Protein methylation inhibits Na+-Ca2+ exchange activity in cardiac sarcolemmal vesicles

Preconditioning beef cattle for long-duration transportation stress with rumen-protected methionine supplementation: A nutrigenetics study

In general, beef cattle long-distance transportation from cow-calf operations to feedlots or from feedlots to abattoirs is a common situation in the beef industry. The aim of this study was to determine the effect of rumen-protected methionine (RPM) supplementation on a proposed gene network for muscle fatigue, creatine synthesis (CKM), and reactive oxygen species (ROS) metabolism after a transportation simulation in a test track. Angus × Simmental heifers (n = 18) were stratified by body weight (408 ± 64 kg; BW) and randomly assigned to dietary treatments: 1) control diet (CTRL) or 2) control diet + 8 gr/hd/day of top-dressed rumen-protected methionine (RPM). After an adaptation period to Calan gates, animals received the mentioned dietary treatment consisting of Bermuda hay ad libitum and a soy hulls and corn gluten feed based supplement. After 45 days of supplementation, animals were loaded onto a trailer and transported for 22 hours (long-term transportation). Longissimus muscle biopsies, BW and blood samples were obtained on day 0 (Baseline), 43 (Pre-transport; PRET), and 46 (Post-transport; POST). Heifers' average daily gain did not differ between baseline and PRET. Control heifer's shrink was 10% of BW while RPM heifers shrink was 8%. Serum cortisol decreased, and glucose and creatine kinase levels increased after transportation, but no differences were observed between treatments. Messenger RNA was extracted from skeletal muscle tissue and gene expression analysis was performed by RT-qPCR. Results showed that AHCY and DNMT3A (DNA methylation), SSPN (Sarcoglycan complex), and SOD2 (Oxidative Stress-ROS) were upregulated in CTRL between baseline and PRET and, decreased between pre and POST while they remained constant for RPM. Furthermore, CKM was not affected by treatments. In conclusion, RPM supplementation may affect ROS production and enhance DNA hypermethylation, after a long-term transportation.

A novel methyltransferase methylates Cucumber mosaic virus 1a protein and promotes systemic spread

In mammalian and yeast systems, methyltransferases have been implicated in the regulation of diverse processes, such as protein-protein interactions, protein localization, signal transduction, RNA processing, and transcription. The Cucumber mosaic virus (CMV) 1a protein is essential not only for virus replication but also for movement. Using a yeast two-hybrid system with tobacco plants, we have identified a novel gene encoding a methyltransferase that interacts with the CMV 1a protein and have designated this gene Tcoi1 (tobacco CMV 1a-interacting protein 1). Tcoi1 specifically interacted with the methyltransferase domain of CMV 1a, and the expression of Tcoi1 was increased by CMV inoculation. Biochemical studies revealed that the interaction of Tcoi1 with CMV 1a protein was direct and that Tcoi1 methylated CMV 1a protein both in vitro and in vivo. The CMV 1a binding activity of Tcoi1 is in the C-terminal domain, which shows the methyltransferase activity. The overexpression of Tcoi1 enhanced the CMV infection, while the reduced expression of Tcoi1 decreased virus infectivity. These results suggest that Tcoi1 controls the propagation of CMV through an interaction with the CMV 1a protein.

Protein methylation is required to maintain optimal HIV-1 infectivity

Background:

Protein methylation is recognized as a major protein modification pathway regulating diverse cellular events such as protein trafficking, transcription, and signal transduction. More recently, protein arginine methyltransferase activity has been shown to regulate HIV-1 transcription via Tat. In this study, adenosine periodate (AdOx) was used to globally inhibit protein methyltransferase activity so that the effect of protein methylation on HIV-1 infectivity could be assessed.

Results:

Two cell culture models were used: HIV-1-infected CEM T-cells and HEK293T cells transfected with a proviral DNA plasmid. In both models, AdOx treatment of cells increased the levels of virion in culture supernatant. However, these viruses had increased levels of unprocessed or partially processed Gag-Pol, significantly increased diameter, and displayed reduced infectivity in a MAGI X4 assay. AdOx reduced infectivity equally in both dividing and non-dividing cells. However, infectivity was further reduced if Vpr was deleted suggesting virion proteins, other than Vpr, were affected by protein methylation. Endogenous reverse transcription was not inhibited in AdOx-treated HIV-1, and infectivity could be restored by pseudotyping HIV with VSV-G envelope protein. These experiments suggest that AdOx affects an early event between receptor binding and uncoating, but not reverse transcription.

Conclusion:

Overall, we have shown for the first time that protein methylation contributes towards maximal virus infectivity. Furthermore, our results also indicate that protein methylation regulates HIV-1 infectivity in a complex manner most likely involving the methylation of multiple viral or cellular proteins and/or multiple steps of replication.

Cytoplasmic ATP-dependent regulation of ion transporters and channels: mechanisms and messengers

Many ion transporters and channels appear to be regulated by ATP-dependent mechanisms when studied in planar bilayers, excised membrane patches, or with whole-cell patch clamp. Protein kinases are obvious candidates to mediate ATP effects, but other mechanisms are also implicated. They include lipid kinases with the generation of phosphatidylinositol phosphates as second messengers, allosteric effects of ATP binding, changes of actin cytoskeleton, and ATP-dependent phospholipases. Phosphatidylinositol-4,5-bisphosphate (PIP2) is a possible membrane-delimited messenger that activates cardiac sodium-calcium exchange, KATP potassium channels, and other inward rectifier potassium channels. Regulation of PIP2 by phospholipase C, lipid phosphatases, and lipid kinases would thus tie surface membrane transport to phosphatidylinositol signaling. Sodium-hydrogen exchange is activated by ATP through a phosphorylation-independent mechanism, whereas ion cotransporters are activated by several protein kinase mechanisms. Ion transport in epithelium may be particularly sensitive to changes of cytoskeleton that are regulated by ATP-dependent cell signaling mechanisms.

Protective effect of S-adenosyl-l-methionine on liver damage induced by biliary obstruction in rats: a histological, ultrastructural and biochemical approach

In human and experimental CCl4-liver damage, S-adenosyl-l-methionine-synthetase and/or the intrahepatic content of S-adenosyl-l-methionine, are diminished and in human cirrhosis phospholipid methyltransferase is markedly reduced. Therefore the aim of this study was to investigate the effect of S-adenosyl-l-methionine administration on liver damage induced by 15-day bile duct ligation. Liver damage was analyzed by histological, ultrastructural and biochemical techniques. Biliary obstruction produced an increase in collagen content, dilation of the bile canaliculi and disorganization of mitochondria. These effects were not observed in the bile-duct-ligated group receiving S-adenosyl-l-methionine. Biochemical results showed that bile duct ligation increased serum bilirubins, and alkaline phosphatase and gamma-glutamyl transpeptidase activities. These effects were prevented significantly by S-adenosyl-l-methionine. On the other hand, glycogen content in the liver was depleted while lipid peroxidation was increased by biliary obstruction, S-adenosyl-l-methionine administration prevented these effects. In the bile-duct-ligated group, hepatocyte and erythrocyte plasma membrane Na+/K+ and Ca(2+)-ATPase were lower than in the control group (p < 0.05). Administration of S-adenosyl-l-methionine preserved ATPase activities. The exogenous S-adenosyl-l-methionine supply is probably responsible for restoring transmethylation lost in liver diseases.

Mechanism of cardiac Na(+)-Ca2+ exchange current stimulation by MgATP: possible involvement of aminophospholipid translocase

1. The sensitivity of outward Na(+)-Ca2+ exchange current to charged amphiphiles and phospholipids was tested in giant excised inside-out membrane patches from guinea-pig and rabbit myocytes. 2. Screening of membrane surface potentials with dimethonium (10 mM), spermine (200 microM) and spermidine (100 microM) was without effect, while the positively charged ionic detergents hexadecyltrimethylammonium and dodecyltrimethylammonium strongly inhibited steady-state outward exchange current (0.1-10 microM). 3. Interventions expected to increase negative surface charge included treatment of the cytoplasmic surface with phospholipase D, application of dodecylsulphate (1-10 microM), application of the short-chain phosphatidylserine derivative, dicapryl phosphatidylserine (C10PS), and inclusion of 1-3% phosphatidylserine in the hydrocarbon mixture used to coat electrodes. Each intervention strongly stimulated Na(+)-Ca2+ exchange current in a similar way to MgATP, reducing the fractional decay of outward exchange current (inactivation) during application of high cytoplasmic sodium. 4. The MgATP-stimulated exchange current was inhibited with a Ki of approximately 1 microM by pentalysine, which is known to associate with phosphatidylserine head groups. After 'deregulation' of the exchanger by chymotrypsin, pentalysine was without effect. 5. Inclusion in the pipette of 0.2 mM-pyridyldithioethylamine (an oxidizing inhibitor of aminophospholipid translocase) abolished stimulation of outward exchange current by MgATP without inhibiting basal outward exchange current or sodium pump current. 6. Application to the cytoplasmic side of 1.5 mM-diamide, which reportedly decreases membrane phospholipid asymmetry, apparently reversed the effect of MgATP. After treatment with diamide and subsequently with dithiothreitol, Na(+)-Ca2+ exchange current was again stimulated by MgATP. Diamide was without effect when secondary exchange regulation had been previously removed by chymotrypsin. 7. Potassium current carried by the surface potential-sensitive ionophore, nonactin, was stimulated by MgATP when extracellular surface charge had been neutralized. The effect was largest (40-90%) when low ionic strength cytoplasmic solutions were employed, consistent with an increase of negative membrane charge on the cytoplasmic side during MgATP application. 8. Potassium current carried by nonactin was inhibited by MgATP when cytoplasmic surface charge had been neutralized and extracellular solutions of low ionic strength were employed, consistent with a decrease of negative membrane charge on the extracellular side. 9. These results indicate that the stimulatory effect of MgATP on Na(+)-Ca2+ exchange current could involve changes of charged membrane lipids, that the effect probably involves a transmembrane, oxidation-sensitive protein, that pentalysine-sensitive sites are involved, that phosphatidylserine mimics the effect of MgATP, and that the effect extends to a simple surface potential-sensitive ionophore.(ABSTRACT TRUNCATED AT 400 WORDS)

Ca2+ extrusion across plasma membrane and Ca2+ uptake by intracellular stores

The aim of this review is to summarize the various systems that remove Ca2+ from the cytoplasm. We will initially focus on the Ca2+ pump and the Na(+)-Ca2+ exchanger of the plasma membrane. We will review the functional regulation of these systems and the recent progress obtained with molecular-biology techniques, which pointed to the existence of different isoforms of the Ca2+ pump. The Ca2+ pumps of the sarco(endo)plasmic reticulum will be discussed next, by summarizing the discoveries obtained with molecular-biology techniques, and by reviewing the physiological regulation of these proteins. We will finally briefly review the mitochondrial Ca(2+)-uptake mechanism.