Heat-shock proteins in host-pathogen interactions: implications for cystic fibrosis

Adaptive responses of human monocytes infected by bordetella pertussis: the role of adenylate cyclase hemolysin

The activation/adaptive responses of human monocytes exposed to Bordetella pertussis parental or mutant strains were evaluated and correlated to the expression of two bacterial toxins: adenylate cyclase-hemolysin and pertussis toxin. The marked rise in intracellular cyclic adenosine monophosphate (cAMP) observed in monocytes infected by B. pertussis parental strain, inversely correlated with (1) the production of tumor necrosis factor alpha; (2) the release of superoxide anion; and (3) the expression of the 72-kDa heat shock/stress protein, Hsp70. Experiments performed with mutants deficient in adenylate cyclase-hemolysin or with purified bacterial toxins confirmed the key role of adenylate cyclase-hemolysin in the control of monocytes' response to infection by B. pertussis. This bacterial strategy primarily involves evasion from antimicrobial defenses and, eventually, the sacrifice of the host cell.

Differential expression of an hsp70 gene during transition from the mycelial to the infective yeast form of the human pathogenic fungus Paracoccidioides brasiliensis

We have isolated and characterized cDNA and genomic clones that encode a 70 kDa heat shock protein (Hsp70) from the dimorphic human pathogenic fungus Paracoccidioides brasiliensis. The gene encodes a 649-amino-acid protein showing high identity with other members of the hsp70 gene family. The hsp70 gene is induced during both heat shock of yeast cells at 42 degrees C and the mycelial to yeast transition. A differential expression of this gene can be observed between mycelial and yeast forms, with a much higher level of expression in the yeast. We found two introns of 178 and 72 nucleotides in the P. brasiliensis hsp70 gene. Splicing of these introns is regulated during the heat shock process and possibly during infection. In order to analyse the differential accumulation of unspliced mRNA following cellular differentiation and/or heat shock, reverse transcriptase-polymerase chain reaction (RT-PCR) experiments were carried out. The temperature-induced mycelial to yeast transition results in the transient accumulation of unspliced hsp70 mRNA transcripts. Yeast cells, after adaptation at 36 degrees C, seem to be more proficient at splicing, at least with respect to hsp70 mRNA because, during a severe heat shock (42 degrees C), the unspliced form of this mRNA does not accumulate. The mycelial to yeast differentiation will have the adaptational effect of increasing the resistance of the organism to environmental stress, which may be necessary for parasite survival in the mammalian host.

Effects of iron deprivation on the pathology and stress protein expression in murine X-linked muscular dystrophy

Duchenne muscular dystrophy (DMD) is caused by dystrophin deficiency, which results in muscle necrosis and the upregulation of heat shock/stress proteins (HSP). We hypothesized that reactive oxygen species, and in particular hydroxyl radicals (.OH), participate in muscle necrosis and HSP expression. It was assumed that iron deprivation decreases .OH generation, restraining the disease process and reducing the oxidant-induced expression of HSP. The role of iron-catalyzed free radical reactions in the pathology of dystrophin-deficient muscle was evaluated in the murine model for Duchenne muscular dystrophy (mdx), by examining the effects of dietary deficiency and supplementation of iron on serum creatine kinase (CK), muscle morphology, lipid peroxidation and HSP levels in mice maintained on diets deficient in or supplemented with iron for 6 weeks. Iron-deprived mdx mice showed a significant decrease in the number of macrophage-invaded necrotic fibers and the expression of the 70-kDa heat shock protein (Hsp70). This suggests that the iron-dependent generation of .OH relates to muscle necrosis in the mdx mouse and modulates the expression of Hsp70 in vivo. In contrast, iron deprivation had no influence on other HSP or on lipid peroxidation in mdx mice, while maintenance on either diet caused a significant decrease in serum creatine kinase activity. The potential therapeutic effects of iron deprivation in mdx should be considered.

Heat shock and proinflammatory stressors induce differential localization of heat shock proteins in human monocytes

Heat shock (HS) proteins (HSP) are a family of molecular chaperones induced by environmental stresses such as oxidative injury, and contribute to protection from and adaptation to cellular stress. We investigated in human monocytes the expression and subcellular distribution of hsp70 and hsc70 after HS and inflammation-related stresses leading to generation of reactive oxygen species by these cells, such as the phorbol ester PMA and erythrophagocytosis (E phi). By combining immunofluorescent staining and Western blot on subcellular fractions, we found that all three stress factors resulted in an increased hsp70 expression, however the subcellular distribution pattern was different depending on the type of stress. While HS induced a rapid translocation of hsp70 into the nucleus, no nuclear translocation of hsp70 was observed after PMA or E phi. Neither of the examined stresses induced membrane expression of hsp70. The observed differences in subcellular distribution pattern might relate to distinct regulation and specific functions of hsp70 in inflammation.

Cell integrity markers for in vitro evaluation of cytotoxic responses to bacteria-containing commercial insecticides

Toxicity of two commercial "BT" products, containing Bacillus thuringiensis subsp. kurstaki spores (Btk) and associated parasporal inclusion body proteins, was tested in vitro using two unrelated lepidoperan cell lines and several markers of cell integrity (morphology, quantification of loss of adherence and electron transport (redox) activity, and degradation of nuclear DNA, actin, hsp-70, and beta-tubulin). With doses of 10(-7), 10(-5), and 10(-3) International Units (IU)/target cell, these markers measured exposure-dependent effects closely linked to cell death, which occurred rapidly once Btk spores germinated, unless inhibited by antibiotic. Derivation of marker half-lives (HL50) revealed that temperature critically affected product performance. Between 34 and 37 degrees C, HL50 was < or = 5 hr, but dose discrimination between 10(-5) and 10(-3) IU was poor. At temperatures less than 34 degrees C, the resolution between different HL50s and doses increased in a manner directly relating to published data obtained from in vivo BT-spore-induced LD50 assays. It was concluded that BT product toxification is complex, essentially enabled by an autobiotransformation process in which dose-response lag is affected by temperature-dependent temporal expression of spore germination and critical buildup of vegetative cells and byproduct toxicants. The in vitro dosimetry assays described here are potentially useful for obtaining mechanistic toxicologic data and in vivo relevant quantifications of subingredient activities in various commercial BT formulations as well as in other microbe-based biotechnology products.

Cloning and characterization of the groE locus from Actinobacillus pleuropneumoniae

A 4.4-kb DNA fragment was cloned from Actinobacillus pleuropneumoniae (strain 4074, serotype 1) by genetic complementation with Escherichia coli groES-groEL mutant strains. Sequence analysis of this fragment revealed a purine nucleoside phosphorylase (DeoD)-encoding gene homolog (deoD), heat-shock response-encoding genes for the small (groES) and large subunits (groEL) and a partial open reading frame encoding an alcohol dehydrogenase homolog (adhE). The predicted amino-acid sequence of groES and groEL genes showed extensive sequence identity (80-95%) with other Pasteurellaceae. The gene organization surrounding the groE locus was different from that of Haemophilus infuenzae. When expressed in E. coli, groES-groEL genes were capable of complementing the growth of a lambda lytic phage, indicating a structural as well as functional conservation.

Transcriptional regulators of oxidative stress-inducible genes in prokaryotes and eukaryotes

It appears that redox regulation is an important mechanism for the control of transcription factor activation. The role of oxidation-reduction is probably determined in part by the structure of the transcription factors. For example, the presence of cysteine residues within the DNA binding sites may sensitize a transcription factor to ROS. The ROS-mediated regulation of transcription factors is specific, some ROS are more efficient than other ROS in activating defined regulators. While the protective antioxidant responses induced by ROS in prokaryotes and eukaryotes are rather conserved (for example, SOD, HSP...), the regulators for these genes do not appear to be conserved. Further studies designed to fully characterize these regulators and understand the subtle mechanisms involved in redox gene regulation are ongoing, and should provide the theoretical basis for clinical approaches using antioxidant therapies in human diseases in which oxidative stress is implicated.

Stress proteins in inflammation

Inflammation provides those searching in the field with a number of "models" allowing them to study, in vivo, in humans and in animals, the regulation and the functions of HSP, which are being considered as a new and promising marker for the severity and the prognosis of inflammatory diseases. HSP are differentially regulated according to the type of inflammation, whether acute or chronic, whether self-limiting (inflammatory cell elimination by apoptosis) or self-perpetuating (inflammatory cell death by necrosis). We propose that mitochondria are a key organelle in determining the outcome of inflammation, because they are both the cellular "switchboard" for apoptosis and a selective target for the protective effects of HSP against the cytotoxic effects of TNF alpha and ROS. On the other hand, HSP exert multiple protective effects in inflammation, including self/non-self discrimination, enhancement of immune responses, immune protection, thermotolerance and protection against the cytotoxicity of inflammatory mediators. The latter protective effects against the deleterious effects of the mediators of inflammation, including ROS and cytokines, open new avenues for the development of original anti-inflammatory therapies, such as non-toxic inducers of a complete HS response. It may well be that the "beneficial effects of fever" already described by Hippocrates actually relate to increased HSP expression during fever, and to their protective effects....