Histone deacetylase 8 is required for centrosome cohesion and influenza A virus entry

Binding mechanism and distant regulation of histone deacetylase 8 by PCI-34051

Histone deacetylase 8 (HDAC8) is a well-known epigenetic regulator for cancer therapy. However, developing targeted inhibitors for HDAC8 is challenging due to a limited understanding of its structural dynamics, which is crucial for ligand interaction. Here, we employed an integrated approach, including native mass spectrometry (native MS), hydrogen-deuterium exchange mass spectrometry (HDX-MS), and molecular dynamics (MD) simulation, to investigate the inhibition mechanism and dynamic regulation of human HDAC8 (hHDAC8) by selective inhibitor PCI-34051, compared with the pan-inhibitor SAHA. Our results revealed that PCI-34051 engages with an expanded set of residues and conforms more aptly to the binding channel of hHDAC8, stabilizing the flexible loops surrounding the binding channel. Moreover, this dynamic stabilization effect is not limited to the binding regions, but also extends to distant regions (such as L2, α5, and α1 + α2), with L3 serving as a critical structural bridge. Overall, these results show the structural and dynamic regulations of hHDAC8 by PCI-34051, which induces a lower energy state for the protein-ligand system compared to SAHA, thus showing better inhibitory effects. In addition, it also suggests that certain regions, specifically loops L2 and L3, within the hHDAC8 protein could be key regions for targeted intervention.

Betrayal From the Core: Centriolar and Cytoskeletal Subversion by Infectious Pathogens

Microbes and parasites have evolved several means to evade and usurp the host cellular machinery to mediate pathogenesis. Being the major microtubule-organizing center (MTOC) of the cell, the centrosome is targeted by multiple viral and nonviral pathogens to mediate their assembly and trafficking within the host cell. This review examines the consequence of such targeting to the centrosome and associated cytoskeletal machinery. We have also amassed a substantial body of evidence of viruses utilizing the cilia within airway epithelium to mediate infection and the hijacking of host cytoskeletal machinery for efficient entry, replication, and egress. While infections have been demonstrated to induce structural, functional, and numerical aberrations in centrosomes, and induce ciliary dysfunction, current literature increasingly supports the notion of a pro-viral role for these organelles. Although less explored, the impact of bacterial and parasitic pathogens on these structures has also been addressed very briefly. Mechanistically, the molecular pathways responsible for these effects remain largely uncharacterized in many instances. Future research focusing on the centriolar triad comprising the centrosome, cilia, and centriolar satellites will undoubtedly provide vital insights into the tactics employed by infectious agents to subvert the host centriole and cytoskeleton-based machinery.

Hypoxia-induced conversion of sensory Schwann cells into repair cells is regulated by HDAC8

After a peripheral nerve injury, Schwann cells (SCs), the myelinating glia of the peripheral nervous system, convert into repair cells that foster axonal regrowth, and then remyelinate or re-ensheath regenerated axons, thereby ensuring functional recovery. The efficiency of this mechanism depends however on the time needed for axons to regrow. Here, we show that ablation of histone deacetylase 8 (HDAC8) in SCs accelerates the regrowth of sensory axons and sensory function recovery. We found that HDAC8 is specifically expressed in sensory SCs and regulates the E3 ubiquitin ligase TRAF7, which destabilizes hypoxia-inducible factor 1-alpha (HIF1α) and counteracts the phosphorylation and upregulation of c-Jun, a major inducer of the repair SC phenotype. Our study indicates that this phenotype switch is regulated by different mechanisms in sensory and motor SCs and is accelerated by HDAC8 downregulation, which promotes sensory axon regeneration and sensory function recovery.

MLL/WDR5 complex recruits centriolar satellite protein Cep72 to regulate microtubule nucleation and spindle formation

Dysfunction of the centrosome, the major microtubule-organizing center of the cell, is implicated in microcephaly. Haploinsufficiency of mixed-lineage leukemia (MLL/KMT2A) protein causes Wiedemann-Steiner syndrome (WSS), a neurodevelopmental disorder associated with microcephaly. However, whether MLL has a function at the centrosome is not clear. Here, we show that loss of the MLL/WDR5 complex affects microtubule nucleation and regrowth. MLL/WDR5 localize to the pericentriolar material and interact with centriolar satellite protein Cep72 and γ-tubulin ring complex proteins (γ-TuRCs). MLL/WDR5 promote the localization of γ-TuRCs and structural proteins like AKAP9 to the centrosome during interphase and mitosis, a phenotype also observed in cells derived from patients with WSS. During mitosis, loss of MLL, WDR5, and Cep72 affects spindle formation and leads to misaligned chromosomes. Last, we show that MLL and WDR5 recruit Cep72 to the centrosome. Our studies provide insight into an undiscovered role of MLL at the centrosome and elucidate how centriolar satellite proteins like Cep72 can be recruited to the centrosome.

Antiviral Effects of Avian Interferon-Stimulated Genes

Interferons (IFNs) stimulate the expression of numerous IFN-stimulating genes via the Janus kinase-signal transducers and activators of the transcription (JAK-STAT) signaling pathway, which plays an important role in the host defense against viral infections. In mammals, including humans and mice, a substantial number of IFN-stimulated genes (ISGs) have been identified, and their molecular mechanisms have been elucidated. It is important to note that avian species are phylogenetically distant from mammals, resulting in distinct IFN-induced ISGs that may have different functions. At present, only a limited number of avian ISGs have been identified. In this review, we summarized the identified avian ISGs and their antiviral activities. As gene-editing technology is widely used in avian breeding, the identification of avian ISGs and the elucidation of their molecular mechanism may provide important support for the breeding of avians for disease resistance.

Histone deacetylase 8 promotes innate antiviral immunity through deacetylation of RIG-I

Histone deacetylates family proteins have been studied for their function in regulating viral replication by deacetylating non-histone proteins. RIG-I (Retinoic acid-inducible gene I) is a critical protein in RNA virus-induced innate antiviral signaling pathways. Our previous research showed that HDAC8 (histone deacetylase 8) involved in innate antiviral immune response, but the underlying mechanism during virus infection is still unclear. In this study, we showed that HDAC8 was involved in the regulation of vesicular stomatitis virus (VSV) replication. Over-expression of HDAC8 inhibited while knockdown promoted VSV replication. Further exploration demonstrated that HDAC8 interacted with and deacetylated RIG-I, which eventually lead to enhance innate antiviral immune response. Collectively, our data clearly demonstrated that HDAC8 inhibited VSV replication by promoting RIG-I mediated interferon production and downstream signaling pathway.

Foot-and-mouth disease virus structural protein VP3 interacts with HDAC8 and promotes its autophagic degradation to facilitate viral replication

Macroautophagy/autophagy has been utilized by many viruses, including foot-and-mouth disease virus (FMDV), to facilitate replication, while the underlying mechanism of the interplay between autophagy and innate immune responses is still elusive. This study showed that HDAC8 (histone deacetylase 8) inhibits FMDV replication by regulating innate immune signal transduction and antiviral response. To counteract the HDAC8 effect, FMDV utilizes autophagy to promote HDAC8 degradation. Further data showed that FMDV structural protein VP3 promotes autophagy during virus infection and interacts with and degrades HDAC8 in an AKT-MTOR-ATG5-dependent autophagy pathway. Our data demonstrated that FMDV evolved a strategy to counteract host antiviral activity by autophagic degradation of a protein that regulates innate immune response during virus infection.Abbreviations: 3-MA: 3-methyladenine; ATG: autophagy related; Baf-A1: bafilomycin A1; CCL5: C-C motif chemokine ligand 5; Co-IP: co-immunoprecipitation; CQ: chloroquine phosphate; DAPI: 4",6-diamidino-2-phenylindole; FMDV: foot-and-mouth disease virus; HDAC8: histone deacetylase 8; ISG: IFN-stimulated gene; IRF3: interferon regulatory factor 3; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MOI: multiplicity of infection; MAVS: mitochondria antiviral signaling protein; OAS: 2"-5'-oligoadenylate synthetase; RB1: RB transcriptional corepressor 1; SAHA: suberoylanilide hydroxamic acid; TBK1: TANK binding kinase 1; TCID50: 50% tissue culture infectious doses; TNF/TNF-α: tumor necrosis factor; TSA: trichostatin A; UTR: untranslated region.

Transcriptomic and Proteomic Analyses of Myzus persicae Carrying Brassica Yellows Virus

Viruses in the genus Polerovirus infect a wide range of crop plants and cause severe economic crop losses. BrYV belongs to the genus Polerovirus and is transmitted by Myzus persicae. However, the changes in transcriptome and proteome profiles of M. persicae during viral infection are unclear. Here, RNA-Seq and TMT-based quantitative proteomic analysis were performed to compare the differences between viruliferous and nonviruliferous aphids. In total, 1266 DEGs were identified at the level of transcription with 980 DEGs being upregulated and 286 downregulated in viruliferous aphids. At the protein level, among the 18 DEPs identified, the number of upregulated proteins in viruliferous aphids was twice that of the downregulated DEPs. Enrichment analysis indicated that these DEGs and DEPs were mainly involved in epidermal protein synthesis, phosphorylation, and various metabolic processes. Interestingly, the expressions of a number of cuticle proteins and tubulins were upregulated in viruliferous aphids. Taken together, our study revealed the complex regulatory network between BrYV and its vector M. persicae from the perspective of omics. These findings should be of great benefit to screening key factors involved in the process of virus circulation in aphids and provide new insights for BrYV prevention via vector control in the field.

Microtubules and viral infection

Microtubules (MTs) form rapidly adaptable, complex intracellular networks of filaments that not only provide structural support, but also form the tracks along which motors traffic macromolecular cargos to specific sub-cellular sites. These dynamic arrays play a central role in regulating various cellular processes including cell shape and motility as well as cell division and polarization. Given their complex organization and functional importance, MT arrays are carefully controlled by many highly specialized proteins that regulate the nucleation of MT filaments at distinct sites, their dynamic growth and stability, and their engagement with other subcellular structures and cargoes destined for transport. This review focuses on recent advances in our understanding of how MTs and their regulatory proteins function, including their active targeting and exploitation, during infection by viruses that utilize a wide variety of replication strategies that occur within different cellular sub-compartments or regions of the cell.

Nonmuscle myosin IIA promotes the internalization of influenza A virus and regulates viral polymerase activity through interacting with nucleoprotein in human pulmonary cells

Influenza A virus (IAV), responsible for seasonal epidemics and recurring pandemics, represents a global threat to public health. Given the risk of a potential IAV pandemic, it is increasingly important to better understand virus-host interactions and develop new anti-viral strategies. Here, we reported nonmuscle myosin IIA (MYH9)-mediated regulation of IAV infection. MYH9 depletion caused a profound inhibition of IAV infection by reducing viral attachment and internalization in human lung epithelial cells. Surprisingly, overexpression of MYH9 also led to a significant reduction in viral productive infection. Interestingly, overexpression of MYH9 retained viral attachment, internalization, or uncoating, but suppressed the viral ribonucleoprotein (vRNP) activity in a minigenome system. Further analyses found that excess MYH9 might interrupt the formation of vRNP by interacting with the viral nucleoprotein (NP) and result in the reduction of the completed vRNP in the nucleus, thereby inhibiting subsequent viral RNA transcription and replication. Together, we discovered that MYH9 can interact with IAV NP protein and engage in the regulation of vRNP complexes, thereby involving viral replication. These findings enlighten new mechanistic insights into the complicated interface of host-IAV interactions, ultimately making it an attractive target for the generation of antiviral drugs.

Enzymatic independent role of sphingosine kinase 2 in regulating the expression of type I interferon during influenza A virus infection

Influenza virus has the ability to circumvent host innate immune system through regulating certain host factors for its effective propagation. However, the detailed mechanism is still not fully understood. Here, we report that a host sphingolipid metabolism-related factor, sphingosine kinase 2 (SPHK2), upregulated during influenza A virus (IAV) infection, promotes IAV infection in an enzymatic independent manner. The enhancement of the virus replication is not abolished in the catalytic-incompetent SPHK2 (G212E) overexpressing cells. Intriguingly, the sphingosine-1-phosphate (S1P) related factor HDAC1 also plays a crucial role in SPHK2-mediated IAV infection. We found that SPHK2 cannot facilitate IAV infection in HDAC1 deficient cells. More importantly, SPHK2 overexpression diminishes the IFN-β promoter activity upon IAV infection, resulting in the suppression of type I IFN signaling. Furthermore, ChIP-qPCR assay revealed that SPHK2 interacts with IFN-β promoter through the binding of demethylase TET3, but not with the other promoters regulated by TET3, such as TGF-β1 and IL6 promoters. The specific regulation of SPHK2 on IFN-β promoter through TET3 can in turn recruit HDAC1 to the IFN-β promoter, enhancing the deacetylation of IFN-β promoter, therefore leading to the inhibition of IFN-β transcription. These findings reveal an enzymatic independent mechanism on host SPHK2, which associates with TET3 and HDAC1 to negatively regulate type I IFN expression and thus facilitates IAV propagation.

HDACs and the epigenetic plasticity of cancer cells: Target the complexity

Cancer cells must adapt to the hostile conditions of the microenvironment in terms of nutrition, space, and immune system attack. Mutations of DNA are the drivers of the tumorigenic process, but mutations must be able to hijack cellular functions to sustain the spread of mutant genomes. Transcriptional control is a key function in this context and is controlled by the rearrangement of the epigenome. Unlike genomic mutations, the epigenome of cancer cells can in principle be reversed. The discovery of the first epigenetic drugs triggered a contaminating enthusiasm. Unfortunately, the complexity of the epigenetic machinery has frustrated this enthusiasm. To develop efficient patient-oriented epigenetic therapies, we need to better understand the nature of this complexity. In this review, we will discuss recent advances in understanding the contribution of HDACs to the maintenance of the transformed state and the rational for their selective targeting.

Histone deacetylase 8 interacts with the GTPase SmRho1 in Schistosoma mansoni

Background

Schistosoma mansoni histone deacetylase 8 (SmHDAC8) has elicited considerable interest as a target for drug discovery. Invalidation of its transcripts by RNAi leads to impaired survival of the worms in infected mice and its inhibition causes cell apoptosis and death. To determine why it is a promising therapeutic target the study of the currently unknown cellular signaling pathways involving this enzyme is essential. Protein partners of SmHDAC8 were previously identified by yeast two-hybrid (Y2H) cDNA library screening and by mass spectrometry (MS) analysis. Among these partners we characterized SmRho1, the schistosome orthologue of human RhoA GTPase, which is involved in the regulation of the cytoskeleton. In this work, we validated the interaction between SmHDAC8 and SmRho1 and explored the role of the lysine deacetylase in cytoskeletal regulation.

Methodology/principal findings

We characterized two isoforms of SmRho1, SmRho1.1 and SmRho1.2. Co- immunoprecipitation (Co-IP)/Mass Spectrometry (MS) analysis identified SmRho1 partner proteins and we used two heterologous expression systems (Y2H assay and Xenopus laevis oocytes) to study interactions between SmHDAC8 and SmRho1 isoforms.

To confirm SmHDAC8 and SmRho1 interaction in adult worms and schistosomula, we performed Co-IP experiments and additionally demonstrated SmRho1 acetylation using a Nano LC-MS/MS approach. A major impact of SmHDAC8 in cytoskeleton organization was documented by treating adult worms and schistosomula with a selective SmHDAC8 inhibitor or using RNAi followed by confocal microscopy.

Conclusions/significance

Our results suggest that SmHDAC8 is involved in cytoskeleton organization via its interaction with the SmRho1.1 isoform. The SmRho1.2 isoform failed to interact with SmHDAC8, but did specifically interact with SmDia suggesting the existence of two distinct signaling pathways regulating S. mansoni cytoskeleton organization via the two SmRho1 isoforms. A specific interaction between SmHDAC8 and the C-terminal moiety of SmRho1.1 was demonstrated, and we showed that SmRho1 is acetylated on K136. SmHDAC8 inhibition or knockdown using RNAi caused extensive disruption of schistosomula actin cytoskeleton.

Schistosoma mansoni is the major parasitic platyhelminth species causing intestinal schistosomiasis. Currently one drug, praziquantel, is the treatment of choice but its use in mass treatment programs means that the development of resistance is likely and renders imperative the development of new therapeutic agents. As new potential targets we have focused on lysine deacetylases, and in particular S. mansoni histone deacetylase 8 (SmHDAC8). Previous studies showed that reduction in the level of transcripts of SmHDAC8 by RNAi led to the impaired survival of the worms after the infection of mice. The analysis of the 3D structure of SmHDAC8 by X-ray crystallography showed that the catalytic domain structure diverges significantly from that of human HDAC8 and this was exploited to develop novel potential anti-schistosomal drugs. The biological roles of SmHDAC8 are unknown. For this reason, we previously characterized its protein binding partners and identified the schistosome orthologue of the human RhoA GTPase, suggesting the involvement of SmHDAC8 in the modulation of cytoskeleton organization. Here we investigated the interaction between SmHDAC8 and SmRho1 and identified two SmRho1 isoforms (SmRho1.1 and SmRho1.2). Our study showed that SmHDAC8 is involved in schistosome cytoskeleton organization.

In Vitro Replication Inhibitory Activity of Xanthorrhizol against Severe Acute Respiratory Syndrome Coronavirus 2

In spite of the large number of repositioned drugs and direct-acting antivirals in clinical trials for the management of the ongoing COVID-19 pandemic, there are few cost-effective therapeutic options for severe acute respiratory syndrome (SARS) coronavirus 2 (SCoV2) infection. In this paper, we show that xanthorrhizol (XNT), a bisabolane-type sesquiterpenoid compound isolated from the Curcuma xanthorrhizza Roxb., a ginger-line plant of the family Zingiberaceae, displays a potent antiviral efficacy in vitro against SCoV2 and other related coronaviruses, including SARS-CoV-1 (SCoV1) and a common cold-causing human coronavirus. XNT reduced infectious SCoV2 titer by ~3-log10 at 20 μM and interfered with the replication of the SCoV1 subgenomic replicon, while it had no significant antiviral effects against hepatitis C virus and noroviruses. Further, XNT exerted similar antiviral functions against SCoV2 variants, such as a GH clade strain and a delta strain currently predominant worldwide. Neither SCoV2 entry into cells nor the enzymatic activity of viral RNA polymerase (Nsp12), RNA helicase (Nsp13), or the 3CL main protease (Nsp5) was inhibited by XNT. While its CoV replication inhibitory mechanism remains elusive, our results demonstrate that the traditional folk medicine XNT could be a promising antiviral candidate that inhibits a broad range of SCoV2 variants of concern and other related CoVs.

Regression plane concept for analysing continuous cellular processes with machine learning

Biological processes are inherently continuous, and the chance of phenotypic discovery is significantly restricted by discretising them. Using multi-parametric active regression we introduce the Regression Plane (RP), a user-friendly discovery tool enabling class-free phenotypic supervised machine learning, to describe and explore biological data in a continuous manner. First, we compare traditional classification with regression in a simulated experimental setup. Second, we use our framework to identify genes involved in regulating triglyceride levels in human cells. Subsequently, we analyse a time-lapse dataset on mitosis to demonstrate that the proposed methodology is capable of modelling complex processes at infinite resolution. Finally, we show that hemocyte differentiation in Drosophila melanogaster has continuous characteristics.

Epigenetic reprogramming mechanisms of immunity during influenza A virus infection

This paper reviews epigenetic mechanisms by which influenza viruses affect cellular gene activity to control their life cycles, aiming to provide new insights into the complexity of functional interactions between viral and cellular factors, as well as to introduce novel targets for therapeutic intervention and vaccine development against influenza infections.

Mammalian and Avian Host Cell Influenza A Restriction Factors

The threat of a new influenza pandemic is real. With past pandemics claiming millions of lives, finding new ways to combat this virus is essential. Host cells have developed a multi-modular system to detect incoming pathogens, a phenomenon called sensing. The signaling cascade triggered by sensing subsequently induces protection for themselves and their surrounding neighbors, termed interferon (IFN) response. This response induces the upregulation of hundreds of interferon-stimulated genes (ISGs), including antiviral effectors, establishing an antiviral state. As well as the antiviral proteins induced through the IFN system, cells also possess a so-called intrinsic immunity, constituted of antiviral proteins that are constitutively expressed, creating a first barrier preceding the induction of the interferon system. All these combined antiviral effectors inhibit the virus at various stages of the viral lifecycle, using a wide array of mechanisms. Here, we provide a review of mammalian and avian influenza A restriction factors, detailing their mechanism of action and in vivo relevance, when known. Understanding their mode of action might help pave the way for the development of new influenza treatments, which are absolutely required if we want to be prepared to face a new pandemic.

Entry of Phenuiviruses into Mammalian Host Cells

Phenuiviridae is a large family of arthropod-borne viruses with over 100 species worldwide. Several cause severe diseases in both humans and livestock. Global warming and the apparent geographical expansion of arthropod vectors are good reasons to seriously consider these viruses potential agents of emerging diseases. With an increasing frequency and number of epidemics, some phenuiviruses represent a global threat to public and veterinary health. This review focuses on the early stage of phenuivirus infection in mammalian host cells. We address current knowledge on each step of the cell entry process, from virus binding to penetration into the cytosol. Virus receptors, endocytosis, and fusion mechanisms are discussed in light of the most recent progress on the entry of banda-, phlebo-, and uukuviruses, which together constitute the three prominent genera in the Phenuiviridae family.

Anticancer Therapy with HDAC Inhibitors: Mechanism-Based Combination Strategies and Future Perspectives

The increasing knowledge of molecular drivers of tumorigenesis has fueled targeted cancer therapies based on specific inhibitors. Beyond "classic" oncogene inhibitors, epigenetic therapy is an emerging field. Epigenetic alterations can occur at any time during cancer progression, altering the structure of the chromatin, the accessibility for transcription factors and thus the transcription of genes. They rely on post-translational histone modifications, particularly the acetylation of histone lysine residues, and are determined by the inverse action of histone acetyltransferases (HATs) and histone deacetylases (HDACs). Importantly, HDACs are often aberrantly overexpressed, predominantly leading to the transcriptional repression of tumor suppressor genes. Thus, histone deacetylase inhibitors (HDACis) are powerful drugs, with some already approved for certain hematological cancers. Albeit HDACis show activity in solid tumors as well, further refinement and the development of novel drugs are needed. This review describes the capability of HDACis to influence various pathways and, based on this knowledge, gives a comprehensive overview of various preclinical and clinical studies on solid tumors. A particular focus is placed on strategies for achieving higher efficacy by combination therapies, including phosphoinositide 3-kinase (PI3K)-EGFR inhibitors and hormone- or immunotherapy. This also includes new bifunctional inhibitors as well as novel approaches for HDAC degradation via PROteolysis-TArgeting Chimeras (PROTACs).

The E3 Ubiquitin Ligase Mind Bomb 1 Controls Adenovirus Genome Release at the Nuclear Pore Complex

Adenoviruses (AdVs) cause respiratory, ocular, and gastrointestinal tract infection and inflammation in immunocompetent people and life-threatening disease upon immunosuppression. AdV vectors are widely used in gene therapy and vaccination. Incoming particles attach to nuclear pore complexes (NPCs) of post-mitotic cells, then rupture and deliver viral DNA (vDNA) to the nucleus or misdeliver to the cytosol. Our genome-wide RNAi screen in AdV-infected cells identified the RING-type E3 ubiquitin ligase Mind bomb 1 (Mib1) as a proviral host factor for AdV infection. Mib1 is implicated in Notch-Delta signaling, ciliary biogenesis, and RNA innate immunity. Mib1 depletion arrested incoming AdVs at NPCs. Induced expression of full-length but not ligase-defective Mib1 in knockout cells triggered vDNA uncoating from NPC-tethered virions, nuclear import, misdelivery of vDNA, and vDNA expression. Mib1 is an essential host factor for AdV uncoating in human cells, and it provides a new concept for licensing virion DNA delivery through the NPC.

An in silico mechanistic insight into HDAC8 activation facilitates the discovery of new small-molecule activators

Research interest in the development of histone deacetylase 8 (HDAC8) activators has substantially increased since loss-of-function HDAC8 mutations were found in patients with Cornelia de Lange syndrome (CdLS). A series of N-acetylthioureas (e.g., TM-2-51) have been identified as HDAC8-selective activators, among others; however, their activation mechanisms remain elusive. Herein, we performed molecular dynamics (MD) simulations and fragment-centric topographical mapping (FCTM) to investigate the mechanism of HDAC8 activation. Our results revealed that improper binding of the coumarin group of fluorescent substrates leads to the "flipping out" of catalytic residue Y306, which reduces the enzymatic activity of HDAC8 towards fluorescent substrates. A pocket between the coumarin group of the substrate and thed catalytic residue Y306 was filled with the activator TM-2-51, which not only enhanced binding between HDAC8 and the fluorescent substrate complex but also stabilized Y306 in a catalytically active conformation. Based on this newly proposed substrate-dependent activation mechanism, we performed structure-based virtual screening and successfully identified low-molecular-weight scaffolds as new HDAC8 activators.

Standing on the Shoulders of Viruses

My coworkers and I have used animal viruses and their interaction with host cells to investigate cellular processes difficult to study by other means. This approach has allowed us to branch out in many directions, including membrane protein characterization, endocytosis, secretion, protein folding, quality control, and glycobiology. At the same time, our aim has been to employ cell biological approaches to expand the fundamental understanding of animal viruses and their pathogenic lifestyles. We have studied mechanisms of host cell entry and the uncoating of incoming viruses as well as the synthesis, folding, maturation, and intracellular movement of viral proteins and molecular assemblies. I have had the privilege to work in institutions in four different countries. The early years in Finland (the University of Helsinki) were followed by 6 years in Germany (European Molecular Biology Laboratory), 16 years in the United States (Yale School of Medicine), and 16 years in Switzerland (ETH Zurich).

Identification of histone deacetylase 8 as a novel therapeutic target for renal fibrosis

Histone deacetylases (HDACs) have been shown to alleviate renal fibrosis, however, the role of individual HDAC isoforms in this process is poorly understood. In this study, we examined the role of HDAC8 in the development of renal fibrosis and partial epithelial-mesenchymal transitions (EMT). In a murine model of renal fibrosis induced by unilateral ureteral obstruction (UUO), HDAC8 was primarily expressed in renal tubular epithelial cells and time-dependently upregulated. This occurred in parallel with the deacetylation of cortactin, a nonhistone substrate of HDAC8, and increased expression of three fibrotic markers: α-smooth muscle actin, collagen 1, and fibronectin. Administration of PCI34051, a highly selective inhibitor of HDAC8, restored acetylation of contactin and reduced expression of those proteins. PCI34051 treatment also reduced the number of renal tubular epithelial cells arrested at the G2/M phase of the cell cycle and suppressed phosphorylation of Smad3, STAT3, β-catenin, and expression of Snail after ureteral obstruction. In contrast, HDAC8 inhibition reversed UUO-induced downregulation of BMP7 and Klotho, two renoprotective proteins. In cultured murine proximal tubular cells, treatment with PCI34051 or specific HDAC8 siRNA was also effective in inhibiting transforming growth factor β1 (TGFβ1)-induced deacetylation of contactin, EMT, phosphorylation of Smad3, STAT3, and β-catenin, upregulation of Snail, and downregulation of BMP7 and Klotho. Collectively, these results suggest that HDAC8 activation is required for the EMT and renal fibrogenesis by activation of multiple profibrotic signaling and transcription factors, and suppression of antifibrotic proteins. Therefore, targeting HDAC8 may be novel therapeutic approach for treatment of renal fibrosis.

Influenza A virus uncoating

Influenza A virus (IAV) is an enveloped virus of the Orthomyxoviridae with a negative-sense single-stranded RNA genome. During virus cell entry, viral and cellular cues are delivered in a stepwise manner within two distinct cellular compartments-the endosomes and the cytosol. Endosome maturation primes the viral core for uncoating by cytosolic host proteins and host-mediated virus disaggregation is essential for genome import and replication in the nucleus. Recent evidence shows that two well-known cellular proteins-histone deacetylase 6 (HDAC6) and karyopherin-β2 (kapβ2)-uncoat influenza virus. HDAC6 is 1 of 11 HDACs and an X-linked, cytosolic lysine deacetylase. Under normal cellular conditions HDAC6 is the tubulin deacetylase. Under proteasomal stress HDAC6 binds unanchored ubiquitin, dynein and myosin II to sequester misfolded protein aggregates for autophagy. Kapβ2 is a member of the importin β family that transports RNA-binding proteins into the nucleus by binding to disordered nuclear localization signals (NLSs) known as PY-NLS. Kapβ2 is emerging as a universal uncoating factor for IAV and human immunodeficiency virus type 1 (HIV-1). Kapβ2 can also reverse liquid-liquid phase separation (LLPS) of RNA-binding proteins by promoting their disaggregation. Thus, it is becoming evident that key players in the management of cellular condensates and membraneless organelles are potent virus uncoating factors. This emerging concept reveals implications in viral pathogenesis, as well as, the promise for cell-targeted therapeutic strategies to block universal virus uncoating pathways hijacked by enveloped RNA viruses.

Microtubules in Influenza Virus Entry and Egress

Influenza viruses are respiratory pathogens that represent a significant threat to public health, despite the large-scale implementation of vaccination programs. It is necessary to understand the detailed and complex interactions between influenza virus and its host cells in order to identify successful strategies for therapeutic intervention. During viral entry, the cellular microenvironment presents invading pathogens with a series of obstacles that must be overcome to infect permissive cells. Influenza hijacks numerous host cell proteins and associated biological pathways during its journey into the cell, responding to environmental cues in order to successfully replicate. The cellular cytoskeleton and its constituent microtubules represent a heavily exploited network during viral infection. Cytoskeletal filaments provide a dynamic scaffold for subcellular viral trafficking, as well as virus-host interactions with cellular machineries that are essential for efficient uncoating, replication, and egress. In addition, influenza virus infection results in structural changes in the microtubule network, which itself has consequences for viral replication. Microtubules, their functional roles in normal cell biology, and their exploitation by influenza viruses will be the focus of this review.

Phenotypic Image Analysis Software Tools for Exploring and Understanding Big Image Data from Cell-Based Assays

Phenotypic image analysis is the task of recognizing variations in cell properties using microscopic image data. These variations, produced through a complex web of interactions between genes and the environment, may hold the key to uncover important biological phenomena or to understand the response to a drug candidate. Today, phenotypic analysis is rarely performed completely by hand. The abundance of high-dimensional image data produced by modern high-throughput microscopes necessitates computational solutions. Over the past decade, a number of software tools have been developed to address this need. They use statistical learning methods to infer relationships between a cell's phenotype and data from the image. In this review, we examine the strengths and weaknesses of non-commercial phenotypic image analysis software, cover recent developments in the field, identify challenges, and give a perspective on future possibilities.

HDAC3 and HDAC8 are required for cilia assembly and elongation

Cilia are extended from mother centrioles in quiescent G0/G1 cells and retracted in dividing cells. Diverse post-translational modifications play roles in the assembly and disassembly of the cilium. Here, we examined class I histone deacetylases (HDACs) as positive regulators of cilia assembly in serum-deprived RPE1 and HK2 cells. We observed that the number of cells with cilia was significantly reduced in HDAC3- and HDAC8-depleted cells. The ciliary length also decreased in HDAC3- and HDAC8-depleted cells compared to that in control cells. A knockdown-rescue experiment showed that wild-type HDAC3 and HDAC8 rescued the cilia assembly and ciliary length in HDAC3- and HDAC8-depleted cells, respectively; however, deacetylase-dead HDAC3 and HDAC8 mutants did not. This suggests that deacetylase activity is critical for both HDAC3 and HDAC8 function in cilia assembly and ciliary length control. This is the first study to report that HDACs are required for the assembly and elongation of the primary cilia.

Summary: We identified that HDAC3 and HDAC8 are required for the assembly and elongation of the primary cilia.

Disrupting the Code: Epigenetic Dysregulation of Lymphocyte Function during Infectious Disease and Lymphoma Development

Lymphocyte differentiation and identity are controlled by signals in the microenvironment that ultimately mediate gene expression in the nucleus. Although much focus has centered on the strategic and often unique roles transcription factors play within lymphocyte subsets, it is increasingly clear that another level of molecular regulation is crucial for regulating gene expression programs. In particular, epigenetic regulation is critical for appropriately regulated temporal and cell-type-specific gene expression during immune responses. As such, mutations in epigenetic modifiers are linked with lymphomagenesis. Furthermore, certain infections can remodel the epigenome in host cells, either through the microenvironment or by directly co-opting host epigenetic mechanisms, leading to inappropriate gene expression and/or ineffective cellular behavior. This review will focus on how histone modifications and DNA methylation, and the enzymes that regulate the epigenome, underpin lymphocyte differentiation and function in health and disease.

Identification and in vivo Efficacy Assessment of Approved Orally Bioavailable Human Host Protein-Targeting Drugs With Broad Anti-influenza A Activity

The high genetic variability of influenza A viruses poses a continual challenge to seasonal and pandemic vaccine development, leaving antiviral drugs as the first line of defense against antigenically different strains or new subtypes. As resistance against drugs targeting viral proteins emerges rapidly, we assessed the antiviral activity of already approved drugs that target cellular proteins involved in the viral life cycle and were orally bioavailable. Out of 15 candidate compounds, four were able to inhibit infection by 10- to 100-fold without causing toxicity, in vitro. Two of the drugs, dextromethorphan and ketotifen, displayed a 50% effective dose between 5 and 50 μM, not only for the classic H1N1 PR8 strain, but also for a pandemic H1N1 and a seasonal H3N2 strain. Efficacy assessment in mice revealed that dextromethorphan consistently resulted in a significant reduction of viral lung titers and also enhanced the efficacy of oseltamivir. Dextromethorphan treatment of ferrets infected with a pandemic H1N1 strain led to a reduction in clinical disease severity, but no effect on viral titer was observed. In addition to identifying dextromethorphan as a potential influenza treatment option, our study illustrates the feasibility of a bioinformatics-driven rational approach for repurposing approved drugs against infectious diseases.

Luteolin decreases the yield of influenza A virus in vitro by interfering with the coat protein I complex expression

Influenza is an acute transmissible respiratory infectious disease in humans and animals with high morbidity and mortality. It was reported that luteolin, extracted from Chinese herbs, could potently inhibit influenza virus replication in vitro. To assess the effect and explore the fundamental mechanism of luteolin, we infected several cell lines with two subtypes of influenza A virus (IAV), including A/Jiangxi/312/2006 (H3N2) and A/Fort Monmouth/1/1947 (H1N1) and demonstrated that luteolin suppressed the replication of IAV by cytopathic effect reduction method, qRT-PCR, immunofluorescence and Western blot assays. A time-of-addition assay indicated that this compound interfered with viral replication at the early stage of infection. In addition, we found that luteolin suppressed coat protein I complex expression, which was related to influenza virus entry and endocytic pathway. Overall, our findings demonstrated the antiviral effect of luteolin against IAV and its novel antiviral mechanism.

Structural exploration of tetrahydroisoquinoline derivatives as HDAC8 inhibitors through multi-QSAR modeling study

Histone deacetylase 8 (HDAC8) is one of the crucial HDACs responsible for influencing the epigenetic functions of the body. Overexpression of HDAC8 is found to be involved in numerous disease conditions such as tumorigenesis, cell proliferation, cancer, viral infections, neuronal disorders and other epigenetic diseases. Therefore, inhibition of HDAC8 is a primary method to combat these diseases. In this article, a multi-QSAR modeling study on tetrahydroisoquinoline derivatives was conducted to identify important contributions of the structural features of these compounds toward HDAC8 inhibition. All these QSAR modeling techniques were individually validated and justified the observations of each other. The results implied that the tetrahydroisoquinoline moiety may be effective as a cap group than as a linker moiety for HDAC8 inhibition. Different substitutions at the tetrahydroisoquinoline scaffold were also found to be crucial in modulating HDAC8 inhibition.Communicated by Ramaswamy H. Sarma.

Host proteins involved in microtubule-dependent HIV-1 intracellular transport and uncoating

Microtubules and microtubule-associated proteins are critical for cargo transport throughout the cell. Many viruses are able to usurp these transport systems for their own replication and spread. HIV-1 utilizes these proteins for many of its early events postentry, including transport, uncoating and reverse transcription. The molecular motor proteins dynein and kinesin-1 are the primary drivers of cargo transport, and HIV-1 utilizes these proteins for infection. In this Review, we highlight recent developments in the understanding of how HIV-1 hijacks motor transport, the key cellular and viral proteins involved, and the ways that transport influences other steps in the HIV-1 lifecycle.

Histone deacetylase 8 (HDAC8) and its inhibitors with selectivity to other isoforms: An overview

The histone deacetylases (HDACs) enzymes provided crucial role in transcriptional regulation of cells through deacetylation of nuclear histone proteins. Discoveries related to the HDAC8 enzyme activity signified the importance of HDAC8 isoform in cell proliferation, tumorigenesis, cancer, neuronal disorders, parasitic/viral infections and other epigenetic regulations. The pan-HDAC inhibitors can confront these conditions but have chances to affect epigenetic functions of other HDAC isoforms. Designing of selective HDAC8 inhibitors is a key feature to combat the pathophysiological and diseased conditions involving the HDAC8 activity. This review is concerned about the structural and positional aspects of HDAC8 in the HDAC family. It also covers the contributions of HDAC8 in the pathophysiological conditions, a preliminary discussion about the recent scenario of HDAC8 inhibitors. This review might help to deliver the structural, functional and computational information in order to identify and design potent and selective HDAC8 inhibitors for target specific treatment of diseases involving HDAC8 enzymatic activity.

The entomopathogenic fungus Metarhizium robertsii communicates with the insect host Galleria mellonella during infection

Parasitic fungi are the only pathogens that can infect insect hosts directly through their proteinaceous exoskeleton. Penetration of the cuticle requires the release of fungal enzymes, including proteinases, which act as virulence factors. Insects can sense fungal infections and activate innate immune responses, including the synthesis of antifungal peptides and proteinase inhibitors that neutralize the incoming proteinases. This well-studied host response is epigenetically regulated by histone acetylation/deacetylation. Here we show that entomopathogenic fungi can in turn sense the presence of insect-derived antifungal peptides and proteinase inhibitors, and respond by inducing the synthesis of chymotrypsin-like proteinases and metalloproteinases that degrade the host-derived defense molecules. The rapidity of this response is dependent on the virulence of the fungal strain. We confirmed the specificity of the pathogen response to host-derived defense molecules by LC/MS and RT-PCR analysis, and correlated this process with the epigenetic regulation of histone acetylation/deacetylation. This cascade of responses reveals that the coevolution of pathogens and hosts can involve a complex series of attacks and counterattacks based on communication between the invading fungal pathogen and its insect host. The resolution of this process determines whether or not pathogenesis is successful.

miR-21-3p Regulates Influenza A Virus Replication by Targeting Histone Deacetylase-8

Influenza A virus (IAV) is responsible for severe morbidity and mortality in animals and humans worldwide. miRNAs are a class of small noncoding single-stranded RNA molecules that can negatively regulate gene expression and play important roles in virus-host interaction. However, the roles of miRNAs in IAV infection are still not fully understood. Here, we profiled the cellular miRNAs of A549 cells infected with A/goose/Jilin/hb/2003 (H5N1) and a comparison A/Beijing/501/2009 (H1N1). miRNA microarray and quantitative PCR analysis showed that several miRNAs were differentially expressed in A549 cells during IAV infection. Subsequently, we demonstrated that IAV replication was essential for the regulation of these miRNAs, and bioinformatic analysis revealed that the targets of these miRNAs affected biological processes relevant to IAV replication. Specifically, miR-21-3p was found to be down-regulated in IAV-infected A549 cells and selected for further detailed analysis. Target prediction and functional study illustrated that miR-21-3p repressed the expression of HDAC8 by targeting its 3′UTR. Furthermore, we confirmed miR-21-3p could promote virus replication, which was similar to the result of knocking down HDAC8, indicating that miR-21-3p promoted IAV replication by suppressing HDAC8 expression. Altogether, our results suggest a potential host defense against IAV through down-regulation of miR-21-3p.

Virus Entry: Looking Back and Moving Forward

Research over a period of more than half a century has provided a reasonably accurate picture of mechanisms involved in animal virus entry into their host cells. Successive steps in entry include binding to receptors, endocytosis, passage through one or more membranes, targeting to specific sites within the cell, and uncoating of the genome. For some viruses, the molecular interactions are known in great detail. However, as more viruses are analyzed, and as the focus shifts from tissue culture to in vivo experiments, it is evident that viruses display considerable redundancy and flexibility in receptor usage, endocytic mechanism, location of penetration, and uncoating mechanism. For many viruses, the picture is still elusive because the interactions that they engage in rely on sophisticated adaptation to complex cellular functions and defense mechanisms.

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Studies using a broad combination of technologies have provided detailed information on the entry and uncoating of many animal viruses.

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Not only the identity of cell surface receptors but their distribution in plasma membrane and in microdomains defines cell tropism and infection efficiency.

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The majority of viruses enter by endocytic mechanisms and penetrate into the cytosol intracellularly from a variety of different organelles.

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The picture is often elusive because many viruses display redundancy in receptor choice and entry strategy.

HATRIC-based identification of receptors for orphan ligands

Cellular responses depend on the interactions of extracellular ligands, such as nutrients, growth factors, or drugs, with specific cell-surface receptors. The sensitivity of these interactions to non-physiological conditions, however, makes them challenging to study using in vitro assays. Here we present HATRIC-based ligand receptor capture (HATRIC-LRC), a chemoproteomic technology that successfully identifies target receptors for orphan ligands on living cells ranging from small molecules to intact viruses. HATRIC-LRC combines a click chemistry-based, protein-centric workflow with a water-soluble catalyst to capture ligand-receptor interactions at physiological pH from as few as 1 million cells. We show HATRIC-LRC utility for general antibody target validation within the native nanoscale organization of the surfaceome, as well as receptor identification for a small molecule ligand. HATRIC-LRC further enables the identification of complex extracellular interactomes, such as the host receptor panel for influenza A virus (IAV), the causative agent of the common flu.

Technologies for identifying receptor-ligand pairs on living cells at physiological conditions remain scarce. Here, the authors develop a mass spectrometry-based ligand receptor capture technology that can identify receptors for a diverse range of ligands at physiological pH with as few as a million cells.

How Computational Models Enable Mechanistic Insights into Virus Infection

An implicit aim in cellular infection biology is to understand the mechanisms how viruses, microbes, eukaryotic parasites, and fungi usurp the functions of host cells and cause disease. Mechanistic insight is a deep understanding of the biophysical and biochemical processes that give rise to an observable phenomenon. It is typically subject to falsification, that is, it is accessible to experimentation and empirical data acquisition. This is different from logic and mathematics, which are not empirical, but built on systems of inherently consistent axioms. Here, we argue that modeling and computer simulation, combined with mechanistic insights, yields unprecedented deep understanding of phenomena in biology and especially in virus infections by providing a way of showing sufficiency of a hypothetical mechanism. This ideally complements the necessity statements accessible to empirical falsification by additional positive evidence. We discuss how computational implementations of mathematical models can assist and enhance the quantitative measurements of infection dynamics of enveloped and non-enveloped viruses and thereby help generating causal insights into virus infection biology.

Histone Deacetylase 1 Plays an Acetylation-Independent Role in Influenza A Virus Replication

Influenza A viruses (IAVs) take advantage of the host acetylation system for their own benefit. Whether the nucleoprotein (NP) of IAVs undergoes acetylation and the interaction between the NP and the class I histone deacetylases (HDACs) were largely unknown. Here, we showed that the NP protein of IAV interacted with HDAC1, which downregulated the acetylation level of NP. Using mass spectrometry, we identified lysine 103 as an acetylation site of the NP. Compared with wild-type protein, two K103 NP mutants, K103A and K103R, enhanced replication efficiency of the recombinant viruses in vitro. We further demonstrated that HDAC1 facilitated viral replication via two paths: promoting the nuclear retention of NP and inhibiting TBK1-IRF3 pathway. Our results lead to a new mechanism for regulating NP acetylation, indicating that HDAC1 may be a possible target for antiviral drugs.

HDAC8 functions in spindle assembly during mouse oocyte meiosis

HDAC8 is a class I histone deacetylase that functions in a variety of biological processes through its non-histone substrates. However, its roles during oocyte meiosis remain elusive. Here, we document that HDAC8 localizes at spindle poles and positively participates in the regulation of microtubule organization and spindle assembly in mouse oocytes. Depletion of HDAC8 by siRNA-based gene silencing results in various spindle defects and chromosome misalignment during oocyte meiotic maturation, accompanied by impaired kinetochore-microtubule attachments. Consequently, a higher incidence of aneuploidy is generated in HDAC8-depleted MII eggs. In addition, inhibition of HDAC8 activity with its selective inhibitor PCI-34051 phenocopies the spindle/chromosome defects resulting from HDAC8 depletion by siRNA injection. Finally, we find that HDAC8 is required for the correct localization of ϕ-tubulin to spindle poles. Collectively, these data reveal that HDAC8 plays a significant role in regulating spindle assembly and thus ensuring the euploidy in mouse eggs.

Microtubule Regulation and Function during Virus Infection

Microtubules (MTs) form a rapidly adaptable network of filaments that radiate throughout the cell. These dynamic arrays facilitate a wide range of cellular processes, including the capture, transport, and spatial organization of cargos and organelles, as well as changes in cell shape, polarity, and motility. Nucleating from MT-organizing centers, including but by no means limited to the centrosome, MTs undergo rapid transitions through phases of growth, pause, and catastrophe, continuously exploring and adapting to the intracellular environment. Subsets of MTs can become stabilized in response to environmental cues, acquiring distinguishing posttranslational modifications and performing discrete functions as specialized tracks for cargo trafficking. The dynamic behavior and organization of the MT array is regulated by MT-associated proteins (MAPs), which include a subset of highly specialized plus-end-tracking proteins (+TIPs) that respond to signaling cues to alter MT behavior. As pathogenic cargos, viruses require MTs to transport to and from their intracellular sites of replication. While interactions with and functions for MT motor proteins are well characterized and extensively reviewed for many viruses, this review focuses on MT filaments themselves. Changes in the spatial organization and dynamics of the MT array, mediated by virus- or host-induced changes to MT regulatory proteins, not only play a central role in the intracellular transport of virus particles but also regulate a wider range of processes critical to the outcome of infection.

Age-Related Loss of Cohesion: Causes and Effects

Aneuploidy is a leading genetic cause of birth defects and lower implantation rates in humans. Most errors in chromosome number originate from oocytes. Aneuploidy in oocytes increases with advanced maternal age. Recent studies support the hypothesis that cohesion deterioration with advanced maternal age represents a leading cause of age-related aneuploidy. Cohesin generates cohesion, and is established only during the premeiotic S phase of fetal development without any replenishment throughout a female's period of fertility. Cohesion holds sister chromatids together until meiosis resumes at puberty, and then chromosome segregation requires the release of sister chromatid cohesion from chromosome arms and centromeres at anaphase I and anaphase II, respectively. The time of cohesion cleavage plays an important role in correct chromosome segregation. This review focuses specifically on the causes and effects of age-related cohesion deterioration in female meiosis.

The Novel HDAC8 Inhibitor WK2-16 Attenuates Lipopolysaccharide-Activated Matrix Metalloproteinase-9 Expression in Human Monocytic Cells and Improves Hypercytokinemia In Vivo

Dysregulated human monocytes/macrophages can synthesize and secrete matrix metalloproteinases (MMPs), which play important roles in the progression of sepsis. In this study, we investigated the effects and mechanism of a novel histone deacetylase (HDAC8) inhibitor, (E)-N-hydroxy-4-methoxy-2-(biphenyl-4-yl)cinnamide (WK2-16), on MMP-9 production and activation in stimulated human monocytic THP-1 cells. Our results demonstrated that the acetylation level of structural maintenance of chromosomes 3 (SMC3) was up-regulated by WK2-16 in THP-1 cells. Consistently, an in vitro enzyme study demonstrated that WK2-16 selectively inhibited HDAC8 activity. Moreover, the WK2-16 concentration dependently suppressed MMP-9-mediated gelatinolysis induced by tumor necrosis factor-α (TNF-α) or lipopolysaccharide (LPS). Additionally, WK2-16 significantly inhibited both MMP-9 protein and mRNA expression without cellular toxicity. Nevertheless, WK2-16 suppressed the extracellular levels of interleukin (IL)-6 from LPS-stimulated THP-1 cells. For the signaling studies, WK2-16 had no effect on LPS/TLR4 downstream signaling pathways, such as the NF-κB and ERK/JNK/P38 MAPK pathways. On the other hand, WK2-16 enhanced the recruitment of acetylated Yin Yang 1 (YY1) with HDAC1. Finally, in vivo studies indicated that WK2-16 could reduce the serum levels of TNF-α and IL-6 in endotoxemic mice. These results suggested that HDAC8 inhibition might provide a novel therapeutic strategy of hypercytokinemia in sepsis.

Role of Host Genes in Influenza Virus Replication

At every step of their replication cycle influenza viruses depend heavily on their host cells. The multifaceted interactions that occur between the virus and its host cell determine the outcome of the infection, including efficiency of progeny virus production, tropism, and pathogenicity. In order to understand viral disease and develop therapies for influenza it is therefore pertinent to study the intricate interplay between influenza viruses and their required host factors. Here, we review the current knowledge on host cell factors required by influenza virus at the different stages of the viral replication cycle. We also discuss the roles of host factors in zoonotic transmission of influenza viruses and their potential for developing novel antivirals.

KAT2A/KAT2B-targeted acetylome reveals a role for PLK4 acetylation in preventing centrosome amplification

Lysine acetylation is a widespread post-translational modification regulating various biological processes. To characterize cellular functions of the human lysine acetyltransferases KAT2A (GCN5) and KAT2B (PCAF), we determined their acetylome by shotgun proteomics. One of the newly identified KAT2A/2B substrate is polo-like kinase 4 (PLK4), a key regulator of centrosome duplication. We demonstrate that KAT2A/2B acetylate the PLK4 kinase domain on residues K45 and K46. Molecular dynamics modelling suggests that K45/K46 acetylation impairs kinase activity by shifting the kinase to an inactive conformation. Accordingly, PLK4 activity is reduced upon in vitro acetylation of its kinase domain. Moreover, the overexpression of the PLK4 K45R/K46R mutant in cells does not lead to centrosome overamplification, as observed with wild-type PLK4. We also find that impairing KAT2A/2B-acetyltransferase activity results in diminished phosphorylation of PLK4 and in excess centrosome numbers in cells. Overall, our study identifies the global human KAT2A/2B acetylome and uncovers that KAT2A/2B acetylation of PLK4 prevents centrosome amplification.

The acetyltransferases KAT2A and KAT2B are essential regulators of transcription, cell cycle progression and DNA repair. Here the authors describe a KAT2A/2B-dependent acetylome, and show that acetylation of the protein kinase PLK4 contributes to the regulation of centrosome number.

HDAC8 Catalyzes the Hydrolysis of Long Chain Fatty Acyl Lysine

The histone deacetylase (HDAC) family regulates many biological pathways through the deacetylation of lysine residues on histone and nonhistone proteins. Mammals have 18 HDACs that are classified into four classes. Class I, II, and IV are zinc-dependent, while class III is nicotinamide adenine dinucleotide (NAD⁺)-dependent lysine deacetylase or sirtuins. HDAC8, a class I HDAC family member, has been shown to have low deacetylation activity compared to other HDACs in vitro. Recent studies showed that several sirtuins, with low deacetylase activities, can actually hydrolyze other acyl lysine modifications more efficiently. Inspired by this, we tested the activity of HDAC8 using a variety of different acyl lysine peptides. Screening a panel of peptides with different acyl lysine modifications, we found that HDAC8 can catalyze the removal of acyl groups with 2-16 carbons from lysine 9 of the histone H3 peptide (H3K9). Interestingly, the catalytic efficiencies (k_cat/K_m) of HDAC8 on octanoyl, dodecanoyl, and myristoyl lysine are several-fold better than that on acetyl lysine. The increased catalytic efficiencies of HDAC8 on larger fatty acyl groups are due to the much lower K_m values. T-cell leukemia Jurkat cells treated with a HDAC8 specific inhibitor, PCI-34051, exhibited an increase in global fatty acylation compared to control treatment. Thus, the de-fatty-acylation activity of HDAC8 is likely physiologically relevant. This is the first report of a zinc-dependent HDAC with de-fatty-acylation activity, and identification of HDAC8 de-fatty-acylation targets will help to further understand the function of HDAC8 and protein lysine fatty acylation.

MC1568 inhibits HDAC6/8 activity and influenza A virus replication in lung epithelial cells: role of Hsp90 acetylation

AIM

Histone deacetylases (HDACs) regulate the life cycle of several viruses. We investigated the ability of different HDAC inhibitors, to interfere with influenza virus A/Puerto Rico/8/34/H1N1 (PR8 virus) replication in Madin-Darby canine kidney and NCI cells.

RESULTS

3-(5-(3-Fluorophenyl)-3-oxoprop-1-en-1-yl)-1-methyl-1H-pyrrol-2-yl)-N-hydroxyacrylamide (MC1568) inhibited HDAC6/8 activity and PR8 virus replication, with decreased expression of viral proteins and their mRNAs. Such an effect may be related to a decrease in intranuclear content of viral polymerases and, in turn, to an early acetylation of Hsp90, a major player in their nuclear import. Later, the virus itself induced Hsp90 acetylation, suggesting a differential and time-dependent role of acetylated proteins in virus replication.

CONCLUSION

The inhibition of HDAC6/8 activity during early steps of PR8 virus replication could lead to novel anti-influenza strategy.

HDAC6 is a Regulator of CTL Function through Control of Lytic Granule Dynamics

Viral infections involve specific stress exposure that can influence the quality and average lifespan of an organism. The immune system acts through virus clearance from the organism. Many aspects of immune cells accounting for this response are still under study. Here, we review recent aspects of the molecular mechanisms involved in the delivery of the lethal hit by Cytotoxic T lymphocytes.