The poly(ADP-ribosyl)ation of FoxO3 mediated by PARP1 participates in isoproterenol-induced cardiac hypertrophy

The cross-talk between PARylation and SUMOylation in C/EBPβ at K134 site participates in pathological cardiac hypertrophy

Poly(ADP-ribosyl)ation (PARylation) and SUMO modification (SUMOylation) are novel post-translational modifications (PTMs) mainly induced by PARP1 and SUMO1. Growing evidence has revealed that C/EBPβ plays multiple roles in biological processes and participates in cardiovascular diseases. However, the cross-talk between C/EBPβ PARylation and SUMOylation during cardiovascular diseases is unknown. This study aims to investigate the effects of C/EBPβ PTMs on cardiac hypertrophy and its underlying mechanism. Abdominal aortic constriction (AAC) and phenylephrine (PE) were conducted to induce cardiac hypertrophy. Intramyocardial delivery of recombinant adenovirus (Ad-PARP1) was taken to induce PARP1 overexpression. In this study, we found C/EBPβ participates in PARP1-induced cardiac hypertrophy. C/EBPβ K134 residue could be both PARylated and SUMOylated individually by PARP1 and SUMO1. Moreover, the accumulation of PARylation on C/EBPβ at K134 site exhibits downregulation of C/EBPβ SUMOylation at the same site. Importantly, C/EBPβ K134 site SUMOylation could decrease C/EBPβ protein stability and participates in PARP1-induced cardiac hypertrophy. Taken together, these findings highlight the importance of the cross-talk between C/EBPβ PTMs at K134 site in determining its protein level and function, suggesting that multi-target pharmacological strategies inhibiting PARP1 and activating C/EBPβ SUMOylation would be potential for treating pathological cardiac hypertrophy.

Anti-tumor activity of the pan-RAF inhibitor TAK-580 in combination with KPT-330 (selinexor) in multiple myeloma

RAS/RAF/MEK/ERK pathway inhibitors exhibit significant anti-tumor effects against various tumor types, including multiple myeloma (MM), and they are predicted to play a pivotal role in precision medicine. The XPO1 inhibitor KPT-330 has also exhibited promising efficacy in combination with other novel drugs in treating relapsed/refractory MM (RRMM). In this study, we explored the anti-tumor effects of a combination of the pan-RAF inhibitor TAK-580 and KPT-330. Importantly, TAK-580 enhanced KPT-330-induced cytotoxicity and apoptosis in human myeloma cell lines and primary myeloma cells from RRMM patients. Moreover, TAK-580 and KPT-330 synergistically inhibited nuclear phospho-FOXO3a and enhanced cytoplasmic phospho-FOXO3a in MM cells, leading to cytoplasmic enhanced Bim expression and finally apoptosis. This indicates that TAK-580 enhances KPT-330-induced cytotoxicity and apoptosis primarily via the FOXO3a-Bim axis. In addition, TAK-580 enhanced the cytotoxicity of KPT-330 against MM cells even in the presence of IGF-1. Taken together, our results demonstrate that a combination of pan-RAF inhibitor and XPO1 inhibitor is a potential therapeutic option in treating MM.

Association of T2285C polymorphism in PARP1 gene coding region with its expression, activity and NSCLC risk along with prognosis

Poly (ADP-ribose) polymerase-1(PARP1), a DNA repair gene, is the crucial player in the maintenance of genome integrity. T2285C polymorphism in coding region of PARP1 has been reported to be associated with susceptibility to tumors. We explored the relation and mechanism of T2285C polymorphism of PARP1 to its expression and activity along with risk and prognosis in NSCLC. mRNA expression was measured using qRT-PCR assay or collected from TCGA dataset. Protein expression was examined with immunoblotting assay. Genotypes were determined by PCR-RFLP and sequencing approaches. PARP1 activity was determined with enzyme activity assay. Regulation of SIRT7 to PARP1 were determined by over-expression and small interference experiment. Association of PARP1 T2285C polymorphism with NSCLC risk was evaluated via multiple logistic regression analysis. Comparison of treatment response and PFS of NSCLC patients among different genotypes or regimens was made by Chi-square test. Results indicated that mRNA and protein expression of PARP1 dramatically increased in NSCLC tissues in comparison to paired para-carcinoma tissues (P<0.05). TC/CC mutant genotypes were associated with markedly enhanced PARP1 mRNA level compared with TT genotype (P=0.011). No significant difference was discovered in PARP1 protein expression among TT, TC or CC genotypes (P>0.05). Subjects with variant allele C had higher risk of NSCLC in comparison to allele T carriers [odds ratio (OR) =1.560; P=0.000]. NSCLC patients carrying mutational TC or CC genotypes were correlated with unfavorable response to platinum-based chemotherapy (TT vs.TC vs.CC, P=0.010), and shorter PFS compared to TT genotype (TT vs.TC vs.CC, P=0.009). T2285C mutation of PARP1 resulted in the enhancement of its mRNA, but the decrease of enzyme activity in tumor cell. Overexpression of SIRT7 attenuated PARP1 expression and activity. These findings suggest the variant allele C of T2285C polymorphism of PARP1 linked to an increase of NSCLC risk, and unfavorable efficacy and prognosis of NSCLC patients with platinum-based chemotherapy, which might be associated with enhancement of its mRNA expression and the diminishment of activity. Identification of PARP1 T2285C polymorphism and mRNA expression may be the promising way for the individualized treatment of NSCLC.

The Role of HECT-Type E3 Ligase in the Development of Cardiac Disease

Despite advances in medicine, cardiac disease remains an increasing health problem associated with a high mortality rate. Maladaptive cardiac remodeling, such as cardiac hypertrophy and fibrosis, is a risk factor for heart failure; therefore, it is critical to identify new therapeutic targets. Failing heart is reported to be associated with hyper-ubiquitylation and impairment of the ubiquitin–proteasome system, indicating an importance of ubiquitylation in the development of cardiac disease. Ubiquitylation is a post-translational modification that plays a pivotal role in protein function and degradation. In 1995, homologous to E6AP C-terminus (HECT) type E3 ligases were discovered. E3 ligases are key enzymes in ubiquitylation and are classified into three families: really interesting new genes (RING), HECT, and RING-between-RINGs (RBRs). Moreover, 28 HECT-type E3 ligases have been identified in human beings. It is well conserved in evolution and is characterized by the direct attachment of ubiquitin to substrates. HECT-type E3 ligase is reported to be involved in a wide range of human diseases and health. The role of HECT-type E3 ligases in the development of cardiac diseases has been uncovered in the last decade. There are only a few review articles summarizing recent advancements regarding HECT-type E3 ligase in the field of cardiac disease. This study focused on cardiac remodeling and described the role of HECT-type E3 ligases in the development of cardiac disease. Moreover, this study revealed that the current knowledge could be exploited for the development of new clinical therapies.

Sorting nexin 3 induces heart failure via promoting retromer-dependent nuclear trafficking of STAT3

Sorting nexins (SNXs), the retromer-associated cargo binding proteins, have emerged as critical regulators of the trafficking of proteins involved in the pathogenesis of diverse diseases. However, studies of SNXs in the development of cardiovascular diseases, especially cardiac hypertrophy and heart failure, are lacking. Here, we ask whether SNX3, the simplest structured isoform in the SNXs family, may act as a key inducer of myocardial injury. An increased level of SNX3 was observed in failing hearts from human patients and mice. Cardiac-specific Snx3 knockout (Snx3-cKO) mice and Snx3 transgenic (Snx3-cTg) mice were generated to evaluate the role of Snx3 in myocardial hypertrophy, fibrosis, and heart function by morphology, echocardiography, histological staining, and hypertrophic biomarkers. We report that Snx3-cKO in mice significantly protected against isoproterenol (ISO)-induced cardiac hypertrophy at 12 weeks. Conversely, Snx3-cTg mice were more susceptible to ISO-induced cardiac hypertrophy at 12 weeks and showed aggravated cardiac injury even heart failure at 24 weeks. Immunoprecipitation-based mass spectrometry, immunofluorescent staining, co-immunoprecipitation, localized surface plasmon resonance, and proximity ligation assay were performed to examine the direct interaction of SNX3-retromer with signal transducer and activator of transcription 3 (STAT3). We discovered that STAT3 was a new interacting partner of SNX3-retromer, and SNX3-retromer served as an essential platform for assembling gp130/JAK2/STAT3 complexes and subsequent phosphorylation of STAT3 by direct combination at EE. SNX3-retromer and STAT3 complexes were transiently imported into the nucleus after hypertrophic stimuli. The pharmacological inhibition or knockdown of STAT3 reversed SNX3 overexpression-induced myocardial injury. STAT3 overexpression blunts the beneficial function of SNX3 knockdown on hypertrophic cardiomyocytes. We show that SNX3-retromer promoted importin α3-mediated STAT3 nuclear trafficking and ultimately leading to cardiac injury. Taken together, our study reveals that SNX3 plays a key role in cardiac function and implicates SNX3 as a potential therapeutic target for cardiac hypertrophy and heart failure.

The poly(ADP-ribosyl)ation of BRD4 mediated by PARP1 promoted pathological cardiac hypertrophy

The bromodomain and extraterminal (BET) family member BRD4 is pivotal in the pathogenesis of cardiac hypertrophy. BRD4 induces hypertrophic gene expression by binding to the acetylated chromatin, facilitating the phosphorylation of RNA polymerases II (Pol II) and leading to transcription elongation. The present study identified a novel post-translational modification of BRD4: poly(ADP-ribosyl)ation (PARylation), that was mediated by poly(ADP-ribose)polymerase-1 (PARP1) in cardiac hypertrophy. BRD4 silencing or BET inhibitors JQ1 and MS417 prevented cardiac hypertrophic responses induced by isoproterenol (ISO), whereas overexpression of BRD4 promoted cardiac hypertrophy, confirming the critical role of BRD4 in pathological cardiac hypertrophy. PARP1 was activated in ISO-induced cardiac hypertrophy and facilitated the development of cardiac hypertrophy. BRD4 was involved in the prohypertrophic effect of PARP1, as implied by the observations that BRD4 inhibition or silencing reversed PARP1-induced hypertrophic responses, and that BRD4 overexpression suppressed the anti-hypertrophic effect of PARP1 inhibitors. Interactions of BRD4 and PARP1 were observed by co-immunoprecipitation and immunofluorescence. PARylation of BRD4 induced by PARP1 was investigated by PARylation assays. In response to hypertrophic stimuli like ISO, PARylation level of BRD4 was elevated, along with enhanced interactions between BRD4 and PARP1. By investigating the PARylation of truncation mutants of BRD4, the C-terminal domain (CTD) was identified as the PARylation modification sites of BRD4. PARylation of BRD4 facilitated its binding to the transcription start sites (TSS) of hypertrophic genes, resulting in enhanced phosphorylation of RNA Pol II and transcription activation of hypertrophic genes. The present findings suggest that strategies targeting inhibition of PARP1-BRD4 might have therapeutic potential for pathological cardiac hypertrophy.

Bone marrow mesenchymal stem cells inhibit cardiac hypertrophy by enhancing FoxO1 transcription

Bone marrow-derived mesenchymal stem cells (BMSCs) have therapeutic potential for certain heart diseases. Previous studies have shown that stem cells inhibit cardiac hypertrophy; however, it is necessary to explore the mechanisms underlying this effect. This study aimed to investigate the possible mechanism underlying the inhibitory effect of BMSCs on cardiomyocyte hypertrophy. We induced cardiomyocyte hypertrophy in cultured rat cells through isoproterenol (ISO) treatment with or without BMSC coculture. A microarray was performed to analyze messenger RNA expression in response to ISO treatment and BMSC coculture. Pathway enrichment analysis showed that the expression of differential genes was closely related to the 5'-adenosine monophosphate-activated protein kinase (AMPK) signaling pathway and that the expression of forkhead box O 1 (FoxO1) was significantly increased in the presence of BMSCs. Furthermore, we determined the expression levels of p-AMPK/AMPK and p-FoxO1/FoxO1 by western blot analysis. The expression of p-AMPK/AMPK was upregulated, whereas that of p-FoxO1/FoxO1 was downregulated upon coculturing with BMSCs. The AMPK-specific antagonist Compound C inhibited the downregulation of p-FoxO1/FoxO1 induced by the BMSC coculture. Furthermore, treatment with the specific FoxO1 antagonist AS1842856 reduced the inhibitory effects of BMSCs on cardiomyocyte hypertrophy in vivo and in vitro. Our present study demonstrates the inhibition of cardiomyocyte hypertrophy by BMSCs, which occurs partly through the AMPK-FoxO1 signaling pathway.

The role of FOXOs and autophagy in cancer and metastasis-Implications in therapeutic development

Autophagy is a highly conserved intracellular degradation process that plays a crucial role in cell survival and stress reactions as well as in cancer development and metastasis. Autophagy process involves several steps including sequestration, fusion of autophagosomes with lysosomes and degradation. Forkhead box O (FOXO) transcription factors regulate the expression of genes involved in cellular metabolic activity and signaling pathways of cancer growth and metastasis. Recent evidence suggests that FOXO proteins are also involved in autophagy regulation. The relationship among FOXOs, autophagy, and cancer has been drawing attention of many who work in the field. This study summarizes the role of FOXO proteins and autophagy in cancer growth and metastasis and analyzes their potential roles in cancer disease management.

E3 Ubiquitin ligase NEDD4 family‑regulatory network in cardiovascular disease

Protein ubiquitination represents a critical modification occurring after translation. E3 ligase catalyzes the covalent binding of ubiquitin to the protein substrate, which could be degraded. Ubiquitination as an important protein post-translational modification is closely related to cardiovascular disease. The NEDD4 family, belonging to HECT class of E3 ubiquitin ligases can recognize different substrate proteins, including PTEN, ENaC, Nav1.5, SMAD2, PARP1, Septin4, ALK1, SERCA2a, TGFβR3 and so on, via the WW domain to catalyze ubiquitination, thus participating in multiple cardiovascular-related disease such as hypertension, arrhythmia, myocardial infarction, heart failure, cardiotoxicity, cardiac hypertrophy, myocardial fibrosis, cardiac remodeling, atherosclerosis, pulmonary hypertension and heart valve disease. However, there is currently no review comprehensively clarifying the important role of NEDD4 family proteins in the cardiovascular system. Therefore, the present review summarized recent studies about NEDD4 family members in cardiovascular disease, providing novel insights into the prevention and treatment of cardiovascular disease. In addition, assessing transgenic animals and performing gene silencing would further identify the ubiquitination targets of NEDD4. NEDD4 quantification in clinical samples would also constitute an important method for determining NEDD4 significance in cardiovascular disease.

Role of FOXO Transcription Factors in Cancer Metabolism and Angiogenesis

Forkhead box O transcription factors (FOXOs) regulate several signaling pathways and play crucial roles in health and disease. FOXOs are key regulators of the expression of genes involved in multiple cellular processes and their deregulation has been implicated in cancer. FOXOs are generally considered tumor suppressors and evidence also suggests that they may have a role in the regulation of cancer metabolism and angiogenesis. In order to continue growing and proliferating, tumor cells have to reprogram their metabolism and induce angiogenesis. Angiogenesis refers to the process of new blood capillary formation from pre-existing vessels, which is an essential driving force in cancer progression and metastasis through supplying tumor cells with oxygen and nutrients. This review summarizes the roles of FOXOs in the regulation of cancer metabolism and angiogenesis. A deeper knowledge of the involvement of FOXOs in these two key processes involved in cancer dissemination may help to develop novel therapeutic approaches for cancer treatment.

Selective targeting of ubiquitination and degradation of PARP1 by E3 ubiquitin ligase WWP2 regulates isoproterenol-induced cardiac remodeling

The elevated expression of poly(ADP-ribose) polymerase-1 (PARP1) and increased PARP1 activity, namely, poly(ADP-ribosyl)ation (PARylation), have been observed in cardiac remodeling, leading to extreme energy consumption and myocardial damage. However, the mechanisms underlying the regulation of PARP1 require further study. WWP2, a HECT-type E3 ubiquitin ligase, is highly expressed in the heart, but its function there is largely unknown. Here, we clarified the role of WWP2 in the regulation of PARP1 and the impact of this regulatory process on cardiac remodeling. We determined that the knockout of WWP2 specifically in myocardium decreased the level of PARP1 ubiquitination and increased the effects of isoproterenol (ISO)-induced PARP1 and PARylation, in turn aggravating ISO-induced myocardial hypertrophy, heart failure, and myocardial fibrosis. Similar findings were obtained in a model of ISO-induced H9c2 cells with WWP2 knockdown, while the reexpression of WWP2 significantly increased PARP1 ubiquitination and decreased PAPR1 and PARylation levels. Mechanistically, coimmunoprecipitation results identified that WWP2 is a novel interacting protein of PARP1 and mainly interacts with its BRCT domain, thus mediating the degradation of PARP1 through the ubiquitin-proteasome system. In addition, lysine 418 (K418) and lysine 249 (K249) were shown to be of critical importance in regulating PARP1 ubiquitination and degradation by WWP2. These findings reveal a novel WWP2-PARP1 signal transduction pathway involved in controlling cardiac remodeling and may provide a basis for exploring new strategies for treating heart disorders related to cardiac remodeling.

SIRT3 inhibits cardiac hypertrophy by regulating PARP-1 activity

Sirtuin 3 (SIRT3) is a type III histone deacetylase that inhibits cardiac hypertrophy. It is mainly localized in the mitochondria and is thus implicated in mitochondrial metabolism. Recent studies have shown that SIRT3 can also accumulate in the nuclear under stressed conditions, and participated in histone deacetylation of target proteins. Poly [ADP-ribose] polymerase 1 (PARP-1) functions as an important PARP isoform that was involved in cardiac hypertrophy. Our experiments showed that SIRT3 accumulated in the nuclear of cardiomyocytes treated with isoproterenol or SIRT3 overexpression. Moreover, overexpression of SIRT3 by adenovirus inhibited the expression of cardiac hypertrophic genes-ANF and BNP, as well as abrogating PARP-1 activation induced by isoproterenol or phenylephrine. In addition, co-immunoprecipitation experiments revealed that SIRT3 could interact with PARP-1, and overexpression of SIRT3 could decrease the acetylation level of PARP-1. Our results indicate that SIRT3 exerts protective effects against cardiac hypertrophy by reducing the level of acetylation and activity of PARP-1, thus providing novel mechanistic insights into SIRT3-mediated cardiprotective actions.

High expression of FOXO3 is associated with poor prognosis in patients with hepatocellular carcinoma

The role of forkhead box O3 (FOXO3) as a tumor suppressor gene and its association with the human lifespan is well documented. However, several studies have indicated that high expression of FOXO3 is also significantly associated with tumorigenesis. The aim of the present study was to determine the clinical significance of FOXO3 in the development and prognosis of hepatocellular carcinoma (HCC). mRNA expression data of FOXO3 from The Cancer Genome Atlas database was analyzed through the UALCAN online tool to compare the expression of FOXO3 between HCC and normal liver tissues. Subsequently, the expression of FOXO3 at the protein level was investigated via immunohistochemical staining of 314 HCC and 150 non-cancerous liver tissue samples. The association between protein expression and clinicopathological parameters was analyzed using the χ² test, and the effect of FOXO3 expression on survival was assessed via Kaplan-Meier analysis. The expression of FOXO3 mRNA was significantly higher in HCC in comparison with healthy tissues. High FOXO3 protein expression was revealed in 43/150 non-cancerous liver tissues, and in 238/314 HCC samples. A significant association was demonstrated between FOXO3 expression and metastasis, Tumor-Node-Metastasis stage, Edmondson grade, α-fetoprotein level and overall survival. In conclusion, the high expression of FOXO3 predicts a poor prognosis in patients with HCC, indicating this protein as a potential therapeutic target in HCC.

Chrysophanol protects against doxorubicin-induced cardiotoxicity by suppressing cellular PARylation

The clinical application of doxorubicin (DOX) in cancer chemotherapy is limited by its life-threatening cardiotoxic effects. Chrysophanol (CHR), an anthraquinone compound isolated from the rhizome of Rheum palmatum L., is considered to play a broad role in a variety of biological processes. However, the effects of CHR׳s cardioprotection in DOX-induced cardiomyopathy is poorly understood. In this study, we found that the cardiac apoptosis, mitochondrial injury and cellular PARylation levels were significantly increased in H9C2 cells treated by Dox, while these effects were suppressed by CHR. Similar results were observed when PARP1 activity was suppressed by its inhibitors 3-aminobenzamide (3AB) and ABT888. Ectopic expression of PARP1 effectively blocked this CHR׳s cardioprotection against DOX-induced cardiomyocyte injury in H9C2 cells. Furthermore, pre-administration with both CHR and 3AB relieved DOX-induced cardiac apoptosis, mitochondrial impairment and heart dysfunction in Sprague-Dawley rat model. These results revealed that CHR protects against DOX-induced cardiotoxicity by suppressing cellular PARylation and provided critical evidence that PARylation may be a novel target for DOX-induced cardiomyopathy.

SESN2 protects against doxorubicin-induced cardiomyopathy via rescuing mitophagy and improving mitochondrial function

The clinical application of doxorubicin (Dox) in cancer therapy is limited by its serious cardiotoxicity. Our previous studies and others have recognized that mitochondrial dysfunction is the common feature of Dox-induced cardiotoxicity. However, mechanisms underlying mitochondrial disorders remained largely unknown. SESN2, a highly conserved and stress-inducible protein, is involved in mitochondrial function and autophagy in cardiovascular diseases. This study aimed to investigate whether SESN2 affects Dox-induced cardiotoxicity and the underlying mechanisms. Sprague-Dawley rats and neonatal rat cardiomyocytes were treated with Dox. SESN2 expression was assessed. The effects of SESN2 on Dox-induced cardiotoxicity were assessed by functional gain and loss experiments. Echocardiographic parameters, morphological and histological analyses, transmission electron microscope and immunofluorescence assays were used to assess cardiac and mitochondrial function. The protein expression of SESN2 was significantly reduced following Dox stimulation. Both knockout of SESN2 by sgRNA and Dox treatment resulted in the inhibition of Parkin-mediated mitophagy, marked cardiomyocytes apoptosis and mitochondria dysfunction. Ectopic expression of SESN2 effectively protected against Dox-induced cardiomyocyte apoptosis, mitochondrial injury and cardiac dysfunction. Mechanistically, SESN2 interacted with Parkin and p62, promoted accumulation of Parkin to mitochondria and then alleviated Dox-caused inhibition of Parkin mediated mitophagy. Ultimately, the clearance of damaged mitochondria and mitochondrial function were improved following SESN2 overexpression. SESN2 protected against Dox-induced cardiotoxicity through improving mitochondria function and mitophagy. These results established SESN2 as a key player in mitochondrial function and provided a potential therapeutic approach to Dox-induced cardiomyopathy.

PARP1 interacts with HMGB1 and promotes its nuclear export in pathological myocardial hypertrophy

High-mobility group box 1 (HMGB1) exhibits various functions according to its subcellular location, which is finely conditioned by diverse post-translational modifications, such as acetylation. The nuclear HMGB1 may prevent from cardiac hypertrophy, whereas its exogenous protein is proven to induce hypertrophic response. This present study sought to investigate the regulatory relationships between poly(ADP-ribose) polymerase 1 (PARP1) and HMGB1 in the process of pathological myocardial hypertrophy. Primary-cultured neonatal rat cardiomyocytes (NRCMs) were respectively incubated with three cardiac hypertrophic stimulants, including angiotensin II (Ang II), phenylephrine (PE), and isoproterenol (ISO), and cell surface area and the mRNA expression of hypertrophic biomarkers were measured. the catalytic activity of PARP1 was remarkably enhanced, meanwhile HMGB1 excluded from the nucleus. PARP1 overexpression by infecting with adenovirus PARP1 (Ad-PARP1) promoted the nuclear export of HMGB1, facilitated its secretion outside the cell, aggravated cardiomyocyte hypertrophy, which could be alleviated by HMGB1 overexpression. PE treatment led to the similar results, while that effect was widely depressed by PARP1 silencing or its specific inhibitor AG14361. Moreover, SD rats were intraperitoneally injected with 3-aminobenzamide (3AB, 20 mg/kg every day, a well-established PARP1 inhibitor) 7 days after abdominal aortic constriction (AAC) surgery for 6 weeks, echocardiography and morphometry of the hearts were measured. Pre-treatment of 3AB relieved AAC-caused the translocation of nuclear HMGB1 protein, cardiac hypertrophy, and heart dysfunction. Our research offers a novel evidence that PARP1 combines with HMGB1 and accelerates its translocation from nucleus to cytoplasm, and the course finally causes cardiac hypertrophy.

Sirtuin 1 represses PKC-ζ activity through regulating interplay of acetylation and phosphorylation in cardiac hypertrophy

BACKGROUND AND PURPOSE

Activation of PKC-ζ is closely linked to the pathogenesis of cardiac hypertrophy. PKC-ζ can be activated by certain lipid metabolites such as phosphatidylinositol (3,4,5)-trisphosphate and ceramide. However, its endogenous negative regulators are not well defined. Here, the role of the sirtuin1-PKC-ζ signalling axis and the underlying molecular mechanisms were investigated in cardiac hypertrophy.

EXPERIMENTAL APPROACH

Cellular hypertrophy in cultures of cardiac myocytes, from neonatal Sprague-Dawley rats, was monitored by measuring cell surface area and the mRNA levels of hypertrophic biomarkers. Interaction between sirtuin1 and PKC-ζ was investigated by co-immunoprecipitation and confocal immunofluorescence microscopy. Sirtuin1 activation was enhanced by resveratrol treatment or Ad-sirtuin1 transfection. A model of cardiac hypertrophy in Sprague-Dawley rats was established by abdominal aortic constriction surgery or induced by isoprenaline in vivo.

KEY RESULTS

Overexpression of PKC-ζ led to cardiac hypertrophy and increased activity of NF-κB, ERK1/2 and ERK5, which was ameliorated by sirtuin1 overexpression. Enhancement of sirtuin1 activity suppressed acetylation of PKC-ζ, hindered its binding to phosphoinositide-dependent kinase 1 and inhibited PKC-ζ phosphorylation in cardiac hypertrophy. Consequently, the downstream pathways of PKC-ζ' were suppressed in cardiac hypertrophy. This regulation loop suggests a new role for sirtuin1 in mediation of cardiac hypertrophy.

CONCLUSIONS AND IMPLICATIONS

Sirtuin1 is an endogenous negative regulator for PKC-ζ and mediates its activity via regulating the acetylation and phosphorylation in the pathogenesis of cardiac hypertrophy. Targeting the sirtuin1-PKC-ζ signalling axis may suggest a novel therapeutic approach against cardiac hypertrophy.

CARM1 contributes to skeletal muscle wasting by mediating FoxO3 activity and promoting myofiber autophagy

Coactivator-associated arginine methyltransferase 1 (CARM1) is involved in a variety of biological processes in different cell types and disease conditions, including myogenesis. However, the specific function of CARM1 in skeletal muscle wasting under pathologic conditions remains unclear. Here, we identify CARM1 as a novel participant in muscular atrophy. Increases in CARM1 protein levels correlated positively with the loss of muscle mass upon denervation in mice. Notably, the knockdown of CARM1 represses the progression of muscle wasting and the expression of the atrophy-related genes Atrogin-1 and MuRF1 in vivo and in vitro. With respect to the underlying mechanism, we show that CARM1 interacts with and asymmetrically dimethylates FoxO3 (a specific transcription factor that controls atrophy-related gene expression). This methylation modification by CARM1 is required for FoxO3-dependent transcription. Accordingly, a CARM1 methyltransferase inhibitor also restrains the expression of Atrogin-1 and MuRF1 and myotube atrophy. Furthermore, CARM1 knockdown induces a remarkable myofiber autophagic deficit during the atrophy process. Altogether, our study identifies a crucial regulator of skeletal muscle atrophy and suggests that CARM1 is a potential target for the prevention of muscle atrophy.

Critical role of FOXO3a in carcinogenesis

FOXO3a is a member of the FOXO subfamily of forkhead transcription factors that mediate a variety of cellular processes including apoptosis, proliferation, cell cycle progression, DNA damage and tumorigenesis. It also responds to several cellular stresses such as UV irradiation and oxidative stress. The function of FOXO3a is regulated by a complex network of processes, including post-transcriptional suppression by microRNAs (miRNAs), post-translational modifications (PTMs) and protein–protein interactions. FOXO3a is widely implicated in a variety of diseases, particularly in malignancy of breast, liver, colon, prostate, bladder, and nasopharyngeal cancers. Emerging evidences indicate that FOXO3a acts as a tumor suppressor in cancer. FOXO3a is frequently inactivated in cancer cell lines by mutation of the FOXO3a gene or cytoplasmic sequestration of FOXO3a protein. And its inactivation is associated with the initiation and progression of cancer. In experimental studies, overexpression of FOXO3a inhibits the proliferation, tumorigenic potential, and invasiveness of cancer cells, while silencing of FOXO3a results in marked attenuation in protection against tumorigenesis. The role of FOXO3a in both normal physiology as well as in cancer development have presented a great challenge to formulating an effective therapeutic strategy for cancer. In this review, we summarize the recent findings and overview of the current understanding of the influence of FOXO3a in cancer development and progression.

G3BP2 is involved in isoproterenol-induced cardiac hypertrophy through activating the NF-κB signaling pathway

The RasGAP SH3 domain-binding proteins (G3BPs) are a family of RNA-binding proteins that can co-ordinate signal transduction and post-transcriptional gene regulation. G3BPs have been shown to be involved in mediating a great diversity of cellular processes such as cell survival, growth, proliferation and apoptosis. But the potential roles of G3BPs in the pathogenesis and progression of cardiovascular diseases remain to be clarified. In the present study, we provide the first evidence that suggests the participation of G3BP2 in cardiac hypertrophy. In cultured neonatal rat cardiomyocytes (NRCMs), treatment with isoproterenol (ISO, 0.1-100 μmol/L) significantly elevated the mRNA and protein levels of G3BP2. Similar results were observed in the hearts of rats subjected to 7D-injection of ISO, accompanied by obvious heart hypertrophy and elevated the expression of hypertrophy marker genes ANF, BNP and β-MHC in heart tissues. Overexpression of G3BP2 in NRCMs led to hypertrophic responses evidenced by increased cellular surface area and the expression of hypertrophy marker genes, whereas knockdown of G3BP2 significantly attenuated ISO-induced hypertrophy of NRCMs. We further showed that G3BP2 directly interacted with IκBα and promoted the aggregation of the NF-κB subunit p65 in the nucleus and increased NF-κB-dependent transcriptional activity. NF-κB inhibition with PDTC (50 μmol/L) or p65 knockdown significantly decreased the hypertrophic responses in NRCMs induced by ISO or G3BP2 overexpression. These results give new insight into the functions of G3BP2 and may help further elucidate the molecular mechanisms underlying cardiac hypertrophy.