JMJD5 is a human arginyl C-3 hydroxylase

Insights into the role of histone lysine demethylases in bone homeostasis and skeletal diseases: A review

Histone lysine demethylases (KDMs), as important epigenetic regulators, are involved in various biological processes such as energy metabolism, apoptosis, and autophagy. Recent research shows that KDMs activate or silence downstream target genes by removing lysine residues from histone tails, and participate in the regulation of bone marrow mesenchymal stem cells (BM-MSCs), osteoblasts (OB), osteoclasts (OC), chondrocytes and other skeletal cell development, differentiation and formation. Moreover, several members of the KDM family affect the occurrence and development of bone diseases such as osteoporosis (OP), osteoarthritis (OA), osteosarcoma (OS), by regulating target genes. Specific regulation mechanisms of KDMs suggest new strategies for bone disease treatment and prevention. Despite the unique function and importance of KDMs in the skeletal system, previous studies have never systematically summarized their specific role, molecular mechanism, and clinical treatment in bone physiology and pathology. Therefore, this review summarises the expression pattern, intracellular signal transduction, and mechanism of action of the KDM family in several bone physiological and pathological conditions, aiming to highlight the important role of KDMs in bone diseases and provide a reference for the future treatment of bone diseases.

Biochemical investigations using mass spectrometry to monitor JMJD6-catalysed hydroxylation of multi-lysine containing bromodomain-derived substrates

Jumonji-C domain-containing protein 6 (JMJD6) is a human 2-oxoglutarate (2OG)/Fe(ii)-dependent oxygenase catalysing post-translational C5 hydroxylation of multiple lysine residues, including in the bromodomain-containing proteins BRD2, BRD3 and BRD4. The role(s) of JMJD6-catalysed substrate hydroxylation are unclear. JMJD6 is important in development and JMJD6 catalysis may promote cancer. We report solid-phase extraction coupled to mass spectrometry assays monitoring JMJD6-catalysed hydroxylation of BRD2-4 derived oligopeptides containing multiple lysyl residues. The assays enabled determination of apparent steady-state kinetic parameters for 2OG, Fe(ii), l-ascorbate, O2 and BRD substrates. The JMJD6 K app m for O2 was comparable to that reported for the structurally related 2OG oxygenase factor inhibiting hypoxia-inducible factor-α (FIH), suggesting potential for limitation of JMJD6 activity by O2 availability in cells, as proposed for FIH and some other 2OG oxygenases. The new assays will help development of small-molecule JMJD6 inhibitors for functional assignment studies and as potential cancer therapeutics.

Dynamic kinetic resolution-mediated synthesis of C-3 hydroxylated arginine derivatives

Hydroxylated amino acids and their derivatives, including those found in proteins, are important in biology and medicinal chemistry. Incubation of N-acetyl-l-arginine with clavaminic acid synthase, a key oxygenase in clavulanic acid biosynthesis, affords a (3R)-hydroxylated product that is identical to material obtained by total synthesis from Boc-beta alanine. The key step employed dynamic kinetic resolution (DKR) of a β-ketoester precursor, achieved in high diastereomeric and enantiomeric excess using an (R)-SEGPHOS/Ru(II) catalyst. The results highlight the utility of DKR for the preparation of C-3 hydroxylated amino acid derivatives.

Fe(II) and 2-oxoglutarate-dependent dioxygenases for natural product synthesis: molecular insights into reaction diversity

Covering: up to 2024Fe(II) and 2-oxoglutarate-dependent dioxygenases (Fe/2OG DOs) are a superfamily of enzymes that play important roles in a variety of catalytic reactions, including hydroxylation, ring formation, ring reconstruction, desaturation, and demethylation. Each member of this family has similarities in their overall structure, but they have varying specific differences, making Fe/2OG DOs attractive for catalytic diversity. With the advancement of current research, more Fe/2OG DOs have been discovered, and their catalytic scope has been further broadened; however, apart from hydroxylation, many reaction mechanisms have not been accurately demonstrated, and there is a lack of a systematic understanding of their molecular basis. Recently, an increasing number of X-ray structures of Fe/2OG DOs have provided new insights into the structural basis of their function and substrate-binding properties. This structural information is essential for understanding catalytic mechanisms and mining potential catalytic reactions. In this review, we summarize most of the Fe/2OG DOs whose structures have been resolved in recent years, focus on their structural features, and explore the relationships between various structural elements and unique catalytic mechanisms and their associated reaction type classification.

Substrate selectivity and inhibition of the human lysyl hydroxylase JMJD7

Jumonji-C (JmjC) domain-containing protein 7 (JMJD7) is a human Fe(II) and 2-oxoglutarate dependent oxygenase that catalyzes stereospecific C3-hydroxylation of lysyl-residues in developmentally regulated GTP binding proteins 1 and 2 (DRG1/2). We report studies exploring a diverse set of lysine derivatives incorporated into the DRG1 peptides as potential human JMJD7 substrates and inhibitors. The results indicate that human JMJD7 has a relatively narrow substrate scope beyond lysine compared to some other JmjC hydroxylases and lysine-modifying enzymes. The geometrically constrained (E)-dehydrolysine is an efficient alternative to lysine for JMJD7-catalyzed C3-hydroxylation. γ-Thialysine and γ-azalysine undergo C3-hydroxylation, followed by degradation to formylglycine. JMJD7 also catalyzes the S-oxidation of DRG1-derived peptides possessing methionine and homomethionine residues in place of lysine. Inhibition assays show that DRG1 variants possessing cysteine/selenocysteine instead of the lysine residue efficiently inhibit JMJD7 via cross-linking. The overall results inform on the substrate selectivity and inhibition of human JMJD7, which will help enable the rational design of selective small-molecule and peptidomimetic inhibitors of JMJD7.

Review and new insights into the catalytic structural domains of the Fe(ll) and 2-Oxoglutarate families

Histone lysine demethylase (KDM), AlkB homolog (ALKBH), and Ten-Eleven Translocation (TET) proteins are members of the 2-Oxoglutarate (2OG) and ferrous iron-dependent oxygenases, each of which harbors a catalytic domain centered on a double-stranded β-helix whose topology restricts the regions directly involved in substrate binding. However, they have different catalytic functions, and the deeply structural biological reasons are not yet clear. In this review, the catalytic domain features of the three protein families are summarized from both sequence and structural perspectives. The construction of the phylogenetic tree and comparison of the structure show ten relatively conserved β-sheets and three key regions with substantial structural differences. We summarize the relationship between three key regions of remarkable differences and the substrate compatibility of the three protein families. This review facilitates research into substrate-selective inhibition and bioengineering by providing new insights into the catalytic domains of KDM, ALKBH, and TET proteins.

Deciphering KDM8 dysregulation and CpG methylation in hepatocellular carcinoma using multi-omics and machine learning

Aim: This study investigates the altered expression and CpG methylation patterns of histone demethylase KDM8 in hepatocellular carcinoma (HCC), aiming to uncover insights and promising diagnostics biomarkers.Materials & methods: Leveraging TCGA-LIHC multi-omics data, we employed R/Bioconductor libraries and Cytoscape to analyze and construct a gene correlation network, and LASSO regression to develop an HCC-predictive model.Results: In HCC, KDM8 downregulation is correlated with CpGs hypermethylation. Differential gene correlation analysis unveiled a liver carcinoma-associated network marked by increased cell division and compromised liver-specific functions. The LASSO regression identified a highly accurate HCC prediction signature, prominently featuring CpG methylation at cg02871891.Conclusion: Our study uncovers CpG hypermethylation at cg02871891, possibly influencing KDM8 downregulation in HCC, suggesting these as promising biomarkers and targets.

Recent Advances and Therapeutic Implications of 2-Oxoglutarate-Dependent Dioxygenases in Ischemic Stroke

Ischemic stroke is a common disease with a high disability rate and mortality, which brings heavy pressure on families and medical insurance. Nowadays, the golden treatments for ischemic stroke in the acute phase mainly include endovascular therapy and intravenous thrombolysis. Some drugs are used to alleviate brain injury in patients with ischemic stroke, such as edaravone and 3-n-butylphthalide. However, no effective neuroprotective drug for ischemic stroke has been acknowledged. 2-Oxoglutarate-dependent dioxygenases (2OGDDs) are conserved and common dioxygenases whose activities depend on O2, Fe2+, and 2OG. Most 2OGDDs are expressed in the brain and are essential for the development and functions of the brain. Therefore, 2OGDDs likely play essential roles in ischemic brain injury. In this review, we briefly elucidate the functions of most 2OGDDs, particularly the effects of regulations of 2OGDDs on various cells in different phases after ischemic stroke. It would also provide promising potential therapeutic targets and directions of drug development for protecting the brain against ischemic injury and improving outcomes of ischemic stroke.

To Erase or Not to Erase: Non-Canonical Catalytic Functions and Non-Catalytic Functions of Members of Histone Lysine Demethylase Families

Histone lysine demethylases (KDMs) play an essential role in biological processes such as transcription regulation, RNA maturation, transposable element control, and genome damage sensing and repair. In most cases, their action requires catalytic activities, but non-catalytic functions have also been shown in some KDMs. Indeed, some strictly KDM-related proteins and some KDM isoforms do not act as histone demethylase but show other enzymatic activities or relevant non-enzymatic functions in different cell types. Moreover, many studies have reported on functions potentially supported by catalytically dead mutant KDMs. This is probably due to the versatility of the catalytical core, which can adapt to assume different molecular functions, and to the complex multi-domain structure of these proteins which encompasses functional modules for targeting histone modifications, promoting protein-protein interactions, or recognizing nucleic acid structural motifs. This rich modularity and the availability of multiple isoforms in the various classes produced variants with enzymatic functions aside from histone demethylation or variants with non-catalytical functions during the evolution. In this review we will catalog the proteins with null or questionable demethylase activity and predicted or validated inactive isoforms, summarizing what is known about their alternative functions. We will then go through some experimental evidence for the non-catalytical functions of active KDMs.

Taking Me away: the function of phosphorylation on histone lysine demethylases

Histone lysine demethylases (KDMs) regulate eukaryotic gene transcription by catalysing the removal of methyl groups from histone proteins. These enzymes are intricately regulated by the kinase signalling system in response to internal and external stimuli. Here, we review the mechanisms by which kinase-mediated phosphorylation influence human histone KDM function. These include the changing of histone KDM subcellular localisation or chromatin binding, the altering of protein half-life, changes to histone KDM complex formation that result in histone demethylation, non-histone demethylation or demethylase-independent effects, and effects on histone KDM complex dissociation. We also explore the structural context of phospho-sites on histone KDMs and evaluate how this relates to function.

JMJD5 inhibits lung cancer progression by facilitating EGFR proteasomal degradation

Aberrant activation of epidermal growth factor receptor (EGFR) signaling is closely related to the development of non-small cell lung cancer (NSCLC). However, targeted EGFR therapeutics such as tyrosine kinase inhibitors (TKIs) face the challenge of EGFR mutation-mediated resistance. Here, we showed that the reduced JmjC domain-containing 5 (JMJD5) expression is negatively associated with EGFR stability and NSCLC progression. Mechanically, JMJD5 cooperated with E3 ligase HUWE1 to destabilize EGFR and EGFR TKI-resistant mutants for proteasomal degradation, thereby inhibiting NSCLC growth and promoting TKI sensitivity. Furthermore, we identified that JMJD5 can be transported into recipient cells via extracellular vesicles, thereby inhibiting the growth of NSCLC. Together, our findings demonstrate the tumor-suppressive role of JMJD5 in NSCLC and suggest a putative therapeutic strategy for EGFR-related NSCLC by targeting JMJD5 to destabilize EGFR.

5-Substituted Pyridine-2,4-dicarboxylate Derivatives Have Potential for Selective Inhibition of Human Jumonji-C Domain-Containing Protein 5

Jumonji-C domain-containing protein 5 (JMJD5) is a 2-oxoglutarate (2OG)-dependent oxygenase that plays important roles in development, circadian rhythm, and cancer through unclear mechanisms. JMJD5 has been reported to have activity as a histone protease, as an Nε-methyl lysine demethylase, and as an arginine residue hydroxylase. Small-molecule JMJD5-selective inhibitors will be useful for investigating its (patho)physiological roles. Following the observation that the broad-spectrum 2OG oxygenase inhibitor pyridine-2,4-dicarboxylic acid (2,4-PDCA) is a 2OG-competing JMJD5 inhibitor, we report that 5-aminoalkyl-substituted 2,4-PDCA derivatives are potent JMJD5 inhibitors manifesting selectivity for JMJD5 over other human 2OG oxygenases. Crystallographic analyses with five inhibitors imply induced fit binding and reveal that the 2,4-PDCA C5 substituent orients into the JMJD5 substrate-binding pocket. Cellular studies indicate that the lead compounds display similar phenotypes as reported for clinically observed JMJD5 variants, which have a reduced catalytic activity compared to wild-type JMJD5.

Kinetic and inhibition studies on human Jumonji-C (JmjC) domain-containing protein 5

Jumonji-C (JmjC) domain-containing protein 5 (JMJD5) is a human 2-oxoglutarate (2OG) and Fe(ii)-dependent oxygenase which catalyses the post-translational C3 hydroxylation of arginyl-residues and which is linked to the circadian rhythm and to cancer biology through as yet unidentified mechanisms. We report robust solid phase extraction coupled to mass spectrometry (SPE-MS)-based JMJD5 assays which enable kinetic and high-throughput inhibition studies. The kinetic studies reveal that some synthetic 2OG derivatives, notably including a 2OG derivative with a cyclic carbon backbone (i.e. (1R)-3-(carboxycarbonyl)cyclopentane-1-carboxylic acid), are efficient alternative cosubstrates of JMJD5 and of factor inhibiting hypoxia-inducible transcription factor HIF-α (FIH), but not of the Jumonji-C (JmjC) histone Nε-methyl lysine demethylase KDM4E, apparently reflecting the closer structural similarity of JMJD5 and FIH. The JMJD5 inhibition assays were validated by investigating the effect of reported 2OG oxygenase inhibitors on JMJD5 catalysis; the results reveal that broad-spectrum 2OG oxygenase inhibitors are also efficient JMJD5 inhibitors (e.g. N-oxalylglycine, pyridine-2,4-dicarboxylic acid, ebselen) whereas most 2OG oxygenase inhibitors that are in clinical use (e.g. roxadustat) do not inhibit JMJD5. The SPE-MS assays will help enable the development of efficient and selective JMJD5 inhibitors for investigating the biochemical functions of JMJD5 in cellular studies.

JMJD5 inhibits lung cancer progression by regulating glucose metabolism through the p53/TIGAR pathway

Metabolic reprogramming is considered one of the main driving forces for tumor progression, providing energy and substrates of biosynthesis to support rapid neoplastic proliferation. Particularly, the tumor suppressor protein p53 was shown to revert the Warburg effect and play complex roles in regulating glucose metabolism. Jumonji C domain-containing protein 5 (JMJD5) has previously been reported as a negative regulator of p53. However, the role of JMJD5 in p53-mediated metabolic reprogramming remains elusive. Here, we discovered that knockdown of JMJD5 significantly enhances TIGAR expression in p53 wild-type non-small cell lung cancer (NSCLC) cells, which could further suppress glycolysis and promote the pentose phosphate pathway. Besides, JMJD5 knockdown promotes the NSCLC cell proliferation in vitro and xenograft tumor growth in vivo, while silencing TIGAR can abolish this effect. Low JMJD5 expression levels are associated with elevated TIGAR levels and correlates with poor prognosis in lung cancer patients. Taken together, our findings suggest that JMJD5 is a key regulator of tumor glucose metabolism by targeting the p53/TIGAR metabolic pathway.

Impaired protein hydroxylase activity causes replication stress and developmental abnormalities in humans

Although protein hydroxylation is a relatively poorly characterized posttranslational modification, it has received significant recent attention following seminal work uncovering its role in oxygen sensing and hypoxia biology. Although the fundamental importance of protein hydroxylases in biology is becoming clear, the biochemical targets and cellular functions often remain enigmatic. JMJD5 is a "JmjC-only" protein hydroxylase that is essential for murine embryonic development and viability. However, no germline variants in JmjC-only hydroxylases, including JMJD5, have yet been described that are associated with any human pathology. Here we demonstrate that biallelic germline JMJD5 pathogenic variants are deleterious to JMJD5 mRNA splicing, protein stability, and hydroxylase activity, resulting in a human developmental disorder characterized by severe failure to thrive, intellectual disability, and facial dysmorphism. We show that the underlying cellular phenotype is associated with increased DNA replication stress and that this is critically dependent on the protein hydroxylase activity of JMJD5. This work contributes to our growing understanding of the role and importance of protein hydroxylases in human development and disease.

Bone Marrow Mesenchymal Stem Cells Reversed Ovarian Aging-related m6A RNA Methylation Modification Profile in Aged Granulosa Cells

BACKGROUND

Ovarian ageing causes endocrine disturbances and the degeneration of systemic tissue and organ functions to seriously affect women's physical and mental health, and effective treatment methods are urgently needed. Based on our previous studies using juvenile rhesus monkey bone marrow mesenchymal stem cells (BMMSCs) to treat ovarian ageing in rhesus monkey, we found that BMMSCs improved ovarian structure and function. This study continues to explore the mechanism by which BMMSCs reversed granulosa cell (GC) ageing.

METHODS

A GC ageing model and coculture system of BMMSCs were established, changes in the level of the N6-methyladenosine (m6A) methylation modification were detected, m6A-modified RNA immunoprecipitation sequencing (MeRIP-seq) were performed, correlations between m6A peaks and mRNA expression were determined, and the expression of hub genes was identified using Q-PCR, immunofluorescence staining, and western blot.

RESULTS

Our results showed that H₂O₂ successfully induced GC ageing and that BMMSCs reversed measures of GC ageing. BMMSCs increased the expression of the FTO protein and reduced the overall level of m6A. We identified 797 m6A peaks (348 hypomethylated and 449 hypermethylated peaks) and 817 differentially expressed genes (DEGs) (412 upregulated and 405 downregulated) after aged GCs were cocultured with BMMSCs, which significantly associated with ovarian function and epigenetic modification. The epigenetic repressive mark and important cell cycle regulator lysine demethylase 8 (KDM8) was downregulated at both the mRNA and protein levels, histone H3 was upregulated in aged GCs after BMMSC coculture, and KDM8 was upregulated after FTO was inhibited through FB23.

CONCLUSIONS

Our study revealed an essential role for m6A in BMMSCs in reversing GC ageing, and FTO regulated KDM8 mediates histone H3 changes may as a novel regulatory mechanism in BMMSCs to reverse GC ageing.

JMJD8 Functions as a Novel AKT1 Lysine Demethylase

JMJD8 is a protein from the JMJD family that only has the JmjC domain. Studies on the function of JMJD8 indicate that JMJD8 is involved in signaling pathways, including AKT/NF-κB, and thus affects cell proliferation and development. Here, we reported the activity of JMJD8 as a non-histone demethylase. We investigated the demethylation of JMJD8 on trimethylated lysine of AKT1 in vivo and in vitro using trimethylated AKT1 short peptide and AKT1 protein, and we tracked the regulation of JMJD8 on AKT1 activity at the cellular level. The results showed that JMJD8, a mini lysine demethylase, altered AKT1 protein function via changing its degree of methylation.

Structural analysis of the 2-oxoglutarate binding site of the circadian rhythm linked oxygenase JMJD5

JmjC (Jumonji-C) domain-containing 5 (JMJD5) plays important roles in circadian regulation in plants and humans and is involved in embryonic development and cell proliferation. JMJD5 is a 2-oxoglutarate (2OG) and Fe(II) dependent oxygenase of the JmjC subfamily, which includes histone Nε-methyl lysine-demethylases (KDMs) and hydroxylases catalysing formation of stable alcohol products. JMJD5 is reported to have KDM activity, but has been shown to catalyse C-3 hydroxylation of arginine residues in sequences from human regulator of chromosome condensation domain-containing protein 1 (RCCD1) and ribosomal protein S6 (RPS6) in vitro. We report crystallographic analyses of human JMJD5 complexed with 2OG analogues, including the widely used hypoxia mimic pyridine-2,4-dicarboxylate, both D- and L-enantiomers of the oncometabolite 2-hydroxyglutarate, and a cyclic N-hydroxyimide. The results support the assignment of JMJD5 as a protein hydroxylase and reveal JMJD5 has an unusually compact 2OG binding pocket suitable for exploitation in development of selective inhibitors. They will be useful in the development of chemical probes to investigate the physiologically relevant roles of JMJD5 in circadian rhythm and development and explore its potential as a medicinal chemistry target.

JMJD family proteins in cancer and inflammation

The occurrence of cancer entails a series of genetic mutations that favor uncontrollable tumor growth. It is believed that various factors collectively contribute to cancer, and there is no one single explanation for tumorigenesis. Epigenetic changes such as the dysregulation of enzymes modifying DNA or histones are actively involved in oncogenesis and inflammatory response. The methylation of lysine residues on histone proteins represents a class of post-translational modifications. The human Jumonji C domain-containing (JMJD) protein family consists of more than 30 members. The JMJD proteins have long been identified with histone lysine demethylases (KDM) and histone arginine demethylases activities and thus could function as epigenetic modulators in physiological processes and diseases. Importantly, growing evidence has demonstrated the aberrant expression of JMJD proteins in cancer and inflammatory diseases, which might serve as an underlying mechanism for the initiation and progression of such diseases. Here, we discuss the role of key JMJD proteins in cancer and inflammation, including the intensively studied histone lysine demethylases, as well as the understudied group of JMJD members. In particular, we focused on epigenetic changes induced by each JMJD member and summarized recent research progress evaluating their therapeutic potential for the treatment of cancer and inflammatory diseases.

Structure and mechanism of histone methylation dynamics in Arabidopsis

Histone methylation plays a central role in regulating chromatin state and gene expression in Arabidopsis and is involved in a variety of physiological and developmental processes. Dynamic regulation of histone methylation relies on both histone methyltransferase "writer" and histone demethylases "eraser" proteins. In this review, we focus on the four major histone methylation modifications in Arabidopsis H3, H3K4, H3K9, H3K27, and H3K36, and summarize current knowledge of the dynamic regulation of these modifications, with an emphasis on the biochemical and structural perspectives of histone methyltransferases and demethylases.

The Novel Protease Activities of JMJD5–JMJD6–JMJD7 and Arginine Methylation Activities of Arginine Methyltransferases Are Likely Coupled

The surreptitious discoveries of the protease activities on arginine-methylated targets of a subfamily of Jumonji domain-containing family including JMJD5, JMJD6, and JMJD7 pose several questions regarding their authenticity, function, purpose, and relations with others. At the same time, despite several decades of efforts and massive accumulating data regarding the roles of the arginine methyltransferase family (PRMTs), the exact function of this protein family still remains a mystery, though it seems to play critical roles in transcription regulation, including activation and inactivation of a large group of genes, as well as other biological activities. In this review, we aim to elucidate that the function of JMJD5/6/7 and PRMTs are likely coupled. Besides roles in the regulation of the biogenesis of membrane-less organelles in cells, they are major players in regulating stimulating transcription factors to control the activities of RNA Polymerase II in higher eukaryotes, especially in the animal kingdom. Furthermore, we propose that arginine methylation by PRMTs could be a ubiquitous action marked for destruction after missions by a subfamily of the Jumonji protein family.

Ribosomal Protein S6: A Potential Therapeutic Target against Cancer?

Ribosomal protein S6 (RPS6) is a component of the 40S small ribosomal subunit and participates in the control of mRNA translation. Additionally, phospho (p)-RPS6 has been recognized as a surrogate marker for the activated PI3K/AKT/mTORC1 pathway, which occurs in many cancer types. However, downstream mechanisms regulated by RPS6 or p-RPS remains elusive, and the therapeutic implication of RPS6 is underappreciated despite an approximately half a century history of research on this protein. In addition, substantial evidence from RPS6 knockdown experiments suggests the potential role of RPS6 in maintaining cancer cell proliferation. This motivates us to investigate the current knowledge of RPS6 functions in cancer. In this review article, we reviewed the current information about the transcriptional regulation, upstream regulators, and extra-ribosomal roles of RPS6, with a focus on its involvement in cancer. We also discussed the therapeutic potential of RPS6 in cancer.

Histone lysine demethylases and their functions in cancer

Histone lysine demethylases (KDMs) are enzymes that remove the methylation marks on lysines in nucleosomes' histone tails. These changes in methylation marks regulate gene transcription during both development and malignant transformation. Depending on which lysine residue is targeted, the effect of a given KDM on gene transcription can be either activating or repressing, and KDMs can regulate the expression of both oncogenes and tumour suppressors. Thus, the functions of KDMs can be regarded as both oncogenic and tumour suppressive, contingent on cell context and the enzyme isoform. Finally, KDMs also demethylate nonhistone proteins and have a variety of demethylase-independent functions. These epigenetic and other mechanisms that KDMs control make them important regulators of malignant tumours. Here, we present an overview of eight KDM subfamilies, their most-studied lysine targets and selected recent data on their roles in cancer stem cells, tumour aggressiveness and drug tolerance.

Roles of HIF and 2-Oxoglutarate-Dependent Dioxygenases in Controlling Gene Expression in Hypoxia

Simple Summary

Hypoxia—reduction in oxygen availability—plays key roles in both physiological and pathological processes. Given the importance of oxygen for cell and organism viability, mechanisms to sense and respond to hypoxia are in place. A variety of enzymes utilise molecular oxygen, but of particular importance to oxygen sensing are the 2-oxoglutarate (2-OG) dependent dioxygenases (2-OGDs). Of these, Prolyl-hydroxylases have long been recognised to control the levels and function of Hypoxia Inducible Factor (HIF), a master transcriptional regulator in hypoxia, via their hydroxylase activity. However, recent studies are revealing that such dioxygenases are involved in almost all aspects of gene regulation, including chromatin organisation, transcription and translation.

Abstract

Hypoxia—reduction in oxygen availability—plays key roles in both physiological and pathological processes. Given the importance of oxygen for cell and organism viability, mechanisms to sense and respond to hypoxia are in place. A variety of enzymes utilise molecular oxygen, but of particular importance to oxygen sensing are the 2-oxoglutarate (2-OG) dependent dioxygenases (2-OGDs). Of these, Prolyl-hydroxylases have long been recognised to control the levels and function of Hypoxia Inducible Factor (HIF), a master transcriptional regulator in hypoxia, via their hydroxylase activity. However, recent studies are revealing that dioxygenases are involved in almost all aspects of gene regulation, including chromatin organisation, transcription and translation. We highlight the relevance of HIF and 2-OGDs in the control of gene expression in response to hypoxia and their relevance to human biology and health.

Human 2-oxoglutarate-dependent oxygenases: nutrient sensors, stress responders, and disease mediators

Fe(II)/2-oxoglutarate (2OG)-dependent oxygenases are a conserved enzyme class that catalyse diverse oxidative reactions across nature. In humans, these enzymes hydroxylate a broad range of biological substrates including DNA, RNA, proteins and some metabolic intermediates. Correspondingly, members of the 2OG-dependent oxygenase superfamily have been linked to fundamental biological processes, and found dysregulated in numerous human diseases. Such findings have stimulated efforts to understand both the biochemical activities and cellular functions of these enzymes, as many have been poorly studied. In this review, we focus on human 2OG-dependent oxygenases catalysing the hydroxylation of protein and polynucleotide substrates. We discuss their modulation by changes in the cellular microenvironment, particularly with respect to oxygen, iron, 2OG and the effects of oncometabolites. We also describe emerging evidence that these enzymes are responsive to cellular stresses including hypoxia and DNA damage. Moreover, we examine how dysregulation of 2OG-dependent oxygenases is associated with human disease, and the apparent paradoxical role for some of these enzymes during cancer development. Finally, we discuss some of the challenges associated with assigning biochemical activities and cellular functions to 2OG-dependent oxygenases.

Shared PKS Module in Biosynthesis of Synergistic Laxaphycins

Cyanobacteria produce a wide range of lipopeptides that exhibit potent membrane-disrupting activities. Laxaphycins consist of two families of structurally distinct macrocyclic lipopeptides that act in a synergistic manner to produce antifungal and antiproliferative activities. Laxaphycins are produced by range of cyanobacteria but their biosynthetic origins remain unclear. Here, we identified the biosynthetic pathways responsible for the biosynthesis of the laxaphycins produced by Scytonema hofmannii PCC 7110. We show that these laxaphycins, called scytocyclamides, are produced by this cyanobacterium and are encoded in a single biosynthetic gene cluster with shared polyketide synthase enzymes initiating two distinct non-ribosomal peptide synthetase pathways. The unusual mechanism of shared enzymes synthesizing two distinct types of products may aid future research in identifying and expressing natural product biosynthetic pathways and in expanding the known biosynthetic logic of this important family of natural products.

A Genetic Map of the Response to DNA Damage in Human Cells

The response to DNA damage is critical for cellular homeostasis, tumor suppression, immunity, and gametogenesis. In order to provide an unbiased and global view of the DNA damage response in human cells, we undertook 31 CRISPR-Cas9 screens against 27 genotoxic agents in the retinal pigment epithelium-1 (RPE1) cell line. These screens identified 890 genes whose loss causes either sensitivity or resistance to DNA-damaging agents. Mining this dataset, we discovered that ERCC6L2 (which is mutated in a bone-marrow failure syndrome) codes for a canonical non-homologous end-joining pathway factor, that the RNA polymerase II component ELOF1 modulates the response to transcription-blocking agents, and that the cytotoxicity of the G-quadruplex ligand pyridostatin involves trapping topoisomerase II on DNA. This map of the DNA damage response provides a rich resource to study this fundamental cellular system and has implications for the development and use of genotoxic agents in cancer therapy.

Hypoxia-driven epigenetic regulation in cancer progression: A focus on histone methylation and its modifying enzymes

The mechanism underlying hypoxia-driven chromatin remodeling is a long-lasting question. For the last two decades, this question has been resolved in part. It is now widely agreed that hypoxia dynamically changes the methylation status of histones to control gene expression. Hypoxia-inducible factor (HIF) plays a central role in cellular responses to hypoxia through transcriptional activation of numerous genes. At least in part, the hypoxic regulation of histone methylation is attributed to the HIF-mediated expression of histone modifying enzymes. Protein hydroxylation and histone demethylation have emerged as the oxygen sensing processes because they are catalyzed by a family of 2-oxoglutarate (2OG)-dependent dioxygenases whose activities depend upon the ambient oxygen level. Recently, it has been extensively investigated that the 2OG dioxygenases oxygen-dependently regulate histone methylation. Nowadays, the hypoxic change in the histone methylation status is regarded as an important event to drive malignant behaviors of cancer cells. In this review, we introduced and summarized the cellular processes that govern hypoxia-driven regulation of histone methylation in the context of cancer biology. We also discussed the emerging roles of histone methyltransferases and demethylases in epigenetic response to hypoxia.

Disruption of the Plasmodium falciparum Life Cycle through Transcriptional Reprogramming by Inhibitors of Jumonji Demethylases

Little is known about the role of the three Jumonji C (JmjC) enzymes in Plasmodium falciparum (Pf). Here, we show that JIB-04 and other established inhibitors of mammalian JmjC histone demethylases kill asexual blood stage parasites and are even more potent at blocking gametocyte development and gamete formation. In late stage parasites, JIB-04 increased levels of trimethylated lysine residues on histones, suggesting the inhibition of P. falciparum Jumonji demethylase activity. These epigenetic defects coincide with deregulation of invasion, cell motor, and sexual development gene programs, including gene targets coregulated by the PfAP2-I transcription factor and chromatin-binding factor, PfBDP1. Mechanistically, we demonstrate that PfJmj3 converts 2-oxoglutarate to succinate in an iron-dependent manner consistent with mammalian Jumonji enzymes, and this catalytic activity is inhibited by JIB-04 and other Jumonji inhibitors. Our pharmacological studies of Jumonji activity in the malaria parasite provide evidence that inhibition of these enzymatic activities is detrimental to the parasite.

The potential underlying mechanism of the leukemia caused by MLL-fusion and potential treatments

A majority of infant and pediatric leukemias are caused by the mixed-lineage leukemia gene (MLL) fused with a variety of candidates. Several underlying mechanisms have been proposed. One currently popular view is that truncated MLL1 fusion and its associated complex constitutively hijacks super elongation complex, including positive transcription elongation factor b, CDK9, and cyclin T1 complex and DOT1L, to enhance the expression of transcription factors that maintain or restore stemness of leukocytes, as well as prevent the differentiation of hematopoietic progenitor cells. An alternative emerging view proposes that MLL1-fusion promotes the recruitment of TATA binding protein and RNA polymerase II (Pol II) initiation complex, so as to increase the expression levels of target genes. The fundamental mechanism of both theories are gain of function for truncated MLL1 fusions, either through Pol II elongation or initiation. Our recent progress in transcription regulation of paused Pol II through JMJD5, JMJD6, and JMJD7, combined with the repressive role of H3K4me3 revealed by others, prompted us to introduce a contrarian hypothesis: the failure to shut down transcribing units by MLL-fusions triggers the transformation: loss of function of truncated MLL1 fusions coupled with the loss of conversion of H3K4me1 to H3K4me3, leading to the constitutive expression of transcription factors that are in charge of maintenance of hematopoietic progenitor cells, may trigger the transformation of normal cells into cancer cells. Following this track, a potential treatment to eliminate these fusion proteins, which may ultimately cure the disease, is proposed.

In Silico Discovery of JMJD6 Inhibitors for Cancer Treatment

The 2-oxoglutarate (2OG)-dependent oxygenase JMJD6 is emerging as a potential anticancer target, but its inhibitors have not been reported so far. In this study, we reported an in silico protocol to discover JMJD6 inhibitors targeting the druggable 2OG-binding site. Following this protocol, one compound, which we named as WL12, was found to be able to inhibit JMJD6 enzymatic activity and JMJD6-dependent cell proliferation. To our best knowledge, this is the first case in drug discovery targeting JMJD6.

Biochemical and structural investigations clarify the substrate selectivity of the 2-oxoglutarate oxygenase JMJD6

JmjC domain-containing protein 6 (JMJD6) is a 2-oxoglutarate (2OG)-dependent oxygenase linked to various cellular processes, including splicing regulation, histone modification, transcriptional pause release, hypoxia sensing, and cancer. JMJD6 is reported to catalyze hydroxylation of lysine residue(s) of histones, the tumor-suppressor protein p53, and splicing regulatory proteins, including u2 small nuclear ribonucleoprotein auxiliary factor 65-kDa subunit (U2AF65). JMJD6 is also reported to catalyze N-demethylation of N-methylated (both mono- and di-methylated) arginine residues of histones and other proteins, including HSP70 (heat-shock protein 70), estrogen receptor α, and RNA helicase A. Here, we report MS- and NMR-based kinetic assays employing purified JMJD6 and multiple substrate fragment sequences, the results of which support the assignment of purified JMJD6 as a lysyl hydroxylase. By contrast, we did not observe N-methyl arginyl N-demethylation with purified JMJD6. Biophysical analyses, including crystallographic analyses of JMJD6Δ344-403 in complex with iron and 2OG, supported its assignment as a lysyl hydroxylase rather than an N-methyl arginyl-demethylase. The screening results supported some, but not all, of the assigned JMJD6 substrates and identified other potential JMJD6 substrates. We envision these results will be useful in cellular and biological work on the substrates and functions of JMJD6 and in the development of selective inhibitors of human 2OG oxygenases.

Exceptionally versatile – arginine in bacterial post-translational protein modifications

Post-translational modifications (PTM) are the evolutionary solution to challenge and extend the boundaries of genetically predetermined proteomic diversity. As PTMs are highly dynamic, they also hold an enormous regulatory potential. It is therefore not surprising that out of the 20 proteinogenic amino acids, 15 can be post-translationally modified. Even the relatively inert guanidino group of arginine is subject to a multitude of mostly enzyme mediated chemical changes. The resulting alterations can have a major influence on protein function. In this review, we will discuss how bacteria control their cellular processes and develop pathogenicity based on post-translational protein-arginine modifications.

The small members of the JMJD protein family: Enzymatic jewels or jinxes?

Jumonji C domain-containing (JMJD) proteins are mostly epigenetic regulators that demethylate histones. However, a hitherto neglected subfamily of JMJD proteins, evolutionarily distant and characterized by their relatively small molecular weight, exerts different functions by hydroxylating proteins and RNA. Recently, unsuspected proteolytic and tyrosine kinase activities were also ascribed to some of these small JMJD proteins, further increasing their enzymatic versatility. Here, we discuss the ten human small JMJD proteins (HIF1AN, HSPBAP1, JMJD4, JMJD5, JMJD6, JMJD7, JMJD8, RIOX1, RIOX2, TYW5) and their diverse physiological functions. In particular, we focus on the roles of these small JMJD proteins in cancer and other maladies and how they are modulated in diseased cells by an altered metabolic milieu, including hypoxia, reactive oxygen species and oncometabolites. Because small JMJD proteins are enzymes, they are amenable to inhibition by small molecules and may represent novel targets in the therapy of cancer and other diseases.

Arabidopsis JMJD5/JMJ30 Acts Independently of LUX ARRHYTHMO Within the Plant Circadian Clock to Enable Temperature Compensation

The circadian system ensures that plants respond appropriately to environmental change by predicting regular transitions that occur during diel cycles. In order to be most useful, the circadian system needs to be compensated against daily and seasonal changes in temperature that would otherwise alter the pace of this biological oscillator. We demonstrate that an evening-phased protein, the putative histone demethylase JMJD5, contributes to temperature compensation. JMJD5 is co-expressed with components of the Evening Complex, an agglomeration of proteins including EARLY FLOWERING3 (ELF3), ELF4, and LUX ARRHYTHYMO (LUX), which also integrates temperature changes into the molecular clockwork. One role of the Evening Complex is to regulate expression of PSEUDORESPONSE REGULATOR9 (PRR9) and PRR7, important components of the temperature compensation mechanism. Surprisingly we find that LUX, but not other Evening Complex components, is dispensable for clock function at low temperatures. Further genetic analysis suggests JMJD5 acts in a parallel pathway to LUX within the circadian system. Although an intact JMJD5 catalytic domain is required for its function within the clock, our findings suggest JMJD5 does not directly regulate H3K36 methylation at circadian loci. Such data refine our understanding of how JMDJ5 acts within the Arabidopsis circadian system.

Adventures in Defining Roles of Oxygenases in the Regulation of Protein Biosynthesis

The 2-oxoglutarate (2OG) dependent oxygenases were first identified as having roles in the post-translational modification of procollagen in animals. Subsequently in plants and microbes, they were shown to have roles in the biosynthesis of many secondary metabolites, including signalling molecules and the penicillin/cephalosporin antibiotics. Crystallographic studies of microbial 2OG oxygenases and related enzymes, coupled to DNA sequence analyses, led to the prediction that 2OG oxygenases are widely distributed in aerobic biology. This personal account begins with examples of the roles of 2OG oxygenases in antibiotic biosynthesis, and then describes efforts to assign functions to other predicted 2OG oxygenases. In humans, 2OG oxygenases have been found to have roles in small molecule metabolism, as well as in the epigenetic regulation of protein and nucleic acid biosynthesis and function. The roles and functions of human 2OG oxygenases are compared, focussing on discussion of their substrate and product selectivities. The account aims to emphasize how scoping the substrate selectivity of, sometimes promiscuous, enzymes can provide insights into their functions and so enable therapeutic work.

The emerging roles of ribosomal histidyl hydroxylases in cell biology, physiology and disease

Hydroxylation is a novel protein modification catalyzed by a family of oxygenases that depend on fundamental nutrients and metabolites for activity. Protein hydroxylases have been implicated in a variety of key cellular processes that play important roles in both normal homeostasis and pathogenesis. Here, in this review, we summarize the current literature on a highly conserved sub-family of oxygenases that catalyze protein histidyl hydroxylation. We discuss the evidence supporting the biochemical assignment of these emerging enzymes as ribosomal protein hydroxylases, and provide an overview of their role in immunology, bone development, and cancer.