Histone H3 deacetylation promotes host cell viability for efficient infection by Listeria monocytogenes

Sirtuins as modulators of infection outcomes in the battle of host-pathogen dynamics

Sirtuins's central role in governing metabolic processes has been known for decades. However, over the past two decades, sirtuin functions have been linked to immune regulation and immunity. Sirtuins are NAD+ dependent protein deacylases involved in the regulation of several important biological processes ranging from energy homeostasis, metabolism, aging, apoptosis, autophagy, immunity, adipocyte, and muscle differentiation. Here, in this review, we discuss the role of sirtuins in several infectious diseases including viral, bacterial, and protozoan infections with detailed emphasis on bacterial-host interactions. We have aimed to explore both host and bacterial sirtuin functions contributing to the infection progression, host responses and their influence on the everlasting host-pathogen tug-of-war. In order to manipulate host pathways, pathogens such as intracellular bacteria have evolved parallelly and harbor bacterial sirtuins. The recent discoveries of bacterial sirtuins influencing the host-pathogen interaction outcomes pave the way for the discovery of potential therapeutic targets.

Diaphorina citri E3 ubiquitin ligase RNF115 inhibits CLas bacterial proliferation by targeting to the host histone H1

The Asian citrus psyllid (ACP), Diaphorina citri, serves as the primary vector for Candidatus Liberibacter asiaticus (CLas), the pathogen responsible for citrus Huanglongbing (HLB). D. citri modulates the expression of its key proteins in response to CLas infection. Previous research has revealed that CLas infection significantly alters the expression levels of E3 ubiquitin ligases in D. citri; however, the specific functions of these E3 ligases remain largely uncharacterized. In this study, a total of 11 E3 ubiquitin ligases were identified from the proteomics database of D. citri, among which E3 ubiquitin ligase RNF115 was significantly upregulated following CLas infection. RING finger protein 115 (RNF115) consists of 156 amino acids and contains a RING finger domain at its N-terminus. Silencing RNF115 via RNA interference (RNAi) and injecting the inhibitor disulfiram, which targets RNF115, significantly increased CLas bacterial content in D. citri. In contrast, injection of recombinant RNF115 protein markedly inhibited CLas bacterial proliferation. Furthermore, interaction between RNF115 and D. citri histone H1 was confirmed using yeast 2-hybrid assay, pull-down experiments and molecular docking analysis. Knockdown of histone H1 via RNAi significantly reduced CLas bacterial content, whereas injection of recombinant histone H1 protein led to an increase in CLas content within D. citri. These findings suggest that CLas infection may induce an upregulation of RNF115 expression in D. citri, leading to subsequent interactions with histone H1 that facilitate the ubiquitination of histone H1, ultimately resulting in reduced expression levels and inhibiting CLas proliferation within D. citri.

Suppressed macrophage response to quorum-sensing-active Streptococcus pyogenes occurs at the level of the nucleus

Streptococcus pyogenes, or Group A Streptococus (GAS), a significant human pathogen, employs quorum sensing (QS) systems to coordinate its behavior and genetic regulation in order to enhance survival. Our previous research established that one such QS system, the Rgg2/3 system, can suppress macrophage NFκB activity and production of pro-inflammatory cytokines. Yet, the scope of suppression and the mechanism by which it occurs remains unknown. In this study, we used transcriptomic and phosphoproteomic approaches to address these unanswered questions. We found QS-ON GAS broadly suppressed most inflammatory transcriptional pathways including those of NFκB, type I and type II interferon responses, and intracellular stress responses. Yet, we found no alternative transcriptional programs were activated after QS-ON GAS infection. Additionally, phosphoproteomics showed no disruption in typical inflammatory pathways such as those related to NFκB and MAPK activation, which was confirmed by western blotting and translocation assays. Instead, the proteomic data highlighted a potential role for epigenetic mechanisms of inflammatory regulation. To determine if epigenetic regulation was involved in QS-mediated immunomodulation, DNA methylation was measured and studies were performed inhibiting various histone and chromatin modifiers. These studies also showed no dijerence between QS-ON compared with QS-OFF infected macrophages. These findings expand our understanding of QS-mediated suppression and of GAS virulence strategies that appear to employ unusual methods of restricting inflammation. Uncovering this mechanism will ojer invaluable insight into GAS, itself, as well as understudied immunological pathways.

Multifaceted regulation of sirtuin 2 (Sirt2) deacetylase activity

Sirtuin 2 (Sirt2) is a member of the sirtuin family of NAD-dependent lysine deacylases and plays important roles in regulation of the cell cycle and gene expression. As a nucleocytoplasmic deacetylase, Sirt2 has been shown to target both histone and nonhistone acetylated protein substrates. The central catalytic domain of Sirt2 is flanked by flexible N and C termini, which vary in length and composition with alternative splicing. These termini are further subject to posttranslational modifications including phosphorylation. Here, we investigate the function of the N and C termini on deacetylation of nuclear substrates by Sirt2. Remarkably, we find that the C terminus autoinhibits deacetylation, while the N terminus enhances deacetylation of proteins and peptides, but not nucleosomes-a chromatin model substrate. Using protein semisynthesis, we characterize the effect of cell cycle-linked N-terminal phosphorylation at two major phosphorylation sites (Ser23/Ser25) and find that these further enhance protein/peptide deacetylation, with no effect on nucleosome deacetylation. Additionally, we find that VRK1, an established binding partner of both Sirt2 and nucleosomes, can stimulate deacetylation of nucleosomes by Sirt2, likely through an electrostatic mechanism. Taken together, these findings reveal multiple mechanisms regulating the activity of Sirt2, which allow for a broad range of activities across its multiple biological roles.

Histone acetylation, BET proteins, and periodontal inflammation

Periodontitis is one of the most common inflammatory diseases in humans. The susceptibility to periodontitis is largely determined by the host response, and the severity of inflammation predicts disease progression. Upon microbial insults, host cells undergo massive changes in their transcription program to trigger an appropriate response (inflammation). It is not surprising that successful keystone pathogens have developed specific mechanisms to manipulate the gene expression network in host cells. Emerging data has indicated that epigenetic regulation plays a significant role in inflammation. Acetylation of lysine residues on histones is a major epigenetic modification of chromatin, highly associated with the accessibility of chromatin and activation of transcription. Specific histone acetylation patterns are observed in inflammatory diseases including periodontitis. Bromo- and extraterminal domain (BET) proteins recognize acetylated histones and then recruit transcription factors and transcription elongation complexes to chromatin. BET proteins are regulated in inflammatory diseases and small molecules blocking the function of BET proteins are promising "epi-drugs" for treating inflammatory diseases.

The RBPome of influenza A virus NP-mRNA reveals a role for TDP-43 in viral replication

Genome-wide approaches have significantly advanced our knowledge of the repertoire of RNA-binding proteins (RBPs) that associate with cellular polyadenylated mRNAs within eukaryotic cells. Recent studies focusing on the RBP interactomes of viral mRNAs, notably SARS-Cov-2, have revealed both similarities and differences between the RBP profiles of viral and cellular mRNAs. However, the RBPome of influenza virus mRNAs remains unexplored. Herein, we identify RBPs that associate with the viral mRNA encoding the nucleoprotein (NP) of an influenza A virus. Focusing on TDP-43, we show that it binds several influenza mRNAs beyond the NP-mRNA, and that its depletion results in lower levels of viral mRNAs and proteins within infected cells, and a decreased yield of infectious viral particles. We provide evidence that the viral polymerase recruits TDP-43 onto viral mRNAs through a direct interaction with the disordered C-terminal domain of TDP-43. Notably, other RBPs found to be associated with influenza virus mRNAs also interact with the viral polymerase, which points to a role of the polymerase in orchestrating the assembly of viral messenger ribonucleoproteins.

microRNA-143 targets SIRT2 to mediate the histone acetylation of PLAUR and modulates functions of astrocytes in spinal cord injury

This study aimed to explore effects of microRNA (miR)-143 on the proliferation, apoptosis, and cytokine secretion in astrocytes after spinal cord injury (SCI). After gain- and loss-of-function assays and transforming growth factor (TGF)-β stimulation in astrocytes, the cell viability, proliferation, and apoptosis were examined. The expression of miR-143, SIRT2, and PLAUR and levels of astrocyte-related glial fibrillary acidic protein (GFAP), Vimentin, chondroitin sulfate proteoglycan (CSPG), and connective tissue growth factor (CTGF) were also measured. The binding relationship between miR-143 and SIRT2 was assessed, as well as the correlation of PLAUR with SIRT2. In established SCI rat models, the locomotion function and astrocyte hyperplasia were detected. The TGF-β stimulation decreased miR-143 but increased SIRT2 expression in astrocytes. Mechanistically, miR-143 negatively targeted SIRT2 and SIRT2 down-regulation inhibited the H3K27 deacetylation of PLAUR promoter to increase PLAUR expression. miR-143 up-regulation inhibited TGF-β stimulated-proliferation, promoted cell apoptosis, and reduced GFAP, Vimentin, CSPG, and CTGF expression in astrocytes, which was counterweighed by SIRT2 overexpression. SIRT2 silencing reduced the proliferation and GFAP, Vimentin, CSPG, and CTGF expression while augmenting the apoptosis in TGF-β stimulated astrocytes, which was abrogated by PLAUR silencing. The injection of miR-143 agomir improved the locomotion function and reduced the astrocyte hyperplasia in SCI rats, which was reversed by silencing PLAUR. miR-143 targeted SIRT2 to affect PLAUR expression via the regulation of histone acetylation, which repressed the astrocyte activation in vivo and in vitro to improve the locomotion function in SCI rats.

Small RNAs contribute to citrus Huanglongbing tolerance by manipulating methyl salicylate signaling and exogenous methyl salicylate primes citrus groves from emerging infection

Citrus production is severely threatened by the devastating Huanglongbing (HLB) disease globally. By studying and analyzing the defensive behaviors of an HLB-tolerant citrus cultivar 'Shatangju', we discovered that citrus can sense Candidatus Liberibacter asiaticus (CLas) infection and induce immune responses against HLB, which can be further strengthened by both endogenously produced and exogenously applied methyl salicylate (MeSA). This immune circuit is turned on by an miR2977-SAMT (encoding a citrus Salicylate [SA] O-methyltransferase) cascade, by which CLas infection leads to more in planta MeSA production and aerial emission. We provided both transgenic and multi-year trail evidences that MeSA is an effective community immune signal. Ambient MeSA accumulation and foliage application can effectively induce defense gene expression and significantly boost citrus performance. We also found that miRNAs are battle fields between citrus and CLas, and about 30% of the differential gene expression upon CLas infection are regulated by miRNAs. Furthermore, CLas hijacks host key processes by manipulating key citrus miRNAs, and citrus employs miRNAs that coordinately regulate defense-related genes. Based on our results, we proposed that miRNAs and associated components are key targets for engineering or breeding resistant citrus varieties. We anticipate that MeSA-based management, either induced expression or external application, would be a promising tool for HLB control.

Metabolic Regulation of Lysine Acetylation: Implications in Cancer

Lysine acetylation is the second most well-studied post-translational modification after phosphorylation. While phosphorylation regulates signaling cascades, one of the most significant roles of acetylation is regulation of chromatin structure. Acetyl-coenzyme A (acetyl-CoA) serves as the acetyl group donor for acetylation reactions mediated by lysine acetyltransferases (KATs). On the other hand, NAD+ serves as the cofactor for lysine deacetylases (KDACs). Both acetyl-CoA and NAD+ are metabolites integral to energy metabolism, and therefore, their metabolic flux can regulate the activity of KATs and KDACs impacting the epigenome. In this chapter, we review our current understanding of how metabolic pathways regulate lysine acetylation in normal and cancer cells.