[Production of 70 kDa recombinant human heat shock protein in baculovirus expression system and assessment of its antiviral activity]

AIM

To obtain human recombinant 70 kDa heat shock protein (Hsp70) in baculovirus expression system and to study its antiviral activity.

MATERIALS AND METHODS

Baculovirus expression system was used to obtain recombinant HSP70. Plasmid pFastBacHTb-Hsp70 containing sequence coding HSP70 gene with insertion of 6 histidine residues in protein reading frame was constructed. Competent cells MAX Efficiency DH 10 Bac were transfected with pFastBacHTb-Hsp70 plasmid with following extraction of recombinant bacmid Bac-Hsp70. In order to obtain baculovirus expressing HSP70, Sf-9 cells were transfected with Bac-Hsp70 bacmid. Hsp70 extraction and purification was performed with column metal-chelating affinity chromatography using Ni2+ ions. Protective efficacy of recombinant human HSP70 was estimated using model of Venezuelan equine encephalitis (VEE) in mice.

RESULTS

Recombinant bacmid Bac-Hsp70 was constructed based on Bac-to-Bac expression system. Baculovirus expressing human HSP70 have been produced after transfection of Sf-9 cells with Bac-Hsp70 bacmid. Cultivation of recombinant baculovirus in Sf-9 cells and application of metal-chelating affinity chromatography allowed to extract purified fraction of HSP70. Experiments on mice infected with VEE virus demonstrated significant protection from death after administration of HSP70 in dose 15 mcg/mice.

CONCLUSION

Application of baculovirus expression system and insect cell line for accumulation of recombinant baculoviruses in combination with Ni(2+)-mediated metal-chelating affinity chromatography allowed to obtain highly purified human recombinant HSP70 with marked antiviral activity.

[Morphologic and molecular manifestations of hybrid dysgenesis in ontogenesis of Drosophila virilis]

Disorders of germ track cell development that take place in crossbreeding of certain lines of Drosophila virilis and lead to hybrid dysgenesis (HD) syndrome have been studied. Polar cells and germ line cells were identified with specific antibodies against Vasa protein. It has been shown that abnormalities of formation of primary gonads takes place already at the 11-12 stage of embryo development and the consequences of germ line cell death lead to disorders of gonad development at the following stages of ontogenesis of dysgenic hybrids. The start point of germ line cell death in embryogenesis as well as initiation of transcription of Penelope retroelement, which is supposed to play a significant role in HD syndrome development in D. virilis, were estimated.

Small RNA-based silencing strategies for transposons in the process of invading Drosophila species

Colonization of a host by an active transposon can increase mutation rates or cause sterility, a phenotype termed hybrid dysgenesis. As an example, intercrosses of certain Drosophila virilis strains can produce dysgenic progeny. The Penelope element is present only in a subset of laboratory strains and has been implicated as a causative agent of the dysgenic phenotype. We have also introduced Penelope into Drosophila melanogaster, which are otherwise naive to the element. We have taken advantage of these natural and experimentally induced colonization processes to probe the evolution of small RNA pathways in response to transposon challenge. In both species, Penelope was predominantly targeted by endo-small-interfering RNAs (siRNAs) rather than by piwi-interacting RNAs (piRNAs). Although we do observe correlations between Penelope transcription and dysgenesis, we could not correlate differences in maternally deposited Penelope piRNAs with the sterility of progeny. Instead, we found that strains that produced dysgenic progeny differed in their production of piRNAs from clusters in subtelomeric regions, possibly indicating that changes in the overall piRNA repertoire underlie dysgenesis. Considered together, our data reveal unexpected plasticity in small RNA pathways in germ cells, both in the character of their responses to invading transposons and in the piRNA clusters that define their ability to respond to mobile elements.

[Effect of the recombinant human heat shock protein HSP70 on the biochemical properties of blood in a model of endotoxic shock in rats]

The protective effects of 70-kDa heat shock proteins (HSP70) were studied following the intravenous administration in rats with endotoxic shock. The antitoxic effects of both bovine HSP70 (bHSP70) and human recombinant HSP70 (hrHSP70) were compared. The preventive uptake of HSP70 decreased the toxic influence of the E. coll endotoxin on the rats' bodies and significantly increased the survival of the animals during the experiment.

[Structural and functional analysis of the representatives of a new class of retroelements in Drosophila species]

Various copies of mobile element Penelope previously described in Drosophila virilis have been investigated in different strains of D. virilis and transgenic strains of D. melanogaster transformed by P-based constructs containing full-size copy of Penelope. It has been demonstrated that most of Penelope copies in both species carry large terminal inverted repeats (TIR) and contain deletions of various size at their 5'end of ORF. Junctions between TIR and ORF usually carry microhomology of various length enabling to postulate a hypothesis explaining the molecular mechanism underlying the origin of such complex structures. Penelope copies usually carry 34 bp repeat located in direct orientation at both end of ORF and target site duplications of various length.

[Comparative analysis of hsp70 gene cluster in Drosophila virilis species group]

We cloned and sequenced one of Drosophila montana hsp70 genes. 3'-flanking region of this particular copy contains fragment of SGM mobile element. Previously this element was found within hsp70 3'-flanking region of other species of the virilis species group namely D. virilis and D. lummei. We have described reorganization of hsp70 gene cluster in one of D. virilis strains involving full-length SGM. Our data enable one to suggest evolutionary conservatism of SGM localization within hsp70 gene cluster of different species of the virilis group of Drosophila and implicate this mobile element in the evolution of hsp70 genes.

[Qualitative and quantitative analyses of the transpositions of P element--based genetic construction into the region of Drosophila melanogaster hsp70 genes]

The hsp70 genes is among the main systems underlying the adaptation of organisms to adverse environmental factors. The ever increasing amount of data in literature demonstrates an important adaptive role of mobile genetic elements in microevolution. Drosophila hsp70 genes are potential target for transpositions of various mobile elements in natural populations. We have analyzed the frequency and localization of a P element-based genetic construction, EPgy2, in the region of Drosophila melanogaster hsp70 genes. A hot spot for the transposition was discovered in the promoter regions of genes hsp70Aa and hsp70Ab. No insertions of this construction in the coding or 3'-flanking regions of hsp70 genes have been recorded. It was demonstrated that the region of 161 to 7800 bp adjacent to the original construction is in certain cases also involved in the transposition. No transpositions of any other mobile elements have been observed. The inserts were shown to change the activity of hsp70 genes and the thermotolerance of transgenic strains.

Molecular mechanisms underlying thermal adaptation of xeric animals

For many years,we and our collaborators have investigated the adaptive role of heat shock proteins in different animals,including the representatives of homothermic and poikilothermic species that inhabit regions with contrasting thermal conditions. Adaptive evolution of the response to hyperthermia has led to different results depending upon the species. The thermal threshold of induction of heat shock proteins in desert thermophylic species is, as a rule, higher than in the species from less extreme climates. In addition,thermoresistant poikilothermic species often exhibit a certain level of heat shock proteins in cells even at a physiologically normal temperature. Furthermore,there is often a positive correlation between the characteristic temperature of the ecological niche of a given species and the amount of Hsp70-like proteins in the cells at normal temperature. Although in most cases adaptation to hyperthermia occurs without changes in the number of heat shock genes, these genes can be amplified in some xeric species. It was shown that mobile genetic elements may play an important role in the evolution and fine-tuning of the heat shock response system,and can be used for direct introduction of mutations in the promoter regions of these genes.

[Mobile elements and evolution]

Mobile elements (ME) represent an important component of the genome of all organisms studied so far. ME belong to two major classes differing by the mechanism of transposition. Class I ME transpose using RNA intermediate and reverse transcriptase, while class II elements encode their own transposase and may transpose by cut and paste mechanism. Intra and intergenomic distribution of various classes of ME is discussed in the review. An important role of various groups of ME in regulation of cellular genes is also documented. The data accumulated enable to suggest that multiple invasions of ME with subsequent amplification in the host genome may significantly contribute to the adaptation of population to drastic changes in environment. Various roles of ME in the evolution of higher organisms including speciation process are discussed.

[Role of general transcription factors and the TFTC complex in transcription activation in vivo as revealed with a model of the hsp70 gene]

General transcription factors (GTFs) were tested for the presence on the promoter of the Drosophila melanogaster hsp70 gene in vivo. TBP, TBP-associated TAF proteins, TFIIB, TFIIF (RAP30), TFIIH (XPB), the TFTC complex (GCN5 and TRRAP), and a Mediator complex subunit (MEDI 3) were detected on the promoter before heat induction. Heat exposure significantly reduced the contents of TBP, TAF proteins, TFIIB, and TFIIF (RAP30), while these proteins were detected in ecdysone-inducible loci. It was assumed on the basis of these findings that a special mechanism induces transcription from the hsp70 promoter and that the apparent presence or absence of GTFs does not always reflect the transcriptional status of a gene.

Exogenous heat shock protein 70 mediates sepsis manifestations and decreases the mortality rate in rats

Mammalian responses to bacterial lipopolysaccharide (LPS) from the outer membrane of Gram-negative bacteria can lead to an uncontrolled inflammatory reaction that can be deadly for the host. We checked whether heat shock protein 70 (Hsp70) protein is able to protect animals from the deleterious effects of bacterial LPS by monitoring the effect of exogenous Hsp70 injections before and after LPS administration. Our research with rats demonstrates for the first time that administration of exogeneous Hsp70 before and after LPS challenges can reduce mortality rates and modify several parameters of hemostasis and hemodynamics. Hsp70 isolated from bovine muscles showed significant protective effects against the impaired coagulation and fibrinolytic systems caused by LPS, and reduced the mortality caused by Escherichia coli and Salmonella typhimurium LPS injections significantly. Characteristically, Hsp70 preparations used in the experiments result in different effects when administered before and after an LPS challenge, and the effects of Hsp70 injections also differ significantly depending on the origin of the LPS (E coli vs S typhimurium). Based on our data, mammalian Hsp70 appears to be an attractive target in therapeutic strategies designed to stimulate endogenous protective mechanisms against many deleterious consequences of septic shock by accelerating the functional recovery of susceptible organs in humans.

Remarkable site specificity of local transposition into the Hsp70 promoter of Drosophila melanogaster

Heat-shock genes have numerous features that ought to predispose them to insertional mutagenesis via transposition. To elucidate the evolvability of heat-shock genes via transposition, we have exploited a local transposition technique and Drosophila melanogaster strains with EPgy2 insertions near the Hsp70 gene cluster at 87A7 to produce numerous novel EPgy2 insertions into these Hsp70 genes. More than 50% of 45 independent insertions were made into two adjacent nucleotides in the proximal promoter at positions -96 and -97, and no insertions were into a coding or 3'-flanking sequence. All inserted transposons were in inverse orientation to the starting transposon. The frequent insertion into nucleotides -96 and -97 is consistent with the DNase hypersensitivity, absence of nucleosomes, flanking GAGA-factor-binding sites, and nucleotide sequence of this region. These experimental insertions recapitulated many of the phenotypes of natural transposition into Hsp70: reduced mRNA expression, less Hsp70 protein, and decreased inducible thermotolerance. The results suggest that the distinctive features of heat-shock promoters, which underlie the massive and rapid expression of heat-shock genes upon heat shock, also are a source of evolutionary variation on which natural selection can act.

[Small heat shock proteins and adaptation to hypertermia in various Drosophila species]

Expression level and kinetics of accumulation of small heat shock proteins (21-27 kDa group) have been investigated in three Drosophila species differing significantly by temperature niche and thermosensitivity. It was shown that low-latitude thermotolerant species D. virilis exceeds the high-latitude thermosensitive closely-related species D. lummei as well as distant thermosensitive species D. melanogaster in terms of small heat shock proteins expression and accumulation after temperature elevation. The data obtained enable to postulate an important role of small heat shock proteins in organism basal thermotolerance and general adaptation to adverse conditions of environment.

Penelope-like elements – a new class of retroelements: distribution, function and possible evolutionary significance

Here we describe a new class of retroelements termed PLE (Penelope-like elements). The only transpositionally active representative of this lineage found so far has been isolated from Drosophila virilis. This element, Penelope, is responsible for the hybrid dysgenesis syndrome in this species, characterized by simultaneous mobilization of several unrelated TE families in the progeny of dysgenic crosses. Several lines of evidence favor the hypothesis of recent Penelope invasion into D. virilis. Moreover, when D. virilisPenelope was introduced by P element-mediated transformation into the genome of D. melanogaster, it underwent extensive amplification in the new host and induced several traits of the dysgenesis syndrome, including gonadal atrophy and numerous mutations. The single ORF encoded by PLE consists of two principal domains: reverse transcriptase (RT) and endonuclease (EN), which is similar to GIY-YIG intron-encoded endonucleases. With the appearance of a large number of PLEs in genome databases from diverse eukaryotes, including amoebae, fungi, cnidarians, rotifers, flatworms, roundworms, fish, amphibia, and reptilia, it becomes possible to resolve their phylogenetic relationships with other RT groups with a greater degree of confidence. On the basis of their peculiar structural features, distinct phylogenetic placement, and structure of transcripts, we conclude that PLE constitute a novel class of eukaryotic retroelements, different from non-LTR and LTR retrotransposons.

[Heat shock proteins: functions and role in adaptation to hyperthermia]

The results are generalized of many-year studies into the adaptive role of heat shock proteins in different animals, including the representatives of cold- and warm-blooded species that inhabit regions with different thermal conditions. Adaptive evolution of the response to hyperthermia can lead to different results depending on the species. The thermal threshold of induction of the heat shock proteins in desert thermophylic species is, as a rule, higher than in the moderate climate species. In addition, thermoresistant species are often characterized by a certain level of heat shock proteins in cells even at a physiologically normal temperature. Although adaptation to hyperthermia is achieved in most cases without changes in the number of heat shock genes, they can be amplified in some cases in termophylic species. The role of mobile elements in evolution of the heat shock genes was shown and approach was developed for directional introduction of mutations in the promoter regions of these genes.

Unusual arrangement of thehsp68locus in thevirilisspecies group ofDrosophilaimplicates evolutionary loss of anhsp68gene

Unlike all other Drosophila species studied to date, species in the virilis group of Drosophila have 2 complete copies of hsp68 arranged in inverted head-to-head orientation. Evidence for this conclusion includes Southern blots for D. virilis, D. lummei, and D. montana, PCR analysis of the former 2 species, in situ hybridization in D. virilis × D. lummei hybrids, and the complete nucleotide sequence of the locus in D. lummei. This organization resembles the primitive state of hsp70 in Diptera. Moreover, the Hsp68 peptide sequence for D. virilis and D. lummei is intermediate between that of Hsp70 and Hsp68 from other Drosophila spp. Therefore, we suggest that the hsp68 locus may have arisen via duplication of the hsp70 locus (or vice versa) early in the history of the genus Drosophila, with 1 hsp68 copy subsequently lost in most other Drosophila species groups.Key words: hsp68, Drosophila, Drosophila virilis, evolution, molecular chaperone, heat-shock protein, molecular evolution, gene duplication, gene loss.

Use of surface-enhanced laser desorption ionization-time-of-flight to identify heat shock protein 70 isoforms in closely related species of the virilis group of Drosophila

The 70-kDa heat shock protein (Hsp) family in all Drosophila species includes 2 environmentally inducible family members, Hsp70 and Hsp68. Two-dimensional gel electrophoresis revealed an unusual pattern of heat shock-inducible proteins in the species of the virilis group. Trypsin fingerprinting and microsequencing of tryptic peptides using ProteinChip Array technology identified the major isoelectric variants of Hsp70 family, including Hsp68 isoforms that differ in both molecular mass and isoelectric point from those in Drosophila melanogaster. The peculiar electrophoretic mobility is consistent with the deduced amino acid sequence of corresponding hsp genes from the species of the virilis group.