METTL3 and N6-Methyladenosine Promote Homologous Recombination-Mediated Repair of DSBs by Modulating DNA-RNA Hybrid Accumulation.

Double-strand breaks (DSBs) are the most deleterious DNA lesions, which, if left unrepaired, may lead to genome instability or cell death. Here, we report that, in response to DSBs, the RNA methyltransferase METTL3 is activated by ATM-mediated phosphorylation at S43. Phosphorylated METTL3 is then localized to DNA damage sites, where it methylates the N6 position of adenosine (m6A) in DNA damage-associated RNAs, which recruits the m6A reader protein YTHDC1 for protection. In this way, the METTL3-m6A-YTHDC1 axis modulates accumulation of DNA-RNA hybrids at DSBs sites, which then recruit RAD51 and BRCA1 for homologous recombination (HR)-mediated repair. METTL3-deficient cells display defective HR, accumulation of unrepaired DSBs, and genome instability. Accordingly, depletion of METTL3 significantly enhances the sensitivity of cancer cells and murine xenografts to DNA damage-based therapy. These findings uncover the function of METTL3 and YTHDC1 in HR-mediated DSB repair, which may have implications for cancer therapy.

DNMT1 determines osteosarcoma cell resistance to apoptosis by associatively modulating DNA and mRNA cytosine-5 methylation.

Cellular apoptosis is a central mechanism leveraged by chemotherapy to treat human cancers. 5-Methylcytosine (m5C) modifications installed on both DNA and mRNA are documented to regulate apoptosis independently. However, the interplay or crosstalk between them in cellular apoptosis has not yet been explored. Here, we reported that promoter methylation by DNMT1 coordinated with mRNA methylation by NSun2 to regulate osteosarcoma cell apoptosis. DNMT1 was induced during osteosarcoma cell apoptosis triggered by chemotherapeutic drugs, whereas NSun2 expression was suppressed. DNMT1 was found to repress NSun2 expression by methylating the NSun2 promoter. Moreover, DNMT1 and NSun2 regulate the anti-apoptotic genes AXL, NOTCH2, and YAP1 through DNA and mRNA methylation, respectively. Upon exposure to cisplatin or doxorubicin, DNMT1 elevation drastically reduced the expression of these anti-apoptotic genes via enhanced promoter methylation coupled with NSun2 ablation-mediated attenuation of mRNA methylation, thus rendering osteosarcoma cells to apoptosis. Collectively, our findings establish crosstalk of importance between DNA and RNA cytosine methylations in determining osteosarcoma resistance to apoptosis during chemotherapy, shedding new light on future treatment of osteosarcoma, and adding additional layers to the control of gene expression at different epigenetic levels.

HuB and HuD repress telomerase activity by dissociating HuR from TERC.

The ubiquitous RNA-binding protein HuR (ELAVL1) promotes telomerase activity by associating with the telomerase noncoding RNA TERC. However, the role of the neural-specific members HuB, HuC, and HuD (ELAVL2-4) in telomerase activity is unknown. Here, we report that HuB and HuD, but not HuC, repress telomerase activity in human neuroblastoma cells. By associating with AU-rich sequences in TERC, HuB and HuD repressed the assembly of the TERT-TERC core complex. Furthermore, HuB and HuD competed with HuR for binding to TERC and antagonized the function of HuR that was previously shown to enhance telomerase activity to promote cell growth. Our findings reveal a novel mechanism controlling telomerase activity in human neuroblastoma cells that involves a competition between HuR and the related, neural-specific proteins HuB and HuD.

The G4 resolvase RHAU modulates mRNA translation and stability to sustain postnatal heart function and regeneration.

Post-transcriptional regulation of mRNA translation and stability is primarily achieved by RNA-binding proteins, which are of increasing importance for heart function. Furthermore, G-quadruplex (G4) and G4 resolvase activity are involved in a variety of biological processes. However, the role of G4 resolvase activity in heart function remains unknown. The present study aims to investigate the role of RNA helicase associated with adenylate- and uridylate-rich element (RHAU), an RNA-binding protein with G4 resolvase activity in postnatal heart function through deletion of Rhau in the cardiomyocytes of postnatal mice. RHAU-deficient mice displayed progressive pathological remodeling leading to heart failure and mortality and impaired neonatal heart regeneration. RHAU ablation reduced the protein levels but enhanced mRNA levels of Yap1 and Hexim1 that are important regulators for heart development and postnatal heart function. Furthermore, RHAU was found to associate with both the 5' and 3' UTRs of these genes to destabilize mRNA and enhance translation. Thus, we have demonstrated the important functions of RHAU in the dual regulation of mRNA translation and stability, which is vital for heart physiology.

E2F1-mediated AUF1 upregulation promotes HCC development and enhances drug resistance via stabilization of AKR1B10.

The AU-rich binding factor 1 (AUF1) is one of the well known adenylate-uridylate-rich element (ARE)-specific RNA-binding proteins (ARE-BPs) for which dysregulation has been reported in various human cancers. However, the involvement of AUF1 in the initiation and progression of hepatocellular carcinoma (HCC) is still elusive. In this study, we aimed at exploring the clinical significance, function, and mechanism of the abnormal expression of AUF1 in HCC. Using a bioinformatics analysis of The Cancer Genome Atlas (TCGA) and Liver Cancer Institute (LCI) database, we identified that AUF1 was abnormally highly expressed in HCC tissues and that the high expression of AUF1 was correlated with poor prognosis in patients with HCC. We also confirmed the increased AUF1 expression and its prognostic value in our HBV-related HCC cohorts. AUF1 overexpression in hepatoma cells promoted cell proliferation and increased the resistance of hepatoma cells toward doxorubicin, whereas knockdown of AUF1 exerted the opposite effects. Mechanistically, we demonstrated that AKR1B10 was a critical target of AUF1 and was essential for sustaining the AUF1-induced proliferation and drug resistance of hepatoma cells. AUF1 increased AKR1B10 expression by binding to the 3'UTR region of AKR1B10 mRNA and stabilizing AKR1B10 mRNA. Additionally, we demonstrated that E2F1 enhanced AUF1 expression in HCC at the transcription level. Our study revealed a novel role of AUF1 in promoting the development and drug resistance of HCC via the post-transcriptional regulation of AKR1B10 expression. The E2F1/AUF1/AKR1B10 axis can serve as a potential therapeutic target in HCC.

NSun2 regulates aneurysm formation by promoting autotaxin expression and T cell recruitment.

Abdominal aortic aneurysm (AAA) is characterized by inflammatory cell infiltration and aggravated by hyperhomocysteinemia (HHcy). It is unknown whether the homocysteine (Hcy)-activated RNA methyltransferase NOP2/Sun domain family member 2 (NSun2) is associated with AAA. Here, we found that NSun2 deficiency significantly attenuated elastase-induced and HHcy-aggravated murine AAA with decreased T cell infiltration in the vessel walls. T cell labeling and adoptive transfer experiments confirmed that NSun2 deficiency inhibited the chemotaxis of vessels to T cells. RNA sequencing of endothelial cells showed that Hcy induced the accumulation of various metabolic enzymes of the phospholipid PC-LPC-LPA metabolic pathway, especially autotaxin (ATX). In the elastase-induced mouse model of AAA, ATX was specifically expressed in the endothelium and the plasma ATX concentration was upregulated and even higher in the HHcy group, which were decreased dramatically by NSun2 knockdown. In vitro Transwell experiments showed that ATX dose-dependently promoted T cell migration. HHcy may upregulate endothelial ATX expression and secretion and in turn recruit T cells into the vessel walls to induce vascular inflammation and consequently accelerate the pathogenesis of AAA. Mechanistically, secreted ATX interacted with T cells by binding to integrin α4, which subsequently activated downstream FAK/Src-RhoA signaling pathways and then induced T cell chemokinesis and adhesion. ATX overexpression in the vessel walls reversed the inhibited development of AAA in the NSun2-deficient mice. Therefore, NSun2 mediates the development of HHcy-aggravated AAA primarily by increasing endothelial ATX expression, secretion and T cell migration, which is a novel mechanism for HHcy-aggravated vascular inflammation and pathogenesis of AAA.

Fine-Tuning of PGC1α Expression Regulates Cardiac Function and Longevity.

RATIONALE: PGC1α (peroxisome proliferator-activated receptor gamma coactivator 1α) represents an attractive target interfering bioenergetics and mitochondrial homeostasis, yet multiple attempts have failed to upregulate PGC1α expression as a therapy, for instance, causing cardiomyopathy. OBJECTIVE: To determine whether a fine-tuning of PGC1α expression is essential for cardiac homeostasis in a context-dependent manner. METHODS AND RESULTS: Moderate cardiac-specific PGC1α overexpression through a ROSA26 locus knock-in strategy was utilized in WT (wild type) mice and in G3Terc-/- (third generation of telomerase deficient; hereafter as G3) mouse model, respectively. Ultrastructure, mitochondrial stress, echocardiographic, and a variety of biological approaches were applied to assess mitochondrial physiology and cardiac function. While WT mice showed a relatively consistent PGC1α expression from 3 to 12 months old, age-matched G3 mice exhibited declined PGC1α expression and compromised mitochondrial function. Cardiac-specific overexpression of PGC1α (PGC1αOE) promoted mitochondrial and cardiac function in 3-month-old WT mice but accelerated cardiac aging and significantly shortened life span in 12-month-old WT mice because of increased mitochondrial damage and reactive oxygen species insult. In contrast, cardiac-specific PGC1α knock in in G3 (G3 PGC1αOE) mice restored mitochondrial homeostasis and attenuated senescence-associated secretory phenotypes, thereby preserving cardiac performance with age and extending health span. Mechanistically, age-dependent defect in mitophagy is associated with accumulation of damaged mitochondria that leads to cardiac impairment and premature death in 12-month-old WT PGC1αOE mice. In the context of telomere dysfunction, PGC1α induction replenished energy supply through restoring the compromised mitochondrial biogenesis and thus is beneficial to old G3 heart. CONCLUSIONS: Fine-tuning the expression of PGC1α is crucial for the cardiac homeostasis because the balance between mitochondrial biogenesis and clearance is vital for regulating mitochondrial function and homeostasis. These results reinforce the importance of carefully evaluating the PGC1α-boosting strategies in a context-dependent manner to facilitate clinical translation of novel cardioprotective therapies.

Changes in levels of coagulation parameters in different trimesters among Chinese pregnant women.

BACKGROUND: This article is to explore changes in levels of coagulation parameters in different trimesters among healthy pregnant women in China. METHODS: A total of 760 eligible women were enrolled (first-trimester group: n = 183, second-trimester group: n = 183, third-trimester group: n = 263, non-pregnant group: n = 131). Seven parameters including prothrombin time (PT), activated partial thromboplastin time (APTT), thrombin time (TT), fibrinogen (FIB), D-dimer (DD), fibrinogen degradation products (FDP), and antithrombin III (ATIII), of all participants were collected. The non-parametric 2.5th-97.5th percentiles reference intervals were calculated for each parameter. RESULTS: The reference intervals for FIB, PT, APTT, TT, FDP, DD, and ATIII at first trimester were 2.11-4.32 g/L, 10.90-13.85 s, 24.60-39.28 s, 12.95-15.88 s, 0.04-2.55 µg/mL, 0.03-1.15 µg/mL, and 75.57%-125.31%, respectively. The reference intervals at second trimester were 2.31-4.77 g/L, 9.70-12.64 s, 24.16-35.43 s, 12.95-15.88 s, 0.15-7.40 µg/mL, 0.08-2.13 µg/mL, and 74.35%-119.28%, respectively. For the third-trimester, the intervals were 2.39-4.96 g/L, 9.20-11.95 s, 23.90-35.51 s, 13.41-18.00 s, 0.55-13.43 µg/mL, 0.15-3.60 µg/mL, and 71.61%-118.29%, respectively. The third-trimester group showed decreased PT, APTT, and ATIII and increased FIB, TT, DD and FDP as compared with the other groups. CONCLUSION: In this study, level changes of coagulation parameters in different trimesters were observed. And the ranges for coagulation parameters were presented, which may provide some reference for clinicians to more accurately monitor the coagulation and fibrinolytic system in pregnant women.

SIRT7 Deacetylates STRAP to Regulate p53 Activity and Stability.

Serine-threonine kinase receptor-associated protein (STRAP) functions as a regulator of both TGF-ß and p53 signaling that participates in the regulation of cell proliferation and cell death in response to various stresses. Here, we demonstrate that STRAP acetylation plays an important role in p53-mediated cell cycle arrest and apoptosis. STRAP is acetylated at lysines 147, 148, and 156 by the acetyltransferases CREB-binding protein (CBP) and that the acetylation is reversed by the deacetylase sirtuin7 (SIRT7). Hypo- or hyperacetylation mutations of STRAP at lysines 147, 148, and 156 (3KR or 3KQ) influence its activation and stabilization of p53. Moreover, following 5-fluorouracil (5-FU) treatment, STRAP is mobilized from the cytoplasm to the nucleus and promotes STRAP acetylation. Our finding on the regulation of STRAP links p53 with SIRT7 influencing p53 activity and stability.

The N6-methyladenosine (m6A)-forming enzyme METTL3 facilitates M1 macrophage polarization through the methylation of STAT1 mRNA.

Compelling evidence indicates that epigenetic regulations orchestrate dynamic macrophage polarization. N6-methyladenosine (m6A) methylation is the most abundant epigenetic modification of mammalian mRNA, but its role in macrophage polarization is still completely unknown. Here, we show that the m6A-catalytic enzyme methyltransferase like 3 (METTL3) is specifically upregulated following the M1 polarization of mouse macrophages. Furthermore, METTL3 knockdown through siRNA transfection markedly inhibited M1, but enhanced M2, macrophage polarization. Conversely, its overexpression via plasmid transfection greatly facilitated M1, but attenuated M2, macrophage polarization. Further methylated RNA immunoprecipitation and in vitro m6A methylation assays suggested that METTL3 directly methylates mRNA encoding signal transducer and activator of transcription 1 (STAT1), a master transcription factor controlling M1 macrophage polarization, at its coding sequence and 3'-untranslated regions. In addition, METTL3-mediated STAT1 mRNA methylation significantly increased mRNA stability and subsequently upregulated STAT1 expression. In conclusion, METTL3 drives M1 macrophage polarization by directly methylating STAT1 mRNA, potentially serving as an anti-inflammatory target.

Deletion of a flippase subunit Tmem30a in hematopoietic cells impairs mouse fetal liver erythropoiesis.

Transmembrane protein 30A (Tmem30a) is the ß-subunit of P4-ATPases which function as flippase that transports aminophospholipids such as phosphatidylserine from the outer to the inner leaflets of the plasma membrane to maintain asymmetric distribution of phospholipids. It has been documented that deficiency of Tmem30a led to exposure of phosphatidylserine. However, the role of Tmem30a in vivo remains largely unknown. Here we found that Vav-Cre-driven conditional deletion of Tmem30a in hematopoietic cells led to embryonic lethality due to severe anemia by embryonic day 16.5. The numbers of erythroid colonies and erythroid cells were decreased in the Tmem30a deficient fetal liver. This was accompanied by increased apoptosis of erythroid cells. Confocal microscopy analysis revealed an increase of localization of erythropoietin receptor to areas of membrane raft microdomains in response to erythropoietin stimulation in Ter119-erythroid progenitors, which was impaired in Tmem30a deficient cells. Moreover, erythropoietin receptor (EPOR)-mediated activation of the STAT5 pathway was significantly reduced in Tmem30a deficient fetal liver cells. Consistently, knockdown of TMEM30A in human CD34+ cells also impaired erythropoiesis. Our findings demonstrate that Tmem30a plays a critical role in erythropoiesis by regulating the EPOR signaling pathway through the formation of membrane rafts in erythroid cells.

NSun2 Deficiency Protects Endothelium From Inflammation via mRNA Methylation of ICAM-1.

RATIONALE: Vascular endothelial inflammation, including the expression of intercellular adhesion molecule 1 (ICAM-1), is a key event in vascular diseases. However, the mechanisms underlying the regulation of ICAM-1 are largely unknown. OBJECTIVE: To investigate the mechanisms on the regulation of ICAM-1 by NOP2/Sun domain family, member 2 (NSun2)-mediated mRNA methylation and the impact of NSun2-ICAM-1 regulatory process in vascular inflammation and allograft arteriosclerosis. METHODS AND RESULTS: By using in vitro, in cells, and in vivo methylation assays, we showed that the tRNA methyltransferase NSun2 methylated the ICAM-1 mRNA. Methylation by NSun2 promoted the translation of ICAM-1, thereby increasing the adhesion of leukocytes to endothelial cells. Tumor necrosis factor-α or homocysteine activated the methyltransferase activity of NSun2 by repressing the phosphorylation of NSun2 by Aurora-B. The levels of ICAM-1 induction and of leukocyte adhesion to vascular endothelium observed with homocysteine treatment in wild-type rats were markedly decreased in NSun2(-/-) rats. In a rat model of aortic allograft, the lack of donor NSun2 impaired the formation of allograft arteriosclerosis. CONCLUSIONS: NSun2 upregulates the expression of ICAM-1 by methylating ICAM-1 mRNA. This regulatory process impacts on vascular inflammation and allograft arteriosclerosis.

NSUN2-Mediated m5C Methylation and METTL3/METTL14-Mediated m6A Methylation Cooperatively Enhance p21 Translation.

N6-methyladenosine (m6A) and m5C methylation are two major types of RNA methylation, but the impact of joint modifications on the same mRNA is unknown. Here, we show that in p21 3'UTR, NSUN2 catalyzes m5C modification and METTL3/METTL14 catalyzes m6A modification. Interestingly, methylation at m6A by METTL3/METTL14 facilitates the methylation of m5C by NSUN2, and vice versa. NSUN2-mediated m5C and METTL3/METTL14-mediated m6A methylation synergistically enhance p21 expression at the translational level, leading to elevated expression of p21 in oxidative stress-induced cellular senescence. Our findings on p21 mRNA methylation and expression reveal that joint m6A and m5C modification of the same RNA may influence each other, coordinately affecting protein expression patterns. J. Cell. Biochem. 118: 2587-2598, 2017. © 2017 Wiley Periodicals, Inc.

Homocysteine upregulates interleukin-17A expression via NSun2-mediated RNA methylation in T lymphocytes.

Interleukin-17A (IL-17A) has been proven to participate in the process of various autoimmune diseases. The elevation of plasma homocysteine (Hcy), known as hyperhomocysteinemia (HHcy), is related to various chronic inflammatory diseases. Though HHcy-induced upregulation of IL-17A expression in T lymphocytes has been examined, the way in which IL-17A is regulated remains unclear. In this study, western blotting assays showed that Hcy (100 µM) upregulated NOP2/Sun domain family, member 2 (NSun2) expression in rat T lymphocytes. HHcy-induced upregulation of IL-17A observed in plasma of wild-type rats was markedly decreased in NSun2-/- rats in vivo. Mechanistically, by using in vitro methylation assays and high-performance liquid chromatography-mass spectrum (HPLC-MS) analysis, we showed that the tRNA methyltransferase NSun2 methylated the IL-17A mRNA in an m5C pattern. The results from bisulfite sequencing indicated that NSun2 methylated IL-17A mRNA at cytosine C466 in vitro and in vivo. Furthermore, we analyzed the activity of pGL3-derived reporters bearing IL-17A mRNA fragments and found that methylation by NSun2 promoted the translation of IL-17A. In conclusion, NSun2 mediates HHcy-induced upregulation of IL-17A expression by methylating IL-17A mRNA and promoting its translation in T lymphocytes.

Proteinase-activated receptor 2 promotes cancer cell migration through RNA methylation-mediated repression of miR-125b.

Proteinase activated-receptor 2 (PAR2) participates in cancer metastasis promoted by serine proteinases. The current study aimed to test the molecular mechanism by which PAR2 promotes cancer cell migration. In different cancer cells, activation of PAR2 by activating peptide (PAR2-AP) dramatically increased cell migration, whereas knock down of PAR2 inhibited cellular motility. The PAR2 activation also repressed miR-125b expression while miR-125b mimic successfully blocked PAR2-induced cell migration. Moreover, Grb associated-binding protein 2 (Gab2) was identified as a novel target gene of miR-125b and it mediated PAR2-induced cell migration. The correlation of PAR2 with miR-125b and Gab2 was further supported by the findings obtained from human colorectal carcinoma specimens. Remarkably, knock down of NOP2/Sun domain family, member 2 (NSun2), a RNA methyltransferase, blocked the reduction in miR-125b induced by PAR2. Furthermore, PAR2 activation increased the level of N(6)-methyladenosine (m(6)A)-containing pre-miR-125b in NSun2-dependent manner. Taken together, our results demonstrated that miR-125b mediates PAR2-induced cancer cell migration by targeting Gab2 and that NSun2-dependent RNA methylation contributes to the down-regulation of miR-125b by PAR2 signaling. These findings suggest a novel epigenetic mechanism by which microenvironment regulates cancer cell migration by altering miRNA expression.

miR-193a-3p functions as a tumor suppressor in lung cancer by down-regulating ERBB4.

ERBB4, one of four ErbB receptor tyrosine kinase family members, plays an important role in the etiology and progression of lung cancer. In this study, we found that the ERBB4 protein levels were consistently up-regulated in lung cancer tissues, whereas the mRNA levels varied randomly, suggesting that a post-transcriptional mechanism was involved in regulating ERBB4 expression. Because microRNAs are powerful post-transcriptional regulators of gene expression, we used bioinformatic analyses to search for microRNAs that can potentially target ERBB4. We identified specific targeting sites for miR-193a-3p in the 3'-UTR of ERBB4. We further identified an inverse correlation between miR-193a-3p levels and ERBB4 protein levels, but not mRNA levels, in lung cancer tissue samples. By overexpressing or knocking down miR-193a-3p in lung cancer cells, we experimentally confirmed that miR-193a-3p directly recognizes the 3'-UTR of the ERBB4 transcript and regulates ERBB4 expression. Furthermore, the biological consequences of the targeting of ERBB4 by miR-193a-3p were examined in vitro via cell proliferation, invasion, and apoptosis assays and in vivo using a mouse xenograft tumor model. We demonstrated that the repression of ERBB4 by miR-193a-3p suppressed proliferation and invasion and promoted apoptosis in lung cancer cells and that miR-193a-3p exerted an anti-tumor effect by negatively regulating ERBB4 in xenograft mice. Taken together, our findings provide the first clues regarding the role of miR-193a-3p as a tumor suppressor in lung cancer through the inhibition of ERBB4 translation.

Cartilage oligomeric matrix protein prevents vascular aging and vascular smooth muscle cells senescence.

Aging-related vascular dysfunction contributes to cardiovascular morbidity and mortality. Cartilage oligomeric matrix protein (COMP), a vascular extracellular matrix protein, has been described as a negative regulatory factor for the vascular aging-related processes including atherosclerosis and vascular calcification. However, whether COMP is implicated in the process of vascular aging remains unclear. Here, we identified a novel function of COMP in preventing vascular aging and vascular smooth muscle cells (VSMCs) senescence. Firstly, vascular COMP expression was decreased in three different senescence-accelerated mouse models and was also declining with age. COMP(-/-) mice displayed elevated senescence-associated markers expression, including p53, p21 and p16, in the aortas compared with their wild type (WT) littermates. In accordance, COMP deficiency induced aging-related vascular dysfunction as evidenced by the significantly reduced phenylephrine-induced contraction and increased vascular stiffness as evaluated by pulse wave velocity. The aortic wall of COMP(-/-) mice was susceptible to senescence by displaying senescence-associated ß-galactosidase (SA ß-gal) activity induced by periadventitial application of CaCl2 to the abdominal aorta. In vitro, COMP knockdown by small interfering (si) RNA led to the elevation of p53, p21 and p16 as well as SA ß-gal activity in VSMCs after H2O2 stimulation. VSMCs isolated from COMP(-/-) mice showed elevated senescence-associated markers expression and supplement of COMP adenovirus to COMP-deficient VSMCs greatly rescued cellular senescence. Taken together, these findings revealed the essential role of COMP in retarding the development of vascular aging and VSMC senescence.

PIASxα ligase enhances SUMO1 modification of PTEN protein as a SUMO E3 ligase.

The tumor suppressor PTEN plays a critical role in the regulation of multiple cellular processes that include survival, cell cycle, proliferation, and apoptosis. PTEN is frequently mutated or deleted in various human cancer cells to promote tumorigenesis. PTEN is regulated by SUMOylation, but the SUMO E3 ligase involved in the SUMOylation of PTEN remains unclear. Here, we demonstrated that PIASxα is a SUMO E3 ligase for PTEN. PIASxα physically interacted with PTEN both in vitro and in vivo. Their interaction depended on the integrity of phosphatase and C2 domains of PTEN and the region of PIASxα comprising residues 134-347. PIASxα enhanced PTEN protein stability by reducing PTEN ubiquitination, whereas the mutation of PTEN SUMO1 conjugation sites neutralized the effect of PIASxα on PTEN protein half-life. Functionally, PIASxα, as a potential tumor suppressor, negatively regulated the PI3K-Akt pathway through stabilizing PTEN protein. Overexpression of PIASxα led to G0/G1 cell cycle arrest, thus triggering cell proliferation inhibition and tumor suppression, whereas PIASxα knockdown or deficiency in catalytic activity abolished the inhibition. Together our studies suggest that PIASxα is a novel SUMO E3 ligase for PTEN, and it positively regulates PTEN protein level in tumor suppression.

Inhibition of fatty acid uptake by TGR5 prevents diabetic cardiomyopathy.

Diabetic cardiomyopathy is characterized by myocardial lipid accumulation and cardiac dysfunction. Bile acid metabolism is known to play a crucial role in cardiovascular and metabolic diseases. Takeda G-protein-coupled receptor 5 (TGR5), a major bile acid receptor, has been implicated in metabolic regulation and myocardial protection. However, the precise involvement of the bile acid-TGR5 pathway in maintaining cardiometabolic homeostasis remains unclear. Here we show decreased plasma bile acid levels in both male and female participants with diabetic myocardial injury. Additionally, we observe increased myocardial lipid accumulation and cardiac dysfunction in cardiomyocyte-specific TGR5-deleted mice (both male and female) subjected to a high-fat diet and streptozotocin treatment or bred on the diabetic db/db genetic background. Further investigation reveals that TGR5 deletion enhances cardiac fatty acid uptake, resulting in lipid accumulation. Mechanistically, TGR5 deletion promotes localization of CD36 on the plasma membrane through the upregulation of CD36 palmitoylation mediated by the palmitoyl acyltransferase DHHC4. Our findings indicate that the TGR5-DHHC4 pathway regulates cardiac fatty acid uptake, which highlights the therapeutic potential of targeting TGR5 in the management of diabetic cardiomyopathy.

HuR promotes triglyceride synthesis and intestinal fat absorption.

Triacylglyceride (TAG) synthesis in the small intestine determines the absorption of dietary fat, but the underlying mechanisms remain to be further studied. Here, we report that the RNA-binding protein HuR (ELAVL1) promotes TAG synthesis in the small intestine. HuR associates with the 3' UTR of Dgat2 mRNA and intron 1 of Mgat2 pre-mRNA. Association of HuR with Dgat2 3' UTR stabilizes Dgat2 mRNA, while association of HuR with intron 1 of Mgat2 pre-mRNA promotes the processing of Mgat2 pre-mRNA. Intestinal epithelium-specific HuR knockout reduces the expression of DGAT2 and MGAT2, thereby reducing the dietary fat absorption through TAG synthesis and mitigating high-fat-diet (HFD)-induced non-alcoholic fatty liver disease (NAFLD) and obesity. Our findings highlight a critical role of HuR in promoting dietary fat absorption.