Activating the PARP-1 sensor component of the groucho/ TLE1 corepressor complex mediates a CaMKinase IIdelta-dependent neurogenic gene activation pathway

Nucleophosmin: A Nucleolar Phosphoprotein Orchestrating Cellular Stress Responses

Nucleophosmin (NPM1) is a key nucleolar protein released from the nucleolus in response to stress stimuli. NPM1 functions as a stress regulator with nucleic acid and protein chaperone activities, rapidly shuttling between the nucleus and cytoplasm. NPM1 is ubiquitously expressed in tissues and can be found in the nucleolus, nucleoplasm, cytoplasm, and extracellular environment. It plays a central role in various biological processes such as ribosome biogenesis, cell cycle regulation, cell proliferation, DNA damage repair, and apoptosis. In addition, it is highly expressed in cancer cells and solid tumors, and its mutation is a major cause of acute myeloid leukemia (AML). This review focuses on NPM1's structural features, functional diversity, subcellular distribution, and role in stress modulation.

Exploring the role of parthanatos in CNS injury: Molecular insights and therapeutic approaches

BACKGROUND

Central nervous system (CNS) injury causes severe organ damage due to both damage resulting from the injury and subsequent cell death. However, there are currently no effective treatments for countering the irreversible loss of cell function. Parthanatos is a poly (ADP-ribose) polymerase 1 (PARP-1)-dependent form of programmed cell death that is partly responsible for neural cell death. Consequently, the mechanism by which parthanatos promotes CNS injury has attracted significant scientific interest.

AIM OF REVIEW

Our review aims to summarize the potential role of parthanatos in CNS injury and its molecular and pathophysiological mechanisms. Understanding the role of parthanatos and related molecules in CNS injury is crucial for developing effective treatment strategies and identifying important directions for future in-depth research.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Parthanatos (from Thanatos, the personification of death according to Greek mythology) is a type of programmed cell death that is initiated by the overactivation of PARP-1. This process triggers a cascade of reactions, including the accumulation of poly(ADP-ribose) (PAR), the nuclear translocation of apoptosis-inducing factor (AIF) after its release from mitochondria, and subsequent massive DNA fragmentation caused by migration inhibitory factor (MIF) forming a complex with AIF. Secondary molecular mechanisms, such as excitotoxicity and oxidative stress-induced overactivation of PARP-1, significantly exacerbate neuronal damage following initial mechanical injury to the CNS. Furthermore, parthanatos is not only associated with neuronal damage but also interacts with various other types of cell death. This review focuses on the latest research concerning the parthanatos cell death pathway, particularly considering its regulatory mechanisms and functions in CNS damage. We highlight the associations between parthanatos and different cell types involved in CNS damage and discuss potential therapeutic agents targeting the parthanatos pathway.

Poly (ADP-Ribose) polymerase 1 and parthanatos in neurological diseases: From pathogenesis to therapeutic opportunities

Poly (ADP-ribose) polymerase-1 (PARP-1) is the most extensively studied member of the PARP superfamily, with its primary function being the facilitation of DNA damage repair processes. Parthanatos is a type of regulated cell death cascade initiated by PARP-1 hyperactivation, which involves multiple subroutines, including the accumulation of ADP-ribose polymers (PAR), binding of PAR and apoptosis-inducing factor (AIF), release of AIF from the mitochondria, the translocation of the AIF/macrophage migration inhibitory factor (MIF) complex, and massive MIF-mediated DNA fragmentation. Over the past few decades, the role of PARP-1 in central nervous system health and disease has received increasing attention. In this review, we discuss the biological functions of PARP-1 in neural cell proliferation and differentiation, memory formation, brain ageing, and epigenetic regulation. We then elaborate on the involvement of PARP-1 and PARP-1-dependant parthanatos in various neuropathological processes, such as oxidative stress, neuroinflammation, mitochondrial dysfunction, excitotoxicity, autophagy damage, and endoplasmic reticulum (ER) stress. Additional highlight contains PARP-1's implications in the initiation, progression, and therapeutic opportunities for different neurological illnesses, including neurodegenerative diseases, stroke, autism spectrum disorder (ASD), multiple sclerosis (MS), epilepsy, and neuropathic pain (NP). Finally, emerging insights into the repurposing of PARP inhibitors for the management of neurological diseases are provided. This review aims to summarize the exciting advancements in the critical role of PARP-1 in neurological disorders, which may open new avenues for therapeutic options targeting PARP-1 or parthanatos.

To Break or Not to Break: The Role of TOP2B in Transcription

Transcription and its regulation pose challenges related to DNA torsion and supercoiling of the DNA template. RNA polymerase tracking the helical groove of the DNA introduces positive helical torsion and supercoiling upstream and negative torsion and supercoiling behind its direction of travel. This can inhibit transcriptional elongation and other processes essential to transcription. In addition, chromatin remodeling associated with gene activation can generate or be hindered by excess DNA torsional stress in gene regulatory regions. These topological challenges are solved by DNA topoisomerases via a strand-passage reaction which involves transiently breaking and re-joining of one (type I topoisomerases) or both (type II topoisomerases) strands of the phosphodiester backbone. This review will focus on one of the two mammalian type II DNA topoisomerase enzymes, DNA topoisomerase II beta (TOP2B), that have been implicated in correct execution of developmental transcriptional programs and in signal-induced transcription, including transcriptional activation by nuclear hormone ligands. Surprisingly, several lines of evidence indicate that TOP2B-mediated protein-free DNA double-strand breaks are involved in signal-induced transcription. We discuss the possible significance and origins of these DSBs along with a network of protein interaction data supporting a variety of roles for TOP2B in transcriptional regulation.

REST, RCOR1 and RCOR2 expression is reduced in osteoarthritic chondrocytes and contributes to increasing MMP13 and ADAMTS5 expression through upregulating HES1

Expression of key transcriptional regulators is altered in chondrocytes in osteoarthritis (OA). This contributes to an increase in production of cartilage-catabolizing enzymes such as MMP13 and ADAMTS5. RCOR1 and RCOR2, binding partners for the transcriptional repressor REST, have previously been found to be downregulated in OA chondrocytes although their function in chondrocytes is unclear. HES1 is a known REST/RCOR1 target gene and HES1 has been shown to promote MMP13 and ADAMTS5 expression in murine OA chondrocytes. The purpose of this study was to determine whether reduced REST/RCOR levels leads to increased HES1 expression in human OA chondrocytes and whether HES1 also promotes ADAMTS5 and MMP13 expression in these cells. Chondrocytes were isolated from osteoarthritic and adjacent macroscopically normal cartilage obtained from patients undergoing total knee arthroplasty. RNA and protein levels of REST, RCOR1 and RCOR2 were lower, but levels of HES1 higher, in chondrocytes isolated from osteoarthritic compared to macroscopically normal cartilage. Over-expression of either REST, RCOR1 or RCOR2 resulted in reduced HES1 levels in OA chondrocytes whereas knockdown of REST, RCOR1 or RCOR2 led to increased HES1 expression in chondrocytes from macroscopically normal cartilage. In OA chondrocytes, ADAMTS5 and MMP13 expression were reduced following HES1 knockdown, but further enhanced following HES1 over-expression. Levels of phosphorylated CaMKII were higher in chondrocytes from OA cartilage consistent with previous findings that HES1 only promotes gene transcription in the presence of active CaMKII. These findings identify the REST/RCOR/HES1 pathway as a contributing factor leading to increased ADAMTS5 and MMP13 expression in OA chondrocytes.

The role of apoptosis in the pathogenesis of osteoarthritis

PURPOSE

Apoptosis is an important physiological process, making a great difference to development and tissue homeostasis. Osteoarthritis (OA) is a chronic joint disease characterized by degeneration and destruction of articular cartilage and bone hyperplasia. This purpose of this study is to provide an updated review of the role of apoptosis in the pathogenesis of osteoarthritis.

METHODS

A comprehensive review of the literature on osteoarthritis and apoptosis was performed, which mainly focused on the regulatory factors and signaling pathways associated with chondrocyte apoptosis in osteoarthritis and other pathogenic mechanisms involved in chondrocyte apoptosis.

RESULTS

Inflammatory mediators such as reactive oxygen species (ROS), nitric oxide (NO), IL-1β, tumor necrosis factor-α (TNF-α), and Fas are closely related to chondrocyte apoptosis. NF-κB signaling pathway, Wnt signaling pathway, and Notch signaling pathway activate proteins and gene targets that promote or inhibit the progression of osteoarthritis disease, including chondrocyte apoptosis and ECM degradation. Long non-coding RNAs (LncRNAs) and microRNAs (microRNAs) have gradually replaced single and localized research methods and become the main research approaches. In addition, the relationship between cellular senescence, autophagy, and apoptosis was also briefly explained.

CONCLUSION

This review offers a better molecular delineation of apoptotic processes that may help in designing new therapeutic options for OA treatment.

Differential cell-cycle control by oscillatory versus sustained Hes1 expression via p21

Oscillatory Hes1 expression activates cell proliferation, while high and sustained Hes1 expression induces quiescence, but the mechanism by which Hes1 differentially controls cell proliferation depending on its expression dynamics is unclear. Here, we show that oscillatory Hes1 expression down-regulates the expression of the cyclin-dependent kinase inhibitor p21 (Cdkn1a), which delays cell-cycle progression, and thereby activates the proliferation of mouse neural stem cells (NSCs). By contrast, sustained Hes1 overexpression up-regulates p21 expression and inhibits NSC proliferation, although it initially down-regulates p21 expression. Compared with Hes1 oscillation, sustained Hes1 overexpression represses Dusp7, a phosphatase for phosphorylated Erk (p-Erk), and increases the levels of p-Erk, which can up-regulate p21 expression. These results indicate that p21 expression is directly repressed by oscillatory Hes1 expression, but indirectly up-regulated by sustained Hes1 overexpression, suggesting that depending on its expression dynamics, Hes1 differentially controls NSC proliferation via p21.

NAD+-Consuming Enzymes in Stem Cell Homeostasis

Nicotinamide adenine dinucleotide (NAD⁺) is a coenzyme used in redox reactions, energy metabolism, and mitochondrial biogenesis. NAD⁺ is also required as a cofactor by nonredox NAD⁺-dependent enzymes. Hundreds of enzymes that consume NAD⁺ have been identified. The NAD⁺-consuming enzymes are involved in a variety of cellular processes such as signal transduction, DNA repair, cellular senescence, and stem cell (SC) homeostasis. In this review, we discussed how different types of NAD⁺-consuming enzymes regulate SC functions and summarized current research on the roles of the NAD⁺ consumers in SC homeostasis. We hope to provide a more global and integrative insight to the mechanism and intervention of SC homeostasis via the regulation of the NAD⁺-consuming enzymes.

Taspase1 Facilitates Topoisomerase IIβ-Mediated DNA Double-Strand Breaks Driving Estrogen-Induced Transcription

The human protease Taspase1 plays a pivotal role in developmental processes and cancerous diseases by processing critical regulators, such as the leukemia proto-oncoprotein MLL. Despite almost two decades of intense research, Taspase1's biology is, however, still poorly understood, and so far its cellular function was not assigned to a superordinate biological pathway or a specific signaling cascade. Our data, gained by methods such as co-immunoprecipitation, LC-MS/MS and Topoisomerase II DNA cleavage assays, now functionally link Taspase1 and hormone-induced, Topoisomerase IIβ-mediated transient DNA double-strand breaks, leading to active transcription. The specific interaction with Topoisomerase IIα enhances the formation of DNA double-strand breaks that are a key prerequisite for stimulus-driven gene transcription. Moreover, Taspase1 alters the H3K4 epigenetic signature upon estrogen-stimulation by cleaving the chromatin-modifying enzyme MLL. As estrogen-driven transcription and MLL-derived epigenetic labelling are reduced upon Taspase1 siRNA-mediated knockdown, we finally characterize Taspase1 as a multifunctional co-activator of estrogen-stimulated transcription.

Targeting the transcription factor HES1 by L-menthol restores protein phosphatase 6 in keratinocytes in models of psoriasis

Protein Phosphatase 6 down-regulation in keratinocytes is a pivotal event that amplifies the inflammatory circuits in psoriasis, indicating that restoration of protein phosphatase 6 can be a rational strategy for psoriasis treatment. Through the phenotypic screen, we here identify L-menthol that ameliorates psoriasis-like skin inflammation by increasing protein phosphatase 6 in keratinocytes. Target identification approaches reveal an indispensable role for the transcription factor hairy and enhancer of split 1 in governing the protein phosphatase 6-upregulating function of L-menthol in keratinocytes. The transcription factor hairy and enhancer of split 1 is diminished in the epidermis of psoriasis patients and imiquimod-induced mouse model, while L-menthol upregulates the transcription factor hairy and enhancer of split 1 by preventing its proteasomal degradation. Mechanistically, the transcription factor hairy and enhancer of split 1 transcriptionally activates the expression of immunoglobulin-binding protein 1 which promotes protein phosphatase 6 expression and inhibits its ubiquitination. Collectively, we discover a therapeutic compound, L-menthol, for psoriasis, and uncover the dysfunctional the transcription factor hairy and enhancer of split 1- immunoglobulin-binding protein 1- protein phosphatase 6 axis that contributes to psoriasis pathology by using L-menthol as a probe.

PARP1: Liaison of Chromatin Remodeling and Transcription

Poly(ADP-ribosyl)ation (PARylation) is a covalent post-translational modification and plays a key role in the immediate response of cells to stress signals. Poly(ADP-ribose) polymerase 1 (PARP1), the founding member of the PARP superfamily, synthesizes long and branched polymers of ADP-ribose (PAR) onto acceptor proteins, thereby modulating their function and their local surrounding. PARP1 is the most prominent of the PARPs and is responsible for the production of about 90% of PAR in the cell. Therefore, PARP1 and PARylation play a pleotropic role in a wide range of cellular processes, such as DNA repair and genomic stability, cell death, chromatin remodeling, inflammatory response and gene transcription. PARP1 has DNA-binding and catalytic activities that are important for DNA repair, yet also modulate chromatin conformation and gene transcription, which can be independent of DNA damage response. PARP1 and PARylation homeostasis have also been implicated in multiple diseases, including inflammation, stroke, diabetes and cancer. Studies of the molecular action and biological function of PARP1 and PARylation provide a basis for the development of pharmaceutic strategies for clinical applications. This review focuses primarily on the role of PARP1 in the regulation of chromatin remodeling and transcriptional activation.

TOP2B Is Required to Maintain the Adrenergic Neural Phenotype and for ATRA-Induced Differentiation of SH-SY5Y Neuroblastoma Cells

The neuroblastoma cell line SH-SY5Y is widely used to study retinoic acid (RA)-induced gene expression and differentiation and as a tool to study neurodegenerative disorders. SH-SY5Y cells predominantly exhibit adrenergic neuronal properties, but they can also exist in an epigenetically interconvertible alternative state with more mesenchymal characteristics; as a result, these cells can be used to study gene regulation circuitry controlling neuroblastoma phenotype. Using a combination of pharmacological inhibition and targeted gene inactivation, we have probed the requirement for DNA topoisomerase IIB (TOP2B) in RA-induced gene expression and differentiation and in the balance between adrenergic neuronal versus mesenchymal transcription programmes. We found that expression of many, but not all genes that are rapidly induced by ATRA in SH-SY5Y cells was significantly reduced in the TOP2B null cells; these genes include BCL2, CYP26A1, CRABP2, and NTRK2. Comparing gene expression profiles in wild-type versus TOP2B null cells, we found that long genes and genes expressed at a high level in WT SH-SY5Y cells were disproportionately dependent on TOP2B. Notably, TOP2B null SH-SY5Y cells upregulated mesenchymal markers vimentin (VIM) and fibronectin (FN1) and components of the NOTCH signalling pathway. Enrichment analysis and comparison with the transcription profiles of other neuroblastoma-derived cell lines supported the conclusion that TOP2B is required to fully maintain the adrenergic neural-like transcriptional signature of SH-SY5Y cells and to suppress the alternative mesenchymal epithelial-like epigenetic state.

Cis- and trans-resveratrol have opposite effects on histone serine-ADP-ribosylation and tyrosine induced neurodegeneration

Serum tyrosine levels increase during aging, neurocognitive, metabolic, and cardiovascular disorders. However, calorie restriction (CR) and sleep lower serum tyrosine levels. We previously showed that tyrosine inhibits tyrosyl-tRNA synthetase (TyrRS)-mediated activation of poly-ADP-ribose polymerase 1 (PARP1). Here, we show that histone serine-ADP-ribosylation is decreased in Alzheimer's Disease (AD) brains, and increased tyrosine levels deplete TyrRS and cause neuronal DNA damage. However, dopamine and brain-derived neurotrophic factor (BDNF) increase TyrRS and histone serine-ADP-ribosylation. Furthermore, cis-resveratrol (cis-RSV) that binds to TyrRS mimicking a 'tyrosine-free' conformation increases TyrRS, facilitates histone serine-ADP-ribosylation-dependent DNA repair, and provides neuroprotection in a TyrRS-dependent manner. Conversely, trans-RSV that binds to TyrRS mimicking a 'tyrosine-like' conformation decreases TyrRS, inhibits serine-ADP-ribosylation-dependent DNA repair, and induces neurodegeneration in rat cortical neurons. Our findings suggest that age-associated increase in serum tyrosine levels may effect neurocognitive and metabolic disorders and offer a plausible explanation for divergent results obtained in clinical trials using resveratrol.

A Long-Lasting PARP1-Activation Mediates Signal-Induced Gene Expression

This overview presents recent evidence for a long-lasting PARP1 activation by a variety of signal transduction mechanisms, mediating signal-induced gene expression and chromatin remodeling. This mode of PARP1 activation has been reported in a variety of cell types, under physiological conditions. In this mechanism, PARP1 is not transiently activated by binding to DNA breaks. Moreover, damaged DNA interfered with this long-lasting PARP1 activation.

Therapeutic Potentials of Poly (ADP-Ribose) Polymerase 1 (PARP1) Inhibition in Multiple Sclerosis and Animal Models: Concept Revisiting

Poly (ADP-ribose) polymerase 1 (PARP1) plays a fundamental role in DNA repair and gene expression. Excessive PARP1 hyperactivation, however, has been associated with cell death. PARP1 and/or its activity are dysregulated in the immune and central nervous system of multiple sclerosis (MS) patients and animal models. Pharmacological PARP1 inhibition is shown to be protective against immune activation and disease severity in MS animal models while genetic PARP1 deficiency studies reported discrepant results. The inconsistency suggests that the function of PARP1 and PARP1-mediated PARylation may be complex and context-dependent. The article reviews PARP1 functions, discusses experimental findings and possible interpretations of PARP1 in inflammation, neuronal/axonal degeneration, and oligodendrogliopathy, three major pathological components cooperatively determining MS disease course and neurological progression, and points out future research directions. Cell type specific PARP1 manipulations are necessary for revisiting the role of PARP1 in the three pathological components prior to moving PARP1 inhibition into clinical trials for MS therapy.

The key players of parthanatos: opportunities for targeting multiple levels in the therapy of parthanatos-based pathogenesis

Parthanatos is a form of regulated cell death involved in the pathogenesis of many diseases, particularly neurodegenerative disorders, such as Parkinson's disease, Alzheimer's disease, Huntington's disease, and amyotrophic lateral sclerosis. Parthanatos is a multistep cell death pathway cascade that involves poly (ADP-ribose) polymerase 1 (PARP-1) overactivation, PAR accumulation, PAR binding to apoptosis-inducing factor (AIF), AIF release from the mitochondria, nuclear translocation of the AIF/macrophage migration inhibitory factor (MIF) complex, and MIF-mediated large-scale DNA fragmentation. All the key players in the parthanatos pathway are pleiotropic proteins with diverse functions. An in-depth understanding of the structure-based activity of the key factors, and the biochemical mechanisms of parthanatos, is crucial for the development of drugs and therapeutic strategies. In this review, we delve into the key players of the parthanatos pathway and reveal the multiple levels of therapeutic opportunities for treating parthanatos-based pathogenesis.

Homodimeric and Heterodimeric Interactions among Vertebrate Basic Helix-Loop-Helix Transcription Factors

The basic helix–loop–helix transcription factor (bHLH TF) family is involved in tissue development, cell differentiation, and disease. These factors have transcriptionally positive, negative, and inactive functions by combining dimeric interactions among family members. The best known bHLH TFs are the E-protein homodimers and heterodimers with the tissue-specific TFs or ID proteins. These cooperative and dynamic interactions result in a complex transcriptional network that helps define the cell’s fate. Here, the reported dimeric interactions of 67 vertebrate bHLH TFs with other family members are summarized in tables, including specifications of the experimental techniques that defined the dimers. The compilation of these extensive data underscores homodimers of tissue-specific bHLH TFs as a central part of the bHLH regulatory network, with relevant positive and negative transcriptional regulatory roles. Furthermore, some sequence-specific TFs can also form transcriptionally inactive heterodimers with each other. The function, classification, and developmental role for all vertebrate bHLH TFs in four major classes are detailed.

Poly (ADP-ribose) polymerase (PARP) inhibition in cancer: Potential impact in cancer stem cells and therapeutic implications

Inhibitors of poly(ADP-ribose) polymerase (PARP) are used in mono- or combination therapies for several malignancies. They are also used as maintenance therapy for some cancers after initial treatment. While the focus of this therapeutic approach is on the effect of PARP inhibition on the bulk tumour cells, in this review, we discuss their effect on the cancer stem cells. We identify key mediators and pathways in cancer stem cells whose response to PARP inhibition is not necessarily the same as the rest of the tumour cells. Since the cancer stem cells are known drivers of growth of tumours and their resistance to therapy, the clinical outcome might be drastically different than what is expected, if the effect of PARP inhibition on the cancer stem cells is not taken into account.

TOP2B's contributions to transcription

Transcription is regulated and mediated by multiprotein complexes in a chromatin context. Transcription causes changes in DNA topology which is modulated by DNA topoisomerases, enzymes that catalyse changes in DNA topology via transient breaking and re-joining of one or both strands of the phosphodiester backbone. Mammals have six DNA topoisomerases, this review focuses on one, DNA topoisomerase II beta (TOP2B). In the absence of TOP2B transcription of many developmentally regulated genes is altered. Long genes seem particularly susceptible to the lack of TOP2B. Biochemical studies of the role of TOP2B in transcription regulated by ligands such as nuclear hormones, growth factors and insulin has revealed PARP1 associated with TOP2B and also PRKDC, XRCC5 and XRCC6. Analysis of publicly available databases of protein interactions confirms these interactions and illustrates interactions with other key transcriptional regulators including TRIM28. TOP2B has been shown to interact with proteins involved in chromosome organisation including CTCF and RAD21. Comparison of publicly available Chip-seq datasets reveals the location at which these proteins interact with genes. The availability of resources such as large datasets of protein-protein interactions, e.g. BioGrid and IntAct and protein-DNA interactions such as Chip-seq in GEO enables scientists to extend models and propose new hypotheses.

Hairy and enhancer of split 1 is a primary effector of NOTCH2 signaling and induces osteoclast differentiation and function

Notch2^tm1.1Ecan mice, which harbor a mutation replicating that found in Hajdu–Cheney syndrome, exhibit marked osteopenia because of increased osteoclast number and bone resorption. Hairy and enhancer of split 1 (HES1) is a Notch target gene and a transcriptional modulator that determines osteoclast cell fate decisions. Transcript levels of Hes1 increase in Notch2^tm1.1Ecan bone marrow–derived macrophages (BMMs) as they mature into osteoclasts, suggesting a role in osteoclastogenesis. To determine whether HES1 is responsible for the phenotype of Notch2^tm1.1Ecan mice and the skeletal manifestations of Hajdu–Cheney syndrome, Hes1 was inactivated in Ctsk-expressing cells from Notch2^tm1.1Ecan mice. Ctsk encodes the protease cathepsin K, which is expressed preferentially by osteoclasts. We found that the osteopenia of Notch2^tm1.1Ecan mice was ameliorated, and the enhanced osteoclastogenesis was reversed in the context of the Hes1 inactivation. Microcomputed tomography revealed that the downregulation of Hes1 in Ctsk-expressing cells led to increased bone volume/total volume in female mice. In addition, cultures of BMMs from Ctsk^Cre/WT;Hes1^Δ/Δ mice displayed a decrease in osteoclast number and size and decreased bone-resorbing capacity. Moreover, activation of HES1 in Ctsk-expressing cells led to osteopenia and enhanced osteoclast number, size, and bone resorptive capacity in BMM cultures. Osteoclast phenotypes and RNA-Seq of cells in which HES1 was activated revealed that HES1 modulates cell–cell fusion and bone-resorbing capacity by supporting sealing zone formation. In conclusion, we demonstrate that HES1 is mechanistically relevant to the skeletal manifestation of Notch2^tm1.1Ecan mice and is a novel determinant of osteoclast differentiation and function.

Poly (ADP-Ribose) Polymerase 1 Regulates Cajal-Retzius Cell Development and Neural Precursor Cell Adhesion

Poly (ADP-ribose) polymerase 1 (PARP1) is a ubiquitously expressed enzyme that regulates DNA damage repair, cell death, inflammation, and transcription. PARP1 functions by adding ADP-ribose polymers (PAR) to proteins including itself, using NAD⁺ as a donor. This post-translational modification known as PARylation results in changes in the activity of PARP1 and its substrate proteins and has been linked to the pathogenesis of various neurological diseases. PARP1 KO mice display schizophrenia-like behaviors, have impaired memory formation, and have defects in neuronal proliferation and survival, while mutations in genes that affect PARylation have been associated with intellectual disability, psychosis, neurodegeneration, and stroke in humans. Yet, the roles of PARP1 in brain development have not been extensively studied. We now find that loss of PARP1 leads to defects in brain development and increased neuronal density at birth. We further demonstrate that PARP1 loss increases the expression levels of genes associated with neuronal migration and adhesion in the E15.5 cerebral cortex, including Reln. This correlates with an increased number of Cajal–Retzius (CR) cells in vivo and in cultures of embryonic neural progenitor cells (NPCs) derived from the PARP1 KO cortex. Furthermore, PARP1 loss leads to increased NPC adhesion to N-cadherin, like that induced by experimental exposure to Reelin. Taken together, these results uncover a novel role for PARP1 in brain development, i.e., regulation of CR cells, neuronal density, and cell adhesion.

A systems approach using Diversity Outbred mice distinguishes the cardiovascular effects and genetics of circulating GDF11 from those of its homolog, myostatin

Growth differentiation factor 11 (GDF11) is a member of the TGF-β protein family that has been implicated in the development of cardiac hypertrophy. While some studies have suggested that systemic GDF11 protects against cardiomyocyte enlargement and left ventricular wall thickening, there remains uncertainty about the true impact of GDF11 and whether its purported effects are actually attributable to its homolog myostatin. This study was conducted to resolve the statistical and genetic relationships among GDF11, myostatin, and cardiac hypertrophy in a mouse model of human genetics, the Diversity Outbred (DO) stock. In the DO population, serum GDF11 concentrations positively correlated with cardiomyocyte cross-sectional area, while circulating myostatin levels were negatively correlated with body weight, heart weight, and left ventricular wall thickness and mass. Genetic analyses revealed that serum GDF11 concentrations are modestly heritable (0.23) and identified a suggestive peak on murine chromosome 3 in close proximity to the gene Hey1, a transcriptional repressor. Bioinformatic analyses located putative binding sites for the HEY1 protein upstream of the Gdf11 gene in the mouse and human genomes. In contrast, serum myostatin concentrations were more heritable (0.57) than GDF11 concentrations, and mapping identified a significant locus near the gene FoxO1, which has binding motifs within the promoter regions of human and mouse myostatin genes. Together, these findings more precisely define the independent cardiovascular effects of GDF11 and myostatin, as well as their distinct regulatory pathways. Hey1 is a compelling candidate for the regulation of GDF11 and will be further evaluated in future studies.

Towards resolving the enigma of the dichotomy of resveratrol: cis- and trans-resveratrol have opposite effects on TyrRS-regulated PARP1 activation

Unlike widely perceived, resveratrol (RSV) decreased the average lifespan and extended only the replicative lifespan in yeast. Similarly, although not widely discussed, RSV is also known to evoke neurite degeneration, kidney toxicity, atherosclerosis, premature senescence, and genotoxicity through yet unknown mechanisms. Nevertheless, in vivo animal models of diseases and human clinical trials demonstrate inconsistent protective and beneficial effects. Therefore, the mechanism of action of RSV that elicits beneficial effects remains an enigma. In a previously published work, we demonstrated structural similarities between RSV and tyrosine amino acid. RSV acts as a tyrosine antagonist and competes with it to bind to human tyrosyl-tRNA synthetase (TyrRS). Interestingly, although both isomers of RSV bind to TyrRS, only the cis-isomer evokes a unique structural change at the active site to promote its interaction with poly-ADP-ribose polymerase 1 (PARP1), a major determinant of cellular NAD+-dependent stress response. However, retention of trans-RSV in the active site of TyrRS mimics its tyrosine-bound conformation that inhibits the auto-poly-ADP-ribos(PAR)ylation of PARP1. Therefore, we proposed that cis-RSV-induced TyrRS-regulated auto-PARylation of PARP1 would contribute, at least in part, to the reported health benefits of RSV through the induction of protective stress response. This observation suggested that trans-RSV would inhibit TyrRS/PARP1-mediated protective stress response and would instead elicit an opposite effect compared to cis-RSV. Interestingly, most recent studies also confirmed the conversion of trans-RSV and its metabolites to cis-RSV in the physiological context. Therefore, the finding that cis-RSV and trans-RSV induce two distinct conformations of TyrRS with opposite effects on the auto-PARylation of PARP1 provides a potential molecular basis for the observed dichotomic effects of RSV under different experimental paradigms. However, the fact that natural RSV exists as a diastereomeric mixture of its cis and trans isomers and cis-RSV is also a physiologically relevant isoform has not yet gained much scientific attention.

New Insights Into the Intricacies of Proneural Gene Regulation in the Embryonic and Adult Cerebral Cortex

Historically, the mammalian brain was thought to lack stem cells as no new neurons were found to be made in adulthood. That dogma changed ∼25 years ago with the identification of neural stem cells (NSCs) in the adult rodent forebrain. However, unlike rapidly self-renewing mature tissues (e.g., blood, intestinal crypts, skin), the majority of adult NSCs are quiescent, and those that become 'activated' are restricted to a few neurogenic zones that repopulate specific brain regions. Conversely, embryonic NSCs are actively proliferating and neurogenic. Investigations into the molecular control of the quiescence-to-proliferation-to-differentiation continuum in the embryonic and adult brain have identified proneural genes encoding basic-helix-loop-helix (bHLH) transcription factors (TFs) as critical regulators. These bHLH TFs initiate genetic programs that remove NSCs from quiescence and drive daughter neural progenitor cells (NPCs) to differentiate into specific neural cell subtypes, thereby contributing to the enormous cellular diversity of the adult brain. However, new insights have revealed that proneural gene activities are context-dependent and tightly regulated. Here we review how proneural bHLH TFs are regulated, with a focus on the murine cerebral cortex, drawing parallels where appropriate to other organisms and neural tissues. We discuss upstream regulatory events, post-translational modifications (phosphorylation, ubiquitinylation), protein-protein interactions, epigenetic and metabolic mechanisms that govern bHLH TF expression, stability, localization, and consequent transactivation of downstream target genes. These tight regulatory controls help to explain paradoxical findings of changes to bHLH activity in different cellular contexts.

Poly(ADP-ribose) Polymerase 1 (PARP1) restrains MyoD-dependent gene expression during muscle differentiation

The myogenic factor MyoD regulates skeletal muscle differentiation by interacting with a variety of chromatin-modifying complexes. Although MyoD can induce and maintain chromatin accessibility at its target genes, its binding and trans-activation ability can be limited by some types of not fully characterized epigenetic constraints. In this work we analysed the role of PARP1 in regulating MyoD-dependent gene expression. PARP1 is a chromatin-associated enzyme, playing a well recognized role in DNA repair and that is implicated in transcriptional regulation. PARP1 affects gene expression through multiple mechanisms, often involving the Poly(ADP-ribosyl)ation of chromatin proteins. In line with PARP1 down-regulation during differentiation, we observed that PARP1 depletion boosts the up-regulation of MyoD targets, such as p57, myogenin, Mef2C and p21, while its re-expression reverts this effect. We also found that PARP1 interacts with some MyoD-binding regions and that its presence, independently of the enzymatic activity, interferes with MyoD recruitment and gene induction. We finally suggest a relationship between the binding of PARP1 and the loss of the activating histone modification H3K4me3 at MyoD-binding regions. This work highlights not only a novel player in the epigenetic control of myogenesis, but also a repressive and catalytic-independent mechanisms by which PARP1 regulates transcription.

Foxi1 inactivation rescues loss of principal cell fate selection in Hes1-deficient kidneys but does not ensure maintenance of principal cell gene expression

The distal nephron and collecting duct segments of the mammalian kidney consist of intercalated cell types intermingled among principal cell types. Notch signaling ensures that a sufficient number of cells select a principal instead of an intercalated cell fate. However, the precise mechanisms by which Notch signaling patterns the distal nephron and collecting duct cell fates is unknown. Here we observed that Hes1, a direct target of Notch signaling pathway, is required within the mouse developing collecting ducts for repression of Foxi1 expression, an essential intercalated cell specific transcription factor. Interestingly, inactivation of Foxi1 in Hes1-deficient collecting ducts rescues the deficiency in principal cell fate selection, overall urine concentrating deficiency, and reduces the occurrence of hydronephrosis. However, Foxi1 inactivation does not rescue the reduction in expression of all principal cell genes in the Hes1-deficient kidney collecting duct cells that select the principal cell fate. Additionally, suppression of Notch/Hes1 signaling in mature principal cells reduces principal cell gene expression without activating Foxi1. We conclude that Hes1 is a Notch signaling target that is essential for normal patterning of the collecting ducts with intermingled cell types by repressing Foxi1, and for maintenance of principal cell gene expression independent of repressing Foxi1.

Contribution of platelet-derived growth factor signaling to retina regeneration in zebrafish

Accumulated evidence indicates that platelet-derived growth factor (PDGF) contributes to various types of tissue regeneration. However, the effects and mechanisms of PDGF signaling for retina regeneration have not been sufficiently investigated. To clarify this, we investigated the role of PDGF signaling in retina regeneration process after needle puncture in zebrafish. Time-course analysis showed a spike peak of pdgf-a at 6 h after injury and a broad peak of pdgf-b during 6-96 h after injury. Inhibition of PDGF signaling with AG1295 suppressed BrdU-positive proliferative cell numbers at 4 days after injury. At the same time, retina regeneration-associated transcription factors, ascl1a and pax6b, were down-regulated by AG1295 treatment. Intravitreal injection of human recombinant PDGF-AA or -BB into intact zebrafish induced the cell proliferation. PDGF-BB injection induced the Müller glia-derived neurogenic cluster; PDGF-AA increased the 4C4-positive microglia. These findings indicate that PDGF signaling contributes to retina regeneration in zebrafish and causes different types of cell proliferation, depending on each subtype of PDGF. (160 words).

NONO and tumorigenesis: More than splicing

The non-POU domain-containing octamer-binding protein NONO/p54^nrb , which belongs to the Drosophila behaviour/human splicing (DBHS) family, is a multifunctional nuclear protein rarely functioning alone. Emerging solid evidences showed that NONO engages in almost every step of gene regulation, including but not limited to mRNA splicing, DNA unwinding, transcriptional regulation, nuclear retention of defective RNA and DNA repair. NONO is involved in many biological processes including cell proliferation, apoptosis, migration and DNA damage repair. Dysregulation of NONO has been found in many types of cancer. In this review, we summarize the current and fast-growing knowledge about the regulation of NONO, its biological function and implications in tumorigenesis and cancer progression. Overall, significant findings about the roles of NONO have been made, which might make NONO to be a new biomarker or/and a possible therapeutic target for cancers.

Whitefly HES1 binds to the intergenic region of Tomato yellow leaf curl China virus and promotes viral gene transcription

Intergenic region of begomovirus genome is vital to virus replication and viral gene transcription in plants. Previous studies have reported that Tomato yellow leaf curl China virus (TYLCCNV), a begomovirus, is able to accumulate and transcribe in its whitefly vector. However, the viral and host components that participate in begomovirus transcription in whiteflies are hitherto unknown. Using a yeast one-hybrid system, we identified >50 whitefly proteins that interacted with TYLCCNV intergenic region. Dual luciferase analysis revealed that one of the identified proteins, the hairy and enhancer of split homolog-1 (HES1), specifically bound to CACGTG motif in TYLCCNV intergenic region. Silencing HES1 decreased viral transcription, accumulation and transmission. These results demonstrate that the interactions between whitefly proteins and the intergenic region of TYLCCNV may contribute to viral transcription in the whitefly vector. Our findings offer valuable clues for the research and development of novel strategies to interfere with begomovirus transmission.

PARylation During Transcription: Insights into the Fine-Tuning Mechanism and Regulation

Transcription is a multistep, tightly regulated process. During transcription initiation, promoter recognition and pre-initiation complex (PIC) formation take place, in which dynamic recruitment or exchange of transcription activators occur. The precise coordination of the recruitment and removal of transcription factors, as well as chromatin structural changes, are mediated by post-translational modifications (PTMs). Poly(ADP-ribose) polymerases (PARPs) are key players in this process, since they can modulate DNA-binding activities of specific transcription factors through poly-ADP-ribosylation (PARylation). PARylation can regulate the transcription at three different levels: (1) by directly affecting the recruitment of specific transcription factors, (2) by triggering chromatin structural changes during initiation and as a response to cellular stresses, or (3) by post-transcriptionally modulating the stability and degradation of specific mRNAs. In this review, we principally focus on these steps and summarise the recent findings, demonstrating the mechanisms through which PARylation plays a potential regulatory role during transcription and DNA repair.

Defective neurogenesis and schizophrenia-like behavior in PARP-1-deficient mice

In the current study we present evidence suggesting that PARP-1 regulates neurogenesis and its deficiency may result in schizophrenia-like behavioral deficits in mice. PARP-1 knockout neural stem cells exhibited a marked upregulation of embryonic stem cell phosphatase that can suppress the proliferative signaling of PI3K-Akt and ERK. The suppressed activity of Akt and ERK in the absence of PARP-1 results in the elevation of FOXO1 activity and its downstream target genes p21 and p27, leading to the inhibition of neural stem cell proliferation. Moreover, expression of neurogenic factors and neuronal differentiation were decreased in the PARP-1 knockout neural stem cells whereas glial differentiation was increased. In accordance with the in vitro data, PARP-1 knockout mice exhibited reduced brain weight with enlarged ventricle as well as decreased adult neurogenesis in the hippocampus. Interestingly, PARP-1 knockout mice exhibited schizophrenia-like symptoms such as anxiety, depression, social interaction deficits, cognitive impairments, and prepulse inhibition deficits. Taken together, our results suggest that PARP-1 regulates neurogenesis during development and in adult and its absence may lead to the schizophrenia-like behavioral abnormality in mice.

Therapeutic considerations of PARP in stem cell biology: Relevance in cancer and beyond

Cancer stem cells (CSCs) are of fundamental importance in tumor progression because of their tumor-initiating properties, their resistance to radio- and chemotherapy, their invasive properties and their propensity to escape immune responses that together contribute to tumor relapse. These highly aggressive features underscore the importance of constantly identifying new and innovative therapeutic solutions to eradicate these cells. In this narrative review we discuss recent findings on the involvement of PARP family members in cancer stem cell biology and the benefit of their inhibition. Nonetheless, an important limitation in the use of PARP inhibitors is the emergence of a prominent function of PARP1 in non-cancer stem cell biology including stem cell maintenance and differentiation during development, neurogenesis or adipogenesis. Thus, we also summarize the dominant discoveries revealing the importance of PARP1 in normal stem cell biology.

PARP1 interacts with HMGB1 and promotes its nuclear export in pathological myocardial hypertrophy

High-mobility group box 1 (HMGB1) exhibits various functions according to its subcellular location, which is finely conditioned by diverse post-translational modifications, such as acetylation. The nuclear HMGB1 may prevent from cardiac hypertrophy, whereas its exogenous protein is proven to induce hypertrophic response. This present study sought to investigate the regulatory relationships between poly(ADP-ribose) polymerase 1 (PARP1) and HMGB1 in the process of pathological myocardial hypertrophy. Primary-cultured neonatal rat cardiomyocytes (NRCMs) were respectively incubated with three cardiac hypertrophic stimulants, including angiotensin II (Ang II), phenylephrine (PE), and isoproterenol (ISO), and cell surface area and the mRNA expression of hypertrophic biomarkers were measured. the catalytic activity of PARP1 was remarkably enhanced, meanwhile HMGB1 excluded from the nucleus. PARP1 overexpression by infecting with adenovirus PARP1 (Ad-PARP1) promoted the nuclear export of HMGB1, facilitated its secretion outside the cell, aggravated cardiomyocyte hypertrophy, which could be alleviated by HMGB1 overexpression. PE treatment led to the similar results, while that effect was widely depressed by PARP1 silencing or its specific inhibitor AG14361. Moreover, SD rats were intraperitoneally injected with 3-aminobenzamide (3AB, 20 mg/kg every day, a well-established PARP1 inhibitor) 7 days after abdominal aortic constriction (AAC) surgery for 6 weeks, echocardiography and morphometry of the hearts were measured. Pre-treatment of 3AB relieved AAC-caused the translocation of nuclear HMGB1 protein, cardiac hypertrophy, and heart dysfunction. Our research offers a novel evidence that PARP1 combines with HMGB1 and accelerates its translocation from nucleus to cytoplasm, and the course finally causes cardiac hypertrophy.

Hes1 attenuates type I IFN responses via VEGF-C and WDFY1

Transcription factor Hes1 acts as a homeostatic negative regulator of type I interferon production to restrain interferon-mediated immune responses, including antiviral immunity and autoimmune conditions. Mechanistically, Hes1 suppresses interferon expression by targeting a regulatory circuit composed of WDFY1 and VEGF-C.

Induction of type I interferons (IFNs) is critical for eliciting competent immune responses, especially antiviral immunity. However, uncontrolled IFN production contributes to pathogenesis of autoimmune and inflammatory diseases. We found that transcription factor Hes1 suppressed production of type I IFNs and expression of IFN-stimulated genes. Functionally, Hes1-deficient mice displayed a heightened IFN signature in vivo, mounted enhanced resistance against encephalomyocarditis virus infection, and showed signs of exacerbated experimental lupus nephritis. Mechanistically, Hes1 did not suppress IFNs via direct transcriptional repression of IFN-encoding genes. Instead, Hes1 attenuated activation of TLR upstream signaling by inhibition of an adaptor molecule, WDFY1. Genome-wide assessment of Hes1 occupancy revealed that suppression of WDFY1 was secondary to direct binding and thus enhancement of expression of VEGF-C by Hes1, making Vegfc a rare example of an Hes1 positively regulated gene. In summary, these results identified Hes1 as a homeostatic negative regulator of type I IFNs for the maintenance of immune balance in the context of antiviral immunity and autoimmune diseases.

Signal-induced PARP1-Erk synergism mediates IEG expression

A recently disclosed Erk-induced PARP1 activation mechanism mediates the expression of immediate early genes (IEGs) in response to a variety of extra- and intracellular signals implicated in memory acquisition, development and proliferation. Here, we review this mechanism, which is initiated by stimulation-induced binding of PARP1 to phosphorylated Erk translocated into the nucleus. This binding maintains long-lasting synergistic activity of these proteins, which offers a new pattern for targeted therapy.

Poly(ADP-Ribose) Polymerases in Host-Pathogen Interactions, Inflammation, and Immunity

The literature review presented here details recent research involving members of the poly(ADP-ribose) polymerase (PARP) family of proteins. Among the 17 recognized members of the family, the human enzyme PARP1 is the most extensively studied, resulting in a number of known biological and metabolic roles. This review is focused on the roles played by PARP enzymes in host-pathogen interactions and in diseases with an associated inflammatory response. In mammalian cells, several PARPs have specific roles in the antiviral response; this is perhaps best illustrated by PARP13, also termed the zinc finger antiviral protein (ZAP). Plant stress responses and immunity are also regulated by poly(ADP-ribosyl)ation. PARPs promote inflammatory responses by stimulating proinflammatory signal transduction pathways that lead to the expression of cytokines and cell adhesion molecules. Hence, PARP inhibitors show promise in the treatment of inflammatory disorders and conditions with an inflammatory component, such as diabetes, arthritis, and stroke. These functions are correlated with the biophysical characteristics of PARP family enzymes. This work is important in providing a comprehensive understanding of the molecular basis of pathogenesis and host responses, as well as in the identification of inhibitors. This is important because the identification of inhibitors has been shown to be effective in arresting the progression of disease.

PARP1 interacts with STAT3 and retains active phosphorylated-STAT3 in nucleus during pathological myocardial hypertrophy

The activation of signal transducer and activator of transcription 3 (STAT3) positively regulates myocardial hypertrophy, and its transcriptional activity is finely conditioned by diverse extracellular growth factors and cytokines. Here, we introduce novel evidence that poly(ADP-ribose) polymerase 1 (PARP1) interacts with STAT3 and promotes its activation in cardiomyocytes and rat heart tissues. PARP1 activity and phosphorylated STAT3 were augmented by hypertrophic stimuli both in vitro and in vivo. Infection of PARP1 adenovirus induced cardiomyocyte hypertrophy, which could be prevented by STAT3 knockdown or inhibition. Additionally, PARP1 enhanced STAT3 phosphorylation level, nuclear accumulation and transcriptional activity. Mechanistically, PARP1 interacts with STAT3 and retains active phosphorylated-STAT3 in nucleus. In conclusion, our findings provide the first evidence that PARP1 exacerbates cardiac hypertrophy by stabilizing active phosphorylated-STAT3, which suggests that multi-target therapeutic strategies counteracting PARP1 activity and STAT3 activation would be potential for treating cardiovascular diseases.

TOP2B: The First Thirty Years

Type II DNA topoisomerases (EC 5.99.1.3) are enzymes that catalyse topological changes in DNA in an ATP dependent manner. Strand passage reactions involve passing one double stranded DNA duplex (transported helix) through a transient enzyme-bridged break in another (gated helix). This activity is required for a range of cellular processes including transcription. Vertebrates have two isoforms: topoisomerase IIα and β. Topoisomerase IIβ was first reported in 1987. Here we review the research on DNA topoisomerase IIβ over the 30 years since its discovery.

Osteoarthritis-Like Changes in Bardet-Biedl Syndrome Mutant Ciliopathy Mice (Bbs1M390R/M390R): Evidence for a Role of Primary Cilia in Cartilage Homeostasis and Regulation of Inflammation

Osteoarthritis (OA) is a debilitating inflammation related disease characterized by joint pain and effusion, loss of mobility, and deformity that may result in functional joint failure and significant impact on quality of life. Once thought of as a simple “wear and tear” disease, it is now widely recognized that OA has a considerable metabolic component and is related to chronic inflammation. Defects associated with primary cilia have been shown to be cause OA-like changes in Bardet–Biedl mice. We examined the role of dysfunctional primary cilia in OA in mice through the regulation of the previously identified degradative and pro-inflammatory molecular pathways common to OA. We observed an increase in the presence of pro-inflammatory markers TGFβ-1 and HTRA1 as well as cartilage destructive protease MMP-13 but a decrease in DDR-2. We observed a morphological difference in cartilage thickness in Bbs1^M390R/M390R mice compared to wild type (WT). We did not observe any difference in OARSI or Mankin scores between WT and Bbs1^M390R/M390R mice. Primary cilia appear to be involved in the upregulation of biomarkers, including pro-inflammatory markers common to OA.

Effect of Notch and PARP Pathways' Inhibition in Leukemic Cells

Differentiation of blood cells is one of the most complex processes in the body. It is regulated by the action of transcription factors in time and space which creates a specific signaling network. In the hematopoietic signaling system, Notch is one of the main regulators of lymphocyte development. The aim of this study was to get insight into the regulation of Notch signalization and the influence of poly(ADP-ribose)polymerase (PARP) activity on this process in three leukemia cell lines obtained from B and T cells. PARP1 is an enzyme involved in posttranslational protein modification and chromatin structure changes. B and T leukemia cells were treated with Notch and PARP inhibitors, alone or in combination, for a prolonged period. The cells did not show cell proliferation arrest or apoptosis. Analysis of gene and protein expression set involved in Notch and PARP pathways revealed increase in JAGGED1 expression after PARP1 inhibition in B cell lines and changes in Ikaros family members in both B and T cell lines after γ-secretase inhibition. These data indicate that Notch and PARP inhibition, although not inducing differentiation in leukemia cells, induce changes in signaling circuits and chromatin modelling factors.

The poly(ADP-ribosyl)ation of FoxO3 mediated by PARP1 participates in isoproterenol-induced cardiac hypertrophy

The Forkhead box-containing protein, O subfamily 3 (FoxO3) transcription factor negatively regulates myocardial hypertrophy, and its transcriptional activity is finely conditioned by diverse posttranslational modifications, such as phosphorylation, acetylation, ubiquitination, methylation and glycosylation. Here, we introduce a novel modification of the FoxO3 protein in cardiomyocytes: poly(ADP-ribosyl)ation (PARylation) mediated by poly(ADP-ribose) polymerase-1 (PARP1). This process catalyzes the NAD⁺-dependent synthesis of polymers of ADP-ribose (PAR) and their subsequent attachment to target proteins by PARPs. Primary-cultured neonatal rat cardiomyocytes were incubated with isoproterenol (ISO) to induce hypertrophy, or were infected with recombinant adenovirus vectors harboring PARP1 cDNA (Ad-PARP1). Sprague-Dawley (SD) rats were treated with ISO to induce cardiac hypertrophy, or were injected with Ad-PARP1 into the anterior and posterior left ventricular walls. Cardiomyocyte surface area, the mRNA expression of hypertrophic biomarkers, echocardiography, morphometry of the hearts were measured. The PARP1 activity was tested by cellular PAR levels. Interactions of PARP1 and FoxO3 were investigated by co-immunoprecipitation and immunofluorescence technique. PARylation of FoxO3 mediated by PARP1 facilitated its phosphorylation at the T32, S252 and S314 sites, triggered its nucleus export and suppressed its transcriptional activity and target genes expression, ultimately inducing cardiac hypertrophy. Additionally, PARP1 silencing or specific inhibition by 3-Aminobenzamide (3AB) and veliparib (ABT-888) alleviated the inhibition of FoxO3 activity by ISO, thus suppressing ISO-induced cardiac hypertrophy. Our data provide the first evidence that PARP1 exacerbates cardiac hypertrophy by PARylation of FoxO3.

Pleiotropic Hes-1 Concomitant with its Differential Activation Mediates Neural Stem Cell Maintenance and Radial Glial Propensity in Developing Neocortex

Notch signaling pathway and its downstream effector Hes-1 are well known for their role in cortical neurogenesis. Despite the canonical activation of Hes-1 in developing neocortex, recent advances have laid considerable emphasis on Notch/CBF1-independent Hes-1 (NIHes-1) expression with poor understanding of its existence and functional significance. Here, using reporter systems and in utero electroporation, we could qualitatively unravel the existence of NIHes-1 expressing neural stem cells from the cohort of dependent progenitors throughout the mouse neocortical development. Though Hes-1 expression is maintained in neural progenitor territory at all times, a simple shift from Notch-independent to -dependent state makes it pleiotropic as the former maintains the neural stem cells in a non-dividing/slow-dividing state, whereas the latter is very much required for maintenance and proliferation of radial glial cells. Therefore, our results provide an additional complexity in neural progenitor heterogeneity regarding differential Hes-1 expression in the germinal zone during neo-cortical development.

Epigenetic modification of TLE1 induce abnormal differentiation in diabetic mice intestinal epithelium

The intestinal epithelium cells (IECs) in diabetes mellitus (DM) patients have been proven to be abnormally differentiated. During the differentiation of IECs, epigenetic modification acts as an important regulator. In this study, we aimed to examine the epigenetic alteration of Transducin-like Enhancer of Split 1 (TLE1), a multitask transcriptional co-repressor, contributing to the differentiation homeostasis in IECs of DM mice. The IECs of type 2 diabetic mice model were isolated and collected. Methylation states of whole genomic DNA promoter regions were investigated by microarray. Methylated-specific PCR was used to detect the methylation state of TLE1 promoter in DM mice IECs. The expression of TLE1, Hes1, and differentiated cell markers were measured through real-time PCR, Western blots, and immunohistochemistry; by transfection assay, TLE1 or Hes1 was independently down-regulated in intestinal epithelium cell line, IEC-6. Subsequent modulation on TLE1, Hes1, and differentiated intestinal cell markers were detected. Global gene promoter regions in DM intestinal epithelium were less methylated comparing to normal control. The expression of TLE1 was significantly increased via hypomethylated activation in DM mice IECs. Hes1 was significantly suppressed and the terminal cell markers abnormally expressed in DM mice IECs (P < 0.05). Inhibition or induction on the abundance of TLE1 in IEC-6 cell line resulted in the corresponding dysregulation of Hes1 and intestinal epithelium differentiation (P < 0.05). Demethylation of TLE1 promoter region activates the self-expression in diabetic mice IECs. Subsequently, TLE1, through the transcriptional suppression on expression of Hes1, contributes to the aberrant differentiation of IECs in DM mice.

MEIS homeodomain proteins facilitate PARP1/ARTD1-mediated eviction of histone H1

PARP1/ARTD1 induces chromatin opening by posttranslational modification of the linker histone H1, but how PARP1 is targeted to physiologically correct gene loci is poorly understood. Hau et al. show that in differentiating neurons, PARP1 is rapidly and specifically recruited to a neuron-specific promoter by the atypical homeodomain protein MEIS2.

Pre–B-cell leukemia homeobox (PBX) and myeloid ecotropic viral integration site (MEIS) proteins control cell fate decisions in many physiological and pathophysiological contexts, but how these proteins function mechanistically remains poorly defined. Focusing on the first hours of neuronal differentiation of adult subventricular zone–derived stem/progenitor cells, we describe a sequence of events by which PBX-MEIS facilitates chromatin accessibility of transcriptionally inactive genes: In undifferentiated cells, PBX1 is bound to the H1-compacted promoter/proximal enhancer of the neuron-specific gene doublecortin (Dcx). Once differentiation is induced, MEIS associates with chromatin-bound PBX1, recruits PARP1/ARTD1, and initiates PARP1-mediated eviction of H1 from the chromatin fiber. These results for the first time link MEIS proteins to PARP-regulated chromatin dynamics and provide a mechanistic basis to explain the profound cellular changes elicited by these proteins.

Molecular mechanisms underlying osteoarthritis development: Notch and NF-κB

Osteoarthritis (OA) is a multi-factorial and highly prevalent joint disorder worldwide. Since the establishment of murine surgical knee OA models in 2005, many of the key molecules and signalling pathways responsible for OA development have been identified. Here we review the roles of two multi-functional signalling pathways in OA development: Notch and nuclear factor kappa-light-chain-enhancer of activated B cells. Previous studies have identified various aspects of articular chondrocyte regulation by these pathways. However, comprehensive understanding of the molecular networks regulating articular cartilage homeostasis and OA pathogenesis is needed.

PARP-1 is required for retrieval of cocaine-associated memory by binding to the promoter of a novel gene encoding a putative transposase inhibitor

Reward-related memory is an important factor in cocaine seeking. One necessary signaling mechanism for long-term memory formation is the activation of poly(ADP-ribose) polymerase-1 (PARP-1), via poly(ADP-ribosyl)ation. We demonstrate herein that auto-poly(ADP-ribosyl)ation of activated PARP-1 was significantly pronounced during retrieval of cocaine-associated contextual memory, in the central amygdala (CeA) of rats expressing cocaine-conditioned place preference (CPP). Intra-CeA pharmacological and short hairpin RNA depletion of PARP-1 activity during cocaine-associated memory retrieval abolished CPP. In contrast, PARP-1 inhibition after memory retrieval did not affect CPP reconsolidation process and subsequent retrievals. Chromatin immunoprecipitation sequencing revealed that PARP-1 binding in the CeA is highly enriched in genes involved in neuronal signaling. We identified among PARP targets in CeA a single gene, yet uncharacterized and encoding a putative transposase inhibitor, at which PARP-1 enrichment markedly increases during cocaine-associated memory retrieval and positively correlates with CPP. Our findings have important implications for understanding drug-related behaviors, and suggest possible future therapeutic targets for drug abuse.

Poly ADP-ribose polymerase-1: Beyond transcription and towards differentiation

Gene regulation mediates the processes of cellular development and differentiation leading to the origin of different cell types each having their own signature gene expression profile. However, the compact chromatin structure and the timely recruitment of molecules involved in various signaling pathways are of prime importance for temporal and spatial gene regulation that eventually contribute towards cell type and specificity. Poly (ADP-ribose) polymerase-1 (PARP-1), a 116-kDa nuclear multitasking protein is involved in modulation of chromatin condensation leading to altered gene expression. In response to activation signals, it adds ADP-ribose units to various target proteins including itself, thus regulating various key cellular processes like DNA repair, cell death, transcription, mRNA splicing etc. This review provides insights into the role of PARP-1 in gene regulation, cell differentiation and multicellular morphogenesis. In addition, the review also explores involvement of PARP-1 in immune cells development and therapeutic possibilities to treat various human diseases.

An Infectious Disease-Associated Il12b Polymorphism Regulates IL-12/23 p40 Transcription Involving Poly(ADP-Ribose) Polymerase 1

IL-12 and IL-23 are important host defense factors produced by APCs against certain intracellular and extracellular pathogens. Their dysregulation has also been implicated in several autoimmune diseases. The nucleotide polymorphism in the promoter region of Il12b (rs41292470 consisting of the long or short allele) encoding the shared subunit of IL-12 and IL-23, p40, has been reported to associate with susceptibility to infectious diseases and autoimmune disorders. How these genetic variants impact Il12b expression at the molecular level was unclear. We established an Il12b promoter-luciferase reporter system containing the long or short allele driving the reporter gene expression and found that the long allele (infection-resistant) displayed ∼2-fold higher transcriptional activity than the short allele (infection-susceptible), associated with a selective and differential nuclear binding activity to the two alleles in activated macrophages. DNA pull-down assays coupled with mass spectrometry analyses identified the specific DNA binding activity as poly(ADP-ribose) polymerase 1 (PARP-1). Small hairpin RNA-mediated knockdown of the endogenous PARP-1 expression resulted in reduced p40 mRNA expression and Il12b promoter activity. Bone marrow-derived macrophages from PARP-1-deficient mice had decreased p40 expression at both mRNA and protein levels. Furthermore, selective PARP-1 inhibitors resulted in impaired production of IL-12p40 and IL-23 in bone-marrow derived macrophages and PBMCs. Chromatin immunoprecipitation assay revealed that PARP-1 could bind specifically to Il12b in LPS-stimulated macrophages. Our study opens the way for further elucidating the molecular mechanism whereby allele-specific immune responses to foreign and self-antigens mediated by IL-12/IL-23 are controlled in an individually variable manner.

Hes1: the maestro in neurogenesis

The process of neurogenesis is well orchestrated by the harmony of multiple cues in a spatiotemporal manner. In this review, we focus on how a dynamic gene, Hes1, is involved in neurogenesis with the view of its regulation and functional implications. Initially, we have reviewed the immense functional significance drawn by this maestro during neural development in a context-dependent manner. How this indispensable role of Hes1 in conferring the competency for neural differentiation partly relies on the direct/indirect mode of repression mediated by very specific structural and functional arms of this protein has also been outlined here. We also review the detailed molecular mechanisms behind the well-tuned oscillatory versus sustained expression of this antineurogenic bHLH repressor, which indeed makes it a master gene to implement the elusive task of neural progenitor propensity. Apart from the functional aspects of Hes1, we also discuss the molecular insights into the endogenous regulatory machinery that regulates its expression. Though Hes1 is a classical target of the Notch signaling pathway, we discuss here its differential expression at the molecular, cellular, and/or regional level. Moreover, we describe how its expression is fine-tuned by all possible ways of gene regulation such as epigenetic, transcriptional, post-transcriptional, post-translational, and environmental factors during vertebrate neurogenesis.