SIRT6 promotes DNA repair under stress by activating PARP1

HBV-induced N6 methyladenosine modification of PARP1 enhanced AFB1-related DNA damage and synergistically contribute to HCC

Hepatitis B virus (HBV) infection and Aflatoxin B1 (AFB1) exposure are major contributors to the high incidence of hepatocellular carcinoma (HCC) in Southern Africa and Southeast Asia. Investigating the synergistic mechanisms between these factors will help to elucidate the pathogenesis, identify potential therapeutic targets, and reduce disease incidence. Oxidative stress in the cell line was assessed using ROS, MDA, and 8-OHdG assays. DNA damage was evaluated through the Comet assay and γ-H2AX detection. Sanger sequencing was employed to detect TP53 R249S mutations. RIP and Me-RIP assays were performed to investigate the interaction between YTH N6-methyladenosine RNA Binding Protein 2 (YTHDF2) and Poly(ADP-ribose) polymerase 1 (PARP1). The exogenous Cytochrome P450 3A4(CYP3A4)-Sodium/Taurocholate Cotransporting Polypeptide(NTCP) expression cell model was validated for its ability to metabolize AFB1 and support HBV infection. HBV infection increased YTHDF2 expression while suppressing PARP1 both in vitro and in vivo. Additionally, HBV infection exacerbated AFB1-induced DNA damage in both experimental settings. Interference with or pharmacological inhibition of PARP1 significantly worsened HBV- and AFB1-induced DNA damage, while PARP1 overexpression partially alleviated the damage. These findings provide compelling evidence that HBV aggravates AFB1-induced DNA damage by inhibiting PARP1. Further investigation revealed that YTHDF2 interference reversed HBV's regulatory effect on PARP1, while exogenous YTHDF2 addition mimicked HBV's effect by promoting PARP1 degradation. RIP (RNA immunoprecipitation) experiments confirmed that YTHDF2 directly binds to PARP1 mRNA, and MeRIP experiments showed that YTHDF2 increases m6A methylation of PARP1 mRNA. CYP3A4-NTCP overexpression enables liver cell lines to metabolize AFB1 and support HBV infection. HBV enhances AFB1-induced DNA damage by promoting PARP1 degradation, thereby synergistically contributing to HCC development.

Down-regulation of serum SIRT6 levels is associated with an increased risk of chronic intestinal inflammation in children exposed to airborne particulate matter and polycyclic aromatic hydrocarbons from e-waste

Informal e-waste recycling releases airborne particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs), which are linked to intestinal barrier dysfunction and chronic inflammation. SIRT6, a histone deacetylase, modulates inflammation by suppressing NF-κB signaling, but its role in mitigating e-waste pollutant-induced childhood enteritis remains unclear. This cross-sectional study evaluated associations between e-waste exposure, intestinal inflammation, and SIRT6 levels in 217 preschool children from Guiyu (e-waste-exposed, n = 109) and Haojiang (non-exposed control, n = 108), China. Airborne pollutant exposure was quantified via the Air Quality Composite Index (AQCI) and average daily dose (ADD) for PM2.5, PM10, NO2, and SO2. Urinary PAH metabolites, serum SIRT6, inflammatory markers (GM-CSF, IL-10), and intestinal barrier biomarkers (IFABP, endotoxins) were measured using GC/MS, ELISA, and automated hematology analyzers. Dietary patterns, residential proximity to e-waste sites, and gastrointestinal symptoms were assessed via questionnaires. Statistical analyses included Spearman correlations, multivariate regression, and Bayesian kernel machine regression (BKMR) to evaluate pollutant effects on SIRT6 and inflammation. Children residing in Guiyu demonstrated significantly elevated urinary PAH metabolites and higher ADD of PM2.5, PM10, NO2, and SO2 compared to reference populations. Concurrently, this cohort exhibited biomarker patterns indicative of intestinal barrier compromise, including elevated IFABP and systemic endotoxin levels. Serum analyses revealed quantifiable reductions in SIRT6 and GM-CSF concentrations, accompanied by increased circulating monocytes and lymphocytes. Notably, BKMR modeling identified non-linear U-shaped associations between mixed PM/PAH exposures and progressive SIRT6 suppression. Proximity to e-waste sites, lower parental education, and poor household ventilation correlated with heightened pollutant exposure and gastrointestinal morbidity. Chronic e-waste exposure was associated with decreased serum SIRT6 levels and concurrent elevation of intestinal inflammatory biomarkers in children. Our cross-sectional analysis revealed significant correlations between SIRT6 downregulation, altered GM-CSF/IL-10 signaling profiles, and disrupted macrophage-Treg homeostasis. These observational findings suggest SIRT6 may serve as a potential protective mediator in environmental enteritis.

Structural Insights Into centSIRT6: Bioinformatic Analysis of N308K and A313S Substitution Effects

Sirtuin 6 (SIRT6), a member of the class III histone deacetylase (HDAC) family, is crucial for the maintenance of general health and is associated with increased life expectancy and resistance to age-related diseases such as cancer and metabolic disorders. A comparative analysis of the SIRT6 gene in Ashkenazi Jewish (AJ) centenarians and noncentenarian controls found a distinct allele, centSIRT6, enriched in the centenarian group. This allele features 2 linked substitutions, N308K and A313S, and exhibits enhanced functions, including more efficient suppression of LINE1 retrotransposons, improved repair of DNA double-strand breaks, and increased efficiency in cancer cell killing. Notably, centSIRT6 shows lower deacetylase activity but higher mono-adenosine diphosphate (ADP) ribosyl transferase activity compared with the wild-type enzyme. This study used several bioinformatics tools to explore the structural changes caused by the N308K and A313S substitutions in centSIRT6 and to elucidate how these alterations contribute to changes in the enzymatic activities of SIRT6. The results indicate that these mutations reduce the structural flexibility of centSIRT6, thus weakening its interactions with acetyl-lysine but strengthening its interactions with ADP-ribose. This research provides useful information for future experimental studies to further investigate the molecular mechanisms of centSIRT6.

New Perspectives on Postmenopausal Osteoporosis: Mechanisms and Potential Therapeutic Strategies of Sirtuins and Oxidative Stress

Estrogen levels are the core factor influencing postmenopausal osteoporosis (PMOP). Estrogen can affect the progression of PMOP by regulating bone metabolism, influencing major signaling pathways related to bone metabolism, and modulating immune responses. When estrogen levels decline, the activity of Sirtuins (SIRTs) is reduced. SIRTs are enzymes that function as NAD+-dependent deacetylases. SIRTs can modulate osteocyte function, sustain mitochondrial homeostasis, and modulate relevant signaling pathways, thereby improving bone metabolic imbalances, reducing bone resorption, and promoting bone formation. In PMOP, SIRT1, SIRT3, and SIRT6 are primarily affected. Oxidative stress (OS) is a crucial factor in PMOP, as it generates excessive reactive oxygen species (ROS) that exacerbate PMOP. There is a certain interplay between SIRTs and OS. The reduced activity of SIRTs leads to intensified OS and the excessive accumulation of ROS. In return, ROS suppresses the AMPK signaling pathway and the synthesis of NAD+, which consequently diminishes the function of SIRTs. Natural SIRT activators and natural antioxidants, which are characterized by high safety, convenience, and minimal side effects, represent a potential therapeutic strategy for PMOP. This study aims to investigate the mechanisms of SIRTs and OS in PMOP and summarize potential therapeutic strategies to assist in the improvement of PMOP.

gdSir2.1 and gdSir2.3 are involved in albendazole resistance in Giardia duodenalis via regulation of the oxidative stress response

Albendazole resistance in Giardia duodenalis includes a complex and multifactorial challenge that potentially involves non-reported pathways such as the participation of metabolic regulators. In this context, sirtuins, known as metabolic sensors in various cellular processes, have emerged as promising candidates for novel anti-parasitic treatments. To investigate their role in albendazole (ABZ) resistance, initially we analyzed the expression of sirtuins in three Giardia strains resistant to 8 μM, 1.5 μM and 250 μM of ABZ that were obtained in our laboratory. Additionally, we used a CRISPRi-based knockdownstrategy to repress several sirtuins in Giardia and analyzed the effect of sirtuins on ABZ resistance. Our findings demonstrated a significant upregulation of sirtuins gdSir2.1, gdSir2.2 and gdSir2.3 in the three distinct albendazole-resistant lines. Knockdown of gdSir2.1 and gdSir2.3 resulted in heightened parasite susceptibility to both albendazole and hydrogen peroxide. Further, our study suggested that sirtuins contribute to the regulation of reactive oxygen species (ROS) levels, oxidative DNA damage, and the expression of oxidative stress response (OSR) genes within the parasite. Collectively, our results demonstrated that gdSir2.1 and gdSir2.3 play a significant role in mediating albendazole resistance, primarily through regulating the oxidative stress response.

Caloric Restriction and Sirtuins as New Players to Reshape Male Fertility

Over the years, caloric intake has remained a subject of profound scrutiny. Within the scientific community, there has been rigorous debate to ascertain which path is most ideal for enhancing quality of life and extending the human lifespan. Caloric restriction has been shown to be a promising contributor towards longevity and delaying the onset of age-related diseases. This diet consists of a reduction in caloric intake while maintaining essential energy and nutritional requirements to achieve optimal health while avoiding malnutrition. However, the effects of this nutritional regimen on male reproductive health have not yet been comprehensively studied. Nevertheless, such a complex process will certainly be regulated by a variety of metabolic sensors, likely sirtuins. Evidence has been gathered regarding this group of enzymes, and their ability to regulate processes such as chromatin condensation, the cell cycle, insulin signaling, and glucose and lipid metabolism, among many others. Concerning testicular function and male fertility, sirtuins can modulate certain metabolic processes through their interaction with the hypothalamic-pituitary-gonadal axis and mitochondrial dynamics, among many others, which remain largely unexplored. This review explores the impact of caloric restriction on male fertility, highlighting the emerging role of sirtuins as key regulators of male reproductive health through their influence on cellular metabolism.

Role of SIRT3 in the regulation of Gadd45α expression and DNA repair in β-cells

In previous studies, we have shown that growth arrest and DNA damage (Gadd) 45α is required for the repair of nitric oxide-mediated DNA damage in β-cells. Gadd45α expression is stimulated by nitric oxide and requires forkhead box protein (Fox) O1 and NAD+-dependent deacetylase activity. Based on inhibitor studies, we attributed this activity to Sirtuin (SIRT)1; however, the inhibitors used in this previous study also attenuate the deacetylase activity of SIRT2, 3, and 6. We now provide experimental evidence that SIRT1 is dispensable for β-cell expression of Gadd45α and that the mitochondrial localized isoform SIRT3, is required for DNA repair in β-cells. We show that siRNA knockdown of Sirt3 attenuates nitric oxide-stimulated Gadd45α mRNA accumulation in both wildtype and Sirt1-/- INS 832/13 cells as well as isolated rat islets and that SIRT3 inhibition increases FoxO1 acetylation and attenuates DNA repair in response to nitric oxide. While SIRT3 is predominantly localized to mitochondria, a small fraction is localized in the nucleus of insulin-containing cells and functions to participate in the regulation of FoxO1-dependent, nitric oxide-stimulated DNA repair.

SIRT5: a potential target for discovering bioactive natural products

Silent information regulator 5 (SIRT5) is the fifth member of the sirtuin family, which is mainly expressed in mitochondrial matrix. SIRT5 plays a key role in metabolism and antioxidant responses, and is an important regulator for maintaining intracellular homeostasis. Given its involvement in multiple cellular processes, dysregulation of SIRT5 activity is associated with a variety of diseases. This review explores the structural characteristics of SIRT5 that influence its substrate specificity, highlights recent research advances, and summarizes its four key enzymatic activities along with their corresponding substrates in disease contexts. We also discuss the natural products that modulate SIRT5 activity and identify potential targets of SIRT5 through virtual docking, which may provide new therapeutic avenues. Although the mechanism of SIRT5 in diseases needs to be further elucidated and deglutathionylation activities are still at an early stage, targeting SIRT5 and its substrates holds significant promise for the development of novel therapeutics.

DNA stimulates the deacetylase SIRT6 to mono-ADP-ribosylate proteins with histidine repeats

Sirtuins are the NAD+-dependent class III lysine deacylases (KDACs). Members of this family have been linked to longevity and a wide array of different diseases, motivating the pursuit of sirtuin modulator compounds. Sirtuin 6 (SIRT6) is a primarily nuclear KDAC that deacetylates histones to facilitate gene repression. In addition to this canonical post-translational modification (PTM) "eraser" function, SIRT6 can use NAD+ instead to "write" mono-ADP-ribosylation (mARylation) on target proteins. This enzymatic function has been primarily associated with SIRT6's role in the DNA damage response. This modification has been challenging to study because it is not clear under what precise cellular contexts it occurs, only a few substrates are known, and potential interference from other ADP-ribosyltransferases in cells, among other reasons. In this work, we used commercially available ADP-ribosylation detection reagents to investigate the mARylation activity of SIRT6 in a reconstituted system. We observed that SIRT6 is activated in its mARylation activity by binding to dsDNA ends. We further identified a surprising target motif within biochemical substrates of SIRT6, polyhistidine (polyHis) repeat tracts, that are present in several previously identified SIRT6 mARylation substrates. This work provides important context for SIRT6 mARylation activity, in contrast to its KDAC activity, and generates a list of new potential SIRT6 mARylation substrates based on the polyHis motif..

Mechanisms of HDACs in cancer development

Histone deacetylases (HDACs) are a class of epigenetic regulators that play pivotal roles in key biological processes such as cell proliferation, differentiation, metabolism, and immune regulation. Based on this, HDAC inhibitors (HDACis), as novel epigenetic-targeted therapeutic agents, have demonstrated significant antitumor potential by inducing cell cycle arrest, activating apoptosis, and modulating the immune microenvironment. Current research is focused on developing highly selective HDAC isoform inhibitors and combination therapy strategies tailored to molecular subtypes, aiming to overcome off-target effects and resistance issues associated with traditional broad-spectrum inhibitors. This review systematically elaborates on the multidimensional regulatory networks of HDACs in tumor malignancy and assesses the clinical translation progress of next-generation HDACis and their prospects in precision medicine, providing a theoretical framework and strategic reference for the development of epigenetic-targeted antitumor drugs.

PARP1: A comprehensive review of its mechanisms, therapeutic implications and emerging cancer treatments

The Poly (ADP-ribose) polymerase-1 (PARP1) enzyme is involved in several signalling pathways related to homologous repair (HR), base excision repair (BER), and non-homologous end joining (NHEJ). Studies demonstrated that the deregulation of PARP1 function and control mechanisms can lead to cancer emergence. On the other side, PARP1 can be a therapeutic target to maximize cancer treatment. This is done by molecules that can modulate radiation effects, such as DNA repair inhibitors (PARPi). With this approach, tumour cell viability can be undermined by targeting DNA repair mechanisms. Thus, treatment using PARPi represents a new era for cancer therapy, and even new horizons can be attained by coupling these molecules with a nano-delivery system. For this, drug delivery systems such as liposomes encompass all the required features due to its excellent biocompatibility, biodegradability, and low toxicity. This review presents a comprehensive overview of PARP1 biological features and mechanisms, its role in cancer development, therapeutic implications, and emerging cancer treatments by PARPi-mediated therapies. Although there are a vast number of studies regarding PARP1 biological function, some PARP1 mechanisms are not clear yet, and full-length PARP1 structure is missing. Nevertheless, literature reports demonstrate already the high usefulness and vast possibilities offered by combined PARPi cancer therapy.

Role of SIRT7 in Prostate Cancer Progression: New Insight Into Potential Therapeutic Target

Prostate cancer (PCa) is the second most common cancer in men worldwide, and understanding its molecular mechanisms is crucial for developing effective treatment strategies. SIRT7, a NAD+-dependent histone deacetylase, has emerged as a key regulator in PCa progression due to its roles in chromatin remodeling, DNA repair, and transcriptional regulation. Analysis of 492 PCa samples from The Cancer Genome Atlas (TCGA) via cBioPortal revealed that high SIRT7 expression is associated with poor prognosis in PCa patients. Mechanistically, SIRT7 deacetylates histone H3 at lysine 18 (H3K18Ac), a marker associated with aggressive tumors, suppressing tumor suppressor genes and promoting cancer cell proliferation and survival. Epithelial-mesenchymal transition (EMT) is a cellular biological process in which epithelial cells undergo specific molecular and morphological changes to transform into cells with characteristics of mesenchymal cells. SIRT7 also regulates EMT, and inhibiting SIRT7 in PCa cell lines reduces cell migration and invasion, highlighting its potential as a therapeutic target. In summary, the clinical significance of SIRT7 expression in PCa requires further research to elucidate its mechanisms. Developing specific inhibitors targeting SIRT7's deacetylase activity is a promising therapeutic strategy. SIRT7 plays a crucial role in regulating biological processes such as cell proliferation, cell cycle, and apoptosis in PCa through its epigenetic control of gene expression and maintenance of genomic stability. Therefore, SIRT7 may be a potential therapeutic target for PCa, and its expression could have prognostic value for PCa patients, providing important guidance for clinical monitoring and diagnosis by physicians.

SIRT6 mitigates oxidative stress and RSL3-induced ferroptosis in HTR-8/SVneo cells

Dysregulation in placental trophoblast cells frequently results in oxidative stress, culminating in pregnancy-related complications. While iron is essential for fetal development, cellular ferroptosis due to elevated iron levels might mediate the emergence of preeclampsia (PE), presenting significant risks during gestation. We found abnormally activated oxidative stress and increased iron concentration in the placental tissues of PE patients. Subsequently, we treated placental trophoblasts with hydrogen peroxide and RSL3 to induce oxidative stress and ferroptosis models. The results revealed that SIRT6 overexpression activates the Nrf2/HO-1 pathway, restores the oxidative imbalance of the cells, and protects the cells from ferroptosis. Meanwhile, activation of the Nrf2/HO-1 pathway alone showed similar results. Thus, we posit that SIRT6, via the Nrf2/HO-1 pathway, alleviates cellular oxidative stress and diminishes ferroptosis, offering a novel therapeutic avenue for PE.

Histone acetylation modulators in breast cancer

Breast cancer is the most prevalent cancer in women worldwide. Aberrant epigenetic reprogramming such as dysregulation of histone acetylation has been associated with the development of breast cancer. Histone acetylation modulators have been targeted as potential treatments for breast cancer. This review comprehensively discusses the roles of these modulators and the effects of their inhibitors on breast cancer. In addition, epigenetic reprogramming not only affects breast cancer cells but also the immunosuppressive myeloid cells, which can facilitate breast cancer progression. Therefore, the review also highlights the roles of these immunosuppressive myeloid cells and summarizes how histone acetylation modulators affect their functions and phenotypes. This review provides insights into histone acetylation modulators as potential therapeutic targets for breast cancer.

FTO suppresses DNA repair by inhibiting PARP1

Maintaining genomic integrity and faithful transmission of genetic information is essential for the survival and proliferation of cells and organisms. DNA damage, which threatens the integrity of the genome, is rapidly sensed and repaired by mechanisms collectively known as the DNA damage response. The RNA demethylase FTO has been implicated in this process; however, the underlying mechanism by which FTO regulates DNA repair remains unclear. Here, we use an unbiased quantitative proteomic approach to identify the proximal interactome of endogenous FTO protein. Our results demonstrate a direct interaction with the DNA damage sensor protein PARP1, which dissociates upon ultraviolet stimulation. FTO inhibits PARP1 catalytic activity and controls its clustering in the nucleolus. Loss of FTO enhances PARP1 enzymatic activity and the rate of PARP1 recruitment to DNA damage sites, accelerating DNA repair and promoting cell survival. Interestingly, FTO regulates PARP1 function and DNA damage response independent of its catalytic activity. We conclude that FTO is an endogenous negative regulator of PARP1 and the DNA damage response in cells beyond its role as an RNA demethylase.

Targeting NAT10 attenuates homologous recombination via destabilizing DNA:RNA hybrids and overcomes PARP inhibitor resistance in cancers

AIMS

RNA metabolism has been extensively studied in DNA double-strand break (DSB) repair. The RNA acetyltransferase N-acetyltransferase 10 (NAT10)-mediated N4-acetylcytidine (ac4C) modification in DSB repair remains largely elusive. In this study, we aim to decipher the role for ac4C modification by NAT10 in DSB repair in hepatocellular carcinoma (HCC).

METHODS

Laser micro-irradiation and chromatin immunoprecipitation (ChIP) were used to assess the accumulation of ac4C modification and NAT10 at DSB sites. Cryo-electron microscopy (cryo-EM) was used to determine the structures of NAT10 in complex with its inhibitor, remodelin. Hepatocyte-specific deletion of NAT10 mouse models were adopted to detect the effects of NAT10 on HCC progression. Subcutaneous xenograft, human HCC organoid and patient-derived xenograft (PDX) model were exploited to determine the therapy efficiency of the combination of a poly (ADP-ribose) polymerase 1 (PARP1) inhibitor (PARPi) and remodelin.

RESULTS

NAT10 promptly accumulates at DSB sites, where it executes ac4C modification on RNAs at DNA:RNA hybrids dependent on PARP1. This in turn enhances the stability of DNA:RNA hybrids and promotes homologous recombination (HR) repair. The ablation of NAT10 curtails HCC progression. Furthermore, the cryo-EM yields a remarkable 2.9 angstroms resolution structure of NAT10-remodelin, showcasing a C2 symmetric architecture. Remodelin treatment significantly enhanced the sensitivity of HCC cells to a PARPi and targeting NAT10 also restored sensitivity to a PARPi in ovarian and breast cancer cells that had developed resistance.

CONCLUSION

Our study elucidated the mechanism of NAT10-mediated ac4C modification in DSB repair, revealing that targeting NAT10 confers synthetic lethality to PARP inhibition in HCC. Our findings suggest that co-inhibition of NAT10 and PARP1 is an effective novel therapeutic strategy for patients with HCC and have the potential to overcome PARPi resistance.

Chlorogenic acid targets SIRT6 to relieve UVB - induced UV damage

Skin photoaging, one of the most critical types of exogenous skin aging, occurs when the skin is exposed to excessive ultraviolet radiation, leading to a series of skin-aging problems. The objective of this study was to utilize keratinocytes (HaCaT) treated with medium wave ultraviolet (UVB) as a photoaging model to investigate the anti-photoaging activity of chlorogenic acid (CGA) and preliminarily elucidate its underlying mechanism. The crystal violet assay shows that both 100 and 150 µM of CGA can significantly suppress the cell damage induced by 21.6 mJ/cm² UVB. Furthermore, the results of comet electrophoresis and Western Blot (WB) experiments demonstrate that CGA and OSS-128,167 (SIRT6 inhibitor) can effectively inhibit DNA damage caused by UVB, thereby alleviating cell apoptosis. The co-immunoprecipitation (CO-IP) and WB results suggest that CGA and OSS-128,167 can effectively suppress the activity and expression of the deacetylase of SIRT6, thus enhancing the expression of DDB2 and activating the nucleotide excision repair (NER) of cells to achieve the anti-photoaging effect. The aforementioned results imply that CGA activates NER repair and protects cells from UVB-induced damage by inhibiting the deacetylation activity of SIRT6 and subsequently decreasing the deacetylation modification of DDB2. The study elucidates the molecular mechanisms underlying the beneficial effects of CGA on skin photoaging and establishes a theoretical basis for the development of CGA based sunscreen formulations.

Myeloid sirtuin 6 deficiency causes obesity in mice by inducing norepinephrine degradation to limit thermogenic tissue function

Brown and beige adipocytes dissipate energy to generate heat through uncoupled respiration, and the hormone norepinephrine plays an important role in stimulating brown fat thermogenesis and beige adipocyte development in white adipose depots. Increasing energy expenditure by promoting the function and development of brown and beige fat is a potential approach to treat obesity and diabetes. Here, we investigated the effects of macrophage sirtuin 6 (SIRT6) on the regulation of the norepinephrine content of brown adipose tissue (BAT) and on obesity in mice. Myeloid SIRT6 deficiency impaired the thermogenic function of BAT, thereby decreasing core body temperatures because of reduced norepinephrine concentrations in BAT and subsequently leading to cold sensitivity. In addition, the oxygen consumption rate was reduced, resulting in severe insulin resistance and obesity. Furthermore, macrophage SIRT6 deficiency inhibited BAT thermogenesis after cold exposure or norepinephrine treatment and cold exposure-induced increases in markers of lipid metabolism and thermogenesis in white adipose tissue. Myeloid-specific SIRT6 deficiency promoted H3K9 acetylation in the promoter regions and the expression of genes encoding the norepinephrine-degrading enzyme MAOA and the norepinephrine transporter SLC6A2 in macrophages in BAT, leading to norepinephrine degradation and obesity. Our findings indicate that SIRT6 in macrophages is essential for maintaining norepinephrine concentrations in BAT in mice.

p53 enhances DNA repair and suppresses cytoplasmic chromatin fragments and inflammation in senescent cells

Genomic instability and inflammation are distinct hallmarks of aging, but the connection between them is poorly understood. Here we report a mechanism directly linking genomic instability and inflammation in senescent cells through a mitochondria-regulated molecular circuit involving p53 and cytoplasmic chromatin fragments (CCF) that are enriched for DNA damage signaling marker γH2A.X. We show that p53 suppresses CCF accumulation and its downstream inflammatory phenotype. p53 activation suppresses CCF formation linked to enhanced DNA repair and genome integrity. Activation of p53 in aged mice by pharmacological inhibition of MDM2 reverses transcriptomic signatures of aging and age-associated accumulation of monocytes and macrophages in liver. Mitochondrial ablation in senescent cells suppresses CCF formation and activates p53 in an ATM-dependent manner, suggesting that mitochondria-dependent formation of γH2A.X + CCF dampens nuclear DNA damage signaling and p53 activity. These data provide evidence for a mitochondria-regulated p53 signaling circuit in senescent cells that controls DNA repair, genome integrity, and senescence- and age-associated inflammation, with relevance to therapeutic targeting of age-associated disease.

hnRNPA2B1 deacetylation by SIRT6 restrains local transcription and safeguards genome stability

Repair of double strand breaks (DSBs) by RNA-binding proteins (RBPs) is vital for ensuring genome integrity. DSB repair is accompanied by local transcriptional repression in the vicinity of transcriptionally active genes, but the mechanism by which RBPs regulate transcriptional regulation is unclear. Here, we demonstrated that RBP hnRNPA2B1 functions as a RNA polymerase-associated factor that stabilizes the transcription complex under physiological conditions. Following a DSB, hnRNPA2B1 is released from damaged chromatin, reducing the efficiency of RNAPII complex assembly, leading to local transcriptional repression. Mechanistically, SIRT6 deacetylates hnRNPA2B1 at K113/173 residues, enforcing its rapid detachment from DSBs. This process disrupts the integrity of the RNAPII complex on active chromatin, which is a pre-requisite for transient but complete repression of local transcription. Functionally, the overexpression of an acetylation mimic stabilizes the transcription complex and facilitates the functioning of the transcription machinery. hnRNPA2B1 acetylation status was negatively correlated with SIRT6 expression, and acetylation mimic enhanced radio-sensitivity in vivo. Our findings demonstrate that hnRNPA2B1 is crucial for transcriptional repression. We have uncovered the missing link between DSB repair and transcriptional regulation in genome stability maintenance, highlighting the potential of hnRNPA2B1 as a therapeutic target.

GCIP and SIRT6 cooperatively suppress ITGAV gene expression by modulating c-myc transcription ability

Grap2 and CyclinD1 interacting protein (GCIP) has been suggested to function as a tumor suppressor and acts as a transcriptional regulator that negatively controls cancer cell growth, invasion, and migration. Knockdown of GCIP reportedly enhances cancer cell migration and invasion, but no previous study has examined the mechanism(s) by which GCIP suppresses migration/invasion in cancer cells. Here, we report that cDNA microarray-based expression profiling of A549 cells without and with knockdown of GCIP reveals that the expression levels of ITGAV and ICAM-1 are negatively regulated by GCIP. In vitro co-immunoprecipitation and in vivo proximity ligation assays reveal that GCIP interacts with c-Myc. Sequence analyses reveal the presence of two c-Myc regulatory motifs (E-boxes) within the ITGAV promoter. Luciferase reporter and ChIP assays indicate that GCIP represses ITGAV transcription by interacting with c-Myc on the E-box binding sites of the ITGAV promoter region. Furthermore, GCIP interacts with SIRT6 in vitro and in vivo and cooperates with SIRT6, thereby linking its activity, to negatively regulate transcription at the E-box by modulating c-Myc transcription ability. Taken together, these findings contribute to our understanding of GCIP in tumorigenesis and identify a previously unrecognized function of GCIP: It can interact with c-Myc and SIRT6 at E-box binding sites of the ITGAV promoter region. Our data collectively reveal a regulatory network involving GCIP, SIRT6, c-Myc, and ITGAV, and suggest that the SIRT6-GCIP complex negatively regulates the oncogenic function of c-Myc in cell proliferation and migration.

Molecular dynamics simulation on the role of CL5D in accelerating the product dissociation of SIRT6

SIRT6 is a member of the NAD+-dependent histone deacetylase family and is integral to maintaining genome stability and regulating metabolic transcription. SIRT6 transfers acetyl groups from the lysine side chains of protein substrates to the cofactor NAD+, generating nicotinamide, 2'-O-acyl-ADP-ribose (ADPr), and a deacetylated substrate. SIRT6 has been found to be activated by small molecule activators, such as CL5D. However, the process of dissociation of the SIRT6 product and the mechanism of activation by small molecule activators are unknown. In this work, we elucidated these activation mechanisms by performing extensive molecular dynamics simulations. The results of random acceleration molecular dynamics and umbrella sampling demonstrated that the dissociation sequence involves the exit of the deacetylated substrate first, followed by ADPr. The binding of CL5D does not alter the dissociation pathway of the products, but it increases the catalytic activity of SIRT6 by facilitating the dissociation of products within SIRT6. Our results suggest a mechanism of SIRT6 activation, which highlights the importance of product dissociation in enzyme catalysis. This result may help facilitate the development of new SIRT6 activators.

Suppressing SENP1 inhibits esophageal squamous carcinoma cell growth via SIRT6 SUMOylation

PURPOSE

Esophageal squamous cell carcinoma (ESCC) is a prevalent tumor in the gastrointestinal tract, but our understanding of the molecular mechanisms underlying ESCC remains incomplete. Existing studies indicate that SUMO specific peptidase 1 (SENP1) plays a crucial role in the development and progression of various malignant tumors through diverse molecular mechanisms. However, the functional mechanism and clinical implications of SENP1 in the progression of ESCC remain unclear.

METHODS

Bulk RNA-Sequencing (RNA-seq) was used to compare potential genes in the esophageal tissues of mice with ESCC to the control group. The up-regulated SENP1 was selected. The protein level of SENP1 in ESCC patient samples was analyzed by immunohistochemistry and western blot. The potential prognostic value of SENP1 on overall survival of ESCC patients was examined using tissue microarray analysis and the Kaplan-Meier method. The biological function was confirmed through in vitro and in vivo knockdown approaches of SENP1. The role of SENP1 in cell cycle progression and apoptosis of ESCC cells was analyzed by flow cytometry and western blot. The downstream signaling pathways regulated by SENP1 were investigated via using RNA-Seq. SENP1-associated proteins were identified through immunoprecipitation. Overexpression of Sirtuin 6 (SIRT6) wildtype and mutant was performed to investigate the regulatory role of SENP1 in ESCC progression in vitro.

RESULTS

Our study discovered that SENP1 was upregulated in ESCC tissues and served as a novel prognostic factor. Moreover, SENP1 enhanced cell proliferation and migration of ESCC cell lines in vitro, as well as promoted tumor growth in vivo. Thymidine kinase 1 (TK1), Geminin (GMNN), cyclin dependent kinase 1(CDK1), and cyclin A2 (CCNA2) were identified as downstream genes of SENP1. Mechanistically, SENP1 deSUMOylated SIRT6 and subsequently inhibited SIRT6-mediated histone 3 lysine 56 (H3K56) deacetylation on those downstream genes. SIRT6 SUMOylation mutant (4KR) rescued the growth inhibition upon SENP1 depletion.

CONCLUSIONS

SENP1 promotes the malignant progression of ESCC by inhibiting the deacetylase activity of SIRT6 pathway through deSUMOylation. Our findings suggest that SENP1 may serve as a valuable biomarker for prognosis and a target for therapeutic intervention in ESCC.

The Chemopreventive Effect of Ginsenoside Compound K Is Regulated by PARP-1 Hyperactivation, Which Is Promoted by p62-Dependent SIRT6 Degradation

BACKGROUND AND AIMS

Ginsenoside compound K (CK), a saponin metabolite of ginseng, exerts anticancer effects; however, its molecular mechanisms of action in lung cancer remain unclear. We investigated the involvement of silent information regulator 6 (SIRT6) and poly (ADP-ribose) polymerase 1 (PARP-1) in the anticancer effects of CK in lung cancer.

METHODS AND RESULTS

CK induced PARP-1 activation-mediated parthanatos via sequestosome-1/p62-mediated SIRT6 degradation and inhibited the proliferation of H460 cells. Although CK reduced procaspase-8 levels, no significant apoptotic cleavage of procaspase-3 or PARP-1 was observed. Furthermore, CK upregulated p27, p21, phospho-p53, and gamma-H2AX levels. CK increased LC3-II levels in a p62-independent manner, but p62 was upregulated by autophagy inhibition, indicating that p62 is involved in CK-induced autophagy. CK-treated cells showed typical features of parthanatos, including PARP-1 hyperactivation, intracellular redistribution of poly ADP-ribose and pro-apoptotic factors, and chromatin fragmentation. SIRT6 was degraded in a CK concentration- and time-dependent manner. SIRT6 protein was upregulated by PARP-1 inhibition, nicotinamide adenine dinucleotide (NAD)+ supplementation, antioxidants, and p62 knockdown, but was decreased by autophagy blockade. PARP-1 activation was negatively correlated with SIRT6 levels, indicating that SIRT6 and PARP-1 activation play complementary roles in CK-induced growth inhibition. Immunofluorescence staining, fractionation studies, and immunoprecipitation were used to confirm the colocalization and interaction between p62 and SIRT6.

CONCLUSIONS

PARP-1 activation is promoted by p62-mediated SIRT6 degradation, which plays an important role in CK-induced growth inhibition. Therefore, SIRT6 is a potential biomarker for the chemopreventive effect of CK in lung cancer cells, but further studies on SIRT6 are needed for the clinical application of CK.

The age-related decline of helicase function-how G-quadruplex structures promote genome instability

The intricate mechanisms underlying transcription-dependent genome instability involve G-quadruplexes (G4) and R-loops. This perspective elucidates the potential link between these structures and genome instability in aging. The co-occurrence of G4 DNA and RNA-DNA hybrid structures (G-loop) underscores a complex interplay in genome regulation and instability. Here, we hypothesize that the age-related decline of sirtuin function leads to an increase in acetylated helicases that bind to G4 DNA and RNA-DNA hybrid structures, but are less efficient in resolving them. We propose that acetylated, less active, helicases induce persistent G-loop structures, promoting transcription-dependent genome instability in aging.

The SIRT6/BAP1/xCT signaling axis mediates ferroptosis in cisplatin-induced AKI

BACKGROUND

Cisplatin is extensively utilized in clinical settings for treating solid tumors; However, its use is restricted because of the kidney damage caused by side effects. Moreover, currently, no effective medications have been approved to prevent or treat acute kidney injury induced by cisplatin. Our research indicates that sirtuin 6 (SIRT6) can inhibit ferroptosis induced by cisplatin, and the use of SIRT6 agonists can alleviate acute kidney injury caused by cisplatin.

METHODS

An animal model of cisplatin-induced acute kidney injury (AKI) was established, followed by RNA sequencing to identify potential differentially expressed genes (DEGs) and associated pathways. To explore the role of SIRT6 in this model, SIRT6 knockout mice were generated, and recombinant adeno-associated virus was employed to achieve SIRT6 overexpression in the mice. In vitro, cells were cultured in a cisplatin-containing medium to establish a cisplatin-induced cell model. The function of SIRT6 was further investigated by overexpressing or knocking down the gene using lentiviral plasmids. To elucidate the underlying molecular mechanisms, we employed RNA sequencing, performed bioinformatics analyses, and conducted chromatin immunoprecipitation assays.

RESULTS

RNA sequencing and Western blot analyses revealed a significant reduction in SIRT6 expression in mice with cisplatin-induced acute kidney injury (AKI). Enhancing SIRT6 expression improved renal function, reduced ferroptosis, and mitigated kidney damage, whereas SIRT6 knockout exacerbated kidney injury and heightened ferroptosis. Mechanistically, RNA sequencing, bioinformatics analysis, and chromatin immunoprecipitation assays demonstrated that SIRT6 inhibits ferroptosis by reducing the acetylation of histone H4K9ac at the BAP1 promoter. Furthermore, in vitro studies demonstrated that the SIRT6 agonist UBCS039 can alleviate cisplatin-induced acute kidney injury, highlighting its potential therapeutic role in mitigating cisplatin's damaging effects. However, further research is needed to fully elucidate the underlying mechanisms and to validate these findings in vivo.

CONCLUSION

Our findings underscore the critical role of the SIRT6/BAP1/xCT axis in regulating ferroptosis, particularly via the downregulation of SIRT6, in the context of cisplatin-induced acute kidney injury (AKI). This suggests that SIRT6 could be a promising therapeutic target for treating cisplatin-induced AKI. However, additional research is required to explore the specific mechanisms and fully assess the therapeutic potential of SIRT6 in this context.

Structure-Guided Discovery of Subtype Selective SIRT6 Inhibitors with a β-Carboline Skeleton for the Treatment of Breast Cancer

SIRT6 promotes the progression of breast cancer by inducing drug resistance by reinforcing DNA damage repair mechanisms. This study utilized a combination of high-throughput virtual screening and FLUOR DE LYS assays. Hit 14 which features a novel β-carboline skeleton as a potent SIRT6 inhibitor was found. Subsequent structure-guided optimization led to the synthesis of 60 3,6,9-position modified derivatives based on the differences analysis of SIRTs family proteins. Of which, 10d inhibited the deacetylase activity of SIRT6, with an IC50 of 5.81 μM and more than 27 times subtype selectivity. Phe64, Met157, and Ser56 were identified as the key residues. Moreover, 10d suppressed breast cancer cell proliferation, migration, invasion, and induced apoptosis in MCF-7 cells by disrupting the DNA damage repair pathway. Additionally, 10d demonstrated a safe and effective antibreast cancer effect in vivo, presenting a promising strategy for the treatment of breast cancer by targeting SIRT6.

Quercetin and Mesenchymal Stem Cell Metabolism: A Comparative Analysis of Young and Senescent States

Quercetin is a natural flavonoid renowned for its potent antioxidant, anti-inflammatory, anti-diabetic, and antibacterial properties, making it a highly promising candidate for the treatment of various medical conditions. Our current study investigates the influence of quercetin on energy metabolism, fatty acid composition, oxidative stress gene expression, and sirtuin expression in early- and late-stage passages of stem cells derived from human exfoliated deciduous teeth (SHEDs). Mitochondrial respiration was analyzed by measuring oxygen consumption following a 24 h quercetin treatment, while fatty acid profiles were examined using gas chromatography-mass spectrometry (GC-MS). Additionally, quantitative PCR (qPCR) was used to assess the expression of oxidative stress genes and sirtuins. In younger SHEDs, quercetin enhances metabolic activity and mitochondrial respiration, although higher doses may decrease mitochondrial activity. Conversely, in older, senescent SHEDs, quercetin supports mitochondrial function at lower concentrations but appears to inhibit respiration at higher doses. These results suggest that quercetin may hold therapeutic potential for maintaining SHED viability and function, especially at lower doses in older cells. Further research is essential to fully elucidate a dose-dependent effect of quercetin and optimize its applications in regenerative medicine.

HMGB1 promotes chemoresistance in small cell lung cancer by inducing PARP1-related nucleophagy

INTRODUCTION

Small cell lung cancer (SCLC) is prone to chemoresistance, which is closely related to genome homeostasis-related processes, such as DNA damage and repair. Nucleophagy is the elimination of specific nuclear substances by cells themselves and is responsible for maintaining genome and chromosome stability. However, the roles of nucleophagy in tumour chemoresistance have not been investigated.

OBJECTIVES

The aim of this work was to elucidate the mechanism of chemoresistance in SCLC and reverse this chemoresistance.

METHODS

RNA-seq data from SCLC cohorts, chemosensitive SCLC cells and the corresponding chemoresistant cells were used to discover genes associated with chemoresistance and patient prognosis. In vitro and in vivo experiments were performed to verify the effect of high-mobility group box 1 (HMGB1) knockdown or overexpression on the chemotherapeutic response in SCLC. The regulatory effect of HMGB1 on nucleophagy was then investigated by coimmunoprecipitation (co-IP) and mass spectrometry (MS), and the underlying mechanism was explored using pharmacological inhibitors and mutant proteins.

RESULTS

HMGB1 is a factor indicating poor prognosis and promotes chemoresistance in SCLC. Mechanistically, HMGB1 significantly increases PARP1-LC3 binding to promote nucleophagy via PARP1 PARylation, which leads to PARP1 turnover from DNA lesions and chemoresistance. Furthermore, chemoresistance in SCLC can be attenuated by blockade of the PARP1-LC3 interaction or PARP1 inhibitor (PARPi) treatment.

CONCLUSIONS

HMGB1 can induce PARP1 self-modification, which promotes the interaction of PARP1 with LC3 to promote nucleophagy and thus chemoresistance in SCLC. HMGB1 could be a predictive biomarker for the PARPi response in patients with SCLC. Combining chemotherapy with PARPi treatment is an effective therapeutic strategy for overcoming SCLC chemoresistance.

The nitration of SIRT6 aggravates neuronal damage during cerebral ischemia-reperfusion in rat

Ischemic stroke is a major cause of death and disability. The activation of neuronal nitric oxide synthase (nNOS) and the resulting production of nitric oxide (NO) via NMDA receptor-mediated calcium influx play an exacerbating role in cerebral ischemia reperfusion injury. The NO rapidly reacts with superoxide (O2-) to form peroxynitrite (ONOO-), a toxic molecule may modify proteins through tyrosine residue nitration, ultimately worsening neuronal damage. SIRT6 has been proven to be crucial in regulating cell proliferation, death, and aging in various pathological settings. We have previous reported that human SIRT6 tyrosine nitration decreased its intrinsic catalytic activity in vitro. However, the exact role of SIRT6 function in the process of cerebral ischemia reperfusion injury is not yet fully elucidated. Herein, we demonstrated that an increase in the nitration of SIRT6 led to reduce its enzymatic activity and aggravated hippocampal neuronal damage in a rat model of four-artery cerebral ischemia reperfusion. In addition, reducing SIRT6 nitration resulted in increase the activity of SIRT6, alleviating hippocampal neuronal damage. Moreover, SIRT6 nitration affected its downstream molecule activity such as PARP1 and GCN5, promoting the process of neuronal ischemic injury in rat hippocampus. Additionally, treatment with NMDA receptor antagonist MK801, or nNOS inhibitor 7-NI, and resveratrol (an antioxidant) diminished SIRT6 nitration and the catalytic activity of downstream molecules like PARP1 and GCN5, thereby reducing neuronal damage. Finally, in the biochemical regulation of SIRT6 activity, tyrosine 257 was essential for its activity and susceptibility to nitration. Replacing tyrosine 257 with phenylalanine in rat SIRT6 attenuated the death of SH-SY5Y neurocytes under oxygen-glucose deprivation (OGD) conditions. These results may offer further understanding of SIRT6 function in the pathogenesis of cerebral ischemic diseases.

Roles of chromatin and genome instability in cellular senescence and their relevance to ageing and related diseases

Ageing is a complex biological process in which a gradual decline in physiological fitness increases susceptibility to diseases such as neurodegenerative disorders and cancer. Cellular senescence, a state of irreversible cell-growth arrest accompanied by functional deterioration, has emerged as a pivotal driver of ageing. In this Review, we discuss how heterochromatin loss, telomere attrition and DNA damage contribute to cellular senescence, ageing and age-related diseases by eliciting genome instability, innate immunity and inflammation. We also discuss how emerging therapeutic strategies could restore heterochromatin stability, maintain telomere integrity and boost the DNA repair capacity, and thus counteract cellular senescence and ageing-associated pathologies. Finally, we outline current research challenges and future directions aimed at better comprehending and delaying ageing.

Autoimmune disease: a view of epigenetics and therapeutic targeting

Autoimmune diseases comprise a large group of conditions characterized by a complex pathogenesis and significant heterogeneity in their clinical manifestations. Advances in sequencing technology have revealed that in addition to genetic susceptibility, various epigenetic mechanisms including DNA methylation and histone modification play critical roles in disease development. The emerging field of epigenetics has provided new perspectives on the pathogenesis and development of autoimmune diseases. Aberrant epigenetic modifications can be used as biomarkers for disease diagnosis and prognosis. Exploration of human epigenetic profiles revealed that patients with autoimmune diseases exhibit markedly altered DNA methylation profiles compared with healthy individuals. Targeted cutting-edge epigenetic therapies are emerging. For example, DNA methylation inhibitors can rectify methylation dysregulation and relieve patients. Histone deacetylase inhibitors such as vorinostat can affect chromatin accessibility and further regulate gene expression, and have been used in treating hematological malignancies. Epigenetic therapies have opened new avenues for the precise treatment of autoimmune diseases and offer new opportunities for improved therapeutic outcomes. Our review can aid in comprehensively elucidation of the mechanisms of autoimmune diseases and development of new targeted therapies that ultimately benefit patients with these conditions.

DNA repair and anti-cancer mechanisms in the long-lived bowhead whale

At over 200 years, the maximum lifespan of the bowhead whale exceeds that of all other mammals. The bowhead is also the second-largest animal on Earth, reaching over 80,000 kg1. Despite its very large number of cells and long lifespan, the bowhead is not highly cancer-prone, an incongruity termed Peto's Paradox2. This phenomenon has been explained by the evolution of additional tumor suppressor genes in other larger animals, supported by research on elephants demonstrating expansion of the p53 gene3-5. Here we show that bowhead whale fibroblasts undergo oncogenic transformation after disruption of fewer tumor suppressors than required for human fibroblasts. However, analysis of DNA repair revealed that bowhead cells repair double strand breaks (DSBs) and mismatches with uniquely high efficiency and accuracy compared to other mammals. The protein CIRBP, implicated in protection from genotoxic stress, was present in very high abundance in the bowhead whale relative to other mammals. We show that CIRBP and its downstream protein RPA2, also present at high levels in bowhead cells, increase the efficiency and fidelity of DNA repair in human cells. These results indicate that rather than possessing additional tumor suppressor genes as barriers to oncogenesis, the bowhead whale relies on more accurate and efficient DNA repair to preserve genome integrity. This strategy which does not eliminate damaged cells but repairs them may be critical for the long and cancer-free lifespan of the bowhead whale.

Sirt6 Mono-ADP-Ribosylates YY1 to Promote Dystrophin Expression for Neuromuscular Transmission

The degeneration of the neuromuscular junction (NMJ) and the decline in motor function are common features of aging, but the underlying mechanisms have remained largely unclear. This study reveals that Sirt6 is reduced in aged mouse muscles. Ablation of Sirt6 in skeletal muscle causes a reduction of Dystrophin levels, resulting in premature NMJ degeneration, compromised neuromuscular transmission, and a deterioration in motor performance. Mechanistic studies show that Sirt6 negatively regulates the stability of the Dystrophin repressor YY1 (Yin Yang 1). Specifically, Sirt6 mono-ADP-ribosylates YY1, causing its disassociation from the Dystrophin promoter and allowing YY1 to bind to the SMURF2 E3 ligase, leading to its degradation. Importantly, supplementation with nicotinamide mononucleotide (NMN) enhances the mono-ADP-ribosylation of YY1 and effectively delays NMJ degeneration and the decline in motor function in elderly mice. These findings provide valuable insights into the intricate mechanisms underlying NMJ degeneration during aging. Targeting Sirt6 could be a potential therapeutic approach to mitigate the detrimental effects on NMJ degeneration and improve motor function in the elderly population.

On the interface of aging, cancer, and neurodegeneration with SIRT6 and L1 retrotransposon protein interaction network

Roles of the sirtuins in aging and longevity appear related to their evolutionarily conserved functions as retroviral-restriction factors. Retrotransposons also promote the aging process, which can be reversed by the inhibition of their activity. SIRT6 can functionally limit the mutation activity of LINE-1 (L1), a retrotransposon causing cancerogenesis-linked mutations accumulating during aging. Here, an overview of the molecular mechanisms of the controlling effects was created by the pathway enrichment and gene function prediction analysis of a protein interaction network of SIRT6 and L1 retrotransposon proteins L1 ORF1p, and L1 ORF2p. The L1-SIRT6 interaction network is enriched in pathways and nodes associated with RNA quality control, DNA damage response, tumor-related and retrotransposon activity-suppressing functions. The analysis also highlighted sumoylation, which controls protein-protein interactions, subcellular localization, and other post-translational modifications; DNA IR Damage and Cellular Response via ATR, and Hallmark Myc Targets V1, which scores are a measure of tumor aggressiveness. The protein node prioritization analysis emphasized the functions of tumor suppressors p53, PARP1, BRCA1, and BRCA2 having L1 retrotransposon limiting activity; tumor promoters EIF4A3, HNRNPA1, HNRNPH1, DDX5; and antiviral innate immunity regulators DDX39A and DDX23. The outline of the regulatory mechanisms involved in L1 retrotransposition with a focus on the prioritized nodes is here demonstrated in detail. Furthermore, a model establishing functional links between HIV infection, L1 retrotransposition, SIRT6, and cancer development is also presented. Finally, L1-SIRT6 subnetwork SIRT6-PARP1-BRCA1/BRCA2-TRIM28-PIN1-p53 was constructed, where all nodes possess L1 retrotransposon activity-limiting activity and together represent candidates for multitarget control.

Sirtuins and their influence on autophagy

Sirtuins and autophagy are well-characterized agents that can promote longevity and protect individual organisms from age-associated diseases like neurodegenerative disorders. In recent years, more and more data has been obtained that discerned potential overlaps and crosstalk between Sirtuin proteins and autophagic activity. This review aims to summarize the advances within the field for each individual Sirtuin in mammalian systems. In brief, most Sirtuins have been implicated in promoting autophagy, with Sirtuin 1 and Sirtuin 6 showing the highest immediate involvement, while Sirtuin 4 and Sirtuin 5 only demonstrate occasional influence. The way Sirtuins regulate autophagy, however, is very diverse, as they have been shown to regulate gene expression of autophagy-associated genes and posttranslational modifications of proteins, with consequences for the activity and cellular localization of these proteins. They have also been shown to determine specific proteins for autophagic degradation. Overall, much data has been accumulated over recent years, yet many open questions remain. Especially although the dynamic between Sirtuin proteins and the immediate regulation of autophagic players like Light Chain 3B has been confirmed, many of these proteins have various orthologues in mammalian systems, and research so far has not exceeded the bona fide components of autophagy.

Temporal regulation of acetylation status determines PARP1 role in DNA damage response and metabolic homeostasis

Poly(ADP-ribose) polymerase 1 (PARP1) is an abundant nuclear protein involved in DNA repair, chromatin structure, and transcription. However, the regulation of its different functions remains poorly understood. Here, we report the role of PARP1 acetylation status in modulating its DNA repair and transactivation functions. We demonstrate that histone deacetylase 5 (HDAC5) determines PARP1 acetylation at Lys498 and Lys521 sites. HDAC5-mediated deacetylation at Lys498 site regulates PARP1 DNA damage response and facilitates efficient recruitment of DNA repair factors at damaged sites, thereby promoting cell survival. Additionally, HDAC5-mediated deacetylation at Lys521 site promotes PARP1 coactivator function, resulting in induction of proliferative and metabolic genes in an activating transcription factor 4-dependent manner. Thus, PARP1 induces metabolic adaptation to spur malignant phenotype. Our studies in mouse tumor models suggest that pharmacological inhibition of PARP1 enzymatic activity does not block tumor progression robustly as transactivation function remains unperturbed. These findings provide key mechanistic insights into PARP1 regulation and expand its role in tumor development.

Discovery of Novel PROTAC SIRT6 Degraders with Potent Efficacy against Hepatocellular Carcinoma

Sirtuin 6 (SIRT6), a member of the SIRT family, plays essential roles in the regulation of metabolism, inflammation, aging, DNA repair, and cancer development, making it a promising anticancer drug target. Herein, we present our use of proteolysis-targeting chimera (PROTAC) technology to formulate a series of highly potent and selective SIRT6 degraders. One of the degraders, SZU-B6, induced the near-complete degradation of SIRT6 in both SK-HEP-1 and Huh-7 cell lines and more potently inhibited hepatocellular carcinoma (HCC) cell proliferation than the parental inhibitors. In preliminary mechanistic studies, SZU-B6 hampered DNA damage repair, promoting the cellular radiosensitization of cancer cells. Our SIRT6 degrader SZU-B6 displayed promising antitumor activity, particularly when combined with the well-known kinase inhibitor sorafenib or irradiation in an SK-HEP-1 xenograft mouse model. Our results suggest that these PROTACs might constitute a potent therapeutic strategy for HCC.

PARticular MARks: Histone ADP-ribosylation and the DNA damage response

Cellular and molecular responses to DNA damage are highly orchestrated and dynamic, acting to preserve the maintenance and integrity of the genome. Histone proteins bind DNA and organize the genome into chromatin. Post-translational modifications of histones have been shown to play an essential role in orchestrating the chromatin response to DNA damage by regulating the DNA damage response pathway. Among the histone modifications that contribute to this intricate network, histone ADP-ribosylation (ADPr) is emerging as a pivotal component of chromatin-based DNA damage response (DDR) pathways. In this review, we survey how histone ADPr is regulated to promote the DDR and how it impacts chromatin and other histone marks. Recent advancements have revealed histone ADPr effects on chromatin structure and the regulation of DNA repair factor recruitment to DNA lesions. Additionally, we highlight advancements in technology that have enabled the identification and functional validation of histone ADPr in cells and in response to DNA damage. Given the involvement of DNA damage and epigenetic regulation in human diseases including cancer, these findings have clinical implications for histone ADPr, which are also discussed. Overall, this review covers the involvement of histone ADPr in the DDR and highlights potential future investigations aimed at identifying mechanisms governed by histone ADPr that participate in the DDR, human diseases, and their treatments.

Subcellular one carbon metabolism in cancer, aging and epigenetics

The crosstalk between metabolism and epigenetics is an emerging field that is gaining importance in different areas such as cancer and aging, where changes in metabolism significantly impacts the cellular epigenome, in turn dictating changes in chromatin as an adaptive mechanism to bring back metabolic homeostasis. A key metabolic pathway influencing an organism's epigenetic state is one-carbon metabolism (OCM), which includes the folate and methionine cycles. Together, these cycles generate S-adenosylmethionine (SAM), the universal methyl donor essential for DNA and histone methylation. SAM serves as the sole methyl group donor for DNA and histone methyltransferases, making it a crucial metabolite for chromatin modifications. In this review, we will discuss how SAM and its byproduct, S-adenosylhomocysteine (SAH), along with the enzymes and cofactors involved in OCM, may function in the different cellular compartments, particularly in the nucleus, to directly regulate the epigenome in aging and cancer.

DNA stimulates SIRT6 to mono-ADP-ribosylate proteins within histidine repeats

Sirtuins are the NAD + -dependent class III lysine deacylases (KDACs). Members of this family have been linked to longevity and a wide array of different diseases, motivating the pursuit of sirtuin modulator compounds. Sirtuin 6 (SIRT6) is a primarily nuclear KDAC that deacetylates histones to facilitate gene repression. In addition to this canonical post-translational modification (PTM) "eraser" function, SIRT6 can use NAD + instead to "write" mono-ADP-ribosylation (mARylation) on target proteins. This enzymatic function has been primarily associated with SIRT6's role in the DNA damage response. This modification has been challenging to study because it is not clear under what precise cellular contexts it occurs, only a few substrates are known, and potential interference from other ADP-ribosyltransferases in cells, among other reasons. In this work, we used commercially available ADP-ribosylation detection reagents to investigate the mARylation activity of SIRT6 in a reconstituted system. We observed that SIRT6 is activated in its mARylation activity by binding to dsDNA ends. We further identified a surprising target motif within biochemical substrates of SIRT6, polyhistidine (polyHis) repeat tracts, that are present in several previously identified SIRT6 mARylation substrates and binding partners. This work provides important context for SIRT6 mARylation activity, in contrast to its KDAC activity, and proposes that SIRT6 is a histidine mARyltransferase enzyme.

Legionella maintains host cell ubiquitin homeostasis by effectors with unique catalytic mechanisms

The intracellular bacterial pathogen Legionella pneumophila modulates host cell functions by secreting multiple effectors with diverse biochemical activities. In particular, effectors of the SidE family interfere with host protein ubiquitination in a process that involves production of phosphoribosyl ubiquitin (PR-Ub). Here, we show that effector LnaB converts PR-Ub into ADP-ribosylated ubiquitin, which is further processed to ADP-ribose and functional ubiquitin by the (ADP-ribosyl)hydrolase MavL, thus maintaining ubiquitin homeostasis in infected cells. Upon being activated by actin, LnaB also undergoes self-AMPylation on tyrosine residues. The activity of LnaB requires a motif consisting of Ser, His and Glu (SHxxxE) present in a large family of toxins from diverse bacterial pathogens. Thus, our study sheds light on the mechanisms by which a pathogen maintains ubiquitin homeostasis and identifies a family of enzymes capable of protein AMPylation.

Effect of quercetin on the protein-substrate interactions in SIRT6: Insight from MD simulations

SIRT6 is of interest for its promising effect in the treatment of aging-related diseases. Studies have shown quercetin (QUE) and its derivatives have varying degrees of effect on the catalytic effect of SIRT6. In the research, the effect of QUE on the protein-substrate interaction in the SIRT6-mediated mono-ADP ribosylation system was investigated by conventional molecular dynamics (MD) simulations combined with MM/PBSA binding free energy calculations. The results show that QUE can bind stably to SIRT6 with the binding energy of -22.8 kcal/mol and further affect the atomic interaction between SIRT6 and NAD+ (or H3K9), resulting in an increased affinity between SIRT6-NAD+ and decreased SIRT6-H3K9 binding capacity. At the same time, the binding of QUE can also alter some structural characteristics of the protein, with large shifts occurring in the residue regions involving the N-terminal (residues 1-27), Rossmann fold regions (residues 55-92), and ZBD (residues 164-179). Thus, QUE shows great potential as a scaffold for the design of novel potent SIRT6 modulators.

Pharmacological Activation of SIRT3 Modulates the Response of Cancer Cells to Acidic pH

Cancer cells modulate their metabolism, creating an acidic microenvironment that, in turn, can favor tumor progression and chemotherapy resistance. Tumor cells adopt strategies to survive a drop in extracellular pH (pHe). In the present manuscript, we investigated the contribution of mitochondrial sirtuin 3 (SIRT3) to the adaptation and survival of cancer cells to a low pHe. SIRT3-overexpressing and silenced breast cancer cells MDA-MB-231 and human embryonic kidney HEK293 cells were grown in buffered and unbuffered media at pH 7.4 and 6.8 for different times. mRNA expression of SIRT3 and CAVB, was measured by RT-PCR. Protein expression of SIRT3, CAVB and autophagy proteins was estimated by western blot. SIRT3-CAVB interaction was determined by immunoprecipitation and proximity ligation assays (PLA). Induction of autophagy was studied by western blot and TEM. SIRT3 overexpression increases the survival of both cell lines. Moreover, we demonstrated that SIRT3 controls intracellular pH (pHi) through the regulation of mitochondrial carbonic anhydrase VB (CAVB). Interestingly, we obtained similar results by using MC2791, a new SIRT3 activator. Our results point to the possibility of modulating SIRT3 to decrease the response and resistance of tumor cells to the acidic microenvironment and ameliorate the effectiveness of anticancer therapy.

The dual role of sirtuins in cancer: biological functions and implications

Sirtuins are pivotal in orchestrating numerous cellular pathways, critically influencing cell metabolism, DNA repair, aging processes, and oxidative stress. In recent years, the involvement of sirtuins in tumor biology has garnered substantial attention, with a growing body of evidence underscoring their regulatory roles in various aberrant cellular processes within tumor environments. This article delves into the sirtuin family and its biological functions, shedding light on their dual roles-either as promoters or inhibitors-in various cancers including oral, breast, hepatocellular, lung, and gastric cancers. It further explores potential anti-tumor agents targeting sirtuins, unraveling the complex interplay between sirtuins, miRNAs, and chemotherapeutic drugs. The dual roles of sirtuins in cancer biology reflect the complexity of targeting these enzymes but also highlight the immense therapeutic potential. These advancements hold significant promise for enhancing clinical outcomes, marking a pivotal step forward in the ongoing battle against cancer.

Unlocking the Nexus of Sirtuins: A Comprehensive Review of Their Role in Skeletal Muscle Metabolism, Development, and Disorders

The sirtuins constitute a group of histone deacetylases reliant on NAD+ for their activity that have gained recognition for their critical roles as regulators of numerous biological processes. These enzymes have various functions in skeletal muscle biology, including development, metabolism, and the body's response to disease. This comprehensive review seeks to clarify sirtuins' complex role in skeletal muscle metabolism, including glucose uptake, fatty acid oxidation, mitochondrial dynamics, autophagy regulation, and exercise adaptations. It also examines their critical roles in developing skeletal muscle, including myogenesis, the determination of muscle fiber type, regeneration, and hypertrophic responses. Moreover, it sheds light on the therapeutic potential of sirtuins by examining their impact on a range of skeletal muscle disorders. By integrating findings from various studies, this review outlines the context of sirtuin-mediated regulation in skeletal muscle, highlighting their importance and possible consequences for health and disease.

SIRT6 in Regulation of Mitochondrial Damage and Associated Cardiac Dysfunctions: A Possible Therapeutic Target for CVDs

Cardiovascular diseases (CVDs) can be described as a global health emergency imploring possible prevention strategies. Although the pathogenesis of CVDs has been extensively studied, the role of mitochondrial dysfunction in CVD development has yet to be investigated. Diabetic cardiomyopathy, ischemic-reperfusion injury, and heart failure are some of the CVDs resulting from mitochondrial dysfunction Recent evidence from the research states that any dysfunction of mitochondria has an impact on metabolic alteration, eventually causes the death of a healthy cell and therefore, progressively directing to the predisposition of disease. Cardiovascular research investigating the targets that both protect and treat mitochondrial damage will help reduce the risk and increase the quality of life of patients suffering from various CVDs. One such target, i.e., nuclear sirtuin SIRT6 is strongly associated with cardiac function. However, the link between mitochondrial dysfunction and SIRT6 concerning cardiovascular pathologies remains poorly understood. Although the Role of SIRT6 in skeletal muscles and cardiomyocytes through mitochondrial regulation has been well understood, its specific role in mitochondrial maintenance in cardiomyocytes is poorly determined. The review aims to explore the domain-specific function of SIRT6 in cardiomyocytes and is an effort to know how SIRT6, mitochondria, and CVDs are related.

The cGAS-Ku80 complex regulates the balance between two end joining subpathways

As the major DNA sensor that activates the STING-TBK1 signaling cascade, cGAS is mainly present in the cytosol. A number of recent reports have indicated that cGAS also plays critical roles in the nucleus. Our previous work demonstrated for the first time that cGAS is translocated to the nucleus upon the occurrence of DNA damage and inhibits homologous recombination (HR), one of the two major pathways of DNA double strand break (DSB) repair. However, whether nuclear cGAS regulates the other DSB repair pathway, nonhomologous end joining (NHEJ), which can be further divided into the less error-prone canonical NHEJ (c-NHEJ) and more mutagenic alternative NHEJ (alt-NHEJ) subpathways, has not been characterized. Here, we demonstrated that cGAS tipped the balance of the two NHEJ subpathways toward c-NHEJ. Mechanistically, the cGAS-Ku80 complex enhanced the interaction between DNA-PKcs and the deubiquitinase USP7 to improve DNA-PKcs protein stability, thereby promoting c-NHEJ. In contrast, the cGAS-Ku80 complex suppressed alt-NHEJ by directly binding to the promoter of Polθ to suppress its transcription. Together, these findings reveal a novel function of nuclear cGAS in regulating DSB repair, suggesting that the presence of cGAS in the nucleus is also important in the maintenance of genome integrity.

Legionella maintains host cell ubiquitin homeostasis by effectors with unique catalytic mechanisms

The reversal of ubiquitination induced by members of the SidE effector family of Legionella pneumophila produces phosphoribosyl ubiquitin (PR-Ub) that is potentially detrimental to host cells. Here we show that the effector LnaB functions to transfer the AMP moiety from ATP to the phosphoryl moiety of PR-Ub to convert it into ADP-ribosylated ubiquitin (ADPR-Ub), which is further processed to ADP-ribose and functional ubiquitin by the (ADP-ribosyl)hydrolase MavL, thus maintaining ubiquitin homeostasis in infected cells. Upon being activated by Actin, LnaB also undergoes self-AMPylation on tyrosine residues. The activity of LnaB requires a motif consisting of Ser, His and Glu (S-HxxxE) present in a large family of toxins from diverse bacterial pathogens. Our study not only reveals intricate mechanisms for a pathogen to maintain ubiquitin homeostasis but also identifies a new family of enzymes capable of protein AMPylation, suggesting that this posttranslational modification is widely used in signaling during host-pathogen interactions.

Electro-Metabolic Coupling of Cumulus-Oocyte Complex

Oocyte-cumulus cell interaction is essential for oocyte maturation and competence. The bidirectional crosstalk network mediated by gap junctions is fundamental for the metabolic cooperation between these cells. As cumulus cells exhibit a more glycolytic phenotype, they can provide metabolic substrates that the oocyte can use to produce ATP via oxidative phosphorylation. The impairment of mitochondrial activity plays a crucial role in ovarian aging and, thus, in fertility, determining the success or failure of assisted reproductive techniques. This review aims to deepen the knowledge about the electro-metabolic coupling of the cumulus-oocyte complex and to hypothesize a putative role of potassium channel modulators in order to improve fertility, promote intracellular Ca2+ influx, and increase the mitochondrial biogenesis and resulting ATP levels in cumulus cells.