RESUMO
Although macrophages have long been considered key players in the course of Leishmania infections, other non-professional phagocytes have lately been shown to maintain low levels of the parasite in safe intracellular niches. Recently, it was demonstrated that the adipose tissue is capable of harboring Old World L. (L.) infantum in mice. However, there is no evidence of experimental adipocyte infection with New World Leishmania species so far. In addition, it was not known whether adipocytes would be permissive for formation of the unique, large and communal parasitophorous vacuoles that are typical of L. (L.) amazonensis in macrophages. Here we evaluated the ability of L. (L.) amazonensis and L. (V.) braziliensis promastigotes and amastigotes to infect 3T3-L1 fibroblast-derived adipocytes (3T3-Ad) using light and transmission electron microscopy. Our results indicate that amastigotes and promastigotes of both species were capable of infecting and surviving inside pre- and fully differentiated 3T3-Ad for up to 144 h. Importantly, L. (L.) amazonensis amastigotes resided in large communal parasitophorous vacuoles in pre-adipocytes, which appeared to be compressed between large lipid droplets in mature adipocytes. In parallel, individual L. (V.) braziliensis amastigotes were detected in single vacuoles 144 h post-infection. We conclude that 3T3-Ad may constitute an environment that supports low loads of viable parasites perhaps contributing to parasite maintenance, since amastigotes of both species recovered from these cells differentiated into replicative promastigotes. Our findings shed light on the potential of a new host cell model that can be relevant to the persistence of New World Leishmania species.
Assuntos
Leishmania , Leishmaniose Cutânea , Leishmaniose , Células 3T3-L1 , Adipócitos , Animais , Leishmaniose/parasitologia , Camundongos , Camundongos Endogâmicos BALB CRESUMO
Eukaryotes from the Excavata superphylum have been used as models to study the evolution of cellular molecular processes. Strikingly, human parasites of the Trypanosomatidae family (T. brucei, T. cruzi and L. major) conserve the complex machinery responsible for selenocysteine biosynthesis and incorporation in selenoproteins (SELENOK/SelK, SELENOT/SelT and SELENOTryp/SelTryp), although these proteins do not seem to be essential for parasite viability under laboratory controlled conditions. Selenophosphate synthetase (SEPHS/SPS) plays an indispensable role in selenium metabolism, being responsible for catalyzing the formation of selenophosphate, the biological selenium donor for selenocysteine synthesis. We solved the crystal structure of the L. major selenophosphate synthetase and confirmed that its dimeric organization is functionally important throughout the domains of life. We also demonstrated its interaction with selenocysteine lyase (SCLY) and showed that it is not present in other stable assemblies involved in the selenocysteine pathway, namely the phosphoseryl-tRNASec kinase (PSTK)-Sec-tRNASec synthase (SEPSECS) complex and the tRNASec-specific elongation factor (eEFSec) complex. Endoplasmic reticulum stress with dithiothreitol (DTT) or tunicamycin upon selenophosphate synthetase ablation in procyclic T. brucei cells led to a growth defect. On the other hand, only DTT presented a negative effect in bloodstream T. brucei expressing selenophosphate synthetase-RNAi. Furthermore, selenoprotein T (SELENOT) was dispensable for both forms of the parasite. Together, our data suggest a role for the T. brucei selenophosphate synthetase in the regulation of the parasite's ER stress response.
Assuntos
Liases/metabolismo , Fosfotransferases/metabolismo , Selenocisteína/biossíntese , Selenoproteínas/metabolismo , Trypanosoma brucei brucei/enzimologia , Conformação Proteica , Proteínas de Protozoários/metabolismo , Selênio/metabolismoRESUMO
Eukaryotes from the Excavata superphylum have been used as models to study the evolution of cellular molecular processes. Strikingly, human parasites of the Trypanosomatidae family (T. brucei, T. cruzi and L. major) conserve the complex machinery responsible for selenocysteine biosynthesis and incorporation in selenoproteins (SELENOK/SelK, SELENOT/SelT and SELENOTryp/SelTryp), although these proteins do not seem to be essential for parasite viability under laboratory controlled conditions. Selenophosphate synthetase (SEPHS/SPS) plays an indispensable role in selenium metabolism, being responsible for catalyzing the formation of selenophosphate, the biological selenium donor for selenocysteine synthesis. We solved the crystal structure of the L. major selenophosphate synthetase and confirmed that its dimeric organization is functionally important throughout the domains of life. We also demonstrated its interaction with selenocysteine lyase (SCLY) and showed that it is not present in other stable assemblies involved in the selenocysteine pathway, namely the phosphoseryl-tRNASec kinase (PSTK)-Sec-tRNASec synthase (SEPSECS) complex and the tRNASec-specific elongation factor (eEFSec) complex. Endoplasmic reticulum stress with dithiothreitol (DTT) or tunicamycin upon selenophosphate synthetase ablation in procyclic T. brucei cells led to a growth defect. On the other hand, only DTT presented a negative effect in bloodstream T. brucei expressing selenophosphate synthetase-RNAi. Furthermore, selenoprotein T (SELENOT) was dispensable for both forms of the parasite. Together, our data suggest a role for the T. brucei selenophosphate synthetase in the regulation of the parasite’s ER stress response.
RESUMO
In a previous study we had shown that membrane cholesterol removal induced unregulated lysosomal exocytosis events leading to the depletion of lysosomes located at cell periphery. However, the mechanism by which cholesterol triggered these exocytic events had not been uncovered. In this study we investigated the importance of cholesterol in controlling mechanical properties of cells and its connection with lysosomal exocytosis. Tether extraction with optical tweezers and defocusing microscopy were used to assess cell dynamics in mouse fibroblasts. These assays showed that bending modulus and surface tension increased when cholesterol was extracted from fibroblasts plasma membrane upon incubation with MßCD, and that the membrane-cytoskeleton relaxation time increased at the beginning of MßCD treatment and decreased at the end. We also showed for the first time that the amplitude of membrane-cytoskeleton fluctuation decreased during cholesterol sequestration, showing that these cells become stiffer. These changes in membrane dynamics involved not only rearrangement of the actin cytoskeleton, but also de novo actin polymerization and stress fiber formation through Rho activation. We found that these mechanical changes observed after cholesterol sequestration were involved in triggering lysosomal exocytosis. Exocytosis occurred even in the absence of the lysosomal calcium sensor synaptotagmin VII, and was associated with actin polymerization induced by MßCD. Notably, exocytosis triggered by cholesterol removal led to the secretion of a unique population of lysosomes, different from the pool mobilized by actin depolymerizing drugs such as Latrunculin-A. These data support the existence of at least two different pools of lysosomes with different exocytosis dynamics, one of which is directly mobilized for plasma membrane fusion after cholesterol removal.
Assuntos
Membrana Celular/efeitos dos fármacos , Colesterol/química , Fibroblastos/efeitos dos fármacos , Lisossomos/metabolismo , beta-Ciclodextrinas/farmacologia , Actinas/genética , Actinas/metabolismo , Animais , Compostos Bicíclicos Heterocíclicos com Pontes/farmacologia , Linhagem Celular , Membrana Celular/ultraestrutura , Colesterol/deficiência , Citoesqueleto/efeitos dos fármacos , Citoesqueleto/ultraestrutura , Exocitose/efeitos dos fármacos , Fibroblastos/citologia , Fibroblastos/metabolismo , Expressão Gênica , Lisossomos/classificação , Fluidez de Membrana/efeitos dos fármacos , Camundongos , RNA Interferente Pequeno/genética , RNA Interferente Pequeno/metabolismo , Sinaptotagminas/antagonistas & inibidores , Sinaptotagminas/genética , Sinaptotagminas/metabolismo , Tiazolidinas/farmacologia , Proteínas rho de Ligação ao GTP/genética , Proteínas rho de Ligação ao GTP/metabolismoRESUMO
Trypanosoma cruzi genomic database was screened for hypothetical proteins that showed high probability of being secreted or membrane anchored and thus, likely involved in host-cell invasion. A sequence that codes for a 21kDa protein that showed high probability of being secreted was selected. After cloning this protein sequence, the results showed that it was a ubiquitous protein and secreted by extracellular amastigotes. The recombinant form (P21-His(6)) adhered to HeLa cells in a dose-dependent manner. Pretreatment of host cells with P21-His(6) inhibited cell invasion by extracellular amastigotes from G and CL strains. On the other hand, when the protein was added to host cells at the same time as amastigotes, an increase in cell invasion was observed. Host-cell pretreatment with P21-His(6) augmented invasion by metacyclic trypomastigotes. Moreover, polyclonal antibody anti-P21 inhibited invasion only by extracellular amastigotes and metacyclic trypomastigotes from G strain. These results suggested that P21 might be involved in T. cruzi cell invasion. We hypothesize that P21 could be secreted in the juxtaposition parasite-host cell and triggers signaling events yet unknown that lead to parasite internalization.
Assuntos
Proteínas de Protozoários/fisiologia , Trypanosoma cruzi/patogenicidade , Fatores de Virulência/fisiologia , Animais , Chlorocebus aethiops , DNA de Protozoário/química , DNA de Protozoário/genética , Células HeLa , Humanos , Dados de Sequência Molecular , Peso Molecular , Ligação Proteica , Proteínas de Protozoários/química , Proteínas de Protozoários/genética , Análise de Sequência de DNA , Trypanosoma cruzi/genética , Células Vero , Fatores de Virulência/química , Fatores de Virulência/genéticaRESUMO
We characterized the extended substrate binding site of recombinant oligopeptidase B enzymes from Trypanosoma cruzi (Tc-OP) and Trypanosoma brucei (Tb-OP), evaluating the specificity of their S3, S2, S1', S2' and S3' subsites. Five series of internally quenched fluorescent peptides based on the substrate Abz-AGGRGAQ-EDDnp [where Abz is o -aminobenzoic acid and EDDnp is N -(2,4-dinitrophenyl)ethylenediamine] were designed to contain amino acid residues with side chains of a minimum size, and each residue position of this substrate was modified. Synthetic peptides of different lengths derived from the human kininogen sequence were also examined, and peptides of up to 17 amino acids were found to be hydrolysed by Tc-OP and Tb-OP. These two oligopeptidases were essentially arginyl hydrolases, since for all peptides examined the only cleavage site was the Arg-Xaa bond. We also demonstrated that Tc-OP and Tb-OP have a very specific carboxypeptidase activity for basic amino acids, which depends on the presence of at least of a pair of basic amino acids at the C-terminal end of the substrate. The peptide with triple Arg residues (Abz-AGRRRAQ-EDDnp) was an efficient substrate for Tc-OP and Tb-OP: the Arg-Ala peptide bond was cleaved first and then two C-terminal Arg residues were successively removed. The S1' subsite seems to be an important determinant of the specificity of both enzymes, showing a preference for Tyr, Ser, Thr and Gln as hydrogen donors. The presence of these amino acids at P1' resulted in substrates that were hydrolysed with K (m) values in the sub-micromolar range. Taken together, this work supports the view that oligopeptidase B is a specialized protein-processing enzyme with a specific carboxypeptidase activity. Excellent substrates were obtained for Tb-OP and Tc-OP (Abz-AMRRTISQ-EDDnp and Abz-AHKRYSHQ-EDDnp respectively), which were hydrolysed with remarkably high k (cat) and low K (m) values.