Features of the PHF8/KIAA1718 histone demethylase

Lysine-specific demethylase 7A (KDM7A): A potential target for disease therapy

Histone demethylation is a kind of epigenetic modification mediated by a variety of enzymes and participates in regulating multiple physiological and pathological events. Lysine-specific demethylase 7A is a kind of α-ketoglutarate- and Fe(II)-dependent demethylase belonging to the PHF2/8 subfamily of the JmjC demethylases. KDM7A is mainly localized in the nucleus and contributes to transcriptional activation via removing mono- and di-methyl groups from the lysine residues 9 and 27 of Histone H3. Mounting studies support that KDM7A is not only necessary for normal embryonic, neural, and skeletal development, but also associated with cancer, inflammation, osteoporosis, and other diseases. Herein, the structure of KDM7A is described by comparing the similarities and differences of its amino acid sequences of KDM7A and other Histone demethylases; the functions of KDM7A in homeostasis and dyshomeostasis are summarized via documenting its content and related signaling; the currently known KDM7A-specific inhibitors and their structural relationship are listed based on their structure optimization and pharmacological activities; and the challenges and opportunities in exploring functions and developing targeted agents of KDM7A are also prospected via presenting encountered problems and potential solutions, which will provide an insight in functional exploration and drug discovery for KDM7A-related diseases.

Histone demethylase PHF8 facilitates the development of chronic myeloid leukaemia by directly targeting BCR::ABL1

Although tyrosine kinase inhibitors (TKIs) have revolutionized the treatment of chronic myeloid leukaemia (CML), TKI resistance remains a major challenge. Here, we demonstrated that plant homeodomain finger protein 8 (PHF8), a histone demethylase was aberrantly enriched in CML samples compared to healthy controls. PHF8 inhibited CML cell differentiation and promoted CML cell proliferation. Furthermore, the proliferation-inhibited function of PHF8-knockdown have stronger effect on imatinib mesylate (IM)-resistant CML cells. Mechanistically, we identified that PHF8 as a transcriptional modulator interacted with the promoter of the BCR::ABL1 fusion gene and alters the methylation levels of H3K9me1, H3K9me2 and H3K27me1, thereby promoting BCR::ABL1 transcription. Overall, our study suggests that targeting PHF8, which directly regulates BCR::ABL1 expression, is a useful therapeutic approach for CML.

Gb_ANR-47 Enhances the Resistance of Gossypium barbadense to Fusarium oxysporum f. sp. vasinfectum (FOV) by Regulating the Content of Proanthocyanidins

Anthocyanidin reductase (ANR) is an important regulator of flavonoid metabolism, and proanthocyanidins, the secondary metabolites of flavonoids, play an important role in the response of plants to pathogenic stress. Therefore, in this study, the expression analysis of the ANR gene family of Gossypium barbadense after inoculation with Fusarium oxysporum f. sp. vasinfectum (FOV) was performed at different time points. It was found that Gb_ANR-47 showed significant differences in the disease-resistant cultivar 06-146 and the susceptible cultivar Xinhai 14, as well as in the highest root expression. It was found that the expression of Gb_ANR-47 in the resistant cultivar was significantly higher than that in the susceptible cultivar by MeJA and SA, and different amounts of methyl jasmonate (MeJA) and salicylic acid (SA) response elements were found in the promoter region of Gb_ANR-47. After silencing GbANR-47 in 06-146 material by VIGS technology, its resistance to FOV decreased significantly. The disease severity index (DSI) was significantly increased, and the anthocyanin content was significantly decreased in silenced plants, compared to controls. Our findings suggest that GbANR-47 is a positive regulator of FOV resistance in Gossypium barbadense. The research results provide an important theoretical basis for in-depth analysis of the molecular mechanism of GbANR-47 and improving the anti-FOV of Gossypium barbadense.

Short-Term Mitochondrial Permeability Transition Pore Opening Modulates Histone Lysine Methylation at the Early Phase of Somatic Cell Reprogramming

Reprogramming of somatic cells to induced pluripotent stem cells reconfigures chromatin modifications. Whether and how this process is regulated by signals originating in the mitochondria remain unknown. Here we show that the mitochondrial permeability transition pore (mPTP), a key regulator of mitochondrial homeostasis, undergoes short-term opening during the early phase of reprogramming and that this transient activation enhances reprogramming. In mouse embryonic fibroblasts, greater mPTP opening correlates with higher reprogramming efficiency. The reprogramming-promoting function of mPTP opening is mediated by plant homeodomain finger protein 8 (PHF8) demethylation of H3K9me2 and H3K27me3, leading to reduction in their occupancies at the promoter regions of pluripotency genes. mPTP opening increases PHF8 protein levels downstream of mitochondrial reactive oxygen species production and miR-101c and simultaneously elevates levels of PHF8's cofactor, α-ketoglutarate. Our findings represent a novel mitochondria-to-nucleus pathway in cell fate determination by mPTP-mediated epigenetic regulation.

The histone demethylase PHF8 is a molecular safeguard of the IFNγ response

A precise immune response is essential for cellular homeostasis and animal survival. The paramount importance of its control is reflected by the fact that its non-specific activation leads to inflammatory events that ultimately contribute to the appearance of many chronic diseases. However, the molecular mechanisms preventing non-specific activation and allowing a quick response upon signal activation are not yet fully understood. In this paper we uncover a new function of PHF8 blocking signal independent activation of immune gene promoters. Affinity purifications coupled with mass spectrometry analysis identified SIN3A and HDAC1 corepressors as new PHF8 interacting partners. Further molecular analysis demonstrated that prior to interferon gamma (IFNγ) stimulation, PHF8 is bound to a subset of IFNγ-responsive promoters. Through the association with HDAC1 and SIN3A, PHF8 keeps the promoters in a silent state, maintaining low levels of H4K20me1. Upon IFNγ treatment, PHF8 is phosphorylated by ERK2 and evicted from the promoters, correlating with an increase in H4K20me1 and transcriptional activation. Our data strongly indicate that in addition to its well-characterized function as a coactivator, PHF8 safeguards transcription to allow an accurate immune response.

Stabilization of histone demethylase PHF8 by USP7 promotes breast carcinogenesis

The histone demethylase PHF8 has been implicated in multiple pathological disorders, including X-linked mental retardation and tumorigenesis. However, it is not clear how the abundance and function of PHF8 are regulated. Here, we report that PHF8 physically associates with the deubiquitinase USP7. Specifically, we demonstrated that USP7 promotes deubiquitination and stabilization of PHF8, leading to the upregulation of a group of genes, including cyclin A2, that are critical for cell growth and proliferation. The USP7-encoding gene was also transcriptionally regulated by PHF8, via positive feedback. USP7 was overexpressed in breast carcinomas, and the level of expression positively correlated with expression of PHF8 and cyclin A2 and with the histological grade of breast cancer. We showed that USP7 promotes breast carcinogenesis by stabilizing PHF8 and upregulating cyclin A2 and that the interaction between USP7 and PHF8 is augmented during DNA damage. Moreover, USP7-promoted PHF8 stabilization conferred cellular resistance to genotoxic insults and was required for the recruitment of BLM and KU70, which are both essential for DNA double-strand break repair. Our study mechanistically links USP7 to epigenetic regulation and DNA repair. Moreover, these data support the pursuit of USP7 and PHF8 as potential targets for breast cancer intervention, especially in combination with chemo- or radiotherapies.

A Neuronal Activity-Dependent Dual Function Chromatin-Modifying Complex Regulates Arc Expression

Chromatin modification is an important epigenetic mechanism underlying neuroplasticity. Histone methylation and acetylation have both been shown to modulate gene expression, but the machinery responsible for mediating these changes in neurons has remained elusive. Here we identify a chromatin-modifying complex containing the histone demethylase PHF8 and the acetyltransferase TIP60 as a key regulator of the activity-induced expression of Arc, an important mediator of synaptic plasticity. Clinically, mutations in PHF8 cause X-linked mental retardation while TIP60 has been implicated in the pathogenesis of Alzheimer's disease. Within minutes of increased synaptic activity, this dual function complex is rapidly recruited to the Arc promoter, where it specifically counteracts the transcriptionally repressive histone mark H3K9me2 to facilitate the formation of the transcriptionally permissive H3K9acS10P, thereby favoring transcriptional activation. Consequently, gain-of-function of the PHF8-TIP60 complex in primary rat hippocampal neurons has a positive effect on early activity-induced Arc gene expression, whereas interfering with the function of this complex abrogates it. A global proteomics screen revealed that the majority of common interactors of PHF8 and TIP60 were involved in mRNA processing, including PSF, an important molecule involved in neuronal gene regulation. Finally, we proceeded to show, using super-resolution microscopy, that PHF8 and TIP60 interact at the single molecule level with PSF, thereby situating this chromatin modifying complex at the crossroads of transcriptional activation. These findings point toward a mechanism by which an epigenetic pathway can regulate neuronal activity-dependent gene transcription, which has implications in the development of novel therapeutics for disorders of learning and memory.

PHD finger protein 2 (PHF2) represses ribosomal RNA gene transcription by antagonizing PHF finger protein 8 (PHF8) and recruiting methyltransferase SUV39H1

Regulation of rDNA transcription is central to cell growth and proliferation. PHF2 and PHF8 belong to a subfamily of histone demethylases that also possess a PHD domain-dependent di-/trimethylated histone 3 lysine 4 (H3K4me2/3) binding activity and are known to be enriched in the nucleolus. In this study, we show that, unlike PHF8 that activates rDNA transcription, PHF2 inhibits rDNA transcription. Depletion of PHF2 by RNA interference increases and overexpression of PHF2 decreases rDNA transcription, respectively, whereas simultaneous depletion of PHF8 and PHF2 restores the level of rDNA transcription. The inhibition of rDNA transcription by PHF2 depends on its H3K4me2/3 binding activity that is also required for PHF2 association with the promoter of rDNA genes but not its demethylase activity. We provide evidence that PHF2 is likely to repress rDNA transcription by competing with PHF8 for binding of rDNA promoter and by recruiting H3K9me2/3 methyltransferase SUV39H1. We also provide evidence that, whereas PHF8 promotes, PHF2 represses the transcriptional activity of RARα, Oct4, and KLF4 and a few PHF8 target genes tested. Taken together, our study demonstrates a repressive role for PHF2 in transcription by RNA polymerase I and II.

Epigenetic Regulation by Lysine Demethylase 5 (KDM5) Enzymes in Cancer

Similar to genetic alterations, epigenetic aberrations contribute significantly to tumor initiation and progression. In many cases, these changes are caused by activation or inactivation of the regulators that maintain epigenetic states. Here we review our current knowledge on the KDM5/JARID1 family of histone demethylases. This family of enzymes contains a JmjC domain and is capable of removing tri- and di- methyl marks from lysine 4 on histone H3. Among these proteins, RBP2 mediates drug resistance while JARID1B is required for melanoma maintenance. Preclinical studies suggest inhibition of these enzymes can suppress tumorigenesis and provide strong rationale for development of their inhibitors for use in cancer therapy.

Signals and combinatorial functions of histone modifications

Alterations of chromatin structure have been shown to be crucial for response to cell signaling and for programmed gene expression in development. Posttranslational histone modifications influence changes in chromatin structure both directly and by targeting or activating chromatin-remodeling complexes. Histone modifications intersect with cell signaling pathways to control gene expression and can act combinatorially to enforce or reverse epigenetic marks in chromatin. Through their recognition by protein complexes with enzymatic activities cross talk is established between different modifications and with other epigenetic pathways, including noncoding RNAs (ncRNAs) and DNA methylation. Here, we review the functions of histone modifications and their exploitation in the programming of gene expression during several events in development.

MassSQUIRM: An assay for quantitative measurement of lysine demethylase activity

In eukaryotes, DNA is wrapped around proteins called histones and is condensed into chromatin. Post-translational modification of histones can result in changes in gene expression. One of the most well-studied histone modifications is the methylation of lysine 4 on histone H3 (H3K4). This residue can be mono-, di- or tri-methylated and these varying methylation states have been associated with different levels of gene expression. Understanding exactly what the purpose of these methylation states is, in terms of gene expression, has been a topic of much research in recent years. Enzymes that can add (methyltransferases) and remove (demethylases) these modifications are of particular interest. The first demethylase discovered, LSD1, is the most well-classified and has been implicated in contributing to human cancers and to DNA damage response pathways. Currently, there are limited methods for accurately studying the activity of demethylases in vitro or in vivo. In this work, we present MassSQUIRM (mass spectrometric quantitation using isotopic reductive methylation), a quantitative method for studying the activity of demethylases capable of removing mono- and di-methyl marks from lysine residues. We focus specifically on LSD1 due to its potential as a prime therapeutic target for human disease. This quantitative approach will enable better characterization of the activity of LSD1 and other chromatin modifying enzymes in vitro, in vivo or in response to inhibitors.

Natural history of the eukaryotic chromatin protein methylation system

In eukaryotes, methylation of nucleosomal histones and other nuclear proteins is a central aspect of chromatin structure and dynamics. The past 15 years have seen an enormous advance in our understanding of the biochemistry of these modifications, and of their role in establishing the epigenetic code. We provide a synthetic overview, from an evolutionary perspective, of the main players in the eukaryotic chromatin protein methylation system, with an emphasis on catalytic domains. Several components of the eukaryotic protein methylation system had their origins in bacteria. In particular, the Rossmann fold protein methylases (PRMTs and DOT1), and the LSD1 and jumonji-related demethylases and oxidases, appear to have emerged in the context of bacterial peptide methylation and hydroxylation systems. These systems were originally involved in synthesis of peptide secondary metabolites, such as antibiotics, toxins, and siderophores. The peptidylarginine deiminases appear to have been acquired by animals from bacterial enzymes that modify cell-surface proteins. SET domain methylases, which display the β-clip fold, apparently first emerged in prokaryotes from the SAF superfamily of carbohydrate-binding domains. However, even in bacteria, a subset of the SET domains might have evolved a chromatin-related role in conjunction with a BAF60a/b-like SWIB domain protein and topoisomerases. By the time of the last eukaryotic common ancestor, multiple SET and PRMT methylases were already in place and are likely to have mediated methylation at the H3K4, H3K9, H3K36, and H4K20 positions, and carried out both asymmetric and symmetric arginine dimethylation. Inference of H3K27 methylation in the ancestral eukaryote appears uncertain, though it was certainly in place a little later in eukaryotic evolution. Current data suggest that unlike SET methylases, which are universally present in eukaryotes, demethylases are not. They appear to be absent in the earliest-branching eukaryotic lineages, and emerged later along with several other chromatin proteins, such as the Dot1-methylase, prior to divergence of the kinetoplastid-heterolobosean lineage from the remaining eukaryotes. This period also corresponds to the point of origin of DNA cytosine methylation by DNMT1. Origin of major lineages of SET domains such as the Trithorax, Su(var)3-9, Ash1, SMYD, and TTLL12 and E(Z) might have played the initial role in the establishment of multiple distinct heterochromatic and euchromatic states that are likely to have been present, in some form, through much of eukaryotic evolution. Elaboration of these chromatin states might have gone hand-in-hand with acquisition of multiple jumonji-related and LSD1-like demethylases, and functional linkages with the DNA methylation and RNAi systems. Throughout eukaryotic evolution, there were several lineage-specific expansions of SET domain proteins, which might be related to a special transcription regulation process in trypanosomes, acquisition of new meiotic recombination hotspots in animals, and methylation and associated modifications of the diatom silaffin proteins involved in silica biomineralization. The use of specific domains to "read" the methylation marks appears to have been present in the ancestral eukaryote itself. Of these the chromo-like domains appear to have been acquired from bacterial secreted proteins that might have a role in binding cell-surface peptides or peptidoglycan. Domain architectures of the primary enzymes involved in the eukaryotic protein methylation system indicate key features relating to interactions with each other and other modifications in chromatin, such as acetylation. They also emphasize the profound functional distinction between the role of demethylation and deacetylation in regulation of chromatin dynamics.