Schistosoma mansoni: an HSP60 homologue is constitutively expressed in cercariae, adults, and sporocysts

Proteins as Targets in Anti-Schistosomal Drug Discovery and Vaccine Development

Proteins hardly function in isolation; they form complexes with other proteins or molecules to mediate cell signaling and control cellular processes in various organisms. Protein interactions control mechanisms that lead to normal and/or disease states. The use of competitive small molecule inhibitors to disrupt disease-relevant protein-protein interactions (PPIs) holds great promise for the development of new drugs. Schistosome invasion of the human host involves a variety of cross-species protein interactions. The pathogen expresses specific proteins that not only facilitate the breach of physical and biochemical barriers present in skin, but also evade the immune system and digestion of human hemoglobin, allowing for survival in the host for years. However, only a small number of specific protein interactions between the host and parasite have been functionally characterized; thus, in-depth understanding of the molecular mechanisms of these interactions is a key component in the development of new treatment methods. Efforts are now focused on developing a schistosomiasis vaccine, as a proposed better strategy used either alone or in combination with Praziquantel to control and eliminate this disease. This review will highlight protein interactions in schistosomes that can be targeted by specific PPI inhibitors for the design of an alternative treatment to Praziquantel.

Stage-specific alternative splicing of the heat-shock transcription factor during the life-cycle of Schistosoma mansoni

Stage-specific alternative splicing of the heat-shock transcription factor of Schistosoma mansoni (SmHSF) generates isoforms with structural diversity that may modulate the activity of SmHSF at different life-stages, and thus may regulate the expression of different genes at different developmental stages. RT-PCR, cloning and DNA-sequence analyses showed stage-specific alternative splicing inside the DNA-binding domain (DBD) involving introns I1 and I2, and beyond the DBD involving introns I4a and I7. Retention of introns I2 and I4 would inactivate SmHSF since they contain termination codons. Retention of intron I1 would add 11 amino acids inside the DBD and may change the DNA-binding specificity of SmHSF; intron I7 would add 13 amino acids to the effector region of HSF. Retention of introns was more pronounced in cercariae (larval stage living in water) than in adult worms (parasitic form in mammals). The isoforms were expressed in bacteria, but functional evaluation was not feasible, because only the isoform lacking introns was soluble while isoforms with introns were insoluble. However, stage-specific alternative splicing that changed HSF function in vivo was evidenced in intact cercariae. The cercarial SmHSF mRNA was enriched with introns I2 and I4a that contain termination codons. Therefore, translation of the SmHSF mRNA was impaired, and the SmHSF protein was undetectable. Consequently, the HSP70 gene could not be transcribed, and the HSP70 mRNA was missing. Alternative splicing was observed for short DNA segments (33-45 bp) bound by splice signals, located in the coding region. These are not bona fida exons since they are not flanked by introns. Yet, they are not regular introns since they are often found in mature mRNA. Alternative splicing of these DNA segments caused structural diversity that could modulate the function of the gene product.

Heat shock and stress response of Taenia solium and T. crassiceps (Cestoda)

Heat shock and stress responses are documented for the first time in larval stages of the cestodes Taenia solium and Taenia crassiceps. Radioactive metabolic labelling after in vitro incubation of cysts at 43 degrees C, revealed the induction of heat shock proteins. In T. crassiceps, the major heat shock proteins were 80, 70 and 60 kDa. After prolonged incubation, a set of low molecular weight heat shock proteins (27, 31, 33 and 38 kDa), were also induced. In vitro incubation of cysts at 4 degrees C, induced the synthesis of stress proteins ranging from 31 to 80 kDa, indicating the parasite is also able to respond to cold shock. T. solium cysts exposure to temperature stress also resulted in an increased synthesis of 2 major heat shock proteins of 80 and 70 kDa. Western blots using the excretory-secretory products of T. solium showed that 2 heat shock proteins were recognized by antibodies in the sera of cysticercotic patients: one of 66 kDa and another migrating close to the run front. The T. solium 66 kDa protein was also recognized by specific antibodies directed to a 60 kDa bacterial heat shock protein, suggesting that it belongs to this family of proteins.

Heat-shock response in a molluscan cell line: characterization of the response and cloning of an inducible HSP70 cDNA

Sublethal heat-shock of cells of the Bge (Biomphalaria glabrata embryonic) snail cell line resulted in increased or new expression of metabolically labeled polypeptides of approximately 21.5, 41, 70, and 74 kDa molecular mass. Regulation of this response appeared to be at the transcriptional level since a similar protein banding pattern was seen upon SDS-PAGE/fluorographic analysis of polypeptides produced by in vitro translation of total RNA from cells subjected to heat shock. Using a yeast (Saccharomyces cerevisiae) 70-kDa heat-shock protein (HSP70) probe to screen a cDNA library from heat-treated Bge cells, we isolated a full-length cDNA clone encoding a putative Bge HSP70. The cDNA was 2453 bp in length and contained an open reading frame of 1908 bp encoding a 636-amino-acid polypeptide with calculated molecular mass of 70,740 Da. Comparison of a conserved region of 209 amino acid residues revealed > 80% identity between the deduced amino acid sequence of Bge HSP70 and that of yeast (81%), the human blood fluke Schistosoma mansoni (for which B. glabrata serves as intermediate host) (81%), Drosophila (81%), human (84%), and the marine gastropod Aplysia californica (88%, 90%). In addition to the extensive sharing of sequence homology, the identification of several eukaryotic HSP70 signature sequences and an N-linked glycosylation site characteristic of cytoplasmic HSPs strongly support the identity of the Bge cDNA as encoding an authentic HSP70. Results of a Northern blot analysis, using Bge HSP70 clone-specific probes, indicated that gene expression was heat inducible and not constitutively expressed. This is the first reported sequence of an inducible HSP70 from cells originating from a freshwater gastropod and provides a first step in the development of a genetic transformation system for molluscs of medical importance.

Heat-shock and stress response of the parasitic nematode Haemonchus contortus

Before and after a stress treatment, larval stages and adult worms of Haemonchus contortus were tested for the induction and expression of heat-shock proteins (HSPs) using immunoblot analysis with HSP70-and HSP65-specific monoclonal antibodies. Stress treatment or heat shock did not alter the signals obtained with these antibodies, but the amount of HSP70 differed between the successive stages. In addition, the different stages were metabolically labeled with [35S]-methionine during a temperature-shock or chemical treatment and proteins were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The shocks resulted in an altered protein pattern. New was the de novo expression of a 20-kDa protein of adult worms after anthelmintic treatment.