Localization of nascent RNA and CREB binding protein with the PML-containing nuclear body

Parallel Proteomic and Transcriptomic Microenvironment Mapping (μMap) of Nuclear Condensates in Living Cells

Cellular activity is spatially organized across different organelles. While several structures are well-characterized, many organelles have unknown roles. Profiling biomolecular composition is key to understanding function but is difficult to achieve in the context of small, dynamic structures. Photoproximity labeling has emerged as a powerful tool for mapping these interaction networks, yet maximizing catalyst localization and reducing toxicity remains challenging in live cell applications. Here, we disclose a new intracellular photocatalyst with minimal cytotoxicity and off-target binding, and we utilize this catalyst for HaloTag-based microenvironment-mapping (μMap) to spatially catalog subnuclear condensates in living cells. We also specifically develop a novel RNA-focused workflow (μMap-seq) to enable parallel transcriptomic and proteomic profiling of these structures. After validating the accuracy of our approach, we generate a spatial map across the nucleolus, nuclear lamina, Cajal bodies, paraspeckles, and PML bodies. These results provide potential new insights into RNA metabolism and gene regulation while significantly expanding the μMap platform for improved live-cell proximity labeling in biological systems.

Targeting Biomolecular Condensation and Protein Aggregation against Cancer

Biomolecular condensates, membrane-less entities arising from liquid-liquid phase separation, hold dichotomous roles in health and disease. Alongside their physiological functions, these condensates can transition to a solid phase, producing amyloid-like structures implicated in degenerative diseases and cancer. This review thoroughly examines the dual nature of biomolecular condensates, spotlighting their role in cancer, particularly concerning the p53 tumor suppressor. Given that over half of the malignant tumors possess mutations in the TP53 gene, this topic carries profound implications for future cancer treatment strategies. Notably, p53 not only misfolds but also forms biomolecular condensates and aggregates analogous to other protein-based amyloids, thus significantly influencing cancer progression through loss-of-function, negative dominance, and gain-of-function pathways. The exact molecular mechanisms underpinning the gain-of-function in mutant p53 remain elusive. However, cofactors like nucleic acids and glycosaminoglycans are known to be critical players in this intersection between diseases. Importantly, we reveal that molecules capable of inhibiting mutant p53 aggregation can curtail tumor proliferation and migration. Hence, targeting phase transitions to solid-like amorphous and amyloid-like states of mutant p53 offers a promising direction for innovative cancer diagnostics and therapeutics.

Regulating the p53 Tumor Suppressor Network at PML Biomolecular Condensates

By forming specific functional entities, nuclear biomolecular condensates play an important function in guiding biological processes. PML biomolecular condensates, also known as PML nuclear bodies (NBs), are macro-molecular sub-nuclear organelles involved in central biological processes, including anti-viral response and cell fate control upon genotoxic stress. PML condensate formation is stimulated upon cellular stress, and relies on protein-protein interactions establishing a PML protein meshwork capable of recruiting the tumor suppressor p53, along with numerous modifiers of p53, thus balancing p53 posttranslational modifications and activity. This stress-regulated process appears to be controlled by liquid-liquid phase separation (LLPS), which may facilitate regulated protein-unmixing of p53 and its regulators into PML nuclear condensates. In this review, we summarize and discuss the molecular mechanisms underlying PML nuclear condensate formation, and how these impact the biological function of p53 in driving the cell death and senescence responses. In addition, by using an in silico approach, we identify 299 proteins which share PML and p53 as binding partners, thus representing novel candidate proteins controlling p53 function and cell fate decision-making at the level of PML nuclear biocondensates.

Insights into the Molecular Mechanisms of Histone Code Recognition by the BRPF3 Bromodomain

Bromodomains are evolutionarily conserved reader modules that recognize acetylated lysine residues on the histone tails to facilitate gene transcription. The bromodomain and PHD finger containing protein 3 (BRPF3) is a scaffolding protein that forms a tetrameric complex with HBO1 histone acetyltransferase (HAT) and two other subunits, which is known to regulate the HAT activity and substrate specificity. However, its molecular mechanism, histone ligands, and biological functions remain unknown. Herein, we identify mono- (H4K5ac) and di- (H4K5acK12ac) acetylated histone peptides as novel interacting partners of the BRPF3 bromodomain. Consistent with this, pull-down assays on purified histones from human cells confirm the interaction of BRPF3 bromodomain with acetylated histone H4. Further, MD simulation studies highlight the binding mode of acetyllysine (Kac) and the stability of bromodomain-histone peptide complexes. Collectively, our findings provide a key insight into how histone targets of the BRPF3 bromodomain direct the recruitment of HBO1 complex to chromatin for downstream transcriptional regulation.

Nuclear condensates of p300 formed though the structured catalytic core can act as a storage pool of p300 with reduced HAT activity

The transcriptional co-activator and acetyltransferase p300 is required for fundamental cellular processes, including differentiation and growth. Here, we report that p300 forms phase separated condensates in the cell nucleus. The phase separation ability of p300 is regulated by autoacetylation and relies on its catalytic core components, including the histone acetyltransferase (HAT) domain, the autoinhibition loop, and bromodomain. p300 condensates sequester chromatin components, such as histone H3 tail and DNA, and are amplified through binding of p300 to the nucleosome. The catalytic HAT activity of p300 is decreased due to occlusion of the active site in the phase separated droplets, a large portion of which co-localizes with chromatin regions enriched in H3K27me3. Our findings suggest a model in which p300 condensates can act as a storage pool of the protein with reduced HAT activity, allowing p300 to be compartmentalized and concentrated at poised or repressed chromatin regions.

The histone acetyltransferase p300 mostly localizes to active chromatin; however, some repressed genes marked with H3K27me3 are also bound by p300. Here the authors show p300 is capable of phase separation, which relies on its catalytic core, and that p300 catalytic activity is decreased in phase-separated droplets that co-localize with H3K27me3-marked chromatin.

Autoantibodies to speckled protein family in primary biliary cholangitis

The autoantibody profile of primary biliary cholangitis (PBC) includes antinuclear antibodies (ANA) which are detectable by indirect immunofluorescence in more than 50% of PBC patients. One of the two immunofluorescence patterns which are historically considered "PBC-specific" is the so-called "multiple nuclear dots" (MND) targeting nuclear body proteins such as Sp100, Sp140, Sp140L proteins, promyelocytic leukemia protein (PML) and small ubiquitin-related modifier proteins (SUMO). It has been hypothesized a role of nuclear body protein alterations in immune disorders such as PBC, thus suggesting novel and more refined therapeutic approaches.

Targeting Epigenetic 'Readers' with Natural Compounds for Cancer Interception

Natural compounds from diverse sources, including botanicals and commonly consumed foods and beverages, exert beneficial health effects via mechanisms that impact the epigenome and gene expression during disease pathogenesis. By targeting the so-called epigenetic 'readers', 'writers', and 'erasers', dietary phytochemicals can reverse abnormal epigenome signatures in cancer cells and preneoplastic stages. Thus, such agents provide avenues for cancer interception via prevention or treatment/therapeutic strategies. To date, much of the focus on dietary agents has been directed towards writers (e.g., histone acetyltransferases) and erasers (e.g., histone deacetylases), with less attention given to epigenetic readers (e.g., BRD proteins). The drug JQ1 was developed as a prototype epigenetic reader inhibitor, selectively targeting members of the bromodomain and extraterminal domain (BET) family, such as BRD4. Clinical trials with JQ1 as a single agent, or in combination with standard of care therapy, revealed antitumor efficacy but not without toxicity or resistance. In pursuit of second-generation epigenetic reader inhibitors, attention has shifted to natural sources, including dietary agents that might be repurposed as 'JQ1-like' bioactives. This review summarizes the current status of nascent research activity focused on natural compounds as inhibitors of BET and other epigenetic 'reader' proteins, with a perspective on future directions and opportunities.

PML nuclear bodies and chromatin dynamics: catch me if you can!

Eukaryotic cells compartmentalize their internal milieu in order to achieve specific reactions in time and space. This organization in distinct compartments is essential to allow subcellular processing of regulatory signals and generate specific cellular responses. In the nucleus, genetic information is packaged in the form of chromatin, an organized and repeated nucleoprotein structure that is a source of epigenetic information. In addition, cells organize the distribution of macromolecules via various membrane-less nuclear organelles, which have gathered considerable attention in the last few years. The macromolecular multiprotein complexes known as Promyelocytic Leukemia Nuclear Bodies (PML NBs) are an archetype for nuclear membrane-less organelles. Chromatin interactions with nuclear bodies are important to regulate genome function. In this review, we will focus on the dynamic interplay between PML NBs and chromatin. We report how the structure and formation of PML NBs, which may involve phase separation mechanisms, might impact their functions in the regulation of chromatin dynamics. In particular, we will discuss how PML NBs participate in the chromatinization of viral genomes, as well as in the control of specific cellular chromatin assembly pathways which govern physiological mechanisms such as senescence or telomere maintenance.

Phase separated microenvironments inside the cell nucleus are linked to disease and regulate epigenetic state, transcription and RNA processing

Proteins and RNAs inside the cell nucleus are organized into distinct phases, also known as liquid-liquid phase separated (LLPS) droplet organelles or nuclear bodies. These regions exist within the spaces between chromatin-rich regions but their function is tightly linked to gene activity. They include major microscopically-observable structures such as the nucleolus, paraspeckle and Cajal body. The biochemical and assembly factors enriched inside these microenvironments regulate chromatin structure, transcription, and RNA processing, and other important cellular functions. Here, we describe published evidence that suggests nuclear bodies are bona fide LLPS droplet organelles and major regulators of the processes listed above. We also outline an updated "Supply or Sequester" model to describe nuclear body function, in which proteins or RNAs are supplied to surrounding genomic regions or sequestered away from their sites of activity. Finally, we describe recent evidence that suggests these microenvironments are both reflective and drivers of diverse pathophysiological states.

Biological function and histone recognition of family IV bromodomain-containing proteins

Bromodomain proteins function as epigenetic readers that recognize acetylated histone tails to facilitate the transcription of target genes. There are approximately 60 known human bromodomains, which are divided into eight sub-families based on structural conservation. The bromodomain-containing proteins in family IV include seven members (BRPF1, BRPF2, BRPF3, BRD7, BRD9, ATAD2, and ATAD2b). The bromodomains of each of these proteins recognize and bind acetyllysine residues on histone tails protruding from the nucleosome. However, the histone marks recognized by each bromodomain protein can be very different. The BRPF1 subunit of the MOZ histone acetyltransferase (HAT) recognizes acetylated histones H2AK5ac, H4K12ac, H3K14ac, H4K8ac, and H4K5ac. While the bromodomain of BRD7, a member of the SWI/SNF complex, was shown to preferentially recognize acetylated histones H3K9ac, H3K14ac, H4K8ac, H4K12ac, and H4K16ac. The bromodomains of BRPF2 and BRPF3 have similar sequences, and function as part of the HBO1 HAT complex, but there is limited data on which histone ligands they bind. Similarly, there is little known about the histone targets of the BRD9 and ATAD2b bromodomain proteins. Interestingly, the ATAD2 bromodomain was recently shown to preferentially bind to the di-acetylated H4K5acK12ac mark found in newly synthesized histones following DNA replication. However, despite the physiological importance of the family IV bromodomains, little is known about how they function at the molecular or atomic level. In this review, we summarize our understanding of how family IV bromodomains recognize and select for acetyllysine marks and discuss the importance of acetylated histone recognition for their biological functions.

Promyelocytic Leukemia Protein, a Protein at the Crossroad of Oxidative Stress and Metabolism

SIGNIFICANCE

Cellular metabolic activity impacts the production of reactive oxygen species (ROS), both positively through mitochondrial oxidative processes and negatively by promoting the production of reducing agents (including NADPH and reduced glutathione). A defined metabolic state in cancer cells is critical for cell growth and long-term self-renewal, and such state is intrinsically associated with redox balance. Promyelocytic leukemia protein (PML) regulates several biological processes, at least in part, through its ability to control the assembly of PML nuclear bodies (PML NBs). Recent Advances: PML is oxidation-prone, and oxidative stress promotes NB biogenesis. These nuclear subdomains recruit many nuclear proteins and regulate their SUMOylation and other post-translational modifications. Some of these cargos-such as p53, SIRT1, AKT, and mammalian target of rapamycin (mTOR)-are key regulators of cell fate. PML was also recently shown to regulate oxidation.

CRITICAL ISSUES

While it was long considered primarily as a tumor suppressor protein, PML-regulated metabolic switch uncovered that this protein could promote survival and/or stemness of some normal or cancer cells. In this study, we review the recent findings on this multifunctional protein.

FUTURE DIRECTIONS

Studying PML scaffolding functions as well as its fine role in the activation of p53 or fatty acid oxidation will bring new insights in how PML could bridge oxidative stress, senescence, cell death, and metabolism. Antioxid. Redox Signal. 26, 432-444.

Role of ND10 nuclear bodies in the chromatin repression of HSV-1

Herpes simplex virus (HSV) is a neurotropic virus that establishes lifelong latent infection in human ganglion sensory neurons. This unique life cycle necessitates an intimate relation between the host defenses and virus counteractions over the long course of infection. Two important aspects of host anti-viral defense, nuclear substructure restriction and epigenetic chromatin regulation, have been intensively studied in the recent years. Upon viral DNA entering the nucleus, components of discrete nuclear bodies termed nuclear domain 10 (ND10), converge at viral DNA and place restrictions on viral gene expression. Meanwhile the infected cell mobilizes its histones and histone-associated repressors to force the viral DNA into nucleosome-like structures and also represses viral transcription. Both anti-viral strategies are negated by various HSV countermeasures. One HSV gene transactivator, infected cell protein 0 (ICP0), is a key player in antagonizing both the ND10 restriction and chromatin repression. On one hand, ICP0 uses its E3 ubiquitin ligase activity to target major ND10 components for proteasome-dependent degradation and thereafter disrupts the ND10 nuclear bodies. On the other hand, ICP0 participates in de-repressing the HSV chromatin by changing histone composition or modification and therefore activates viral transcription. Involvement of a single viral protein in two seemingly different pathways suggests that there is coordination in host anti-viral defense mechanisms and also cooperation in viral counteraction strategies. In this review, we summarize recent advances in understanding the role of chromatin regulation and ND10 dynamics in both lytic and latent HSV infection. We focus on the new observations showing that ND10 nuclear bodies play a critical role in cellular chromatin regulation. We intend to find the connections between the two major anti-viral defense pathways, chromatin remodeling and ND10 structure, in order to achieve a better understanding of how host orchestrates a concerted defense and how HSV adapts with and overcomes the host immunity.

Suppression of type I interferon production by porcine epidemic diarrhea virus and degradation of CREB-binding protein by nsp1

Type I interferons (IFN-α/β) are the major components of the innate immune response of hosts, and in turn many viruses have evolved to modulate the host response during infection. We found that the IFN-β production was significantly suppressed during PEDV infection in cells. To identify viral IFN antagonists and to study their suppressive function, viral coding sequences for the entire structural and nonstructural proteins were cloned and expressed. Of 16 PEDV nonstructural proteins (nsps), nsp1, nsp3, nsp7, nsp14, nsp15 and nsp16 were found to inhibit the IFN-β and IRF3 promoter activities. The sole accessory protein ORF3, structure protein envelope (E), membrane (M), and nucleocapsid (N) protein were also shown to inhibit such activities. PEDV nsp1 did not interfere the IRF3 phosphorylation and nuclear translocation but interrupted the enhanceosome assembly of IRF3 and CREB-binding protein (CBP) by degrading CBP. A further study showed that the CBP degradation by nsp1 was proteasome-dependent. Our data demonstrate that PEDV modulates the host innate immune responses by degrading CBP and suppressing ISGs expression.

PML-mediated signaling and its role in cancer stem cells

The promyelocytic leukemia (PML) protein, initially discovered as a part of the PML/retinoic acid receptor alpha fusion protein, has been found to be a critical player in oncogenesis and tumor progression. Multiple cellular activities, including DNA repair, alternative lengthening of telomeres, transcriptional control, apoptosis and senescence, are regulated by PML and its featured subcellular structure, the PML nuclear body. In correspondence with its role in many important life processes, PML mediates several complex downstream signaling pathways. The determinant function of PML in tumorigenesis and cancer progression raises the interest in its involvement in cancer stem cells (CSCs), a subpopulation of cancer cells that share properties with stem cells and are critical for tumor propagation. Recently, there are exciting discoveries concerning the requirement of PML in CSC maintenance. Growing evidences strongly suggest a positive role of PML in regulating CSCs in both hematopoietic cancers and solid tumors, whereas the underlying mechanisms may be different and remain elusive. Here we summarize and discuss the PML-mediated signaling pathways in cancers and their potential roles in regulating CSCs.

MOZ increases p53 acetylation and premature senescence through its complex formation with PML

Monocytic leukemia zinc finger (MOZ)/KAT6A is a MOZ, Ybf2/Sas3, Sas2, Tip60 (MYST)-type histone acetyltransferase that functions as a coactivator for acute myeloid leukemia 1 protein (AML1)- and Ets family transcription factor PU.1-dependent transcription. We previously reported that MOZ directly interacts with p53 and is essential for p53-dependent selective regulation of p21 expression. We show here that MOZ is an acetyltransferase of p53 at K120 and K382 and colocalizes with p53 in promyelocytic leukemia (PML) nuclear bodies following cellular stress. The MOZ-PML-p53 interaction enhances MOZ-mediated acetylation of p53, and this ternary complex enhances p53-dependent p21 expression. Moreover, we identified an Akt/protein kinase B recognition sequence in the PML-binding domain of MOZ protein. Akt-mediated phosphorylation of MOZ at T369 has a negative effect on complex formation between PML and MOZ. As a result of PML-mediated suppression of Akt, the increased PML-MOZ interaction enhances p21 expression and induces p53-dependent premature senescence upon forced PML expression. Our research demonstrates that MOZ controls p53 acetylation and transcriptional activity via association with PML.

The adenoviral oncogene E1A-13S interacts with a specific isoform of the tumor suppressor PML to enhance viral transcription

PML nuclear bodies (PML NBs), also called ND10, are matrix-bound nuclear structures that have been implicated in a variety of functions, including DNA repair, transcriptional regulation, protein degradation, and tumor suppression. These domains are also known for their potential to mediate an intracellular defense mechanism against many virus types. This is likely why they are targeted and subsequently manipulated by numerous viral proteins. Paradoxically, the genomes of various DNA viruses become associated with PML NBs, and initial sites of viral transcription/replication centers are often juxtaposed to these domains. The question is why viruses start their transcription and replication next to their supposed antagonists. Here, we report that PML NBs are targeted by the adenoviral (Ad) transactivator protein E1A-13S. Alternatively spliced E1A isoforms (E1A-12S and E1A-13S) are the first proteins expressed upon Ad infection. E1A-13S is essential for activating viral transcription in the early phase of infection. Coimmunoprecipitation assays showed that E1A-13S preferentially interacts with only one (PML-II) of at least six nuclear human PML isoforms. Deletion mapping located the interaction site within E1A conserved region 3 (CR3), which was previously described as the transcription factor binding region of E1A-13S. Indeed, cooperation with PML-II enhanced E1A-mediated transcriptional activation, while deleting the SUMO-interacting motif (SIM) of PML proved even more effective. Our results suggest that in contrast to PML NB-associated antiviral defense, PML-II may help transactivate viral gene expression and therefore play a novel role in activating Ad transcription during the early viral life cycle.

Cytoplasmic localization of PML particles in laminopathies

There is growing evidence that laminopathies, diseases associated with mutations in the LMNA gene, are caused by a combination of mechanical and gene regulatory distortions. Strikingly, there is a large variability in disease symptoms between individual patients carrying an identical LMNA mutation. This is why classical genetic screens for mutations appear to have limited predictive value for disease development. Recently, the widespread occurrence of repetitive nuclear ruptures has been described in fibroblast cultures from various laminopathy patients. Since this phenomenon was strongly correlated with disease severity, the identification of biomarkers that report on these rupture events could have diagnostic relevance. One such candidate marker is the PML nuclear body, a structure that is normally confined to the nuclear interior, but leaks out of the nucleus upon nuclear rupture. Here, we show that a variety of laminopathies shows the presence of these cytoplasmic PML particles (PML CPs), and that the amount of these protein aggregates increases with severity of the disease. In addition, between clinically healthy individuals, carrying LMNA mutations, significant differences can be found. Therefore, we postulate that detection of PML CPs in patient fibroblasts could become a valuable marker for diagnosis of disease development.

The cell biology of disease: Acute promyelocytic leukemia, arsenic, and PML bodies

Acute promyelocytic leukemia (APL) is driven by a chromosomal translocation whose product, the PML/retinoic acid (RA) receptor α (RARA) fusion protein, affects both nuclear receptor signaling and PML body assembly. Dissection of APL pathogenesis has led to the rediscovery of PML bodies and revealed their role in cell senescence, disease pathogenesis, and responsiveness to treatment. APL is remarkable because of the fortuitous identification of two clinically effective therapies, RA and arsenic, both of which degrade PML/RARA oncoprotein and, together, cure APL. Analysis of arsenic-induced PML or PML/RARA degradation has implicated oxidative stress in the biogenesis of nuclear bodies and SUMO in their degradation.

TRIM involvement in transcriptional regulation

Members of the tripartite motif (TRIM) protein family are found in all multicellular eukaryotes and function in a wide range of cellular processes such as cell cycle regulation, differentiation, development, oncogenesis and viral response. Over the past few years, several TRIM proteins have been reported to control gene expression through regulation of the transcriptional activity of numerous sequence-specific transcription factors. These proteins include the transcriptional intermediary factor 1 (TIF1) regulators, the promyelocytic leukemia tumor suppressor PML and the RET finger protein (RFP). In this chapter, we will consider the molecular interactions made by these TRIM proteins and will attempt to clarify some of the molecular mechanisms underlying their regulatory effect on transcription.

PML nuclear bodies and other TRIM-defined subcellular compartments

Tripartite motif (TRIM) proteins are defined by their possession of a RING, B-box and predicted coiled coil (RBCC) domain. The coiled-coil region facilitates the oligomerisation of TRIMs and contributes to the formation of high molecular weight complexes that show interesting subcellular compartmentalisations and structures. TRIM protein compartments include both nuclear and cytoplasmic filaments and aggregates (bodies), as well as diffuse subcellular distributions. TRIM 19, otherwise known as promyelocytic leukaemia (PML) protein forms nuclear aggregates termed PML nuclear bodies (PML NBs), at which a number of functionally diverse proteins transiently or covalently associate. PML NBs are therefore implicated in a wide variety of cellular functions such as transcriptional regulation, viral response, apoptosis and nuclear protein storage.

Loss of the promyelocytic leukemia protein in gastric cancer: implications for IP-10 expression and tumor-infiltrating lymphocytes

Gastric cancer is one of the most common causes of cancer-related mortality worldwide. Expression of the tumor suppressor, promyelocytic leukemia (PML) protein, is reduced or abolished in gastric carcinomas, in association with an increased level of lymphatic invasion, development of higher pTNM staging, and unfavorable prognosis. Herein, we investigated the relationship between the extent of tumor-infiltrating lymphocytes and the status of PML protein expression in advanced gastric carcinoma. We observed higher numbers of infiltrating T-cells in gastric carcinoma tissues in which PML expression was reduced or abolished, compared to tissues positive for PML. The extent of T-cell migration toward culture supernatants obtained from interferon-gamma (IFN-γ-stimulated gastric carcinoma cell lines was additionally affected by expression of PML in vitro. Interferon-gamma-inducible protein 10 (IP-10/CXCL10) expression was increased in gastric carcinoma tissues displaying reduced PML levels. Moreover, both Pml knockout and knockdown cells displayed enhanced IP-10 mRNA and protein expression in the presence of IFN-γ. PML knockdown increased IFN-γ-mediated Signal Transducer and Activator of Transcription-1 (STAT-1) binding to the IP-10 promoter, resulting in elevated transcription of the IP-10 gene. Conversely, PML IV protein expression suppressed IP-10 promoter activation. Based on these results, we propose that loss of PML protein expression in gastric cancer cells contributes to increased IP-10 transcription via enhancement of STAT-1 activity, which, in turn, promotes lymphocyte trafficking within tumor regions.

Nuclear organization in genome stability: SUMO connections

Recent findings show that chromatin dynamics and nuclear organization are not only important for gene regulation and DNA replication, but also for the maintenance of genome stability. In yeast, nuclear pores play a role in the maintenance of genome stability by means of the evolutionarily conserved family of SUMO-targeted Ubiquitin ligases (STUbLs). The yeast Slx5/Slx8 STUbL associates with a class of DNA breaks that are shifted to nuclear pores. Functionally Slx5/Slx8 are needed for telomere maintenance by an unusual recombination-mediated pathway. The mammalian STUbL RNF4 associates with Promyelocytic leukaemia (PML) nuclear bodies and regulates PML/PML-fusion protein stability in response to arsenic-induced stress. A subclass of PML bodies support telomere maintenance by the ALT pathway in telomerase-deficient tumors. Perturbation of nuclear organization through either loss of pore subunits in yeast, or PML body perturbation in man, can lead to gene amplifications, deletions, translocations or end-to-end telomere fusion events, thus implicating SUMO and STUbLs in the subnuclear organization of select repair events.

PML nuclear bodies

PML nuclear bodies are matrix-associated domains that recruit an astonishing variety of seemingly unrelated proteins. Since their discovery in the early 1960s, PML bodies have fascinated cell biologists because of their beauty and their tight association with cellular disorders. The identification of PML, a gene involved in an oncogenic chromosomal translocation, as the key organizer of these domains drew instant interest onto them. The multiple levels of PML body regulation by a specific posttranslational modification, sumoylation, have raised several unsolved issues. Functionally, PML bodies may sequester, modify or degrade partner proteins, but in many ways, PML bodies still constitute an enigma.

Co-localization of the amyloid precursor protein and Notch intracellular domains in nuclear transcription factories

The beta-amyloid precursor protein (APP) plays a major role in Alzheimer's disease. The APP intracellular domain (AICD), together with Fe65 and Tip60, localizes to spherical nuclear AFT complexes, which may represent sites of transcription. Despite a lack of co-localization with several described nuclear compartments, we have identified a close apposition between AFT complexes and splicing speckles, Cajal bodies and PML bodies. Live imaging revealed that AFT complexes were highly mobile within nuclei and following pharmacological inhibition of transcription fused into larger assemblies. We have previously shown that AICD regulates the expression of its own precursor APP. In support of our earlier findings, transfection of APP promoter plasmids as substrates resulted in cytosolic AFT complex formation at labeled APP promoter plasmids. In addition, identification of chromosomal APP or KAI1 gene loci by fluorescence in situ hybridization showed their close association with nuclear AFT complexes. The transcriptional activator Notch intracellular domain (NICD) localized to the same nuclear spots as occupied by AFT complexes suggesting that these nuclear compartments correspond to transcription factories. Fe65 and Tip60 also co-localized with APP in the neurites of primary neurons. Pre-assembled AFT complexes may serve to assist fast nuclear signaling upon endoproteolytic APP cleavage.

PML nuclear body component Sp140 is a novel autoantigen in primary biliary cirrhosis

OBJECTIVES

Some patients with primary biliary cirrhosis (PBC) have antinuclear antibodies (ANAs). These ANAs include the "multiple nuclear dots" (MND) staining pattern, targeting promyelocytic leukemia protein (PML) nuclear body (NB) components, such as "speckled 100-kD" protein (Sp100) and PML. A new PML NB protein, designated as Sp140, was identified using serum from a PBC patient. The aim of this study was to analyze the immune response against Sp140 protein in PBC patients.

METHODS

We studied 135 PBC patients and 157 pathological controls with type 1 autoimmune hepatitis, primary sclerosing cholangitis, and systemic lupus erythematosus. We used indirect immunofluorescence and a neuroblastoma cell line expressing Sp140 for detecting anti-Sp140 antibodies, and a commercially available immunoblot for detecting anti-Sp100 and anti-PML antibodies.

RESULTS

Anti-Sp140 antibodies were present in 20 (15%) PBC patients but not in control samples, with a higher frequency in antimitochondrial antibody (AMA)-negative cases (53 vs. 9%, P<0.0001). Anti-Sp140 antibodies were found together with anti-Sp100 antibodies in all but one case (19 of 20, 90%) and with anti-PML antibodies in 12 (60%) cases. Anti-Sp140 positivity was not associated with a specific clinical feature of PBC.

CONCLUSIONS

Our study identifies Sp140 as a new, highly specific autoantigen in PBC for the first time. The very frequent coexistence of anti-Sp140, anti-Sp100 and anti-PML antibodies suggests that the NB is a multiantigenic complex in PBC and enhances the diagnostic significance of these reactivities, which are particularly useful in AMA-negative cases.

Interplay between Herpesvirus Infection and Host Defense by PML Nuclear Bodies

In recent studies we and others have identified the cellular proteins PML, hDaxx, and Sp100, which form a subnuclear structure known as nuclear domain 10 (ND10) or PML nuclear bodies (PML-NBs), as host restriction factors that counteract herpesviral infections by inhibiting viral replication at different stages. The antiviral function of ND10, however, is antagonized by viral regulatory proteins (e.g., ICP0 of herpes simplex virus; IE1 of human cytomegalovirus) which induce either a modification or disruption of ND10. This review will summarize the current knowledge on how viral replication is inhibited by ND10 proteins. Furthermore, herpesviral strategies to defeat this host defense mechanism are discussed.

CBP and p300 are cytoplasmic E4 polyubiquitin ligases for p53

p300 and CREB-binding protein (CBP) act as multifunctional regulators of p53 via acetylase and polyubiquitin ligase (E4) activities. Prior work in vitro has shown that the N-terminal 595 aa of p300 encode both generic ubiquitin ligase (E3) and p53-directed E4 functions. Analysis of p300 or CBP-deficient cells revealed that both coactivators were required for endogenous p53 polyubiquitination and the normally rapid turnover of p53 in unstressed cells. Unexpectedly, p300/CBP ubiquitin ligase activities were absent in nuclear extracts and exclusively cytoplasmic. Consistent with the cytoplasmic localization of its E3/E4 activity, CBP deficiency specifically stabilized cytoplasmic, but not nuclear p53. The N-terminal 616 aa of CBP, which includes the conserved Zn(2+)-binding C/H1-TAZ1 domain, was the minimal domain sufficient to destabilize p53 in vivo, and it included within an intrinsic E3 autoubiquitination activity and, in a two-step E4 assay, exhibited robust E4 activity for p53. Cytoplasmic compartmentalization of p300/CBP's ubiquitination function reconciles seemingly opposed functions and explains how a futile cycle is avoided-cytoplasmic p300/CBP E4 activities ubiquitinate and destabilize p53, while physically separate nuclear p300/CBP activities, such as p53 acetylation, activate p53.

Role of chromatin during herpesvirus infections

DNA viruses have long served as model systems to elucidate various aspects of eukaryotic gene regulation, due to their ease of manipulation and relatively low complexity of their genomes. In some cases, these viruses have revealed mechanisms that are subsequently recognized to apply also to cellular genes. In other cases, viruses adopt mechanisms that prove to be exceptions to the more general rules. The double-stranded DNA viruses that replicate in the eukaryotic nucleus typically utilize the host cell RNA polymerase II (RNAP II) for viral gene expression. As a consequence, these viruses must reckon with the impact of chromatin on active transcription and replication. Unlike the small DNA tumor viruses, such as polyomaviruses and papillomaviruses, the relatively large genomes of herpesviruses are not assembled into nucleosomes in the virion and stay predominantly free of histones during lytic infection. In contrast, during latency, the herpesvirus genomes associate with histones and become nucleosomal, suggesting that regulation of chromatin per se may play a role in the switch between the two stages of infection, a long-standing puzzle in the biology of herpesviruses. In this review we will focus on how chromatin formation on the herpes simplex type-1 (HSV-1) genome is regulated, citing evidence supporting the hypothesis that the switch between the lytic and latent stages of HSV-1 infection might be determined by the chromatin state of the HSV-1.

Transcriptional coactivators are not required for herpes simplex virus type 1 immediate-early gene expression in vitro

Virion protein 16 (VP16) of herpes simplex virus type 1 (HSV-1) is a potent transcriptional activator of viral immediate-early (IE) genes. The VP16 activation domain can recruit various transcriptional coactivators to target gene promoters. However, the role of transcriptional coactivators in HSV-1 IE gene expression during lytic infection had not been fully defined. We showed previously that transcriptional coactivators such as the p300 and CBP histone acetyltransferases and the BRM and Brg-1 chromatin remodeling complexes are recruited to viral IE gene promoters in a manner dependent mostly on the presence of the activation domain of VP16. In this study, we tested the hypothesis that these transcriptional coactivators are required for viral IE gene expression during infection of cultured cells. The disrupted expression of the histone acetyltransferases p300, CBP, PCAF, and GCN5 or the BRM and Brg-1 chromatin remodeling complexes did not diminish IE gene expression. Furthermore, IE gene expression was not impaired in cell lines that lack functional p300, or BRM and Brg-1. We also tested whether these coactivators are required for the VP16-dependent induction of IE gene expression from transcriptionally inactive viral genomes associated with high levels of histones in cultured cells. We found that the disruption of coactivators also did not affect IE gene expression in this context. Thus, we conclude that the transcriptional coactivators that can be recruited by VP16 do not contribute significantly to IE gene expression during lytic infection or the induction of IE gene expression from nucleosomal templates in vitro.

New insights into the role of the subnuclear structure ND10 for viral infection

Nuclear domains 10 (ND10), alternatively termed PML nuclear bodies (PML-NBs) or PML oncogenic domains (PODs), have been discovered approximately 15 years ago as a nuclear substructure that is targeted by a variety of viruses belonging to different viral families. This review will summarize the most important structural and functional characteristics of ND10 and its major protein constituents followed by a discussion of the current view regarding the role of this subnuclear structure for various DNA and RNA viruses with an emphasis on herpesviruses. It is concluded that accumulating evidence argues for an involvement of ND10 in host antiviral defenses either via mediating an intrinsic immune response against specific viruses or via acting as a component of the cellular interferon pathway.

ZNF451 is a novel PML body- and SUMO-associated transcriptional coregulator

Covalent modification by small ubiquitin-related modifiers (SUMOs) is an important means to regulate dynamic residency of transcription factors within nuclear compartments. Here, we identify a multi-C(2)H(2)-type zinc finger protein (ZNF), ZNF451, as a novel nuclear protein that can be associated with promyelocytic leukemia bodies. In keeping with its interaction with SUMO E2 conjugase Ubc9 and SUMOs, ZNF451 is covalently modified by SUMOs (sumoylated) at several, albeit nonconsensus, sites. Interestingly, noncovalent SUMO-binding activity of ZNF451 (SUMO-interacting motif) is also important for its sumoylation. SUMO modifications regulate the nuclear compartmentalization of ZNF451, since coexpression of ZNF451 with SUMO-specific proteases SENP1 or SENP2, both capable of desumoylating the protein, redistributes ZNF451 from nuclear domains to speckles and nucleoplasm. Interaction of ZNF451 with PIAS1 (protein inhibitor of activated STAT 1) is not manifested as PIAS1's E3 SUMO ligase activity towards ZNF451 but results in disintegration of ZNF451 nuclear domains and recruitment of ZNF451 to androgen receptor (AR) speckles. ZNF451 interacts weakly, but in a SUMO-1-enhanced fashion, with AR. ZNF451 does not harbor an intrinsic transcription activation function, but interestingly, ablation of endogenous ZNF451 in prostate cancer cells significantly decreases expression of several AR target genes. Thus, we suggest that ZNF451 exerts its effects via SUMO modification machinery and trafficking of transcription regulators between promyelocytic leukemia bodies and nucleoplasm.

The mobility of Bach2 nuclear foci is regulated by SUMO-1 modification

The small ubiquitin-like modifier-1 (SUMO-1) modulates the functions of nuclear proteins by changing their structure and/or subnuclear localization. Several nuclear proteins form dynamic higher order nuclear structures, termed non-chromatin nuclear domains, which are involved in the regulation of nuclear function. However, the role that SUMO modification of the component proteins plays in the regulation of the activity and function of nuclear domains is unclear. Here we demonstrate that nuclear domains formed by Bach2, a transcription repressor, show restricted movement and undergo fusion events upon oxidative stress. Mutation of the SUMO-acceptor lysines in Bach2 alters the behavior of these nuclear foci and results in a decreased frequency of fusion events. We propose that SUMO modification is an important regulatory system for the mobility of the nuclear domains formed by Bach2.

A nucleolar targeting signal in PML-I addresses PML to nucleolar caps in stressed or senescent cells

The promyelocytic leukemia (PML) tumour suppressor is the organiser of PML nuclear bodies, which are domains the precise functions of which are still disputed. We show that upon several types of stress, endogenous PML proteins form nucleolar caps and eventually engulf nucleolar components. Only two specific PML splice variants (PML-I and PML-IV) are efficiently targeted to the nucleolus and the abundant PML-I isoform is required for the targeting of endogenous PML proteins to this organelle. We identified a nucleolar targeting domain within the evolutionarily conserved C-terminus of PML-I. This domain contains a predicted exonuclease III fold essential for the targeting of the PML-I C-terminus to nucleolar fibrillar centres. Furthermore, spontaneous or oncogene retrieval-induced senescence is associated with the formation of very large PML nuclear bodies that initially contain nucleolar components. Later, poly-ubiquitin conjugates are found on the outer shell or within most of these senescence-associated PML bodies. Thus, unexpectedly, the scarcely studied PML-I isoform links PML bodies, nucleolus, senescence and proteolysis.

Chromatin movement visualized with photoactivable GFP-labeled histone H4

The cell nucleus is highly organized with chromosomes occupying discrete, partially overlapping territories, and proteins that localize to specific nuclear compartments. This spatial organization of the nucleus is considered to be dynamic in response to environmental and cellular conditions to support changes in transcriptional programs. Chromatin, however, is relatively immobile when analyzed in living cells and shows a constrained Brownian type of movement. A possible explanation for this relative immobility is that chromatin interacts with a nuclear matrix structure and/or with nuclear compartments. Here, we explore the use of photoactivatable GFP fused to histone H4 as a potential tool to analyze the mobility of chromatin at various nuclear compartments. Selective photoactivation of photoactivatable-GFP at defined nuclear regions was achieved by two-photon excitation with 820 nm light. Nuclear speckles, which are considered storage sites of splicing factors, were visualized by coexpression of a fluorescent protein fused to splicing factor SF2/ASF. The results reveal a constrained chromatin motion, which is not affected by transcriptional inhibition, and suggests an intimate interaction of chromatin with speckles.

Advances in imaging the interphase nucleus using thin cryosections

The mammalian genome is partitioned amongst various chromosomes and encodes for approximately 30,000 protein-coding genes. Gene expression occurs after exit from mitosis, when chromosomes partially decondense within the cell nucleus to allow the enzymatic activities that work on chromatin to access each gene in a regulated fashion. Differential patterns of gene expression evolve during cell differentiation to give rise to the over 200 cell types in higher eukaryotes. The architectural organisation of the genome inside the interphase cell nucleus, and associated enzymatic activities, reveals dynamic and functional compartmentalization of the genome. In this review, I highlight the advantages of Tokuyasu cryosectioning on the investigation of nuclear structure and function.

Alterations to nuclear architecture and genome behavior in senescent cells

The organization of the genome within interphase nuclei, and how it interacts with nuclear structures is important for the regulation of nuclear functions. Many of the studies researching the importance of genome organization and nuclear structure are performed in young, proliferating, and often transformed cells. These studies do not reveal anything about the nucleus or genome in nonproliferating cells, which may be relevant for the regulation of both proliferation and replicative senescence. Here, we provide an overview of what is known about the genome and nuclear structure in senescent cells. We review the evidence that nuclear structures, such as the nuclear lamina, nucleoli, the nuclear matrix, nuclear bodies (such as promyelocytic leukemia bodies), and nuclear morphology all become altered within growth-arrested or senescent cells. Specific alterations to the genome in senescent cells, as compared to young proliferating cells, are described, including aneuploidy, chromatin modifications, chromosome positioning, relocation of heterochromatin, and changes to telomeres.

Association with Coregulators Is the Major Determinant Governing Peroxisome Proliferator-activated Receptor Mobility in Living Cells

The nucleus is an extremely dynamic compartment, and protein mobility represents a key factor in transcriptional regulation. We showed in a previous study that the diffusion of peroxisome proliferator-activated receptors (PPARs), a family of nuclear receptors regulating major cellular and metabolic functions, is modulated by ligand binding. In this study, we combine fluorescence correlation spectroscopy, dual color fluorescence cross-correlation microscopy, and fluorescence resonance energy transfer to dissect the molecular mechanisms controlling PPAR mobility and transcriptional activity in living cells. First, we bring new evidence that in vivo a high percentage of PPARs and retinoid X receptors is associated even in the absence of ligand. Second, we demonstrate that coregulator recruitment (and not DNA binding) plays a crucial role in receptor mobility, suggesting that transcriptional complexes are formed prior to promoter binding. In addition, association with coactivators in the absence of a ligand in living cells, both through the N-terminal AB domain and the AF-2 function of the ligand binding domain, provides a molecular basis to explain PPAR constitutive activity.

Recruitment of activated IRF-3 and CBP/p300 to herpes simplex virus ICP0 nuclear foci: Potential role in blocking IFN-beta induction

The host innate response to viral infection includes the production of interferons, which is dependent on the coordinated activity of multiple transcription factors. Herpes simplex virus 1 (HSV-1) has been shown to block efficient interferon expression by multiple mechanisms. We and others have demonstrated that HSV-1 can inhibit the transcription of genes promoted by interferon regulatory factor-3 (IRF-3), including interferon beta (IFN-beta), and that the immediate-early ICP0 protein is sufficient for this function. However, the exact mechanism by which ICP0 blocks IRF-3 activity has yet to be determined. Unlike some other viral proteins that inhibit IRF-3 activity, ICP0 does not appear to affect phosphorylation and dimerization of IRF-3. Here, we show that a portion of activated IRF-3 co-localizes with nuclear foci containing ICP0 at early times after virus infection. Co-localization to ICP0-containing foci is also seen with the IRF-3-binding partners and transcriptional co-activators, CBP and p300. In addition, using immunoprecipitation of infected cell lysates, we can immunoprecipitate a complex containing ICP0, IRF-3, and CBP. Thus we hypothesize that ICP0 recruits activated IRF-3 and CBP/p300 to nuclear structures, away from the host chromatin. This leads to the inactivation and accelerated degradation of IRF-3, resulting in reduced transcription of IFN-beta and an inhibition of the host response. Therefore, ICP0 provides an example of how viruses can block IFN-beta induction by sequestration of important transcription factors essential for the host response.

The promyelocytic leukemia protein functions as a negative regulator of IFN-gamma signaling

IFN-gamma is an immunomodulatory cytokine and uses the STAT-1alpha transcription factor to mediate gene expression. The promyelocytic leukemia (PML) protein regulates transcription as an activator or repressor, depending on the gene under investigation. Herein, we examined the influence of PML on IFN-gamma signaling, using PML wild-type (Pml(+/+)) and deficient (Pml(-/-)) mouse embryonic fibroblasts (MEF). Pml(-/-) MEF exhibit enhanced IFN-gamma-induced STAT-1alpha transcriptional activity compared with Pml(+/+) cells. Moreover, reconstitution of PML in Pml(-/-) MEF reduced STAT-1alpha transcriptional activity to levels comparable to Pml(+/+) MEF. Numerous endogenous IFN-gamma-regulated genes were up-regulated in Pml(-/-) MEF compared with Pml(+/+) MEF. IFN-gamma-mediated STAT-1alpha DNA-binding activity was enhanced in Pml(-/-) cells compared with Pml(+/+) cells. Lastly, IFN-gamma enhanced the formation of a PML-STAT-1alpha complex in the nucleus. These data suggest a novel function for PML in the IFN-gamma signaling pathway by inhibiting STAT-1alpha DNA binding and transcriptional activity.

Transcriptional regulation is affected by subnuclear targeting of reporter plasmids to PML nuclear bodies

Whereas the PML protein has been reported to have both transcriptional coactivator and corepressor potential, the contribution of the PML nuclear body (PML NB) itself to transcriptional regulation is not well understood. Here we demonstrate that plasmid DNA artificially tethered to PML or the PML NB-targeting domain of Sp100 is preferentially localized to PML NBs. Using the tethering technique, we targeted a simian virus 40 promoter-driven luciferase reporter plasmid to PML NBs, resulting in the repression of the transgene transcriptional activity. Conversely, the tethering of a cytomegalovirus promoter-containing reporter plasmid resulted in activation. Targeting a minimal eukaryotic promoter did not affect its activity. The expression of targeted promoters could be modulated by altering the cellular concentration of PML NB components, including Sp100 and isoforms of the PML protein. Finally, we demonstrate that ICP0, the promiscuous herpes simplex virus transactivator, increases the level of transcriptional activation of plasmid DNA tethered to the PML NB. We conclude that when PML NB components are artificially tethered to reporter plasmids, the PML NB contributes to the regulation of the tethered DNA in a promoter-dependent manner. Our findings demonstrate that transient transcription assays are sensitive to the subnuclear localization of the transgene plasmid.

Evidence for a role of the cellular ND10 protein PML in mediating intrinsic immunity against human cytomegalovirus infections

Several viruses, including human cytomegalovirus (HCMV), encode proteins that colocalize with a cellular subnuclear structure known as ND10. Since only viral DNA deposited at ND10 initiates transcription, ND10 structures were hypothesized to be essential for viral replication. On the other hand, interferon treatment induces an up-regulation of ND10 structures and viruses have evolved polypeptides that disperse the dot-like accumulation of ND10 proteins, suggesting that ND10 could also be part of an intrinsic defense mechanism. In order to obtain evidence for either a proviral or an antiviral function of ND10, we generated primary human fibroblasts with a stable, short interfering RNA-mediated knockdown (kd) of PML. In these cells, other ND10-associated proteins like hDaxx showed a diffuse nuclear distribution. Interestingly, we observed that HCMV infection induced the de novo formation of ND10-like hDaxx and Sp100 accumulations that colocalized with IE2 and were disrupted, in the apparent absence of PML, in an IE1-dependent manner during the first hours after infection. Furthermore, infection of PML-kd cells with wild-type HCMV at a low multiplicity of infection resulted in enhanced replication. In particular, a significantly increased plaque formation was detected, suggesting that more cells are able to support initiation of replication in the absence of PML. While there was no difference in viral DNA uptake between PML-kd and control cells, we observed a considerable increase in the number of immediate-early (IE) protein-positive cells, indicating that the depletion of PML augments the initiation of viral IE gene expression. These results strongly suggest that PML functions as part of an intrinsic immune mechanism against cytomegalovirus infections.

PML nuclear bodies are highly organised DNA-protein structures with a function in heterochromatin remodelling at the G2 phase

We have recently demonstrated that heterochromatin HP1 proteins are aberrantly distributed in lymphocytes of patients with immunodeficiency, centromeric instability and facial dysmorphy (ICF) syndrome. The three HP1 proteins accumulate in one giant body over the 1qh and 16qh juxtacentromeric heterochromatins, which are hypomethylated in ICF. The presence of PML (promyelocytic leukaemia) protein within this body suggests it to be a giant PML nuclear body (PML-NB). The structural integrity of PML-NBs is of major importance for normal cell functioning. Nevertheless, the structural organisation and the functions of these nuclear bodies remain unclear. Here, we take advantage of the large size of the giant body to demonstrate that it contains a core of satellite DNA with proteins being organised in ordered concentric layers forming a sphere around it. We extend these results to normal PML-NBs and propose a model for the general organisation of these structures at the G2 phase. Moreover, based on the presence of satellite DNA and the proteins HP1, BRCA1, ATRX and DAXX within the PML-NBs, we propose that these structures have a specific function: the re-establishment of the condensed heterochromatic state on late-replicated satellite DNA. Our findings that chromatin-remodelling proteins fail to accumulate around satellite DNA in PML-deficient NB4 cells support a central role for PML protein in this cellular function.

Role for centromeric heterochromatin and PML nuclear bodies in the cellular response to foreign DNA

Nuclear spatial positioning plays an important role in the epigenetic regulation of eukaryotic gene expression. Here we show a role for nuclear spatial positioning in regulating episomal transgenes that are delivered by virus-like particles (VLPs). VLPs mediate the delivery of plasmid DNA (pDNA) to cell nuclei but lack viral factors involved in initiating and regulating transcription. By tracking single fluorescently labeled VLPs, coupled with luciferase reporter gene assays, we found that VLPs transported pDNA to cell nuclei efficiently but transgenes were immediately silenced by the cell. An investigation of the nuclear location of fluorescent VLPs revealed that the pDNAs were positioned next to centromeric heterochromatin. The activation of transcription by providing viral factors or inhibiting histone deacetylase activity resulted in the localization to euchromatin regions. Further, the activation of transcription induced the recruitment of PML nuclear bodies (PML-NBs) to the VLPs. This association did not play a role in regulating transgene expression, but PML protein was necessary for the inhibition of transgene expression with alpha interferon (IFN-alpha). These results support a model whereby cells can prevent foreign gene expression at two levels: by positioning transgenes next to centromeric heterochromatin or, if that is overcome, via the type I IFN response facilitated by PML-NB recruitment.

HATs and HDACs in neurodegeneration: a tale of disconcerted acetylation homeostasis

Gradual disclosure of the molecular basis of selective neuronal apoptosis during neurodegenerative diseases reveals active participation of acetylating and deacetylating agents during the process. Several studies have now successfully manipulated neuronal vulnerability by influencing the dose and enzymatic activity of histone acetyltransferases (HATs) and histone deacetylases (HDACs), enzymes regulating acetylation homeostasis within the nucleus, thus focusing on the importance of balanced acetylation status in neuronal vitality. It is now increasingly becoming clear that acetylation balance is greatly impaired during neurodegenerative conditions. Herein, we attempt to illuminate molecular means by which such impairment is manifested and how the compromised acetylation homeostasis is intimately coupled to neurodegeneration. Finally, we discuss the therapeutic potential of reinstating the HAT-HDAC balance to ameliorate neurodegenerative diseases.