Involvement of PRMT1 in hnRNPQ activation and internalization of insulin receptor

Mechanism of action and the uses betaine in pig production

Betaine, the trimethyl derivative of glycine, is a good methyl group donor, and an important component in pig production. However, betaine has not been extensively studied in this field. Therefore, in this study, we reviewed the effects of betaine in pig production performance, meat quality and reproductive performance, as well as its mechanisms, to provide a theoretical basis for the optimal use and development of this compound.

Betaine in Inflammation: Mechanistic Aspects and Applications

Betaine is known as trimethylglycine and is widely distributed in animals, plants, and microorganisms. Betaine is known to function physiologically as an important osmoprotectant and methyl group donor. Accumulating evidence has shown that betaine has anti-inflammatory functions in numerous diseases. Mechanistically, betaine ameliorates sulfur amino acid metabolism against oxidative stress, inhibits nuclear factor-κB activity and NLRP3 inflammasome activation, regulates energy metabolism, and mitigates endoplasmic reticulum stress and apoptosis. Consequently, betaine has beneficial actions in several human diseases, such as obesity, diabetes, cancer, and Alzheimer's disease.

Synaptotagmin 7 and SYNCRIP proteins are ubiquitously expressed in the rat brain and co-localize in Purkinje neurons

Synaptotagmin 7 (SYT7) is ubiquitously expressed calcium sensor, involved in neuronal membrane trafficking. Immunoprecipitation experiments demonstrated that SYT7 interacts with Synaptotagmin-binding, cytoplasmic RNA-interacting protein (SYNCRIP). SYNCRIP is a component of mRNA granules, which are transported to dendrites and are prerequisite for synaptic plasticity. Given the potential significance of SYT7 regulation in processes of neurodegeneration, which are characterized by high level of synaptic vulnerability, we aimed to analyse and compare the distribution of SYT7 and SYNCRIP proteins in the adult rat striatum, hippocampus, cerebral and cerebellar cortex. We investigated the degree of SYT7-SYNCRIP co-localization in order to examine possible functional interaction of these two proteins. We found that SYT7 is abundantly distributed in neuropil of all examined anatomical areas of the brain, most prominently in axons. On the contrary, SYNCRIP had cytoplasmic somatodendritic pattern of expression, which was most prominent in the hippocampus and cerebellum. In the striatum, hippocampus and cerebral cortex SYT7 and SYNCRIP immunofluorescent signals were mutually excluded, thus diminishing the probability for their physiological interaction. In somata of Purkinje neurons in the cerebellar cortex, both SYT7 and SYNCRIP were expressed and partially co-localized suggesting possible functional connection between SYT7 and SYNCRIP proteins in Purkinje neurons.

The acidic domain is a unique structural feature of the splicing factor SYNCRIP

The splicing factor SYNCRIP (hnRNP Q) is involved in viral replication, neural morphogenesis, modulation of circadian oscillation, and the regulation of the cytidine deaminase APOBEC1. It consists of three globular RNA-recognition motifs (RRM) domains flanked by an N-terminal acid-rich acidic sequence segment domain (AcD12-97 ) and a C-terminal domain containing an arginine-glycine-rich sequence motif (RGG/RXG box), which are located near to the N- and C-terminals, respectively. The acid-rich sequence segment is unique to SYNCRIP and the closely related protein hnRNP R, and is involved in interactions with APOBEC1. Here, we show that while AcD12-97 does not form a globular domain, structure-based annotation identified a self-folding globular domain with an all α-helix architecture, AcD24-107 . The NMR structure of AcD24-107 is fundamentally different from previously reported AcD molecular models. In addition to negatively charged surface areas, it contains a large hydrophobic cavity and a positively charged surface area as potential epitopes for intermolecular interactions.

Identification and characterization of new molecular partners for the protein arginine methyltransferase 6 (PRMT6)

PRMT6 is a protein arginine methyltransferase that has been implicated in transcriptional regulation, DNA repair, and human immunodeficiency virus pathogenesis. Only few substrates of this enzyme are known and therefore its cellular role is not well understood. To identify in an unbiased manner substrates and potential regulators of PRMT6 we have used a yeast two-hybrid approach. We identified 36 new putative partners for PRMT6 and we validated the interaction in vivo for 7 of them. In addition, using invitro methylation assay we identified 4 new substrates for PRMT6, extending the involvement of this enzyme to other cellular processes beyond its well-established role in gene expression regulation. Holistic approaches create molecular connections that allow to test functional hypotheses. The assembly of PRMT6 protein network allowed us to formulate functional hypotheses which led to the discovery of new molecular partners for the architectural transcription factor HMGA1a, a known substrate for PRMT6, and to provide evidences for a modulatory role of HMGA1a on the methyltransferase activity of PRMT6.

S-adenosylmethionine-dependent protein methylation is required for expression of selenoprotein P and gluconeogenic enzymes in HepG2 human hepatocytes

Cellular methylation processes enable expression of gluconeogenic enzymes and metabolism of the nutrient selenium. Selenium status has been proposed to relate to type II diabetes risk, and plasma levels of selenoprotein P (SEPP1) have been positively correlated with insulin resistance. Increased expression of gluconeogenic enzymes glucose-6-phosphatase (G6PC) and phosphoenolpyruvate carboxykinase 1 (PCK1) has negative consequences for blood glucose management in type II diabetics. Transcriptional regulation of SEPP1 is directed by the same transcription factors that control the expression of G6PC and PCK1, and these factors are activated by methylation of arginine residues. We sought to determine whether expression of SEPP1 and the aforementioned glucoconeogenic enzymes are regulated by protein methylation, the levels of which are reliant upon adequate S-adenosylmethionine (SAM) and inhibited by S-adenosylhomocysteine (SAH). We treated a human hepatocyte cell line, HepG2, with inhibitors of adenosylhomocysteine hydrolase (AHCY) known to increase concentration of SAH before analysis of G6PC, PCK1, and SEPP1 expression. Increasing SAH decreased 1) the SAM/SAH ratio, 2) protein-arginine methylation, and 3) expression of SEPP1, G6PC, and PCK1 transcripts. Furthermore, hormone-dependent induction of gluconeogenic enzymes was reduced by inhibition of protein methylation. When protein-arginine methyltransferase 1 expression was reduced by siRNA treatment, G6PC expression was inhibited. These findings demonstrate that hepatocellular SAM-dependent protein methylation is required for both SEPP1 and gluconeogenic enzyme expression and that inhibition of protein arginine methylation might provide a route to therapeutic interventions in type II diabetes.

Betaine improves nonalcoholic fatty liver and associated hepatic insulin resistance: a potential mechanism for hepatoprotection by betaine

Nonalcoholic fatty liver (NAFL) is a common liver disease, associated with insulin resistance. Betaine has been tested as a treatment for NAFL in animal models and in small clinical trials, with mixed results. The present study aims to determine whether betaine treatment would prevent or treat NAFL in mice and to understand how betaine reverses hepatic insulin resistance. Male mice were fed a moderate high-fat diet (mHF) containing 20% of calories from fat for 7 (mHF) or 8 (mHF8) mo without betaine, with betaine (mHFB), or with betaine for the last 6 wk (mHF8B). Control mice were fed standard chow containing 9% of calories from fat for 7 mo (SF) or 8 mo (SF8). HepG2 cells were made insulin resistant and then studied with or without betaine. mHF mice had higher body weight, fasting glucose, insulin, and triglycerides and greater hepatic fat than SF mice. Betaine reduced fasting glucose, insulin, triglycerides, and hepatic fat. In the mHF8B group, betaine treatment significantly improved insulin resistance and hepatic steatosis. Hepatic betaine content significantly decreased in mHF and increased significantly in mHFB. Betaine treatment reversed the inhibition of hepatic insulin signaling in mHF and in insulin-resistant HepG2 cells, including normalization of insulin receptor substrate 1 (IRS1) phosphorylation and of downstream signaling pathways for gluconeogenesis and glycogen synthesis. Betaine treatment prevents and treats fatty liver in a moderate high-dietary-fat model of NAFL in mice. Betaine also reverses hepatic insulin resistance in part by increasing the activation of IRS1, with resultant improvement in downstream signaling pathways.

Alterations in the developing testis transcriptome following embryonic vinclozolin exposure

The current study investigates the direct effects of in utero vinclozolin exposure on the developing F1 generation rat testis transcriptome. Previous studies have demonstrated that exposure to vinclozolin during embryonic gonadal sex determination induces epigenetic modifications of the germ line and transgenerational adult onset disease states. Microarray analyses were performed to compare control and vinclozolin treated testis transcriptomes at embryonic days 13, 14 and 16. A total of 576 differentially expressed genes were identified and the major cellular functions and pathways associated with these altered transcripts were examined. The sets of regulated genes at the different development periods were found to be transiently altered and distinct. Categorization by major known functions of altered genes was performed. Specific cellular process and pathway analyses suggest the involvement of Wnt and calcium signaling, vascular development and epigenetic mechanisms as potential mediators of the direct F1 generation actions of vinclozolin.

Protein arginine methyltransferases: nuclear receptor coregulators and beyond

Protein arginine methyltransferases (PRMTs) are a family of enzymes that play a crucial role in diverse cellular functions. Several PRMTs have been associated with gene expression regulation, in which PRMTs act as histone methyltransferases, secondary coregulators of transcription, or facilitate mRNA splicing and stability. Additional functions include modulation of protein localization, ribosomal assembly, and signal transduction. At the organismal level, several PRMTs appear to be important for development and may play an important role in cancer. The relationships between their cellular and organismal functions are poorly understood; at least in part due to the large body of enzymatic substrates for PRMTs and their transcriptional targets that remain to be determined. Specific PRMT inhibitors have been developed in recent years, which should help to shed light on their diverse biological roles. Connecting PRMT cellular functions with their global effects on an organism will facilitate development of novel treatments for human diseases.

Impaired PRMT1 activity in the liver and pancreas of type 2 diabetic Goto-Kakizaki rats

AIMS

Arginine methylation catalyzed by protein N-arginine methyltransferase (PRMT) 1 is implicated in a variety of cellular processes, although the potential role of PRMT1-mediated methylation in glucose intolerance has not been defined. This study aims to investigate whether alteration of PRMT1 activity contributes to the clinical features of type 2 diabetes.

MAIN METHODS

Goto-Kakizaki (GK) rats were used as a rodent model of type 2 diabetes. Catalytic activity of PRMT1 and arginine methylation were determined by an in vitro methyltransferase assay and immunoblotting, respectively. Hepatic insulin signaling events, insulin secretion, and pancreatic glucose metabolism were assessed by studies using HepG2 hepatoma cells and isolated pancreatic islets. Methyltransferase activity was attenuated by transfection of a small interfering RNA against PRMT1 (PRMT1-siRNA) or by pretreatment with an inhibitor of methyltransferase, 5'-deoxy-5'-(methylthio)adenosine (MTA).

KEY FINDINGS

Non-obese, diabetic GK rats exhibited a decrease in their hepatic and pancreatic PRMT1 activity, as compared to the control Wistar rats, which was associated with the impaired arginine methylation of several proteins in the tissues. Transfection of PRMT1-siRNA diminished the agonist-induced activation of insulin signaling and the subsequent suppression of gluconeogenic genes expression in the liver-derived cells. Pretreatment with MTA attenuated the glucose-stimulated insulin secretion, but not glucose utilization, in isolated pancreatic islets of Wistar controls, and its pattern was comparable to that of the GK rats undergoing similar modulation.

SIGNIFICANCE

The present data demonstrates that the impaired PRMT1 activity may be implicated in glucose intolerance in GK rats through the disturbed hepatic glucose metabolism and insulin secretion.