Arginine Methylation of MDH1 by CARM1 Inhibits Glutamine Metabolism and Suppresses Pancreatic Cancer.

Distinctive from their normal counterparts, cancer cells exhibit unique metabolic dependencies on glutamine to fuel anabolic processes. Specifically, pancreatic ductal adenocarcinoma (PDAC) cells rely on an unconventional metabolic pathway catalyzed by aspartate aminotransferase, malate dehydrogenase 1 (MDH1), and malic enzyme 1 to rewire glutamine metabolism and support nicotinamide adenine dinucleotide phosphate (NADPH) production. Here, we report that methylation on arginine 248 (R248) negatively regulates MDH1. Protein arginine methyltransferase 4 (PRMT4/CARM1) methylates and inhibits MDH1 by disrupting its dimerization. Knockdown of MDH1 represses mitochondria respiration and inhibits glutamine metabolism, which sensitizes PDAC cells to oxidative stress and suppresses cell proliferation. Meanwhile, re-expression of wild-type MDH1, but not its methylation-mimetic mutant, protects cells from oxidative injury and restores cell growth and clonogenic activity. Importantly, MDH1 is hypomethylated at R248 in clinical PDAC samples. Our study reveals that arginine methylation of MDH1 by CARM1 regulates cellular redox homeostasis and suppresses glutamine metabolism of pancreatic cancer.

Hepatic Small Ubiquitin-Related Modifier (SUMO)-Specific Protease 2 Controls Systemic Metabolism Through SUMOylation-Dependent Regulation of Liver-Adipose Tissue Crosstalk.

BACKGROUND AND AIMS: NAFLD, characterized by aberrant triglyceride accumulation in liver, affects the metabolic remodeling of hepatic and nonhepatic tissues by secreting altered hepatokines. Small ubiquitin-related modifier (SUMO)-specific protease 2 (SENP2) is responsible for de-SUMOylation of target protein, with broad effects on cell growth, signal transduction, and developmental processes. However, the role of SENP2 in hepatic metabolism remains unclear. APPROACH AND RESULTS: We found that SENP2 was the most dramatically increased SENP in the fatty liver and that its level was modulated by fed/fasted conditions. To define the role of hepatic SENP2 in metabolic regulation, we generated liver-specific SENP2 knockout (Senp2-LKO) mice. Senp2-LKO mice exhibited resistance to high-fat diet-induced hepatic steatosis and obesity. RNA-sequencing analysis showed that Senp2 deficiency up-regulated genes involved in fatty acid oxidation and down-regulated genes in lipogenesis in the liver. Additionally, ablation of hepatic SENP2 activated thermogenesis of adipose tissues. Improved energy homeostasis of both the liver and adipose tissues by SENP2 disruption prompted us to detect the hepatokines, with FGF21 identified as a key factor markedly elevated in Senp2-LKO mice that maintained metabolic homeostasis. Loss of FGF21 obviously reversed the positive effects of SENP2 deficiency on metabolism. Mechanistically, by screening transcriptional factors of FGF21, peroxisome proliferator-activated receptor alpha (PPARα) was defined as the mediator for SENP2 and FGF21. SENP2 interacted with PPARα and deSUMOylated it, thereby promoting ubiquitylation and subsequent degradation of PPARα, which in turn inhibited FGF21 expression and fatty acid oxidation. Consistently, SENP2 overexpression in liver facilitated development of metabolic disorders. CONCLUSIONS: Our finding demonstrated a key role of hepatic SENP2 in governing metabolic balance by regulating liver-adipose tissue crosstalk, linking the SUMOylation process to metabolic regulation.

Gut microbiota as a promising therapeutic target for age-related sarcopenia.

Sarcopenia is characterized by a progressive loss of skeletal muscle mass and function with aging. Recently, sarcopenia has been shown to be closely related with gut microbiota. Strategies such as probiotics and fecal microbiota transplantation have shown potential to ameliorate the muscle loss. This review will focus on the age-related sarcopenia, in particular on the relationship between gut microbiota and age-related sarcopenia, how gut microbiota is engaged in sarcopenia, and the potential role of gut microbiota in the treatment of age-related sarcopenia.

Downregulation of ANP32B, a novel substrate of caspase-3, enhances caspase-3 activation and apoptosis induction in myeloid leukemic cells.

The acidic leucine-rich nuclear phosphoprotein 32 (ANP32)B has been reported to regulate gene expression by acting as a histone chaperone or modulate messenger RNA trafficking by serving as a HuR ligand. However, its exact cellular functions are poorly understood. By utilizing a proteomics-based approach, in this work, we identify that the human ANP32B protein is cleaved during apoptosis induction by NSC606985, a novel camptothecin analog. Further investigation shows that various apoptosis inducers cause a decrease of full-length ANP32B in multiple cell lines with a concomitant increase of an approximately 17 kDa fragment. The proteolytic cleavage of ANP32B is inhibited by a specific caspase-3 inhibitor Z-DEVD-fmk, and it cannot be seen in NSC606985-induced death of caspase-3-deficient MCF-7 cells. In vitro caspase cleavage assay and mutagenesis experiment reveal that ANP32B is a direct substrate of caspase-3 and it is primarily cleaved at the sequence of Ala-Glu-Val-Asp, after Asp-163. Additionally, the reduced expression of endogenous ANP32B by specific small interfering RNA enhances caspase-3 activation and apoptosis induction by NSC606985 and etoposide. These results suggest that ANP32B is a novel substrate for caspase-3 and acts as a negative regulator for apoptosis, the mechanism of which remains to be explored.

NDRG1 is down-regulated in the early apoptotic event induced by camptothecin analogs: the potential role in proteolytic activation of PKC delta and apoptosis.

We previously reported that NSC606985, a new camptothecin analog, induces apoptosis of acute myeloid leukemic cells, which is triggered by proteolytic activation of protein kinase C delta (PKC delta). Here, we performed quantitative proteomic analysis of NSC606985-treated and untreated leukemic U937 cells with two-dimensional fluorescence difference gel electrophoresis (2-D DIGE) in combination with matrix-assisted laser desorption/ionization time-of-flight/time-of-flight tandem mass spectrometry. Thirty-three proteins were found to be deregulated. Then, we focused on N-myc downstream regulated gene 1 (NDRG1) down-regulated during apoptosis induction. The results demonstrated that the down-regulation of NDRG1 protein but not its mRNA was an early event prior to proteolytic activation of PKC delta in U937 cells under treatments of NSC606985 as well as other camptothecin analogs. With the ectopic expression of NDRG1, the proteolytic activation of PKC delta in NSC606985-treated leukemic cells was delayed and the cells were less sensitive to apoptosis. On the contrary, the suppression of NDRG1 expression by specific small interfering RNA significantly enhanced NSC606985-induced activation of PKC delta and apoptosis of U937 cells. In summary, our study suggests that the down-regulation of NDRG1 is involved in proteolytic activation of PKC delta during apoptosis induction, which would shed new light on the understanding the apoptotic process initiated by camptothecin.

Small ubiquitin-like modifier protein-specific protease 1 and prostate cancer.

Small ubiquitin-like modifier protein (SUMO) modification is a highly dynamic process, catalyzed by SUMO-specific activating (E1), conjugating (E2) and ligating (E3) enzymes, and reversed by a family of SUMO-specific proteases (SENPs). There are six members of the human SENP family, and each SENP has different cellular locations and substrate specificities. However, the precise roles of SENPs in cellular processes have not been elucidated to date. This brief review will focus on recent advances pertaining to the identified targets of SENP1 and its potential role in prostate cancer.

Nuclear PTEN safeguards pre-mRNA splicing to link Golgi apparatus for its tumor suppressive role.

Dysregulation of pre-mRNA alternative splicing (AS) is closely associated with cancers. However, the relationships between the AS and classic oncogenes/tumor suppressors are largely unknown. Here we show that the deletion of tumor suppressor PTEN alters pre-mRNA splicing in a phosphatase-independent manner, and identify 262 PTEN-regulated AS events in 293T cells by RNA sequencing, which are associated with significant worse outcome of cancer patients. Based on these findings, we report that nuclear PTEN interacts with the splicing machinery, spliceosome, to regulate its assembly and pre-mRNA splicing. We also identify a new exon 2b in GOLGA2 transcript and the exon exclusion contributes to PTEN knockdown-induced tumorigenesis by promoting dramatic Golgi extension and secretion, and PTEN depletion significantly sensitizes cancer cells to secretion inhibitors brefeldin A and golgicide A. Our results suggest that Golgi secretion inhibitors alone or in combination with PI3K/Akt kinase inhibitors may be therapeutically useful for PTEN-deficient cancers.

SENP2 negatively regulates cellular antiviral response by deSUMOylating IRF3 and conditioning it for ubiquitination and degradation.

Transcription factor IRF3-mediated type I interferon induction is essential for antiviral innate immunity. We identified the deSUMOylating enzyme Sentrin/SUMO-specific protease  (SENP) 2 as a negative regulator of virus-triggered IFN-ß induction. Overexpression of SENP2 caused IRF3 deSUMOylation, K48-linked ubiquitination, and degradation, whereas depletion of SENP2 had opposite effects. Both the SUMOylation and K48-linked ubiquitination of IRF3 occurred at lysines 70 and 87, and these processes are competitive. The level of virus-triggered IFN-ß was markedly up-regulated and viral replication was reduced in SENP2-deficient cells comparing with wild-type controls. Our findings suggest that SENP2 regulates antiviral innate immunity by deSUMOylating IRF3 and conditioning it for ubiquitination and degradation, and provide an example of cross-talk between the ubiquitin and SUMO pathways in innate immunity.

Protein kinase Cdelta stimulates proteasome-dependent degradation of C/EBPalpha during apoptosis induction of leukemic cells.

BACKGROUND: The precise regulation and maintenance of balance between cell proliferation, differentiation and death in metazoan are critical for tissue homeostasis. CCAAT/enhancer-binding protein alpha (C/EBPalpha) has been implicated as a key regulator of differentiation and proliferation in various cell types. Here we investigated the potential dynamic change and role of C/EBPalpha protein during apoptosis induction. METHODOLOGY/PRINCIPAL FINDINGS: Upon onset of apoptosis induced by various kinds of inducers such as NSC606985, etoposide and others, C/EBPalpha expression presented a profound down-regulation in leukemic cell lines and primary cells via induction of protein degradation and inhibition of transcription, as assessed respectively by cycloheximide inhibition test, real-time quantitative RT-PCR and luciferase reporter assay. Applying chemical inhibition, forced expression of dominant negative mutant and catalytic fragment (CF) of protein kinase Cdelta (PKCdelta), which was proteolytically activated during apoptosis induction tested, we showed that the active PKCdelta protein contributed to the increased degradation of C/EBPalpha protein. Three specific proteasome inhibitors antagonized C/EBPalpha degradation during apoptosis induction. More importantly, ectopic expression of PKCdelta-CF stimulated the ubiquitination of C/EBPalpha protein, while the chemical inhibition of PKCdelta action significantly inhibited the enhanced ubiquitination of C/EBPalpha protein under NSC606985 treatment. Additionally, silencing of C/EBPalpha expression by small interfering RNAs enhanced, while inducible expression of C/EBPalpha inhibited NSC606985/etoposide-induced apoptosis in leukemic cells. CONCLUSIONS/SIGNIFICANCE: These observations indicate that the activation of PKCdelta upon apoptosis results in the increased proteasome-dependent degradation of C/EBPalpha, which partially contributes to PKCdelta-mediated apoptosis.

[SUMO-specific protease 1 and cancer].

Post-translational modifiers of the small ubiquitin-like modifier protein (SUMO) family have emerged as key regulators of protein function and localization. SUMO modification is a dynamic process, catalyzed by SUMO-specific E1, E2, and E3 enzymes and reversed by a family of SUMO-specific proteases (SENPs). Although six human SENPs have been identified, each with different cellular locations and substrate specificities, the precise roles of SENPs in cellular processes involved has not been well-defined. This brief review will focus on recent advances about the identified targets of SENP1 and its potential role in tumorigenesis.