MDM2 E3 ligase-mediated ubiquitination and degradation of HDAC1 in vascular calcification

The Epigenetic Landscape of Vascular Calcification: An Integrative Perspective

Vascular calcification (VC) is an important complication among patients of advanced age, those with chronic kidney disease, and those with diabetes mellitus. The pathophysiology of VC encompasses passive occurrence of physico-chemical calcium deposition, active cellular secretion of osteoid matrix upon exposure to metabolically noxious stimuli, or a variable combination of both processes. Epigenetic alterations have been shown to participate in this complex environment, through mechanisms including DNA methylation, non-coding RNAs, histone modifications, and chromatin changes. Despite such importance, existing reviews fail to provide a comprehensive view of all relevant reports addressing epigenetic processes in VC, and cross-talk between different epigenetic machineries is rarely examined. We conducted a systematic review based on PUBMED and MEDLINE databases up to 30 September 2019, to identify clinical, translational, and experimental reports addressing epigenetic processes in VC; we retrieved 66 original studies, among which 60.6% looked into the pathogenic role of non-coding RNA, followed by DNA methylation (12.1%), histone modification (9.1%), and chromatin changes (4.5%). Nine (13.6%) reports examined the discrepancy of epigenetic signatures between subjects or tissues with and without VC, supporting their applicability as biomarkers. Assisted by bioinformatic analyses blending in each epigenetic component, we discovered prominent interactions between microRNAs, DNA methylation, and histone modification regarding potential influences on VC risk.

Considering the Role of Murine Double Minute 2 in the Cardiovascular System?

The E3 ubiquitin ligase Murine double minute 2 (MDM2) is the main negative regulator of the tumor protein p53 (TP53). Extensive studies over more than two decades have confirmed MDM2 oncogenic role through mechanisms both TP53-dependent and TP53-independent oncogenic function. These studies have contributed to designate MDM2 as a therapeutic target of choice for cancer treatment and the number of patents for MDM2 antagonists has increased immensely over the last years. However, the question of the physiological functions of MDM2 has not been fully resolved yet, particularly when expressed and regulated physiologically in healthy tissue. Cardiovascular complications are almost an inescapable side-effect of anti-cancer therapies. While several MDM2 antagonists are entering phase I, II and even III of clinical trials, this review proposes to bring awareness on the physiological role of MDM2 in the cardiovascular system.

The Deubiquitinase USP38 Promotes NHEJ Repair through Regulation of HDAC1 Activity and Regulates Cancer Cell Response to Genotoxic Insults

The DNA damage response (DDR) is essential for maintaining genome integrity. Mounting evidence reveals that protein modifications play vital roles in the DDR. Here, we show that USP38 is involved in the DDR by regulating the activity of HDAC1. In response to DNA damage, USP38 interacted with HDAC1 and specifically removed the K63-linked ubiquitin chain promoting the deacetylase activity of HDAC1. As a result, HDAC1 was able to deacetylate H3K56. USP38 deletion resulted in persistent focal accumulation of nonhomologous end joining (NHEJ) factors at DNA damage sites and impaired NHEJ efficiency, causing genome instability and sensitizing cancer cells to genotoxic insults. Knockout of USP38 rendered mice hypersensitive to irradiation and shortened survival. In addition, USP38 was expressed at low levels in certain types of cancers including renal cell carcinoma, indicating dysregulation of USP38 expression contributes to genomic instability and may lead to tumorigenesis. In summary, this study identifies a critical role of USP38 in modulating genome integrity and cancer cell resistance to genotoxic insults by deubiquitinating HDAC1 and regulating its deacetylation activity. SIGNIFICANCE: This study demonstrates that USP38 regulates genome stability and mediates cancer cell resistance to DNA-damaging therapy, providing insight into tumorigenesis and implicating USP38 as a potential target for cancer diagnosis.

Heart failure with preserved ejection fraction: present status and future directions

The clinical importance of heart failure with preserved ejection fraction (HFpEF) has recently become apparent. HFpEF refers to heart failure (HF) symptoms with normal or near-normal cardiac function on echocardiography. Common clinical features of HFpEF include diastolic dysfunction, reduced compliance, and ventricular hypokinesia. HFpEF differs from the better-known HF with reduced ejection fraction (HFrEF). Despite having a "preserved ejection fraction," patients with HFpEF have symptoms such as shortness of breath, excessive tiredness, and limited exercise capability. Furthermore, the mortality rate and cumulative survival rate are as severe in HFpEF as they are in HFrEF. While beta-blockers and renin-angiotensin-aldosterone system modulators can improve the survival rate in HFrEF, no known therapeutic agents show similar effectiveness in HFpEF. Researchers have examined molecular events in the development of HFpEF using small and middle-sized animal models. This review discusses HFpEF with regard to etiology and clinical features and introduces the use of mouse and other animal models of human HFpEF.

Characterization of Circular RNAs in Vascular Smooth Muscle Cells with Vascular Calcification

Circular RNAs (circRNAs) are generally formed by back splicing and are expressed in various cells. Vascular calcification (VC), a common complication of chronic kidney disease (CKD), is often associated with cardiovascular disease. The relationship between circRNAs and VC has not yet been studied. Inorganic phosphate (Pi) was used to treat rat vascular smooth muscle cells to induce VC. circRNAs were identified by analyzing RNA sequencing (RNA-seq) data, and their expression change during VC was validated. The selected circRNAs, including circSamd4a, circSmoc1-1, circMettl9, and circUxs1, were resistant to RNase R digestion and mostly localized in the cytoplasm. While silencing circSamd4a promoted VC, overexpressing it reduced VC in calcium assay and Alizarin red S (ARS) staining. In addition, microRNA (miRNA) microarray, luciferase reporter assay, and calcium assay suggested that circSamd4a could act as a miRNA suppressor. Our data show that circSamd4a has an anti-calcification role by functioning as a miRNA sponge. Moreover, mRNAs that can interact with miRNAs were predicted from RNA-seq and bioinformatics analysis, and the circSamd4a-miRNA-mRNA axis involved in VC was verified by luciferase reporter assay and calcium assay. Since circSamd4a is conserved in humans, it can serve as a novel therapeutic target in resolving VC.

TRIM7 promotes proliferation and migration of vascular smooth muscle cells in atherosclerosis through activating c-Jun/AP-1

Atherosclerosis (AS), with associated risk of stroke or cerebrovascular disease, is one of the most common causes of death globally. It has been well established that tripartite motif-containing protein 7 Tripartite Motif-containing 7 (Trim7), as an E3 ubiquitin protein ligase, is involved in protein ubiquitination and thus regulating cellular proliferation. Moreover, TRIM7 is upregulated in advanced carotid AS. However, the detailed mechanism of TRIM7 on regulation of AS remains unclear. In the present study, we firstly discovered that TRIM7 expression was robustly induced in platelet-derived growth factor type BB-treated vascular smooth muscle cells (VSMCs) and human atherosclerotic plaques. Functional approaches established that knockdown of TRIM7 inhibited proliferation and migration of VSMCs, as well as arrested the cell cycle at G1-S, thus suppressing AS progression. Our results also identified that c-Jun/activator protein 1 (AP-1) signaling pathway was activated by TRIM7. Moreover, gain- and loss-of-function studies revealed that TRIM7 could promote proliferation and migration of VSMCs via activation of c-Jun/AP-1 signaling pathway. Finally, by using atherogenic apolipoprotein E-deficient (apoE-/-) C57BL/6 mice with high-fat diet AS model, we demonstrated that interference of TRIM7 could effectively mitigate in vivo AS via inactivation of c-Jun/AP-1 signaling pathway. In general, activation of c-Jun/AP-1 signaling pathway via TRIM7 could be an important mechanism in AS progression, thus shedding light on the development of novel therapeutics to the treatment of the disease.

Zinc-finger protein p52-ZER6 accelerates colorectal cancer cell proliferation and tumour progression through promoting p53 ubiquitination

Background

Aberrant expression of p53 and its downstream gene p21 is closely related to alterations in cell cycle and cell proliferation, and is common among cancer patients. However, the underlying molecular mechanism has not been fully unravelled. ZER6 is a zinc-finger protein with two isoforms possessing different amino termini (N-termini) in their proteins, p52-ZER6 and p71-ZER6. The biological function of ZER6 isoforms, as well as their potential involvement in tumourigenesis and the regulation of p53 remain elusive.

Methods

The effect of ZER6 isoforms on p53 and p21 was determined using specific knockdown and overexpression. p52-ZER6 expression in tumours was analysed using clinical specimens, while gene modulation was used to explore p52-ZER6 roles in regulating cell proliferation and tumourigenesis. The mechanism of p52-ZER6 regulation on the p53/p21 axis was studied using molecular biology and biochemical methods.

Findings

p52-ZER6 was highly expressed in tumour tissues, and was closely related with tumour progression. Mechanistically, p52-ZER6 bound to p53 through a truncated KRAB (tKRAB) domain in its N-terminus and enhanced MDM2/p53 complex integrity, leading to increased p53 ubiquitination and degradation. p52-ZER6-silencing induced G₀-G₁ phase arrest, and subsequently reduced cell proliferation and tumourigenesis. Intriguingly, this regulation on p53 was specific to p52-ZER6, whereas p71-ZER6 did not affect p53 stability, most likely due to the presence of a HUB-1 domain.

Interpretation

We identified p52-ZER6 as a novel oncogene that enhances MDM2/p53 complex integrity, and might be a potential target for anti-cancer therapy.

Ubiquitin-based modifications in endothelial cell-cell contact and inflammation

Endothelial cell-cell contacts are essential for vascular integrity and physiology, protecting tissues and organs from edema and uncontrolled invasion of inflammatory cells. The vascular endothelial barrier is dynamic, but its integrity is preserved through a tight control at different levels. Inflammatory cytokines and G-protein-coupled receptor agonists, such as histamine, reduce endothelial integrity and increase vascular leakage. This is due to elevated myosin-based contractility, in conjunction with phosphorylation of proteins at cell-cell contacts. Conversely, reducing contractility stabilizes or even increases endothelial junctional integrity. Rho GTPases are key regulators of such cytoskeletal dynamics and endothelial cell-cell contacts. In addition to signaling-induced regulation, the expression of junctional proteins, such as occludin, claudins and vascular endothelial cadherin, also controls endothelial barrier function. There is increasing evidence that, in addition to protein phosphorylation, ubiquitylation (also known as ubiquitination) is an important and dynamic post-translational modification that regulates Rho GTPases, junctional proteins and, consequently, endothelial barrier function. In this Review, we discuss the emerging role of ubiquitylation and deubiquitylation events in endothelial integrity and inflammation. The picture that emerges is one of increasing complexity, which is both fascinating and promising given the clinical relevance of vascular integrity in the control of inflammation, and of tissue and organ damage.

Histone deacetylase 1 induced by neddylation inhibition contributes to drug resistance in acute myelogenous leukemia

Objective

This study aimed to investigate the function and mechanism of neddylation of HDAC1 underlying drug resistance of AML cells.

Methods

Evaluation experiments of effects of HDAC1 on drug resistance of AML cells were performed with AML cell transfected with constructs overexpressing HDAC1 or multi-drug resistance AML cells transfected with siRNA for HDAC1 through observing cell viability, percentage of apoptotic cell, doxorubicin-releasing index and multidrug resistance associated protein 1 (MRP1) expression. Neddylation or ubiquitination of HDAC1 was determined by immunoprecipitation or Ni2⁺ pull down assay followed by western blot. The role of HDAC1 was in vivo confirmed by xenograft in mice.

Results

HDAC1 was significantly upregulated in refractory AML patients, and in drug-resistant AML cells (HL-60/ADM and K562/A02). Intracellular HDAC1 expression promoted doxorubicin resistance of HL-60, K562, and primary bone marrow cells (BMCs) of remission AML patients as shown by increasing cell viability and doxorubicin-releasing index, inhibiting cell apoptosis. Moreover, HDAC1 protein level in AML cells was regulated by the Nedd8-mediated neddylation and ubiquitination, which further promoted HDAC1 degradation. In vivo, HDAC1 overexpression significantly increased doxorubicin resistance; while HDACs inhibitor Panobinostat markedly improved the inhibitory effect of doxorubicin on tumor growth. Furthermore, HDAC1 silencing by Panobinostat and/or lentivirus mediated RNA interference against HDAC1 effectively reduced doxorubicin resistance, resulting in the inhibition of tumor growth in AML bearing mice.

Conclusion

Our findings suggested that HDAC1 contributed to the multidrug resistance of AML and its function turnover was regulated, at least in part, by post-translational modifications, including neddylation and ubiquitination.

Electronic supplementary material

The online version of this article (10.1186/s12964-019-0393-8) contains supplementary material, which is available to authorized users.

Mdm2 is required for HDAC3 monoubiquitination and stability

HDAC3, one of the class I histone deacetylase modulates epigenetic landscape through histone modification. HDAC3 also interacts with non-histone proteins including p53 for deacetylation. Moreover, HDAC3 serves as a transcriptional repressor, interacting with NCor1/SMRT complex. Although HDAC3 plays a critical role for cellular homeostasis, regulatory mechanism of HDAC3 have been poorly understood. Here we report a novel regulatory mechanism of HDAC3 about its monoubiquitination and stabilization by Mdm2. HDAC3 levels were increased by ectopic expression of Mdm2 and decreased by Mdm2 ablation in various cell lines. We found that Mdm2 directly interacts with HDAC3 and induces HDAC3 protein levels without alteration of mRNA levels. Ectopic expression of wild type but not RING mutant of Mdm2 increased HDAC3 monoubiquitination. In addition, MdmX is beneficial for mdm2-mediated HDAC3 regulation. Ablation of Mdm2 and Mdm2/MdmX decreased cell migration along with the decrease of HDAC3 levels. These data provide an evidence that Mdm2 positively regulates HDAC3 monoubiquitination and stability.

Inhibition of acetylation of histones 3 and 4 attenuates aortic valve calcification

Aortic valve calcification develops in patients with chronic kidney disease who have calcium and phosphate metabolic disorders and poor prognoses. There is no effective treatment except valve replacement. However, metabolic disorders put patients at high risk for surgery. Increased acetylation of histones 3 and 4 is present in interstitial cells from human calcific aortic valves, but whether it is involved in aortic valve calcification has not been studied. In this study, we found that treating cultured porcine aortic valve interstitial cells with a high-calcium/high-phosphate medium induced calcium deposition, apoptosis, and expression of osteogenic marker genes, producing a phenotype resembling valve calcification in vivo. These phenotypic changes were attenuated by the histone acetyltransferase inhibitor C646. C646 treatment increased the levels of class I histone deacetylase members and decreased the acetylation of histones 3 and 4 induced by the high-calcium/high-phosphate treatment. Conversely, the histone deacetylase inhibitor suberoylanilide hydroxamic acid promoted valve interstitial cell calcification. In a mouse model of aortic valve calcification induced by adenine and vitamin D treatment, the levels of acetylated histones 3 and 4 were increased in the calcified aortic valves. Treatment of the models with C646 attenuated aortic valve calcification by restoring the levels of acetylated histones 3 and 4. These observations suggest that increased acetylation of histones 3 and 4 is part of the pathogenesis of aortic valve calcification associated with calcium and phosphate metabolic disorders. Targeting acetylated histones 3 and 4 may be a potential therapy for inoperable aortic valve calcification in chronic kidney disease patients.

Long noncoding RNAs in vascular smooth muscle cells regulate vascular calcification

Vascular calcification is characterized by the accumulation of hydroxyapatite crystals, which is a result of aberrant mineral metabolism. Although many clinical studies have reported its adverse effects on cardiovascular morbidity, the molecular mechanism of vascular calcification, especially the involvement of long noncoding RNAs (lncRNAs), is not yet reported. From the transcriptomic analysis, we discovered hundreds of lncRNAs differentially expressed in rat vascular smooth muscle cells (VSMCs) treated with inorganic phosphate, which mimics vascular calcification. We focused on Lrrc75a-as1 and elucidated its transcript structure and confirmed its cytoplasmic localization. Our results showed that calcium deposition was elevated after knockdown of Lrrc75a-as1, while its overexpression inhibited calcium accumulation in A10 cells. In addition, Lrrc75a-as1 attenuated VSMCs calcification by decreasing the expression of osteoblast-related factors. These findings suggest that Lrrc75a-as1 acts as a negative regulator of vascular calcification, and may serve as a possible therapeutic target in vascular calcification.

HDAC Inhibitors: Therapeutic Potential in Fibrosis-Associated Human Diseases

Fibrosis is characterized by excessive deposition of the extracellular matrix and develops because of fibroblast differentiation during the process of inflammation. Various cytokines stimulate resident fibroblasts, which differentiate into myofibroblasts. Myofibroblasts actively synthesize an excessive amount of extracellular matrix, which indicates pathologic fibrosis. Although initial fibrosis is a physiologic response, the accumulated fibrous material causes failure of normal organ function. Cardiac fibrosis interferes with proper diastole, whereas pulmonary fibrosis results in chronic hypoxia; liver cirrhosis induces portal hypertension, and overgrowth of fibroblasts in the conjunctiva is a major cause of glaucoma surgical failure. Recently, several reports have clearly demonstrated the functional relevance of certain types of histone deacetylases (HDACs) in various kinds of fibrosis and the successful alleviation of the condition in animal models using HDAC inhibitors. In this review, we discuss the therapeutic potential of HDAC inhibitors in fibrosis-associated human diseases using results obtained from animal models.

Histone deacetylase 6 reduction promotes aortic valve calcification via an endoplasmic reticulum stress-mediated osteogenic pathway

OBJECTIVE

Aortic valve (AoV) calcification occurs via a pathophysiologic process that includes osteoblastic differentiation of valvular interstitial cells (VICs). Histone deacetylases (HDACs) have been shown to be involved in the pathogenesis of vascular diseases. Here, we investigated the role of HDAC6 in AoV calcification.

METHODS

AoV cusps from patients with aortic stenosis (n = 7) and normal controls (n = 7) were subjected to determination of calcified nodules and HDAC6 expression. Human VICs were cultured in osteogenic media and treated with 10 uM tubacin or HDAC6 small interfering RNA silencing to inhibit HDAC6. Treatment with 100 uM tauroursodeoxycholic acid was used to suppress endoplasmic reticulum stress. Activating transcription factor 4 (ATF4) small interfering RNA was used to knock down ATF4. Alizarin red staining was used to evaluate calcified nodules formation of VICs cultured with osteogenic media for 14 days.

RESULTS

HDAC6 expression was significantly reduced in AoV tissue of patients with aortic stenosis compared with controls. Tubacin treatment or HDAC6 silencing markedly promoted osteoblastic differentiation accompanied by endoplasmic reticulum stress activation in VICs. The HDAC6 inhibition-induced osteogenic pathway was mediated by endoplasmic reticulum stress/ATF4 pathway as indicated by tauroursodeoxycholic acid pretreatment or ATF4 silencing. Finally, alizarin red staining showed that HDAC6 inhibition promoted osteoblastic differentiation of VICs, which could be suppressed by tauroursodeoxycholic acid.

CONCLUSIONS

HDAC6 inhibition promotes AoV calcification via an endoplasmic reticulum stress/ATF4-mediated osteogenic pathway. HDAC6 may be a novel target for AoV calcification prevention and treatment.

Ubiquitin Regulation: The Histone Modifying Enzyme's Story

Histone post-translational modifications influence many fundamental cellular events by regulating chromatin structure and gene transcriptional activity. These modifications are highly dynamic and tightly controlled, with many enzymes devoted to the addition and removal of these modifications. Interestingly, these modifying enzymes are themselves fine-tuned and precisely regulated at the level of protein turnover by ubiquitin-proteasomal processing. Here, we focus on recent progress centered on the mechanisms regulating ubiquitination of histone modifying enzymes, including ubiquitin proteasomal degradation and the reverse process of deubiquitination. We will also discuss the potential pathophysiological significance of these processes.

Reducing histone acetylation rescues cognitive deficits in a mouse model of Fragile X syndrome

Fragile X syndrome (FXS) is the most prevalent inherited intellectual disability, resulting from a loss of fragile X mental retardation protein (FMRP). Patients with FXS suffer lifelong cognitive disabilities, but the function of FMRP in the adult brain and the mechanism underlying age-related cognitive decline in FXS is not fully understood. Here, we report that a loss of FMRP results in increased protein synthesis of histone acetyltransferase EP300 and ubiquitination-mediated degradation of histone deacetylase HDAC1 in adult hippocampal neural stem cells (NSCs). Consequently, FMRP-deficient NSCs exhibit elevated histone acetylation and age-related NSC depletion, leading to cognitive impairment in mature adult mice. Reducing histone acetylation rescues both neurogenesis and cognitive deficits in mature adult FMRP-deficient mice. Our work reveals a role for FMRP and histone acetylation in cognition and presents a potential novel therapeutic strategy for treating adult FXS patients.

Loss of fragile X mental retardation protein (FMRP) leads to fragile X syndrome, associated with cognitive dysfunction. Here the authors show that mice lacking FMRP show reduced hippocampal neurogenesis and cognitive deficits, which can be rescued by reducing histone acetylation.

Degradation for better survival? Role of ubiquitination in epithelial morphogenesis

As a prevalent post-translational modification, ubiquitination is essential for many developmental processes. Once covalently attached to the small and conserved polypeptide ubiquitin (Ub), a substrate protein can be directed to perform specific biological functions via its Ub-modified form. Three sequential catalytic reactions contribute to this process, among which E3 ligases serve to identify target substrates and promote the activated Ub to conjugate to substrate proteins. Ubiquitination has great plasticity, with diverse numbers, topologies and modifications of Ub chains conjugated at different substrate residues adding a layer of complexity that facilitates a huge range of cellular functions. Herein, we highlight key advances in the understanding of ubiquitination in epithelial morphogenesis, with an emphasis on the latest insights into its roles in cellular events involved in polarized epithelial tissue, including cell adhesion, asymmetric localization of polarity determinants and cytoskeletal organization. In addition, the physiological roles of ubiquitination are discussed for typical examples of epithelial morphogenesis, such as lung branching, vascular development and synaptic formation and plasticity. Our increased understanding of ubiquitination in epithelial morphogenesis may provide novel insights into the molecular mechanisms underlying epithelial regeneration and maintenance.

ABIN1 inhibits HDAC1 ubiquitination and protects it from both proteasome- and lysozyme-dependent degradation

ABIN1, an important immune regulator, has been shown to be involved in various cellular functions, such as immunity, development, tissue homeostasis, and tumor progression. It inhibits TNF- and TLR-induced NF-κB signaling activation and the consequent gene expression. Despite its functional significance, the mechanism of ABIN1 in the regulation of various cellular functions remains unclear. In this study, we identified HDAC1, a key regulator of eukaryotic gene expression and many important cellular events, including cell proliferation, differentiation, cancer and immunity, as an interacting partner of ABIN1. The results showed that ABIN1 acted as a modulator to down-regulate HDAC1 ubiquitination via three different linkages, thereby stabilizing HDAC1 by inhibiting its lysosomal and proteasomal degradation. Interestingly, the inhibitory function of ABIN1 required direct binding with HDAC1. Moreover, the level of p53, which was a tumor suppressor and a well-studied substrate of HDAC1, was under the regulation of ABIN1 via the modulation of HDAC1 levels, suggesting that ABIN1 was physiologically significant in tumor progression. This study has revealed a new function of ABIN1 in mediating HDAC1 modification and stability.

New Aspects of Vascular Calcification: Histone Deacetylases and Beyond

Vascular calcification is a pathologic phenomenon in which calcium phosphate is ectopically deposited in the arteries. Previously, calcification was considered to be a passive process in response to metabolic diseases, vascular or valvular diseases, or even aging. However, now calcification is recognized as a highly-regulated consequence, like bone formation, and many clinical trials have been carried out to elucidate the correlation between vascular calcification and cardiovascular events and mortality. As a result, vascular calcification has been implicated as an independent risk factor in cardiovascular diseases. Many molecules are now known to be actively associated with this process. Recently, our laboratory found that posttranslational modification of histone deacetylase (HDAC) 1 is actively involved in the development of vascular calcification. In addition, we found that modulation of the activity of HDAC as well as its protein stability by MDM2, an HDAC1-E3 ligase, may be a therapeutic target in vascular calcification. In the present review, we overview the pathomechanism of vascular calcification and the involvement of posttranslational modification of epigenetic regulators.

Epigenome alterations in aortic valve stenosis and its related left ventricular hypertrophy

Aortic valve stenosis is the most common cardiac valve disease, and with current trends in the population demographics, its prevalence is likely to rise, thus posing a major health and economic burden facing the worldwide societies. Over the past decade, it has become more than clear that our traditional genetic views do not sufficiently explain the well-known link between AS, proatherogenic risk factors, flow-induced mechanical forces, and disease-prone environmental influences. Recent breakthroughs in the field of epigenetics offer us a new perspective on gene regulation, which has broadened our perspective on etiology of aortic stenosis and other aortic valve diseases. Since all known epigenetic marks are potentially reversible this perspective is especially exciting given the potential for development of successful and non-invasive therapeutic intervention and reprogramming of cells at the epigenetic level even in the early stages of disease progression. This review will examine the known relationships between four major epigenetic mechanisms: DNA methylation, posttranslational histone modification, ATP-dependent chromatin remodeling, and non-coding regulatory RNAs, and initiation and progression of AS. Numerous profiling and functional studies indicate that they could contribute to endothelial dysfunctions, disease-prone activation of monocyte-macrophage and circulatory osteoprogenitor cells and activation and osteogenic transdifferentiation of aortic valve interstitial cells, thus leading to valvular inflammation, fibrosis, and calcification, and to pressure overload-induced maladaptive myocardial remodeling and left ventricular hypertrophy. This is especcialy the case for small non-coding microRNAs but was also, although in a smaller scale, convincingly demonstrated for other members of cellular epigenome landscape. Equally important, and clinically most relevant, the reported data indicate that epigenetic marks, particularly certain microRNA signatures, could represent useful non-invasive biomarkers that reflect the disease progression and patients prognosis for recovery after the valve replacement surgery.

Identification of XBP1-u as a novel regulator of the MDM2/p53 axis using an shRNA library

Cell cycle progression is a tightly controlled fundamental process in living cells, with any defects being closely linked to various abnormalities. The tumor suppressor p53/p21 axis is a core pathway controlling cell cycle progression; however, its regulatory mechanism has not been fully elucidated. In an effort to unravel this crucial network, we screened a short hairpin RNA expression vector library and identified unspliced X-box binding protein 1 (XBP1-u) as a novel and critical regulator of the p53/p21 axis. Specifically, XBP1-u negatively regulates the p53/p21 axis by enhancing p53 ubiquitination, which in turn down-regulates p21 expression. We show that XBP1-u suppression induces G₀-G₁ phase arrest and represses cell proliferation. We further report that the carboxyl terminus of XBP1-u, which differs from that of its spliced form (XBP1-s) due to a codon shift, binds and stabilizes mouse double minute homolog 2 (MDM2) protein, a negative regulator of p53, by inhibiting its self-ubiquitination. Concomitantly, XBP-u overexpression enhances tumorigenesis by positively regulating MDM2. Together, our findings suggest that XBP1-u functions far beyond being merely a precursor of XBP1-s and, instead, is involved in fundamental biological processes. Furthermore, this study provides new insights regarding the regulation of the MDM2/p53/p21 axis.

Histone Deacetylase 2 Is a Component of Influenza A Virus-Induced Host Antiviral Response

Host cells produce variety of antiviral factors that create an antiviral state and target various stages of influenza A virus (IAV) life cycle to inhibit infection. However, IAV has evolved various strategies to antagonize those antiviral factors. Recently, we reported that a member of class I host histone deacetylases (HDACs), HDAC1 possesses an anti-IAV function. Herein, we provide evidence that HDAC2, another class I member and closely related to HDAC1 in structure and function, also possesses anti-IAV properties. In turn, IAV, like HDAC1, dysregulates HDAC2, mainly at the polypeptide level through proteasomal degradation to potentially minimize its antiviral effect. We found that IAV downregulated the HDAC2 polypeptide level in A549 cells in an H1N1 strain-independent manner by up to 47%, which was recovered to almost 100% level in the presence of proteasome-inhibitor MG132. A further knockdown in HDAC2 expression by up to 90% via RNA interference augmented the growth kinetics of IAV in A549 cells by more than four-fold after 24 h of infection. Furthermore, the knockdown of HDAC2 expression decreased the IAV-induced phosphorylation of the transcription factor, Signal Transducer and Activator of Transcription I (STAT1) and the expression of interferon-stimulated gene, viperin in infected cells by 41 and 53%, respectively. The role of HDAC2 in viperin expression was analogous to that of HDAC1, but it was not in the phosphorylation of STAT1. This indicated that, like HDAC1, HDAC2 is a component of IAV-induced host innate antiviral response and performs both redundant and non-redundant functions vis-a-vis HDAC1; however, IAV dysregulates them both in a redundant manner.

Ubiquitin Ligases and Posttranslational Regulation of Energy in the Heart: The Hand that Feeds

Heart failure (HF) is a costly and deadly syndrome characterized by the reduced capacity of the heart to adequately provide systemic blood flow. Mounting evidence implicates pathological changes in cardiac energy metabolism as a contributing factor in the development of HF. While the main source of fuel in the healthy heart is the oxidation of fatty acids, in the failing heart the less energy efficient glucose and glycogen metabolism are upregulated. The ubiquitin proteasome system plays a key role in regulating metabolism via protein-degradation/regulation of autophagy and regulating metabolism-related transcription and cell signaling processes. In this review, we discuss recent research that describes the role of the ubiquitin-proteasome system (UPS) in regulating metabolism in the context of HF. We focus on ubiquitin ligases (E3s), the component of the UPS that confers substrate specificity, and detail the current understanding of how these E3s contribute to cardiac pathology and metabolism. © 2017 American Physiological Society. Compr Physiol 7:841-862, 2017.

Influenza A Virus Dysregulates Host Histone Deacetylase 1 That Inhibits Viral Infection in Lung Epithelial Cells

Viruses dysregulate the host factors that inhibit virus infection. Here, we demonstrate that human enzyme, histone deacetylase 1 (HDAC1) is a new class of host factor that inhibits influenza A virus (IAV) infection, and IAV dysregulates HDAC1 to efficiently replicate in epithelial cells. A time-dependent decrease in HDAC1 polypeptide level was observed in IAV-infected cells, reducing to <50% by 24 h of infection. A further depletion (97%) of HDAC1 expression by RNA interference increased the IAV growth kinetics, increasing it by >3-fold by 24 h and by >6-fold by 48 h of infection. Conversely, overexpression of HDAC1 decreased the IAV infection by >2-fold. Likewise, a time-dependent decrease in HDAC1 activity, albeit with slightly different kinetics to HDAC1 polypeptide reduction, was observed in infected cells. Nevertheless, a further inhibition of deacetylase activity increased IAV infection in a dose-dependent manner. HDAC1 is an important host deacetylase and, in addition to its role as a transcription repressor, HDAC1 has been lately described as a coactivator of type I interferon response. Consistent with this property, we found that inhibition of deacetylase activity either decreased or abolished the phosphorylation of signal transducer and activator of transcription I (STAT1) and expression of interferon-stimulated genes, IFITM3, ISG15, and viperin in IAV-infected cells. Furthermore, the knockdown of HDAC1 expression in infected cells decreased viperin expression by 58% and, conversely, the overexpression of HDAC1 increased it by 55%, indicating that HDAC1 is a component of IAV-induced host type I interferon antiviral response.

IMPORTANCE

Influenza A virus (IAV) continues to significantly impact global public health by causing regular seasonal epidemics, occasional pandemics, and zoonotic outbreaks. IAV is among the successful human viral pathogens that has evolved various strategies to evade host defenses, prevent the development of a universal vaccine, and acquire antiviral drug resistance. A comprehensive knowledge of IAV-host interactions is needed to develop a novel and alternative anti-IAV strategy. Host produces a variety of factors that are able to fight IAV infection by employing various mechanisms. However, the full repertoire of anti-IAV host factors and their antiviral mechanisms has yet to be identified. We have identified here a new host factor, histone deacetylase 1 (HDAC1) that inhibits IAV infection. We demonstrate that HDAC1 is a component of host innate antiviral response against IAV, and IAV undermines HDAC1 to limit its role in antiviral response.