EEF2) at Lys525. Publicly available data from The Cancer Dependency Map project indicate high dependence of hundreds of human cancer cell lines on FAM86A expression. This classifies FAM86A among numerous other KMTs as potential targets for future anticancer therapies. However, selective inhibition of KMTs by small molecules can be challenging due to high conservation within the S-adenosyl methionine (SAM) cofactor binding domain among KMT subfamilies. Therefore, understanding the unique interactions within each KMT-substrate pair can facilitate developing highly specific inhibitors. The FAM86A gene encodes an N-terminal FAM86 domain of unknown function in addition to its C-terminal methyltransferase domain. Here, we used a combination of X-ray crystallography, the AlphaFold algorithms, and experimental biochemistry to identify an essential role of the FAM86 domain in mediating EEF2 methylation by FAM86A. To facilitate our studies, we also generated a selective EEF2K525 methyl antibody. Overall, this is the first report of a biological function for the FAM86 structural domain in any species and an example of a noncatalytic domain participating in protein lysine methylation. The interaction between the FAM86 domain and EEF2 provides a new strategy for developing a specific FAM86A small molecule inhibitor, and our results provide an example in which modeling a protein-protein interaction with AlphaFold expedites experimental biology.

Antibody toolkit to investigate eEF1A methylation dynamics in mRNA translation elongation.

Protein synthesis is a fundamental step in gene expression, with modulation of mRNA translation at the elongation step emerging as an important regulatory node in shaping cellular proteomes. In this context, five distinct lysine methylation events on eukaryotic elongation factor 1A (eEF1A), a fundamental nonribosomal elongation factor, are proposed to influence mRNA translation elongation dynamics. However, a lack of affinity tools has hindered progress in fully understanding how eEF1A lysine methylation impacts protein synthesis. Here we develop and characterize a suite of selective antibodies to investigate eEF1A methylation and provide evidence that methylation levels decline in aged tissue. Determination of the methyl state and stoichiometry on eEF1A in various cell lines by mass spectrometry shows modest cell-to-cell variability. We also find by Western blot analysis that knockdown of individual eEF1A-specific lysine methyltransferases leads to depletion of the cognate lysine methylation event and indicates active crosstalk between different sites. Further, we find that the antibodies are specific in immunohistochemistry applications. Finally, application of the antibody toolkit suggests that several eEF1A methylation events decrease in aged muscle tissue. Together, our study provides a roadmap for leveraging methyl state and sequence-selective antibody reagents to accelerate discovery of eEF1A methylation-related functions and suggests a role for eEF1A methylation, via protein synthesis regulation, in aging biology.

Coordination of stress signals by the lysine methyltransferase SMYD2 promotes pancreatic cancer.

Pancreatic ductal adenocarcinoma (PDAC) is a lethal form of cancer with few therapeutic options. We found that levels of the lysine methyltransferase SMYD2 (SET and MYND domain 2) are elevated in PDAC and that genetic and pharmacological inhibition of SMYD2 restricts PDAC growth. We further identified the stress response kinase MAPKAPK3 (MK3) as a new physiologic substrate of SMYD2 in PDAC cells. Inhibition of MAPKAPK3 impedes PDAC growth, identifying a potential new kinase target in PDAC. Finally, we show that inhibition of SMYD2 cooperates with standard chemotherapy to treat PDAC cells and tumors. These findings uncover a pivotal role for SMYD2 in promoting pancreatic cancer.

Lysine methylation of the NF-κB subunit RelA by SETD6 couples activity of the histone methyltransferase GLP at chromatin to tonic repression of NF-κB signaling.

Signaling via the methylation of lysine residues in proteins has been linked to diverse biological and disease processes, yet the catalytic activity and substrate specificity of many human protein lysine methyltransferases (PKMTs) are unknown. We screened over 40 candidate PKMTs and identified SETD6 as a methyltransferase that monomethylated chromatin-associated transcription factor NF-κB subunit RelA at Lys310 (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 the histone methyltransferase GLP, which under basal conditions promoted a repressed chromatin state at RelA target genes through GLP-mediated methylation of histone H3 Lys9 (H3K9). NF-κB-activation-linked phosphorylation of RelA at Ser311 by protein kinase C-ζ (PKC-ζ) blocked the binding of GLP to RelAK310me1 and relieved repression of the target gene. Our findings establish a previously uncharacterized mechanism by which chromatin signaling regulates inflammation programs.

The PZP Domain of AF10 Senses Unmodified H3K27 to Regulate DOT1L-Mediated Methylation of H3K79.

AF10, a DOT1L cofactor, is required for H3K79 methylation and cooperates with DOT1L in leukemogenesis. However, the molecular mechanism by which AF10 regulates DOT1L-mediated H3K79 methylation is not clear. Here we report that AF10 contains a "reader" domain that couples unmodified H3K27 recognition to H3K79 methylation. An AF10 region consisting of a PHD finger-Zn knuckle-PHD finger (PZP) folds into a single module that recognizes amino acids 22-27 of H3, and this interaction is abrogated by H3K27 modification. Structural studies reveal that H3 binding triggers rearrangement of the PZP module to form an H3(22-27)-accommodating channel and that the unmodified H3K27 side chain is encased in a compact hydrogen-bond acceptor-lined cage. In cells, PZP recognition of H3 is required for H3K79 dimethylation, expression of DOT1L-target genes, and proliferation of DOT1L-addicted leukemic cells. Together, our results uncover a pivotal role for H3K27-via readout by the AF10 PZP domain-in regulating the cancer-associated enzyme DOT1L.

Direct readout of heterochromatic H3K9me3 regulates DNMT1-mediated maintenance DNA methylation.

In mammals, repressive histone modifications such as trimethylation of histone H3 Lys9 (H3K9me3), frequently coexist with DNA methylation, producing a more stable and silenced chromatin state. However, it remains elusive how these epigenetic modifications crosstalk. Here, through structural and biochemical characterizations, we identified the replication foci targeting sequence (RFTS) domain of maintenance DNA methyltransferase DNMT1, a module known to bind the ubiquitylated H3 (H3Ub), as a specific reader for H3K9me3/H3Ub, with the recognition mode distinct from the typical trimethyl-lysine reader. Disruption of the interaction between RFTS and the H3K9me3Ub affects the localization of DNMT1 in stem cells and profoundly impairs the global DNA methylation and genomic stability. Together, this study reveals a previously unappreciated pathway through which H3K9me3 directly reinforces DNMT1-mediated maintenance DNA methylation.

Cardioinformatics: the nexus of bioinformatics and precision cardiology.

Cardiovascular disease (CVD) is the leading cause of death worldwide, causing over 17 million deaths per year, which outpaces global cancer mortality rates. Despite these sobering statistics, most bioinformatics and computational biology research and funding to date has been concentrated predominantly on cancer research, with a relatively modest footprint in CVD. In this paper, we review the existing literary landscape and critically assess the unmet need to further develop an emerging field at the multidisciplinary interface of bioinformatics and precision cardiovascular medicine, which we refer to as 'cardioinformatics'.

Nuclear PI5P, Uhrf1, and the road not taken.

In this issue of Molecular Cell, Gelato et al. (2014) identify the signaling molecule phosphatidylinositol 5-phosphate (PI5P) as an allosteric regulator that determines the mode of chromatin binding for the DNA methylation maintenance factor Uhrf1. This work links nuclear lipids to chromatin signaling in the maintenance of DNA methylation and epigenetic regulation.