Cold shock response in Escherichia coli

Sensing a sudden change of the growth temperature, all living organisms produce heat shock proteins or cold shock proteins to adapt to a given temperature. In a heat shock response, the heat shock sigma factor plays a major role in the induction of heat shock proteins including molecular chaperones and proteases, which are well-conserved from bacteria to human. In contrast, no such a sigma factor has been identified for the cold shock response. Instead, RNAs and RNA-binding proteins play a major role in cold shock response. This review describes what happens in the cell upon cold shock, how E. coli responds to cold shock, how the expression of cold shock proteins is regulated, and what their functions are.     

Stressors, Stress Reactions, and Survival of Bacteria: A Review

Recent data on the molecular mechanisms of the stress responses of bacteria are reviewed, with emphasis on their reactions to a variety of stressors (heat, oxidation, cold, osmotic shock, etc.). The mechanisms underlying the phenomenon of sensoring are discussed. It is shown that cross-resistance to stressors and cell-to-cell communication, mediated by chemical metabolites, affect bacterial survival in food products. The stress-antagonizing activity of bacteria is discussed in relation to food product biotechnology.     

Stressors, stress reactions, and survival of bacteria (a review)

Recent data on the molecular mechanisms of stress responses of bacteria are reviewed, with emphasis on their reactions to a variety of stressors (heat, oxidation, cold, osmotic shock, etc.). Mechanisms underlying the phenomenon of sensoring are discussed. It is shown that cross-resistance to stressors and cell-to-cell communication of bacteria, mediated by chemical metabolites, affect their survival in food products. Stress-antiagonizing activity of bacteria is discussed in relation to food product biotechnology.     

How cells protect themselves against stress?

The current evidence on the mechanisms underlying cell response to heat shock is reviewed. The response dynamics, induction, and attenuation as well as heat shock proteins and the mechanisms through which they protect cells from stress are considered. The role of these proteins in regulating the signaling cascades, including apoptosis suppression, is shown.     

How Cells Protect Themselves against Stress?

The current evidence on the mechanisms underlying cell response to heat shock is reviewed. The response dynamics, induction, and attenuation as well as heat shock proteins and the mechanisms through which they protect cells from stress are considered. The role of these proteins in regulating the signaling cascades, including apoptosis suppression, is shown.     

DNA topology and the thermal stress response, a tale from mesophiles and hyperthermophiles

During heat shock and cold shock, plasmid DNA supercoiling changes transiently both in mesophilic bacteria and in hyperthermophilic archaea, despite a different overall topology (negative supercoiling versus relaxation to positive supercoiling). Transient changes in DNA supercoiling might be essential to generate the stress response, but they could also be a consequence of the physical effects of temperature on cellular components. Indeed, both appear intertwined. Comparison of the mechanisms acting in the two biological systems suggests that the dependence on temperature of the activity of different DNA topoisomerases, as well as of protein binding, are key factors for the control of DNA topology during stress, which may in turn be relevant for the expression of stress-induced genes.     

Is Catalytic Activity of Chaperones a Selectable Trait for the Emergence of Heat Shock Response?

Although heat shock response is ubiquitous in bacterial cells, the underlying physical chemistry behind heat shock response remains poorly understood. To study the response of cell populations to heat shock we employ a physics-based ab initio model of living cells where protein biophysics (i.e., folding and protein-protein interactions in crowded cellular environments) and important aspects of proteins homeostasis are coupled with realistic population dynamics simulations. By postulating a genotype-phenotype relationship we define a cell division rate in terms of functional concentrations of proteins and protein complexes, whose Boltzmann stabilities of folding and strengths of their functional interactions are exactly evaluated from their sequence information. We compare and contrast evolutionary dynamics for two models of chaperon action. In the active model, foldase chaperones function as nonequilibrium machines to accelerate the rate of protein folding. In the passive model, holdase chaperones form reversible complexes with proteins in their misfolded conformations to maintain their solubility. We find that only cells expressing foldase chaperones are capable of genuine heat shock response to the increase in the amount of unfolded proteins at elevated temperatures. In response to heat shock, cells’ limited resources are redistributed differently for active and passive models. For the active model, foldase chaperones are overexpressed at the expense of downregulation of high abundance proteins, whereas for the passive model; cells react to heat shock by downregulating their high abundance proteins, as their low abundance proteins are upregulated.     

Control of DNA topology during thermal stress in hyperthermophilic archaea: DNA topoisomerase levels, activities and induced thermotolerance during heat and cold shock in Sulfolobus

Plasmid topology varies transiently in hyperthermophilic archaea during thermal stress. As in mesophilic bacteria, DNA linking number (Lk) increases during heat shock and decreases during cold shock. Despite this correspondence, plasmid DNA topology and proteins presumably involved in DNA topological control in each case are different. Plasmid DNA in hyperthermophilic archaea is found in a topological form from relaxed to positively supercoiled in contrast to the negatively supercoiled state typical of bacteria, eukaryotes and mesophilic archaea. We have analysed the regulation of DNA topological changes during thermal stress in Sulfolobus islandicus (kingdom Crenarchaeota), which harbours two plasmids, pRN1 and pRN2. In parallel with plasmid topological variations, we analysed levels of reverse gyrase, topoisomerase VI (Topo VI) and the small DNA-binding protein Sis7, as well as topoisomerase activities in crude extracts during heat shock from 80 degrees C to 85-87 degrees C, and cold shock from 80 degrees C to 65 degrees C. Quantitative changes in reverse gyrase, Topo VI and Sis7 were not significant. In support of this, inhibition of protein synthesis in S. islandicus during shocks did not alter plasmid topological dynamics, suggesting that an increase in topoisomerase levels is not needed for control of DNA topology during thermal stress. A reverse gyrase activity was detected in crude extracts, which was strongly dependent on the assay temperature. It was inhibited at 65 degrees C, but was greatly enhanced at 85 degrees C. However, the intrinsic reverse gyrase activity did not vary with heat or cold shock. These results suggest that the control of DNA topology during stress in Sulfolobus relies primarily on the physical effect of temperature on topoisomerase activities and on the geometry of DNA itself. Additionally, we have detected an enhanced thermoresistance of reverse gyrase activities in cultures subject to prolonged heat shock (but not cold shock). This acquired thermotolerance at the enzymatic level is abolished when cultures are treated with puromycin, suggesting a requirement for protein synthesis.     

The absence of direct relationship between the ability of yeasts to grow at elevated temperatures and their survival after lethal heat shock

The study of the growth of the yeasts Rhodotorula rubra, Saccharomyces cerevisiae, and Debaryomyces vanriji at elevated temperatures and their survival after transient lethal heat shock showed that the ability of these yeasts to grow at supraoptimal temperatures (i.e., their thermoresistance) and their ability to tolerate lethal heat shocks (i.e., their thermotolerance) are determined by different mechanisms. The thermotolerance of the yeasts is suggested to be mainly determined by the division rate of cells before their exposure to heat shock.     

Non-coding RNAs turn up the heat: An emerging layer of novel regulators in the mammalian heat shock response

The field of non-coding RNA (ncRNA) has expanded over the last decade following the discoveries of several new classes of regulatory ncRNA. A growing amount of evidence now indicates that ncRNAs are involved even in the most fundamental of cellular processes. The heat shock response is no exception as ncRNAs are being identified as integral components of this process. Although this area of research is only in its infancy, this article focuses on several classes of regulatory ncRNA (i.e., miRNA, lncRNA, and circRNA), while summarizing their activities in mammalian heat shock. We also present an updated model integrating the traditional heat shock response with the activities of regulatory ncRNA. Our model expands on the mechanisms for efficient execution of the stress response, while offering a more comprehensive summary of the major regulators and responders in heat shock signaling. It is our hope that much of what is discussed herein may help researchers in integrating the fields of heat shock and ncRNA in mammals.     

Effects of hyperthermia on spermatogenesis, apoptosis, gene expression, and fertility in adult male mice.

Testicular heat shock was used to characterize cellular and molecular mechanisms involved in male fertility. This model is relevant because heat shock proteins (HSPs) are required for spermatogenesis and also protect cells from environmental hazards such as heat, radiation, and chemicals. Cellular and molecular methods were used to characterize effects of testicular heat shock (43 degrees C for 20 min) at different times posttreatment. Mating studies confirmed conclusions, based on histopathology, that spermatocytes are the most susceptible cell type. Apoptosis in spermatocytes was confirmed by TUNEL, and was temporally correlated with the expression of stress-inducible Hsp70-1 and Hsp70-3 proteins in spermatocytes. To further characterize gene expression networks associated with heat shock-induced effects, we used DNA microarrays to interrogate the expression of 2208 genes and thousands more expression sequence tags expressed in mouse testis. Of these genes, 27 were up-regulated and 151 were down-regulated after heat shock. Array data were concordant with the disruption of meiotic spermatogenesis, the heat-induced expression of HSPs, and an increase in apoptotic spermatocytes. Furthermore, array data indicated increased expression of four additional non-HSP stress response genes, and eight cell-adhesion, signaling, and signal-transduction genes. Decreased expression was recorded for 10 DNA repair and recombination genes; 9 protein synthesis, folding, and targeting genes; 9 cell cycle genes; 5 apoptosis genes; and 4 glutathione metabolism genes. Thus, the array data identify numerous candidate genes for further analysis in the heat-shocked testis model, and suggest multiple possible mechanisms for heat shock-induced infertility.     

The Absence of a Direct Relationship between the Ability of Yeasts to Grow at Elevated Temperatures and Their Survival after Lethal Heat Shock

The study of the growth of the yeasts Rhodotorula rubra, Saccharomyces cerevisiae, and Debaryomyces vanriji at elevated temperatures and their survival after transient lethal heat shock showed that the ability of these yeasts to grow at supraoptimal temperatures (i.e., their thermoresistance) and their ability to tolerate lethal heat shocks (i.e., their thermotolerance) are determined by different mechanisms. It is suggested that the thermotolerance of the yeasts is mainly determined by the division rate of cells before their exposure to heat shock.     

Commensal bacteria, redox stress, and colorectal cancer: mechanisms and models

The potential role for commensal bacteria in colorectal carcinogenesis is explored in this review. Most colorectal cancers (CRCs) occur sporadically and arise from the gradual accumulation of mutations in genes regulating cell growth and DNA repair. Genetic mutations followed by clonal selection result in the transformation of normal cells into malignant derivatives. Numerous toxicological effects of colonic bacteria have been reported. However, those recognized as damaging epithelial cell DNA are most easily reconciled with the currently understood genetic basis for sporadic CRC. Thus, we focus on mechanisms by which particular commensal bacteria may convert dietary procarcinogens into DNA damaging agents (e.g., ethanol and heterocyclic amines) or directly generate carcinogens (e.g., fecapentaenes). Although these and other metabolic activities have yet to be linked directly to sporadic CRC, several lines of investigation are reviewed to highlight difficulties and progress in the area. Particular focus is given to commensal bacteria that alter the epithelial redox environment, such as production of oxygen radicals by Enterococcus faecalis or production of hydrogen sulfide by sulfate-reducing bacteria (SRB). Super-oxide-producing E. faecalis has conclusively been shown to cause colonic epithelial cell DNA damage. Though SRB-derived hydrogen sulfide (H(2)S) has not been reported thus far to induce DNA damage or function as a carcinogen, recent data demonstrate that this reductant activates molecular pathways implicated in CRC. These observations combined with evidence that SRB carriage may be genetically encoded evoke a working model that incorporates multifactorial gene-environment interactions that appear to underlie the development of sporadic CRC.