Search Results (78)

DNA double-strand breaks (DSBs) can be induced by cellular byproducts or genotoxic agents. Improper processing of these lesions leads to increased genome instability, which constitutes a hallmark of pathological conditions and fuels carcinogenesis. DSBs are primarily repaired by homologous recombination (HR) and non-homologous end joining (NHEJ) and the proper balance between these two pathways is finely modulated by specific molecular events. Here, we report that the histone chaperone DAXX plays a fundamental role in the response to DSBs. Indeed, in human cells, DSBs induce ATM/ATR-dependent phosphorylation of DAXX on serine 424 and 712 and promote its binding to chromatin and the deposition of the histone variant H3.3 in proximity to DNA breaks. Enrichment of H3.3 at DSBs promotes 53BP1 recruitment to these lesions and the repair of DNA breaks by HR pathways. Moreover, H3.3-specific post translational modifications, particularly K36 tri-methylation, play a key role in these processes. Altogether, these findings indicate that DAXX and H3.3 mutations may contribute to tumorigenesis-enhancing genome instability. Full article

The past decade has seen significant advancement in our understanding of DNA replication-coupled chromatin assembly, especially parental histone recycling that is essential for epigenetic inheritance. Leading strand-specific and lagging strand-specific pathways have been found to promote the transfer of parental histones H3-H4 to nascent DNA. It is now clear that the replisome initially characterized as the machinery that carries out the duplication of genomic DNA is also responsible for parental histone recycling. A series of replisome components including CMG (Cdc45-MCM-GINS) replicative helicase, DNA polymerases Polε, Polδ, Polα-primase, and FPC (Fork Protection Complex) that promote parental histone recycling exhibit histone-binding activities. Structural analyses of native and reconstituted replisomes, together with AlphaFold modeling of histone (H3-H4)₂ tetramer binding by replisome components, provided a framework for understanding the molecular mechanisms of parental histone recycling. A working model has emerged in which the mobile histone chaperone FACT (Facilitates Chromatin Transcription) binds parental histone (H3-H4)₂ tetramer or (H3-H4)₂-(H2A-H2B) hexamer on the front of the replication fork, and escorts it across the replisome to the daughter strands in the wake of the replication fork. In this model, parental histones transiently associate with the histone-binding modules in the replisome as steppingstones during their movement. Future studies are needed to elucidate the spatiotemporal coordination of the functions of replisome factors in parental histone transfer. Full article

This review presents soybean responses to drought, heat, and salinity within a signal–transcript–chromatin framework. In this framework, calcium/reactive oxygen species and abscisic acid cues converge on abscisic acid-responsive element binding factor (ABF/AREB), dehydration-responsive element binding protein (DREB), NAC, and heat shock factor (HSF) families. These processes are modulated by locus-specific chromatin and non-coding RNA layers. Base-resolved methylomes reveal a high level of CG methylation in the gene body, strong CHG methylation in heterochromatin, and dynamic CHH ‘islands’ at the borders of transposable elements. CHH methylation increases over that of transposable elements during seed development, and GmDMEa editing is associated with seed size. Chromatin studies in soybean and model species implicate the reconfiguration of salt-responsive histone H3 lysine 27 trimethylation (H3K27me3) in G. max and heat-linked H2A.Z dynamics at thermoresponsive promoters characterized in Arabidopsis and other plants, suggesting that a conserved chromatin layer likely operates in soybean. miR169–NF-YA, miR398–Cu/Zn Superoxide Dismutases(CSD)/copper chaperone of CSD(CCS), miR393–transporter inhibitor response1/auxin signaling F-box (TIR1/AFB), and miR396–growth regulating factors (GRF) operate across leaves, roots, and nodules. Overexpression of lncRNA77580 enhances drought tolerance, but with context-dependent trade-offs under salinity. Single-nucleus and spatial atlases anchor these circuits in cell types and microenvironments relevant to stress and symbiosis. We present translational routes, sentinel epimarkers (bisulfite amplicons, CUT&Tag), haplotype-by-epigenotype prediction, and precise cis-regulatory editing to accelerate marker development, genomic prediction and the breeding of resilient soybean varieties with stable yields. Full article

Yeast +1 nucleosomes positioned at transcription start sites must be reorganized to allow transcription initiation. Nucleosome reorganization involves multiple factors including histone chaperone FACT (FAcilitates Chromatin Transcription), histone acetylation, and histone variant H2A.Z; however, the mechanism of this process is not fully understood. Here we investigated nucleosome unfolding in the presence of these factors by combining biochemical assays with single-particle Förster resonance energy transfer (spFRET) microscopy. The presence of the H3:K56Ac mimic (H3:K56Q) alone or together with H2A.Z (but not H2A.Z alone) facilitates the Nhp6-dependent unfolding of nucleosomes by FACT. In contrast to canonical nucleosomes, the unfolding of nucleosomes with the studied variant histones promotes the eviction of core histones from nucleosomal DNA. Furthermore, H2A.Z alone or in synergy with H3:K56Q facilitates transcription through a nucleosome as efficiently as FACT facilitates transcription through canonical nucleosomes. The data suggest that FACT, together with H3:K56 acetylation and H2A.Z, unfold promoter nucleosomes and participate in the eviction of histones to increase the accessibility of the transcription start site, thereby stimulating transcription initiation and possibly early elongation. Full article

Spastic paraplegia 80 (SPG80), caused by mutations in ubiquitin-associated protein 1 (UBAP1), is a pure form of juvenile-onset hereditary spastic paraplegia (HSP) and leads to progressive motor dysfunction. Despite recent advances in the molecular analyses of HSP, disease-modifying therapy has not been established for HSP including SPG80. In the present study, we evaluated the therapeutic potential of 4-phenylbutyric acid (4-PBA), a chemical chaperone and histone deacetylase inhibitor, in Ubap1 knock-in (KI) mice expressing a disease-associated truncated UBAP1 variant. We found that 4-PBA administration significantly improved the motor performance of KI mice in the rotarod and beam walk tests, with maximal benefits achieved when given during pre- or early-symptomatic stages. Partial efficacy was also observed when treatment began after symptom onset in KI mice. Furthermore, 4-PBA attenuated spinal microglial activation and partially restored microglial morphology, although astrocytic reactivity remained unchanged. These findings support 4-PBA as a candidate therapeutic compound for SPG80 and highlight the potential of proteostasis-targeted interventions in HSPs. Full article

Eukaryotic transcription involves a complex interplay of protein factors that dynamically engage with chromatin at distinct stages. Among these, the histone chaperone FACT (Facilitates Chromatin Transcription) plays a unique role in nucleosome disassembly and reassembly during transcription, replication, and repair. While its functional importance is well established, the underlying structural mechanisms involved in these activities remain incompletely understood. The remarkable functional versatility of FACT in regulating genetic information processing likely stems from its distinctive structural and mechanical properties. This review focuses on the structural organization of FACT and analysis of the mechanisms involved in chromatin reorganization by this unusual histone chaperone. Full article

Spermatogenesis is a complex and highly regulated process involving the proliferation, differentiation, and apoptosis of germ cells. This process is controlled by various hormonal, genetic, and environmental factors, including temperature. In hormonal regulation, follicle-stimulating hormone (FSH), luteinizing hormone (LH), and testosterone (T) are essential for correct spermatogenesis development from the early stages and spermatogonia proliferation to germ cell maturation. Other hormones, like inhibin and activin, finely participate tuning the process of spermatogenesis. Genetic regulation involves various transcription factors, such as SOX9, SRY, and DMRT1, which are crucial for the development and maintenance of the testis and germ cells. MicroRNAs (miRNAs) play a significant role by regulating gene expression post-transcriptionally. Epigenetic modifications, including DNA methylation, histone modifications, and chromatin remodelling, are also vital. Temperature regulation is another critical aspect, with the testicular temperature maintained around 2–4 °C below body temperature, essential for efficient spermatogenesis. Heat shock proteins (HSPs) protect germ cells from heat-induced damage by acting as molecular chaperones, ensuring proper protein folding and preventing the aggregation of misfolded proteins during thermal stress. Elevated testicular temperature can impair spermatogenesis, increasing germ cell apoptosis and inducing oxidative stress, DNA damage, and the disruption of the blood–testis barrier, leading to germ cell death and impaired differentiation. The cellular mechanisms of germ cell proliferation, differentiation, and death include the mitotic divisions of spermatogonia to maintain the germ cell pool and produce spermatocytes. Spermatocytes undergo meiosis to produce haploid spermatids, which then differentiate into mature spermatozoa. Apoptosis, or programmed cell death, ensures the removal of defective germ cells and regulates the germ cell population. Hormonal imbalance, genetic defects, and environmental stress can trigger apoptosis during spermatogenesis. Understanding these mechanisms is crucial for addressing male infertility and developing therapeutic interventions. Advances in molecular biology and genetics continue to uncover the intricate details of how spermatogenesis is regulated at multiple levels, providing new insights and potential targets for treatment. Full article

A thermodynamic analysis of the binary complex formation of the highly positively charged linker histone H1 and the highly negatively charged chaperone prothymosin α (ProTα) is detailed. ProTα and H1 have large opposite net charges (−44 and +53, respectively) and form complexes at physiological salt concentrations with high affinities. The data obtained for the binary complex formation are analyzed by a thermodynamic model that is based on counterion condensation modulated by hydration effects. The analysis demonstrates that the release of the counterions mainly bound to ProTα is the main driving force, and effects related to water release play no role within the limits of error. A strongly negative Δc_p (=−0.87 kJ/(K mol)) is found, which is due to the loss of conformational degrees of freedom. Full article

The objective of this study was to identify differentially expressed genes and their potential influence on the carcinogenesis of serous-type ovarian cancer tumors. Serous cancer is an epithelial ovarian cancer subtype and is the most common type of ovarian cancer. Transcriptomic profiles of serous cancer and non-cancerous datasets were obtained from the Gene Expression Omnibus (GEO-NCBI). Differentially expressed genes were then derived from those profiles; the identified genes were consistently upregulated in three or more transcriptomic profiles. These genes were considered as the serous ovarian cancer gene set for further study. The serous gene set derived from the transcriptomic profiles was then evaluated for ontological functional analysis using the Molecular Signatures Database. Next, we examined the mutational impact of this serous gene set on the transcriptomic profile of high-grade serous ovarian (HGSO) adenocarcinoma using the cBioPortal database. Results from OncoPrint revealed that 26 genes were amplified in more than 5% of HGSO cancer patients. Interestingly, several of these genes are involved in cell cycle processes, including genes ATPase family AAA domain containing 2 (ATAD2), recQ-like helicase 4 (RECQL4), cyclin E1 (CCNE1), anti-silencing function 1B histone chaperone (ASF1B), ribonuclease H2 subunit A (RNASEH2A), structural maintenance of chromosome 4 (SMC4), cell division cycle associated 20 (CDC20), and cell division cycle associated 8 (CDCA8). The receiver operating characteristic (ROC) curve results also revealed higher specificity and sensitivity for this subtype of tumors. Furthermore, these genes may affect the recurrence of serous ovarian carcinogenesis. Overall, our analytical study identifies cell cycle-related genes that can potentially be targeted as diagnostic and prognostic markers for serous ovarian cancer. Full article

Recycling histone proteins from parental chromatin, a process known as parental histone transfer, is an important component in chromosome replication and is essential for epigenetic inheritance. We review recent advances in our understanding of the recycling mechanism of parental histone H3-H4 tetramers (parH3:H4tet), emphasizing the pivotal role of the DNA replisome. In particular, we highlight the function of the MCM2-7 helicase subunit Mcm2 as a histone H3-H4 tetramer chaperone. Disruption of this histone chaperone’s functions affects mouse embryonic stem cell differentiation and can lead to embryonic lethality in mice, underscoring the crucial role of the replisome in maintaining epigenomic stability. Full article

The incorporation of histone variants has structural ramifications on nucleosome dynamics and stability. Due to their unique sequences, histone variants can alter histone–histone or histone–DNA interactions, impacting the folding of DNA around the histone octamer and the overall higher-order structure of chromatin fibers. These structural modifications alter chromatin compaction and accessibility of DNA by transcription factors and other regulatory proteins to influence gene regulatory processes such as DNA damage and repair, as well as transcriptional activation or repression. Histone variants can also generate a unique interactome composed of histone chaperones and chromatin remodeling complexes. Any of these perturbations can contribute to cellular plasticity and the progression of human diseases. Here, we focus on a frequently overlooked group of histone variants lying within the four human histone gene clusters and their contribution to breast cancer. Full article

Histone chaperones are integral to chromatin dynamics, facilitating the assembly and disassembly of nucleosomes, thereby playing a crucial role in regulating gene expression and maintaining genomic stability. Moreover, they prevent aberrant histone interactions prior to chromatin assembly. Disruption in histone chaperone function may result in genomic instability, which is implicated in pathogenesis. This review aims to elucidate the role of histone chaperones in cancer pathologies and explore their potential as therapeutic targets. Histone chaperones have been found to be dysregulated in various cancers, with alterations in expression levels, mutations, or aberrant interactions leading to tumorigenesis and cancer progression. In addition, this review intends to highlight the molecular mechanisms of interactions between histone chaperones and oncogenic factors, underscoring their roles in cancer cell survival and proliferation. The dysregulation of histone chaperones is significantly correlated with cancer development, establishing them as active contributors to cancer pathology and viable targets for therapeutic intervention. This review advocates for continued research into histone chaperone-targeted therapies, which hold potential for precision medicine in oncology. Future advancements in understanding chaperone functions and interactions are anticipated to lead to novel cancer treatments, enhancing patient care and outcomes. Full article

Histones are nuclear proteins essential for packaging genomic DNA and epigenetic gene regulation. Paralogs that can substitute core histones (H2A, H2B, H3, and H4), named histone variants, are constitutively expressed in a replication-independent manner throughout the cell cycle. With specific chaperones, they can be incorporated to chromatin to modify nucleosome stability by modulating interactions with nucleosomal DNA. This allows the regulation of essential fundamental cellular processes for instance, DNA damage repair, chromosomal segregation, and transcriptional regulation. Among all the histone families, histone H2A family has the largest number of histone variants reported to date. Each H2A variant has multiple functions apart from their primary role and some, even be further specialized to perform additional tasks in distinct lineages, such as testis specific shortH2A (sH2A). In the past decades, the discoveries of genetic alterations and mutations in genes encoding H2A variants in cancer had revealed variants’ potentiality in driving carcinogenesis. In addition, there is growing evidence that H2A variants may act as novel prognostic indicators or biomarkers for both early cancer detection and therapeutic treatments. Nevertheless, no studies have ever concluded all identified variants in a single report. Here, in this review, we summarize the respective functions for all the 19 mammalian H2A variants and their roles in cancer biology whilst potentiality being used in clinical setting. Full article

Histone deacetylase SIRT1 represses gene expression through the deacetylation of histones and transcription factors and is involved in the protective cell response to stress and aging. However, upon endoplasmic reticulum (ER) stress, SIRT1 impairs the IRE1α branch of the unfolded protein response (UPR) through the inhibition of the transcriptional activity of XBP-1 and SIRT1 deficiency is beneficial under these conditions. We hypothesized that SIRT1 deficiency may unlock the blockade of transcription factors unrelated to the UPR promoting the synthesis of chaperones and improving the stability of immature proteins or triggering the clearance of unfolded proteins. SIRT1+/+ and SIRT1−/− fibroblasts were exposed to the ER stress inducer tunicamycin and cell survival and expression of heat shock proteins were analyzed 24 h after the treatment. We observed that SIRT1 loss significantly reduced cell sensitivity to ER stress and showed that SIRT1−/− but not SIRT1+/+ cells constitutively expressed high levels of phospho-STAT3 and heat shock proteins. Hsp70 silencing in SIRT1−/− cells abolished the resistance to ER stress. Furthermore, accumulation of ubiquitinated proteins was lower in SIRT1−/− than in SIRT1+/+ cells. Our data showed that SIRT1 deficiency enabled chaperones upregulation and boosted the proteasome activity, two processes that are beneficial for coping with ER stress. Full article

HIRIP3 is a mammalian protein homologous to the yeast H2A.Z deposition chaperone Chz1. However, the structural basis underlying Chz’s binding preference for H2A.Z over H2A, as well as the mechanism through which Chz1 modulates histone deposition or replacement, remains enigmatic. In this study, we aimed to characterize the function of HIRIP3 and to identify its interacting partners in HeLa cells. Our findings reveal that HIRIP3 is specifically associated in vivo with H2A–H2B dimers and CK2 kinase. While bacterially expressed HIRIP3 exhibited a similar binding affinity towards H2A and H2A.Z, the associated CK2 kinase showed a notable preference for H2A phosphorylation at serine 1. The recombinant HIRIP3 physically interacted with the H2A αC helix through an extended CHZ domain and played a crucial role in depositing the canonical core histones onto naked DNA. Our results demonstrate that mammalian HIRIP3 acts as an H2A histone chaperone, assisting in its selective phosphorylation by Ck2 kinase at serine 1 and facilitating its deposition onto chromatin. Full article