Heat-shock induced protein modifications and modulation of enzyme activities

A translational and multidisciplinary approach to studying the Garcia effect, a higher form of learning with deep evolutionary roots

Animals, including humans, learn and remember to avoid a novel food when its ingestion is followed, hours later, by sickness - a phenomenon initially identified during World War II as a potential means of pest control. In the 1960s, John Garcia (for whom the effect is now named) demonstrated that this form of conditioned taste aversion had broader implications, showing that it is a rapid but long-lasting taste-specific food aversion with a fundamental role in the evolution of behaviour. From the mid-1970s onward, the principles of the Garcia effect were translated to humans, showing its role in different clinical conditions (e.g. side-effects linked to chemotherapy). However, in the last two decades, the number of studies on the Garcia effect has undergone a considerable decline. Since its discovery in rodents, this form of learning was thought to be exclusive to mammals; however, we recently provided the first demonstration that a Garcia effect can be formed in an invertebrate model organism, the pond snail Lymnaea stagnalis. Thus, in this Commentary, after reviewing the experiments that led to the first characterization of the Garcia effect in rodents, we describe the recent evidence for the Garcia effect in L. stagnalis, which may pave the way for future studies in other invertebrates and mammals. This article aims to inspire future translational and ecological studies that characterize the conserved mechanisms underlying this form of learning with deep evolutionary roots, which can be used to address a range of different biological questions.

Heat Shock Protein Augmentation of Angelica gigas Nakai Root Hot Water Extract on Adipogenic Differentiation in Murine 3T3-L1 Preadipocytes

There is a high association of heat shock on the alteration of energy and lipid metabolism. The alterations associated with thermal stress are composed of gene expression changes and adaptation through biochemical responses. Previous study showed that Angelica gigas Nakai (AGN) root extract promoted adipogenic differentiation in murine 3T3-L1 preadipocytes under the normal temperature condition. However, its effect in heat shocked 3T3-L1 cells has not been established. In this study, we investigated the effect of AGN root hot water extract in the adipogenic differentiation of murine 3T3-L1 preadipocytes following heat shock and its possible mechanism of action. Thermal stress procedure was executed within the same stage of preadipocyte confluence (G0) through incubation at 42°C for one hour and then allowed to recover at normal incubation temperature of 37°C for another hour before AGN treatment for both cell viability assay and Oil Red O. Cell viability assay showed that AGN was able to dose dependently (0 to 400 μg/mL) increase cell proliferation under normal incubation temperature and also was able to prevent cytotoxicity due to heat shock accompanied by cell proliferation. Confluent preadipocytes were subjected into heat shock procedure, recovery and then AGN treatment prior to stimulation with the differentiation solution. Heat shocked preadipocytes exhibited reduced differentiation as supported by decreased amount of lipid accumulation in Oil Red O staining and triglyceride measurement. However, those heat shocked preadipocytes that then were given AGN extract showed a dose dependent increase in lipid accumulation as shown by both evaluation procedures. In line with these results, real-time polymerase chain reaction (RT-PCR) and Western blot analysis showed that AGN increased adipogenic differentiation by upregulating heat shock protection related genes and proteins together with the adipogenic markers. These findings imply the potential of AGN in heat shock amelioration among 3T3-L1 preadipocytes through heat shock factor and proteins augmentation and enhanced adipogenic marker expression.

Hyperthermia differently affects connexin43 expression and gap junction permeability in skeletal myoblasts and HeLa cells

Stress kinases can be activated by hyperthermia and modify the expression level and properties of membranous and intercellular channels. We examined the role of c-Jun NH2-terminal kinase (JNK) in hyperthermia-induced changes of connexin43 (Cx43) expression and permeability of Cx43 gap junctions (GJs) in the rabbit skeletal myoblasts (SkMs) and Cx43-EGFP transfected HeLa cells. Hyperthermia (42°C for 6 h) enhanced the activity of JNK and its target, the transcription factor c-Jun, in both SkMs and HeLa cells. In SkMs, hyperthermia caused a 3.2-fold increase in the total Cx43 protein level and enhanced the efficacy of GJ intercellular communication (GJIC). In striking contrast, hyperthermia reduced the total amount of Cx43 protein, the number of Cx43 channels in GJ plaques, the density of hemichannels in the cell membranes, and the efficiency of GJIC in HeLa cells. Both in SkMs and HeLa cells, these changes could be prevented by XG-102, a JNK inhibitor. In HeLa cells, the changes in Cx43 expression and GJIC under hyperthermic conditions were accompanied by JNK-dependent disorganization of actin cytoskeleton stress fibers while in SkMs, the actin cytoskeleton remained intact. These findings provide an attractive model to identify the regulatory players within signalosomes, which determine the cell-dependent outcomes of hyperthermia.

Effects of cadmium on cellular protein and glutathione synthesis and expression of stress proteins in eastern oysters, Crassostrea virginica Gmelin

Cadmium (Cd) is an important toxicant in estuarine and coastal environments that can strongly affect energy balance of aquatic organisms by increasing the organism's basal energy demand and reducing its aerobic capacity. Mechanisms of cadmium-induced increase in basal metabolic costs are not well understood and may involve elevated detoxification costs due to the synthesis of cellular protective proteins and glutathione. We studied the short-term effects of cadmium exposure (4 h) on protein and glutathione (GSH) synthesis and expression of stress proteins (heat shock proteins HSP60, HSP70 and HSP90) and metallothioneins in isolated gill and hepatopancreas cells of the eastern oyster, Crassostrea virginica. Our study showed that exposure to cadmium resulted in a dose-dependent increase in the rate of protein synthesis in oyster cells, which reached 150% of the control at the highest tested Cd level (2000 micromol l(-1)). GSH synthesis was significantly inhibited by the highest Cd concentrations, especially in hepatopancreas, which resulted in a slight but significant decrease in the total GSH concentrations. Elevated protein synthesis was associated with the increased expression of metallothioneins and heat shock proteins. Interestingly, stress protein response differed considerably between gill and hepatopancreas cells. In hepatopancreas, expression of metallothionein mRNA (measured by real-time PCR) increased 2-8-fold in response to Cd exposure, whereas no significant increase in metallothionein expression was found in Cd-exposed gill cells. By contrast, HSP60 and HSP70 protein levels increased significantly in Cd-exposed gill cells (by 1.5-2-fold) but not in hepatopancreas. No change in HSP90 expression was detected in response to Cd exposure in oyster cells. These data indicate that metallothionein expression may provide sufficient protection against Cd-induced damage to intracellular proteins in hepatopancreas, alleviating the need for overexpression of molecular chaperones. By contrast, Cd detoxification mechanisms such as inducible metallothioneins and GSH appear to be insufficient to fully prevent protein damage in gill cells, thus necessitating induction of HSPs as a secondary line of cellular defense. Therefore, gills are likely to be among the most Cd-sensitive tissues in oysters, which may have important implications for impaired oxygen uptake contributing to energy misbalance and reduced aerobic scope in Cd-exposed oysters.

Glycosylation of stress glycoprotein GP62 in cells exposed to heat-shock and subculturing

GP62 is a member of the stress glycoprotein family that was proposed to have a chaperone-like function in the heat-shock response. Using lectin blotting we have studied glycosylation of GP62 and determined that in addition to heat-shock, even simple subculturing of cells is a sufficient stimulus to provoke induction of GP62. Interestingly, both kinetics of induction and glycosylation of GP62 induced by subculturing were different than when GP62 was induced by heat-shock. While GP62 induced by heat-shock was recognized by SNA, DSA and PHA-E lectins, and not by BSA I, Con A, RCA I, SJA, UEA I, VVA, and WGA lectins, GP62 induced by subculturing was also recognized by RCA I and WGA lectins.

Stimulation of survival capacity in heat shocked cells by subsequent exposure to minute amounts of chemical stressors; role of similarity in hsp-inducing effects

A brief and moderate heat shock to Reuber H35 hepatoma cells causes a rapid increase in the synthesis of heat shock proteins (hsp) and initiates the development of thermotolerance, which results in an increased ability to survive exposure to otherwise lethal temperatures. We now demonstrate that low doses of various chemical stressors (arsenite, cadmium, mercury, lead, copper, menadione and diethyldithiocarbamate (ddtc)), at concentrations that do not exert any effect in control cultures, are able to enhance the synthesis of hsps and to stimulate the development of thermotolerance when applied to cultures which were pretreated with a mild heat shock. The degree of stimulation appears to be stressor-specific, which is not only observed in the ensuing development of thermotolerance but also in the enhancement of the heat shock-induced synthesis of stress proteins. The different hsps that show an enhanced induction when heat shocked cultures are exposed to the various secondary applied low doses of chemical stressors, were found to resemble the hsp pattern that is characteristic for the secondary stressor and not for the initial heat shock. In other words, the nature of the post-treatment determines the observed pattern of enhanced synthesis of hsps. In order to analyze the origin of the stimulation of survival capacity by low doses of the mentioned stressors, we studied whether the degree of stimulation is determined by the degree of similarity between the overall stress response to heat shock and to the second stress condition when applied singly. The degree in which low doses of chemical stressors stimulate tolerance development and enhance the synthesis of hsps in cells that were previously heat shocked, appears to be related to the degree of similarity in the hsp pattern induced by both stressors. Our results support the notion that low doses of toxic compounds may, under certain conditions, have beneficial effects related to a stimulation of endogenous cytoprotective mechanisms.

Heat-shock proteins, molecular chaperones, and the stress response: evolutionary and ecological physiology

Molecular chaperones, including the heat-shock proteins (Hsps), are a ubiquitous feature of cells in which these proteins cope with stress-induced denaturation of other proteins. Hsps have received the most attention in model organisms undergoing experimental stress in the laboratory, and the function of Hsps at the molecular and cellular level is becoming well understood in this context. A complementary focus is now emerging on the Hsps of both model and nonmodel organisms undergoing stress in nature, on the roles of Hsps in the stress physiology of whole multicellular eukaryotes and the tissues and organs they comprise, and on the ecological and evolutionary correlates of variation in Hsps and the genes that encode them. This focus discloses that (a) expression of Hsps can occur in nature, (b) all species have hsp genes but they vary in the patterns of their expression, (c) Hsp expression can be correlated with resistance to stress, and (d) species' thresholds for Hsp expression are correlated with levels of stress that they naturally undergo. These conclusions are now well established and may require little additional confirmation; many significant questions remain unanswered concerning both the mechanisms of Hsp-mediated stress tolerance at the organismal level and the evolutionary mechanisms that have diversified the hsp genes.