Repressor Activator Protein Research Articles

Tdh3 and Rom2 are functional modulators of a conserved condensate-resident RNA-binding protein, Scd6, in Saccharomyces cerevisiae.

Arginine-glycine-glycine motif proteins play a crucial role in determining mRNA fate. Suppressor of clathrin deficiency 6 (Scd6) is a conserved arginine-glycine-glycine motif containing ribonucleoprotein (RNP) condensate-resident, translation repressor, and decapping activator protein in Saccharomyces cerevisiae. Identifying protein factors that can modulate Scd6 function is critical to understanding the regulation of mRNA fate by Scd6. In this study, using an approach that combined mRNA tethering assay with flow cytometry, we screened 50 genes for their role in modulating the translation repression activity of Scd6. We identified 8 conserved modulators with human homologs. Of these, we further characterized in detail guanine nucleotide exchange factor Rho1 multicopy suppressor 2 (Rom2) and glycolytic enzyme triose phosphate dehydrogenase 3 (Tdh3), which, respectively, impede and promote translation repression activity of Scd6. Our study reveals that Rom2 negatively regulates the arginine methylation of Scd6 and antagonizes its localization to P-bodies. Tdh3, on the other hand, promotes Scd6 interaction with Hmt1, thereby promoting the arginine methylation of Scd6 and enhanced eIF4G1 interaction, which is known to promote its repression activity. Identifying these novel modulators provides exciting new insights into the role of a metabolic enzyme of the glycolytic pathway and guanine nucleotide exchange factor implicated in the cell wall integrity pathway in regulating Scd6 function and, thereby, cytoplasmic mRNA fate.

β-Cyclocitral from Lavandula angustifolia Mill. Exerts Anti-Aging Effects on Yeasts and Mammalian Cells via Telomere Protection, Antioxidative Stress, and Autophagy Activation.

We used a replicative lifespan (RLS) experiment of K6001 yeast to screen for anti-aging compounds within lavender extract (Lavandula angustifolia Mill.), leading to the discovery of β-cyclocitral (CYC) as a potential anti-aging compound. Concurrently, the chronological lifespan (CLS) of YOM36 yeast and mammalian cells confirmed the anti-aging effect of CYC. This molecule extended the yeast lifespan and inhibited etoposide (ETO)-induced cell senescence. To understand the mechanism of CYC, we analyzed its effects on telomeres, oxidative stress, and autophagy. CYC administration resulted in notable increases in the telomerase content, telomere length, and the expression of the telomeric shelterin protein components telomeric-repeat binding factor 2 (TRF2) and repressor activator protein 1 (RAP1). More interestingly, CYC reversed H2O2-induced telomere damage and exhibited strong antioxidant capacity. Moreover, CYC improved the survival rate of BY4741 yeast under oxidative stress induced by 6.2 mM H2O2, increasing the antioxidant enzyme activity while reducing the reactive oxygen species (ROS), reactive nitrogen species (RNS), and malondialdehyde (MDA) levels. Additionally, CYC enhanced autophagic flux and free green fluorescent protein (GFP) expression in the YOM38-GFP-ATG8 yeast strain. However, CYC did not extend the RLS of K6001 yeast mutants, such as Δsod1, Δsod2, Δcat, Δgpx, Δatg2, and Δatg32, which lack antioxidant enzymes or autophagy-related genes. These findings reveal that CYC acts as an anti-aging agent by modifying telomeres, oxidative stress, and autophagy. It is a promising compound with potential anti-aging effects and warrants further study.

Shelterin dysfunction promotes CD4+ T cell senescence in Behçet's disease.

To investigate the potential role of shelterin dysfunction in naïve CD4+ T cells in the pathogenesis of Behçet's disease (BD). Naïve CD4+ T cells were isolated from 40 BD patients and 40 sex- and age-matched healthy controls (HC). Senescent profiles, shelterin subunits expression, telomere length, telomerase activity and critical DNA damage response (DDR) were evaluated. Telomere repeat factor-2 (TRF2) silencing was conducted for further validation. Compared with HC, BD patients had significantly decreased naïve CD4+ T cells, increased cell apoptosis, senescence, and productions of TNF-α and IFN-γ upon activation. Notably, BD naïve CD4+ T cells had shortened telomere, impaired telomerase activity, and expressed lower levels of shelterin subunits TRF2, TRF1- and TRF2-Interacting Nuclear Protein 2 (TIN2) and Repressor/Activator Protein 1 (RAP1). Furthermore, BD naïve CD4+ T cells exhibited significantly increased DDR, evidenced by elevated phosphorylated ataxia telangiectasia (AT) mutated (pATM), phosphorylated p53 (pp53) and p21. Finally, TRF2 silencing markedly upregulated DDR, apoptosis and proinflammatory cytokines production in HC naïve CD4+ T cells. Our study demonstrated that TRF2 deficiency in BD naïve CD4+ T cells promoted cell apoptosis and senescence, leading to proinflammatory cytokines overproduction. Therefore, restoring TRF2 might be a promising therapeutic strategy for BD.

PI(3,4,5)P3 allosteric regulation of repressor activator protein 1 controls antigenic variation in trypanosomes

African trypanosomes evade host immune clearance by antigenic variation, causing persistent infections in humans and animals. These parasites express a homogeneous surface coat of variant surface glycoproteins (VSGs). They transcribe one out of hundreds of VSG genes at a time from telomeric expression sites (ESs) and periodically change the VSG expressed by transcriptional switching or recombination. The mechanisms underlying the control of VSG switching and its developmental silencing remain elusive. We report that telomeric ES activation and silencing entail an on/off genetic switch controlled by a nuclear phosphoinositide signaling system. This system includes a nuclear phosphatidylinositol 5-phosphatase (PIP5Pase), its substrate PI(3,4,5)P3, and the repressor-activator protein 1 (RAP1). RAP1 binds to ES sequences flanking VSG genes via its DNA binding domains and represses VSG transcription. In contrast, PI(3,4,5)P3 binds to the N-terminus of RAP1 and controls its DNA binding activity. Transient inactivation of PIP5Pase results in the accumulation of nuclear PI(3,4,5)P3, which binds RAP1 and displaces it from ESs, activating transcription of silent ESs and VSG switching. The system is also required for the developmental silencing of VSG genes. The data provides a mechanism controlling reversible telomere silencing essential for the periodic switching in VSG expression and its developmental regulation.

PI(3,4,5)P3 allosteric regulation of repressor activator protein 1 controls antigenic variation in trypanosomes.

African trypanosomes evade host immune clearance by antigenic variation, causing persistent infections in humans and animals. These parasites express a homogeneous surface coat of variant surface glycoproteins (VSGs). They transcribe one out of hundreds of VSG genes at a time from telomeric expression sites (ESs) and periodically change the VSG expressed by transcriptional switching or recombination. The mechanisms underlying the control of VSG switching and its developmental silencing remain elusive. We report that telomeric ES activation and silencing entail an on/off genetic switch controlled by a nuclear phosphoinositide signaling system. This system includes a nuclear phosphatidylinositol 5-phosphatase (PIP5Pase), its substrate PI(3,4,5)P3, and the repressor-activator protein 1 (RAP1). RAP1 binds to ES sequences flanking VSG genes via its DNA binding domains and represses VSG transcription. In contrast, PI(3,4,5)P3 binds to the N-terminus of RAP1 and controls its DNA binding activity. Transient inactivation of PIP5Pase results in the accumulation of nuclear PI(3,4,5)P3, which binds RAP1 and displaces it from ESs, activating transcription of silent ESs and VSG switching. The system is also required for the developmental silencing of VSG genes. The data provides a mechanism controlling reversible telomere silencing essential for the periodic switching in VSG expression and its developmental regulation.

Context-dependent function of the transcriptional regulator Rap1 in gene silencing and activation in Saccharomyces cerevisiae

In Saccharomyces cerevisiae, heterochromatin is formed through interactions between site-specific DNA-binding factors, including the transcriptional activator Repressor Activator Protein (Rap1), and Sir proteins. Despite an understanding of the establishment and maintenance of Sir-silenced chromatin, the mechanism of gene silencing by Sir proteins has remained a mystery. Utilizing high-resolution chromatin immunoprecipitation, we found that Rap1, the native activator of the bidirectional HMLα promoter, bound its recognition sequence in silenced chromatin, and its binding was enhanced by the presence of Sir proteins. In contrast to prior results, various components of transcription machinery were not able to access HMLα in the silenced state. These findings disproved the long-standing model of indiscriminate steric occlusion by Sir proteins and led to investigation of the role of the transcriptional activator Rap1 in Sir-silenced chromatin. Using a highly sensitive assay that monitors loss-of-silencing events, we identified a role for promoter-bound Rap1 in the maintenance of silent chromatin through interactions with the Sir complex. We also found that promoter-bound Rap1 activated HMLα when in an expressed state, and aided in the transition from transcription initiation to elongation. Highlighting the importance of epigenetic context in transcription factor function, these results point toward a model in which the duality of Rap1 function was mediated by local chromatin environment rather than binding-site availability.

Targeting Rho kinase to restore endothelial barrier function following vascular scaffold implantation

Vascular scaffold implantation induces injury to the intimal layer and causes discontinuity of the regenerated endothelial monolayer, compromising barrier integrity, increasing permeability, and allowing the transmigration of leukocytes and lipoproteins into the subendothelial space. Mechanical vascular wall stretching triggers Ras homolog family member A (RhoA)/Rho kinase-mediated actomyosin contractility and destabilization of adherens junctions, leading to endothelial barrier dysfunction. Assembly of intercellular adhesion and actin cytoskeletal organization of interendothelial junctions are controlled by downregulation of RhoA guanosine triphosphatase (GTPase)-mediated barrier-disruptive activity and upregulation of repressor-activator protein 1 (Rap1) and Ras-related C3 botulinum toxin substrate 1 (Rac1) GTPase-mediated cytoskeletal reorganization, leading to endothelial barrier stabilization. This review highlights the involvement of Rho GTPases in the disruption of endothelial barrier integrity following vascular scaffold implantation and the targeting of downstream Rho-associated protein kinases, which signal the network to restore endothelial barrier integrity and stability.

Genome-wide gene expression responses to experimental manipulation of Saccharomyces cerevisiae repressor activator protein 1 (Rap1) expression level

Precise regulation of transcription in gene expression is critical for all aspects of normal organism form, fitness, and function and even minor alterations in the level, location, and timing of gene expression can result in phenotypic variation within and between species including evolutionary innovations and human disease states. Eukaryotic transcription is regulated by a complex interplay of multiple factors working both at a physical and molecular levels influencing this process. In Saccharomyces cerevisiae, the TF with the greatest number of putative regulatory targets is the essential gene Repressor Activator Protein 1 (RAP1). While much is known about the roles of Rap1 in gene regulation and numerous cellular processes, the response of Rap1 target genes to systematic titration of RAP1 expression level remains unknown. To fill this knowledge gap, we used a strain with a tetracycline-titratable promoter replacing wild-type regulatory sequences of RAP1 to systematically reduce the expression level of RAP1 and followed this with RNA sequencing (RNA-seq) to measure genome-wide gene expression responses. Previous research indicated that Rap1 plays a significant regulatory role in particular groups of genes including telomere-proximal genes, homothallic mating (HM) loci, glycolytic genes, DNA repair genes, and ribosomal protein genes; therefore, we focused our analyses on these groups and downstream targets to determine how they respond to reductions in RAP1 expression level. Overall, despite being known as both an activator and as a repressor of its target genes, we found that Rap1 acts as an activator for more target genes than as a repressor. Additionally, we found that Rap1 functions as an activator of ribosomal protein genes and a repressor for HM loci genes consistent with predictions from the literature. Unexpectedly, we found that Rap1 functions as a repressor of glycolytic enzyme genes contrary to prior reports of it having the opposite effect. We also compared the expression of RAP1 to five different genes related to DNA repair pathway and found that decreasing RAP1 downregulated four of those five genes. Finally, we found no effect of RAP1 depletion on telomere-proximal genes despite its functioning to silence telomeric repeat-containing RNAs. Together our results enrich our understanding of this important transcriptional regulator.

CAMP-Epac1 signaling is activated in DDAVP-induced endolymphatic hydrops of guinea pigs

ObjectiveTo explore whether Cyclic Adenosine Monophosphate (cAMP)-Epac1 signaling is activated in 1-Desamino-8-D-arginine-Vasopressin-induced Endolymphatic Hydrops (DDAVP-induced EH) and to provide new insight for further in-depth study of DDAVP-induced EH. MethodsEighteen healthy, red-eyed guinea pigs (36 ears) weighing 200–350 g were randomly divided into three groups: the control group, which received intraperitoneal injection of sterile saline (same volume as that in the other two groups) for 7 consecutive days; the DDAVP-7d group, which received intraperitoneal injection of 10 mg/mL/kg DDAVP for 7 consecutive days; and the DDAVP-14d group, which received intraperitoneal injection of 10 μg/mL/kg DDAVP for 14 consecutive days. After successful modeling, all animals were sacrificed, and cochlea tissues were collected to detect the mRNA and protein expression of the exchange protein directly activated by cAMP-1 and 2 (Epac1, Epac2), and Repressor Activator Protein-1 (Rap1) by Reverse Transcription (RT)-PCR and western blotting, respectively. ResultsCompared to the control group, the relative mRNA expression of Epac1, Epac2, Rap1A, and Rap1B in the cochlea tissue of the DDAVP-7d group was significantly higher (p < 0.05), while no significant difference in Rap1 GTPase activating protein (Rap1gap) mRNA expression was found between the two groups. The relative mRNA expression of Epac1, Rap1A, Rap1B, and Rap1gap in the cochlea tissue of the DDAVP-14d group was significantly higher than that of the control group (p < 0.05), while no significant difference in Epac2 mRNA expression was found between the DDAVP-14d and control groups. Comparison between the DDAVP-14d and DDAVP-7d groups showed that the DDAVP-14d group had significantly lower Epac2 and Rap1A (p < 0.05) and higher Rap1gap (p < 0.05) mRNA expression in the cochlea tissue than that of the DDAVP-7d group, while no significant differences in Epac1 and Rap1B mRNA expression were found between the two groups. Western blotting showed that Epac1 protein expression in the cochlea tissue was the highest in the DDAVP-14d group, followed by that in the DDAVP-7d group, and was the lowest in the control group, showing significant differences between groups (p < 0.05); Rap1 protein expression in the cochlea tissue was the highest in the DDAVP-7d group, followed by the DDAVP-14d group, and was the lowest in the control group, showing significant differences between groups (p < 0.05); no significant differences in Epac2 protein expression in the cochlea tissue were found among the three groups. ConclusionDDAVP upregulated Epac1 protein expression in the guinea pig cochlea, leading to activation of the inner ear cAMP-Epac1 signaling pathway. This may be an important mechanism by which DDAVP regulates endolymphatic metabolism to induce EH and affect inner ear function. Oxford Centre for Evidence-Based Medicine 2011 Levels of EvidenceLevel 5.

Associations of Rap1 with Cell Wall Integrity, Biofilm Formation, and Virulence in Candida albicans.

Rap1 (repressor activator protein 1) is a multifunctional protein, playing important roles in telomeric and nontelomeric functions in many eukaryotes. Candida albicans Rap1 has been previously shown to be involved in telomeric regulation, but its other functions are still mostly unknown. In this study, we found that the deletion of the RAP1 gene altered cell wall properties, composition, and gene expression. In addition, deletion of RAP1 affected C. albicans biofilm formation and modulated phagocytosis and cytokine release by host immune cells. Finally, the RAP1 gene deletion mutant showed attenuation of C. albicans virulence in a Galleria mellonella infection model. Therefore, these findings provide new insights into Rap1 functions that are particularly relevant to pathogenesis and virulence of C. albicans. IMPORTANCE C. albicans is an important fungal pathogen of humans. The cell wall is the outermost layer of C. albicans and is important for commensalism and infection by this pathogen. Moreover, the cell wall is also an important target for antifungals. Studies of how C. albicans maintains its cell wall integrity are critical for a better understanding of fungal pathogenesis and virulence. This work focuses on exploring unknown functions of C. albicans Rap1 and reveals its contribution to cell wall integrity, biofilm formation, and virulence. Notably, these findings will also improve our general understanding of complex machinery to control pathogenesis and virulence of fungal pathogens.

Arginine glycosylation regulates UDP-GlcNAc biosynthesis in Salmonella enterica

The Salmonella enterica SseK1 protein is a type three secretion system effector that glycosylates host proteins during infection on specific arginine residues with N-acetyl glucosamine (GlcNAc). SseK1 also Arg-glycosylates endogenous bacterial proteins and we thus hypothesized that SseK1 activities might be integrated with regulating the intrabacterial abundance of UPD-GlcNAc, the sugar-nucleotide donor used by this effector. After searching for new SseK1 substrates, we found that SseK1 glycosylates arginine residues in the dual repressor-activator protein NagC, leading to increased DNA-binding affinity and enhanced expression of the NagC-regulated genes glmU and glmS. SseK1 also glycosylates arginine residues in GlmR, a protein that enhances GlmS activity. This Arg-glycosylation improves the ability of GlmR to enhance GlmS activity. We also discovered that NagC is a direct activator of glmR expression. Salmonella lacking SseK1 produce significantly reduced amounts of UDP-GlcNAc as compared with Salmonella expressing SseK1. Overall, we conclude that SseK1 up-regulates UDP-GlcNAc synthesis both by enhancing the DNA-binding activity of NagC and by increasing GlmS activity through GlmR glycosylation. Such regulatory activities may have evolved to maintain sufficient levels of UDP-GlcNAc for both bacterial cell wall precursors and for SseK1 to modify other bacterial and host targets in response to environmental changes and during infection.

Highly tunable TetR-dependent target gene expression in the acetic acid bacterium Gluconobacter oxydans

For the acetic acid bacterium (AAB) Gluconobacter oxydans only recently the first tight system for regulatable target gene expression became available based on the heterologous repressor-activator protein AraC from Escherichia coli and the target promoter ParaBAD. In this study, we tested pure repressor-based TetR- and LacI-dependent target gene expression in G. oxydans by applying the same plasmid backbone and construction principles that we have used successfully for the araC-ParaBAD system. When using a pBBR1MCS-5-based plasmid, the non-induced basal expression of the Tn10-based TetR-dependent expression system was extremely low. This allowed calculated induction ratios of up to more than 3500-fold with the fluorescence reporter protein mNeonGreen (mNG). The induction was highly homogeneous and tunable by varying the anhydrotetracycline concentration from 10 to 200 ng/mL. The already strong reporter gene expression could be doubled by inserting the ribosome binding site AGGAGA into the 3’ region of the Ptet sequence upstream from mNG. Alternative plasmid constructs used as controls revealed a strong influence of transcription terminators and antibiotics resistance gene of the plasmid backbone on the resulting expression performance. In contrast to the TetR-Ptet-system, pBBR1MCS-5-based LacI-dependent expression from PlacUV5 always exhibited some non-induced basal reporter expression and was therefore tunable only up to 40-fold induction by IPTG. The leakiness of PlacUV5 when not induced was independent of potential read-through from the lacI promoter. Protein-DNA binding simulations for pH 7, 6, 5, and 4 by computational modeling of LacI, TetR, and AraC with DNA suggested a decreased DNA binding of LacI when pH is below 6, the latter possibly causing the leakiness of LacI-dependent systems hitherto tested in AAB. In summary, the expression performance of the pBBR1MCS-5-based TetR-Ptet system makes this system highly suitable for applications in G. oxydans and possibly in other AAB.Key Points• A pBBR1MCS-5-based TetR-Ptet system was tunable up to more than 3500-fold induction.• A pBBR1MCS-5-based LacI-PlacUV5 system was leaky and tunable only up to 40-fold.• Modeling of protein-DNA binding suggested decreased DNA binding of LacI at pH < 6.

Engineering an oleaginous yeast Candida tropicalis SY005 for enhanced lipid production.

Candida tropicalis has recently emerged as a valuable yeast species with respect to lipid metabolism, not only for its oleaginous characteristics but also for its ability to utilize diverse range of substrates. Hence, it can be explored as an ideal host for lipid metabolic engineering, although inadequate genetic transformation system for developing the stable transformant has limited this scope. To resolve this existing constraint, we have come up with a novel strategy of a genomic integrating system in the oleaginous strain SY005 of C. tropicalis. Employing this system, comprising of host-specific regulatable promoter, transcription terminator, and integration locus, we have first examined the expression of a reporter gene, and then ectopically expressed a transcription factor CtRAP1 encoding the repressor activator protein 1 of C. tropicalis SY005. A maximum lipid content of 0.37g/g dry cell weight was achieved in the engineered strain upon galactose induction, leading to 60% (w/w) increase relative to the wild type strain SY005. This work demonstrates the use of a markerlessintegrative transformation system to promote lipid accumulation in the diploid yeast without applying nutrient stress and hampering cell growth. The findings of this study will augment the research on lipid metabolic engineering and exploit the enormous potential of C. tropicalis as an industrial lipid feedstock. Key points •A transformation system was established in oleaginous yeast Candida tropicalis SY005 •Activity of host-specific molecular elements was verified by reporter gene expression •SY005 was engineered to ectopically express a transcriptional regulator geneCtRAP1 •The engineered strain exhibited 60% increase in lipid content on galactose induction •The increase in lipid content was correlated with the induced expression of CtRAP1.

Loss of Repressor Activator Protein 1 Precipitates Cardiac Aging in Mice via p53/PPARα Signaling

BackgroundTelomere dysfunction has been linked to many aspects of the aging process. Increasing evidence indicates that telomere dysfunction leads to cardiac mitochondrial defects. Mammalian repressor activator protein 1 (Rap1) is one of the components of shelterin complex and essential for the maintenance of telomere length and structural integrity. Our preliminary work showed that aged Rap1 knockout (Rap1−/−) mice exhibited more pronounced aging‐associated phenotypes (including earlier hair graying, hair loss, reduced body weight). However, the effects of Rap1 on mitochondrial function and its contribution to cardiac aging are largely unknown. Thus, the present study investigated whether or not loss of Rap1 in mice precipitates cardiac aging and explored the underlying mechanisms.Methods and ResultsMice cardiac function was assessed with transthoracic echocardiography performed noninvasively using a Vevo 2100 high‐resolution imaging system. Deletion of Rap1 in mice aggravated aging‐related cardiac structural changes and dysfunction, as evidenced by increased left ventricular (LV) posterior wall end‐diastole and LV mass, reductions in ejection fraction and fractional shortening, as well as significantly reduced myocardial performance index (all p &lt; 0.05, Rap1−/− vs. age‐matched counterparts). These changes were associated with greater cardiac senescence (enhanced SA‐β‐gal staining), cardiac hypertrophy (enhanced wheat germ agglutinin staining and increased the ratio of heart weight with body weight), abnormalities in the mitochondrial ultrastructure (cristae fragmentation, vacuolization). Mechanistically, Rap1 deficiency led to shorter telomere (T/S ratio), enhanced DNA damage (γH2AX) and increased nuclear p53 level in vivo in the myocardium and in primary cardiomyocytes when compared to age‐matched counterparts (one year old). Chromatin immunoprecipitation revealed that p53 directly binded to the promote site of PPARα [a central regulator of cardiac fatty acid metabolism (FAM)] and repressed its expression. Rap1 deficiency impaired FAM (reduced CD36, CPT1α, ACADL level and palmitate‐induced oxygen consumption), while PFTα (a p53 inhibitor, i.p. 1.1 mg/kg/day) treatment in Rap1−/− mice significantly alleviated cardiac aging and enhanced FAM by restoration of PPARα.ConclusionsWith aging, Rap1 deficiency may lead to shorter telomere length, increase DNA damage and thereby activate p53, which in turn suppresses PPARα, leading to impaired FAM and mitochondrial defects with abnormal cardiac structure and dysfunction. These findings may identify a new cardiac dimension in the physiological role played by telomere‐Rap1.Support or Funding InformationThe authors’ work was supported by the General Research Fund (17123718M, Research Grants Council of Hong Kong).

Rap1 exacerbates myocardial ischemia/reperfusion injury through activation of NFκB signaling pathway and NLRP3 inflammasome

BackgroundIschemic heart disease is a leading cause of morbidity and mortality worldwide. Activation of nuclear factor kappa B (NFκB)‐mediated inflammation has been demonstrated in various models of experimental myocardial ischemia/reperfusion injury (I/RI). Repressor activator protein 1 (Rap1), an established telomere‐associated protein, is a novel modulator of NFκB‐mediated inflammatory response. However, it is unknown whether Rap1 modulates NFκB signaling in cardiomyocytes to contribute to myocardial I/RI. Therefore, the present study aimed to explore the potential pro‐inflammatory role of Rap1 in myocardial I/RI and to determine the underlying molecular mechanism.Methods and ResultsIn a mouse model of myocardial I/RI (30 minutes of left descending coronary artery ligation followed by 24 hours reperfusion), Rap1 deficiency significantly reduced myocardial infarct size and improved cardiac systolic/diastolic function (all p &lt; 0.05, Rap1−/− I/R vs. Rap1+/+ I/R). This was associated with a reduction in NFκB activity [reduced phosphorylation, degradation of IκBα and phosphorylation of p65] and suppressed production of NFκB‐mediated pro‐inflammatory cytokines, including tumor necrosis factor α (TNFα), interleukin (IL)6 and IL1β in the post‐ischemic myocardium (all p &lt; 0.05, Rap1−/− I/R vs. Rap1+/+ I/R). In cultured cardiac origin H9C2 cardiomyocytes, Rap1 knockdown did not significantly influence the pro‐inflammatory response in hypoxia/reoxygenation or in lipopolysaccharide‐stimulated H9C2 cells, but deletion of Rap1 significantly attenuated macrophage infiltration into the post‐ischemic myocardium of mice (p &lt; 0.05, Rap1−/− I/R vs. Rap1+/+ I/R). Also, knockdown of Rap1 significantly suppressed NLRP3 inflammasome formation in THP‐1 macrophages in response to LPS and ATP (p &lt; 0.05, Rap1KD vs. Rap1WT). When post‐hypoxic H9C2 cardiomyocytes were co‐cultured with mock‐ or Rap1‐siRNA transfected THP‐1 macrophages, knockdown of Rap1 in macrophages significantly attenuated macrophage‐mediated/exacerbated cardiomyocyte injury (p &lt; 0.05, Rap1KD vs. Rap1WT).ConclusionsThese data collectively suggest that Rap1 may exacerbate myocardial I/RI through enhancing activation of NFκB signaling pathway and NLRP3 inflammasome formation, which may yield a novel therapeutic target for myocardial I/RI.Support or Funding InformationThe work was supported by the National Natural Science Foundation of China (No. 81800245) and General Research Fund (17117217M, 17123718M Research Grants Council of Hong Kong).

Repressor Activator Protein 1 Worsens Cardiomyopathy in Diet‐induced Type 2 Diabetic Mice

BackgroundDiabetic cardiomyopathy is defined by the structural and functional abnormalities of the myocardium in the absence of other cardiac risk factors in diabetic patients. In diabetes, the increment of fatty acid metabolism and subsequently cardiac inefficiency and myocardial lipid accumulation may underlie the pathology of diabetic cardiomyopathy. The telomeric protein repressor activator protein 1 (Rap1) is an identified regulator that regulates gene transcription by binding to non‐telomeric sites. In particular, Rap1 can bind to nuclear PPARα (an important transcriptional regulator of lipid metabolism) loci, and regulate transcription of PPARα and its target genes, including CD36 (fatty acid transporter). However, the effects of Rap1 on diabetic cardiomyopathy are largely unknown. Thus, the present study investigated if Rap1 deficiency protects against diabetic cardiomyopathy and explored the underlying mechanisms.Methods and ResultsHigh fat diet feeding is a widely used protocol to induce type 2 diabetes in mice. Upon high fat feeding (60% fat) for 12 weeks, male Rap1 knockout (KO) mice displayed significantly reduced body weight gain compared with their wild type (WT) littermates. The glucose tolerance test and insulin tolerance test showed that Rap1 deficiency in the high fat diet fed‐mice led to improved glucose intolerance and insulin action. Furthermore, Rap1 deficiency attenuates high fat diet‐induced cardiac structural remodeling and dysfunction in mice, as evidenced by significantly reduction in left ventricular internal dimension in systole (LVIDs), left ventricular mass, increment in ejection fraction (EF) and fractional shortening (FS), as well as improving of myocardial performance index (MPI). These changes were associated with remarkable reductions in the mRNA and protein expression of PPARα and CD36 in the myocardium of high fat fed‐Rap1 KO mice, indicating that Rap1 deficiency may protect against diabetic cardiomyopathy via the suppression of PPARα/CD36 signaling.ConclusionIn summary, these results suggest that Rap1 impairment has cardioprotective consequences in the high fat diet‐induced diabetes model, identifying a new dimension in the roles of endogenous Rap1.Support or Funding InformationThe authors’ work was supported by The General Research Fund (17117217M, 17123718M, Research Grants Council of Hong Kong) and The National Natural Science Foundation of China (No. 81800245).

Deletion of Rap1 protects against myocardial ischemia/reperfusion injury through suppressing cell apoptosis via activation of STAT3 signaling.

Ischemic heart disease is a leading cause of morbidity and mortality. Repressor activator protein 1 (Rap1), an established telomere-associated protein, is a novel modulator of hypoxia-induced apoptosis. This study aimed to explore the potential direct role of Rap1 in myocardial ischemia/reperfusion injury (I/RI) and to determine the underlying molecular mechanism. In a mouse model of myocardial I/RI (30-min of left descending coronary artery ligation followed by 2-h reperfusion), Rap1 deficiency significantly reduced myocardial infarct size (IS) and improved cardiac systolic/diastolic function. This was associated with a reduction in apoptosis in the post-ischemic myocardium. In H9C2 and primary cardiomyocytes, Rap1 knockdown or knockout significantly suppressed hypoxia/reoxygenation (H/R)-induced cell injury and apoptosis through increasing the phosphorylation/activation of STAT3 at site Ser727 and translocation of STAT3 to the nucleus. We surmise this since Stattic (selective STAT3 inhibitor) pretreatment canceled the abovementioned protective effect. Furthermore, co-immunoprecipitation assay revealed a direct interaction between Rap1 and STAT3, but not JAK2, suggesting that the association of Rap1 with STAT3 may contribute to the reduced activity of STAT3 (Ser727 ) upon H/R stimulation. In conclusion, Rap1 deficiency protects the heart from ischemic damage through STAT3-dependent reduction of cardiomyocyte apoptosis, which may yield viable target for pharmacological intervention in ischemic heart disease.

The Sir4 H-BRCT domain interacts with phospho-proteins to sequester and repress yeast heterochromatin.

In Saccharomyces cerevisiae, the silent information regulator (SIR) proteins Sir2/3/4 form a complex that suppresses transcription in subtelomeric regions and at the homothallic mating-type (HM) loci. Here, we identify a non-canonical BRCA1 C-terminal domain (H-BRCT) in Sir4, which is responsible for tethering telomeres to the nuclear periphery. We show that Sir4 H-BRCT and the closely related Dbf4 H-BRCT serve as selective phospho-epitope recognition domains that bind to a variety of phosphorylated target peptides. We present detailed structural information about the binding mode of established Sir4 interactors (Esc1, Ty5, Ubp10) and identify several novel interactors of Sir4 H-BRCT, including the E3 ubiquitin ligase Tom1. Based on these findings, we propose a phospho-peptide consensus motif for interaction with Sir4 H-BRCT and Dbf4 H-BRCT. Ablation of the Sir4 H-BRCT phospho-peptide interaction disrupts SIR-mediated repression and perinuclear localization. In conclusion, the Sir4 H-BRCT domain serves as a hub for recruitment of phosphorylated target proteins to heterochromatin to properly regulate silencing and nuclear order.

TSPYL5 Depletion Induces Specific Death of ALT Cells through USP7-Dependent Proteasomal Degradation of POT1.

A significant fraction (∼10%) of cancer cells maintain their telomere length via a telomerase-independent mechanism known as alternative lengthening of telomeres (ALT). There are no known molecular, ALT-specific, therapeutic targets. We have identified TSPYL5 (testis-specific Y-encoded-like protein 5) as a PML body component, co-localizing with ALT telomeres and critical for ALT+ cell viability. TSPYL5 was described as an inhibitor of the USP7 deubiquitinase. We report that TSPYL5 prevents the poly-ubiquitination of POT1-a shelterin component-and protects POT1 from proteasomal degradation exclusively in ALT+ cells. USP7 depletion rescued POT1 poly-ubiquitination and loss, suggesting thatthe deubiquitinase activates POT1 E3 ubiquitin ligase(s). Similarly, PML depletion suppressed POT1 poly-ubiquitination, suggesting an interplay between USP7 and PML to trigger POT1 degradation in TSPYL5-depleted ALT+ cells. We demonstrate that ALT telomeres need to be protected from POT1 degradation in ALT-associated PML bodies and identify TSPYL5 as an ALT+ cancer-specific therapeutic target.

Deletion of Telomere‐Rap1 aggravates cardiac aging by impairing fatty acid oxidation via PPARα signaling

The heart undergoes multiple functional and structural declining with aging, including impaired fatty acid metabolism, cardiac dysfunction and hypertrophy. Repressor activator protein 1 (Rap1) as a component of shelterin complex is essential for the maintenance of telomere function. Moreover, Rap1 also regulates gene transcription by binding to non‐telomeric sites such as the nuclear hormone receptor ‐ peroxisome proliferator‐activated receptor α (PPARα) which plays a central role in the cardiac fatty acid metabolism and mitochondrial function. However, it's still not clear whether or not the heart of Rap1−/− mice also suffers more aging associated disorders. Thus, the present study aims at the role of Rap1 in cardiac aging and its possible mechanism. Echocardiography showed enlarged left ventricular internal dimension (LVID) and LV mass, which suggested dilated hypertrophy, and elevated myocardial performance index (MPI) in Rap1−/− mice at age of 85weeks, indicating systolic and diastolic dysfunction (all P&lt;0.05 vs. Rap1+/+). The greater adverse cardiac remodeling in aged Rap1−/− mice was paralleled by elevated cardiomyocyte area showed by Wheat germ agglutinin (WGA) staining (P&lt;0.05 vs. Rap1+/+). p53 as a senescence marker was also increased indicating more severe cellular senescence in cardiomyocyte of Rap1−/− mice (P&lt;0.05 vs. Rap1+/+). From apex cordis of Rap1 wildtype and knockout mice, electron microscopy showed more enlarged pleomorphic mitochondria containing cristae fragmentation, vacuolization and disrupted external membranes in aged Rap1 knockout mice compared to age‐matched wildtype counterparts. Decreased Acetyl‐CoA carboxylase (ACC) (catalyzes the production of malonyl‐CoA) and Elevated Carnitine palmitoyl transferase I (CPT‐1) (transports fatty acyl‐CoA into mitochondria) and Acyl‐CoA dehydrogenase long chain (ACADL, catalyzes most of fatty acid β‐oxidation) were detected in aged Rap1 knockout mice(all P&lt;0.05 vs. Rap1+/+), indicating Rap1 deficiency may lead to reduced fatty acid oxidation during aging. In the heart of aged Rap1−/− mice, PPARα was reduced compared with age‐matched wildtype counterparts (P&lt;0.05 vs. Rap1+/+), suggesting that with aging, Rap1 may down‐regulate PPARα signaling in the heart and control fatty acid metabolism resulting in cardiac dysfunction and hypertrophy. In conclusion, Rap1 deficiency may impair myocardial fatty acid oxidation via PPARα signaling, leading to more severe cardiac aging as cardiac dysfunction and hypertrophy. These findings may identify a new extratelomeric role of Rap1 in cardiac metabolism during aging.Support or Funding InformationThe authors' work was supported by the Health and Medical Research Fund (04151816, Hong Kong) and General Research Fund (17121315M, 17123915M and 17117217M, Research Grants Council of Hong Kong).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.