Putative SF2 helicases of the early-branching eukaryote Giardia lamblia are involved in antigenic variation and parasite differentiation into cysts

BACKGROUND: Regulation of surface antigenic variation in Giardia lamblia is controlled post-transcriptionally by an RNA-interference (RNAi) pathway that includes a Dicer-like bidentate RNase III (gDicer). This enzyme, however, lacks the RNA helicase domain present in Dicer enzymes from higher eukaryotes. The participation of several RNA helicases in practically all organisms in which RNAi was studied suggests that RNA helicases are potentially involved in antigenic variation, as well as during Giardia differentiation into cysts. RESULTS: An extensive in silico analysis of the Giardia genome identified 32 putative Super Family 2 RNA helicases that contain almost all the conserved RNA helicase motifs. Phylogenetic studies and sequence analysis separated them into 22 DEAD-box, 6 DEAH-box and 4 Ski2p-box RNA helicases, some of which are homologs of well-characterized helicases from higher organisms. No Giardia putative helicase was found to have significant homology to the RNA helicase domain of Dicer enzymes. Additionally a series of up- and down-regulated putative RNA helicases were found during encystation and antigenic variation by qPCR experiments. Finally, we were able to recognize 14 additional putative helicases from three different families (RecQ family, Swi2/Snf2 and Rad3 family) that could be considered DNA helicases. CONCLUSIONS: This is the first comprehensive analysis of the Super Family 2 helicases from the human intestinal parasite G. lamblia. The relative and variable expression of particular RNA helicases during both antigenic variation and encystation agrees with the proposed participation of these enzymes during both adaptive processes. The putatives RNA and DNA helicases identified in this early-branching eukaryote provide initial information regarding the biological role of these enzymes in cell adaptation and differentiation

Cytokines, Antibodies, and Histopathological Profiles during Giardia Infection and Variant-Specific Surface Protein-Based Vaccination.

Giardiasis is one of the most common human intestinal diseases worldwide. Several experimental animal models have been used to evaluat

Protein SUMOylation is Involved in Cell-cycle Progression and Cell Morphology in Giardia lamblia

The unicellular protozoa Giardia lamblia is a food- and waterborne parasite that causes giardiasis. This illness is manifested as acute and self-limited diarrhea and can evolve to long-term complications. Successful establishment of infection by Giardia trophozoites requires adhesion to host cells and colonization of the small intestine, where parasites multiply by mitotic division. The tight binding of trophozoites to host cells occurs by means of the ventral adhesive disc, a spiral array of microtubules and associated proteins such as giardins. In this work we show that knock down of the Small Ubiquitin-like MOdifier (SUMO) results in less adhesive trophzoites, decreased cell proliferation and deep morphological alterations, including at the ventral disc. Consistent with the reduced proliferation, SUMO knocked-down trophozoites were arrested in G1 and in S phases of the cell cycle. Mass spectrometry analysis of anti-SUMO immunoprecipitates was performed to identify SUMO substrates possibly involved in these events. Among the identified SUMOylation targets, -tubulin was further validated by Western blot and confirmed to be a SUMO target in Giardia trophozoites.Fundacao de Amparo a Pesquisa do Estado de Sao PauloUniv Fed Sao Paulo, Escola Paulista Med, Dept Microbiol Imunol & Parasitol, RuaBotucatu 862, BR-04023062 Sao Paulo, SP, BrazilInst Butantan, Ctr Toxinas Resposta Imune & Sinalizacao Celular, Lab Especial Ciclo Celular, Ave Vital Brasil 1500, BR-05503900 Sao Paulo, SP, BrazilUCC, CONICET, Fac Med, Lab Bioquim & Biol Mol, Ave Armada Argentina 3555 X5016DHK, Cordoba, ArgentinaUniv Fed Sao Paulo, Inst Ciencias Ambientais Quim & Farmaceut, Dept Ciencias Biol, Rua Sao Nicolau 210, BR-09913030 Diadema, SP, BrazilUniv Fed Sao Paulo, Escola Paulista Med, Dept Microbiol Imunol & Parasitol, RuaBotucatu 862, BR-04023062 Sao Paulo, SP, BrazilUniv Fed Sao Paulo, Inst Ciencias Ambientais Quim & Farmaceut, Dept Ciencias Biol, Rua Sao Nicolau 210, BR-09913030 Diadema, SP, BrazilFAPESP: 2010/15042-2FAPESP: 2013/04272-5Web of Scienc

Efficient oral vaccination by bioengineering virus-like particles with protozoan surface proteins

Giardia lamblia express a dense coat of variant-specific surface proteins (VSPs) on trophozoites that protects the parasite inside the host´s intestine. Here the authors show that stability and immunomodulatory properties of VSPs can be exploited to both protect and adjuvant vaccine antigens for oral administration

Antibodies to variable surface antigens induce antigenic variation in the intestinal parasite Giardia lamblia

Abstract The genomes of most protozoa encode families of variant surface antigens. In some parasitic microorganisms, it has been demonstrated that mutually exclusive changes in the expression of these antigens allow parasites to evade the host’s immune response. It is widely assumed that antigenic variation in protozoan parasites is accomplished by the spontaneous appearance within the population of cells expressing antigenic variants that escape antibody-mediated cytotoxicity. Here we show, both in vitro and in animal infections, that antibodies to Variant-specific Surface Proteins (VSPs) of the intestinal parasite Giardia lamblia are not cytotoxic, inducing instead VSP clustering into liquid-ordered phase membrane microdomains that trigger a massive release of microvesicles carrying the original VSP and switch in expression to different VSPs by a calcium-dependent mechanism. This novel mechanism of surface antigen clearance throughout its release into microvesicles coupled to the stochastic induction of new phenotypic variants not only changes current paradigms of antigenic switching but also provides a new framework for understanding the course of protozoan infections as a host/parasite adaptive process