Inhibition of the biosynthesis of SRP polypeptides and secretory proteins by aflatoxin B1 can disrupt protein targeting

Cell culture and western blotting studies revealed that aflatoxin B(1) (AFB(1)) inhibits the biosynthesis of two of the constituent polypeptides of signal recognition particle (SRP) (SRP54 and 72). SRP escorts polyribosomes carrying signal peptides from free form in the cytosol to the bound form on endoplasmic reticulum (ER) membrane during protein targeting. These effects of AFB(1) on SRP biosynthesis may inhibit the formation of functional SRP. Our experiments have further shown that AFB(1) also inhibits the biosynthesis/translocation of a secretory protein, preprolactin, which fails to appear in the lumen of ER consequent to the treatment with this hepatocarcinogen. The results of the experiments presented in this article therefore enable us to infer for the first time that aflatoxin B(1) may inhibit the functioning of SRP as an escort and deplete the ER of polyribosomes for secretory protein synthesis. As these secretory proteins are important components of the plasma membrane, gap junctions and intercellular matrix, their absence from these locations could disturb cell to cell communication leading to tumorigenesis.     

Mammalian Rad9 plays a role in telomere stability, S- and G2-phase-specific cell survival, and homologous recombinational repair

The protein products of several rad checkpoint genes of Schizosaccharomyces pombe (rad1+, rad3+, rad9+, rad17+, rad26+, and hus1+) play crucial roles in sensing changes in DNA structure, and several function in the maintenance of telomeres. When the mammalian homologue of S. pombe Rad9 was inactivated, increases in chromosome end-to-end associations and frequency of telomere loss were observed. This telomere instability correlated with enhanced S- and G2-phase-specific cell killing, delayed kinetics of gamma-H2AX focus appearance and disappearance, and reduced chromosomal repair after ionizing radiation (IR) exposure, suggesting that Rad9 plays a role in cell cycle phase-specific DNA damage repair. Furthermore, mammalian Rad9 interacted with Rad51, and inactivation of mammalian Rad9 also resulted in decreased homologous recombinational (HR) repair, which occurs predominantly in the S and G2 phases of the cell cycle. Together, these findings provide evidence of roles for mammalian Rad9 in telomere stability and HR repair as a mechanism for promoting cell survival after IR exposure.     

Kinetic characterization of Zinc transport process and its inhibition by Cadmium in isolated rat renal basolateral membrane vesicles: In vitro and In vivo studies

We firstly characterized zinc uptake phenomenon across basolateral membrane vesicles (BLMVs) isolated from normal rat kidney. The process was found to be time, temperature, and substrate concentration dependent, and displayed saturability. Zn²⁺ uptake was competitively inhibited in the presence of 2 mM Cd with Ki of 3.9 mM. Zinc uptake was also inhibited in the presence of sulfhydryl reacting compound suggesting involvement of {–}SH groups in the transport process. Further, to elucidate the effect of in vivo Cd on zinc transport in BLMVs, Cd nephrotoxicity was induced by subcutaneous administration of CdCl₂ at dose of 0.6 mg/kg/d for 5 days in a week for 12 weeks. An indolent renal failure developed in Cd exposed rats was accompanied with a significantly high urinary excretion of Cd²⁺, Zn²⁺ and proteins. The histopathology and electron microscopy of kidneys of Cd exposed rats documented changes of proximal tubular degeneration. Notably, Cd content in renal cortex of Cd exposed rats was 215 μg/g tissue that was higher than the critical concentration of Cd in kidneys which was associated with significantly higher Zn and metallothionein (MT) contents. Zinc uptake in BLMVs isolated from kidneys of Cd exposed rats was significantly reduced. Further, kinetic studies revealed that decrease in zinc uptake synchronized with decrease in maximal velocity (V_max) and increase in affinity constant which is suggestive of decreased number of active zinc transporters. Furthermore, conformational modulation of Zn transporter in BLM was further supported by observed variation in transition temperature for zinc transport in BLMVs isolated from Cd-exposed kidney.     

Novel frequenin-modulated Ca2+-signaling membrane guanylate cyclase (ROS-GC) transduction pathway in bovine hippocampus

Frequenin is a member of the neuronal Ca²⁺ sensor protein family, implicated in being the modulator of the neurotransmitter release, potassium channels, phosphatidylinositol signaling pathway and the Ca²⁺-dependent exocytosis of dense-core granules in the PC12 cells. Frequenin exhibits these biological activities through its Ca²⁺ myristoyl switch, yet the switch is functionally inactive. These structural and functional traits of frequenin have been derived through the use of recombinant frequenin. In the present study, frequenin (BovFrq) native to the bovine hippocampus has been purified, sequenced for its 9 internal fragments, cloned, and studied. The findings show that structure of the BovFrq is identical to its form present in chicken, rat, mouse and human, indicating its evolutionary conservation. Its Ca²⁺ myristoyl switch is active in the hippocampus. And, BovFrq physically interacts and turns on yet undisclosed ONE-GC-like ROS-GC membrane guanylate cyclase transduction machinery in the hippocampal neurons. This makes BovFrq a new Ca²⁺-sensor modulator of a novel ROS-GC transduction machinery. The study demonstrates the presence and mechanistic features of this cyclic GMP signaling pathway in the hippocampal neurons, and also provides one more support for the evolving concept where the Ca²⁺-modulated membrane guanylate cyclase transduction machinery in its variant forms is a central operational component of all neurons.     

Plant Growth–Promoting Pseudomonas sp. Strains Reduce Natural Occurrence of Anthracnose in Soybean (Glycine max L.) in Central Himalayan Region

Biological control is an accepted important component of current plant disease management strategies. Introduction of bacterized seeds carrying bacterial isolates with proven growth-promotion capabilities and antagonistic characteristics offer a valid alternative to chemical protectants. Root colonization of disease-susceptible (PS 1024) and moderately resistant (PS1042) varieties of soyabean (Glycine Max L) by fluorescent pseudomonad (FLPs) strains GRP₃, PEn-4, PRS₁, and WRS-24 was studied in relation to natural occurrence of anthracnose caused by Colletotrichum dematium (Pers Ex Fr.) Grove. Rhizoplane population of FLPs was maintained at a critical level (5.3 cfu) up to 30 days of plant growth, followed by a steep decline. Indigenous FLPs population, however, remained nearly unchanged (3.0 to 2.4 log g⁻¹ root) between 30 days and 75 days of plant growth. The relative FLPs population in rhizosphere was lower than that in rhizoplane. Although intervarietal difference was observed, the root/shoot length remained unaffected. Compared to nonbacterized control, dry root weight was improved by FLPs treatment. Severity of foliar anthracnose was reduced significantly after FLPs treatment in the variety PS 1042. Because the point of FLPs treatment (seed bacterization) was away from the site of disease appearance (leaf), operation of induced systemic resistance in strains PEn-4 and GRP₃ appears imminent.     

Phosphate Metabolism in the Cyanobacterium Anabaena doliolum Under Salt Stress

In the present study, we have investigated the effects of NaCl concentrations on the growth and phosphate metabolism of an Anabaena doliolum strain isolated from a paddy field, in order to determine the possible effects of salinization. Growth rate, chlorophyll content, and protein content decreased with increasing salt concentration in the growth medium, while carbohydrate concentration increased. Phosphate content and phosphate uptake rate decreased. There was an increase in total alkaline phosphatase activity, with an approximately 7-fold increase in extracellular activity compensating for an approximately 3-fold decrease in cell-bound activity. NaCl effects on protein and chlorophyll concentrations were greater in P-deficient medium, while presence or absence of P in the medium had little effect on cellular carbohydrate concentrations. It is concluded that growth in high salt likely leads to reduced phosphate uptake in A. doliolum.     

Influences of AT1 receptor blockade on tissue metabolism in obese men

ANG II applied to the interstitial space influences carbohydrate and lipid metabolism in a tissue-specific fashion. Thus endogenous ANG II may have a tonic effect on tissue metabolism that could be reversed with ANG II type 1 (AT1) receptor blockade, particularly during adrenergic stimulation. We studied 14 obese men. They were treated for 10 days with the AT1 receptor blocker irbesartan or with placebo in a double-blind and crossover fashion. At the end of each treatment period, we assessed skeletal muscle and adipose tissue metabolism using the microdialysis technique. The ethanol dilution technique was applied to follow changes in tissue blood flow. Measurements were obtained at baseline and during application of incremental isoproterenol concentrations through the microdialysis catheter. Blood pressure decreased from 133 +/- 3/84 +/- 3 to 128 +/- 3/79 +/- 2 mmHg for systolic and diastolic blood, respectively (P = 0.02 and 0.006, respectively) with AT1 receptor blockade. Isoproterenol perfusion caused a dose-dependent increase in dialysate glycerol in adipose tissue and in skeletal muscle. Irbesartan slightly reduced the isoproterenol-induced glycerol response in adipose tissue (P < 0.05 by ANOVA). Ethanol ratio, interstitial glucose supply, and lactate production in adipose tissue and skeletal muscle were similar with placebo and irbesartan. We conclude that AT1 receptor blockade in obese men does not reveal a major tonic ANG II effect on interstitial glucose supply, lipolysis, or glycolysis in skeletal muscle, either at rest or during beta-adrenergic stimulation. Endogeneous ANG II may slightly increase adipose tissue lipolysis. The mechanism may promote the redistribution of triglycerides from adipose tissue toward other organs.