RESUMO
In dipteran insects, invading pathogens are selectively recognized by four major pathways, namely Toll, IMD, JNK, and JAK/STAT, and trigger the activation of several immune effectors. Although substantial advances have been made in understanding the immunity of model insects such as Drosophila melanogaster, knowledge on the activation of immune responses in other arthropods such as ticks remains limited. Herein, we have deepened our understanding of the intracellular signalling pathways likely to be involved in tick immunity by combining a large-scale in silico approach with high-throughput gene expression analysis. Data from in silico analysis revealed that although both the Toll and JAK/STAT signalling pathways are evolutionarily conserved across arthropods, ticks lack central components of the D. melanogaster IMD pathway. Moreover, we show that tick immune signalling-associated genes are constitutively transcribed in BME26 cells (a cell lineage derived from embryos of the cattle tick Rhipicephalus microplus) and exhibit different transcriptional patterns in response to microbial challenge. Interestingly, Anaplasma marginale, a pathogen that is naturally transmitted by R. microplus, causes downregulation of immune-related genes, suggesting that this pathogen may manipulate the tick immune system, favouring its survival and vector colonization.
Assuntos
Anaplasma marginale/imunologia , Rhipicephalus/imunologia , Rhipicephalus/microbiologia , Transdução de Sinais/imunologia , Animais , Bovinos , Linhagem Celular , Proteínas de Drosophila/imunologia , Drosophila melanogaster/imunologia , Perfilação da Expressão Gênica , Ensaios de Triagem em Larga Escala , Proteínas Quinases JNK Ativadas por Mitógeno/imunologia , Janus Quinases/imunologia , Rhipicephalus/genética , Fatores de Transcrição STAT/imunologia , Transdução de Sinais/genética , Receptores Toll-Like/imunologiaRESUMO
The selenium-dependent glutathione peroxidase (SeGPx) is a well-studied enzyme that detoxifies organic and hydrogen peroxides and provides cells or extracellular fluids with a key antioxidant function. The presence of a SeGPx has not been unequivocally demonstrated in insects. In the present work, we identified the gene and studied the function of a Rhodnius prolixus SeGPx (RpSeGPx). The RpSeGPx mRNA presents the UGA codon that encodes the active site selenocysteine (Sec) and a corresponding Sec insertion sequence (SECIS) in the 3' UTR region. The encoded protein includes a signal peptide, which is consistent with the high levels of GPx enzymatic activity in the insect's hemolymph, and clusters phylogenetically with the extracellular mammalian GPx03. This result contrasts with all other known insect GPxs, which use a cysteine residue instead of Sec and cluster with the mammalian phospholipid hydroperoxide GPx04. RpSeGPx is widely expressed in insect organs, with higher expression levels in the fat body. RNA interference (RNAi) was used to reduce RpSeGPx gene expression and GPx activity in the hemolymph. Adult females were apparently unaffected by RpSeGPx RNAi, whereas first instar nymphs showed a three-day delay in ecdysis. Silencing of RpSeGPx did not alter the gene expression of the antioxidant enzymes catalase, xanthine dehydrogenase and a cysteine-GPx, but it reduced the levels of the dual oxidase and NADPH oxidase 5 transcripts that encode for enzymes releasing extracellular hydrogen peroxide/superoxide. Collectively, our data suggest that RpSeGPx functions in the regulation of extracellular (hemolymph) redox homeostasis of R. prolixus.
Assuntos
Glutationa Peroxidase/química , Glutationa Peroxidase/genética , Rhodnius/enzimologia , Rhodnius/genética , Selênio/química , Animais , Feminino , Inativação Metabólica/genética , Muda , Filogenia , Interferência de RNA , Coelhos , Rhodnius/crescimento & desenvolvimento , Selenocisteína/químicaRESUMO
Cyclin-dependent kinases (CDKs) are a family of serine/threonine kinases essential for cell cycle progression. Herein, we describe the participation of CDKs in the physiology of Rhipicephalus microplus, the southern cattle tick and an important disease vector. Firstly, amino acid sequences homologous with CDKs of other organisms were identified from a R. microplus transcriptome database in silico. The analysis of the deduced amino acid sequences of CDK1 and CDK10 from R. microplus showed that both have caspase-3/7 cleavage motifs despite their differences in motif position and length of encoded proteins. CDK1 has two motifs (DKRGD and SAKDA) located opposite to the ATP binding site while CDK10 has only one motif (SLLDN) for caspase 3-7 near the ATP binding site. Roscovitine (Rosco), a purine derivative that inhibits CDK/cyclin complexes by binding to the catalytic domain of the CDK molecule at the ATP binding site, which prevents the transfer of ATP's γphosphoryl group to the substrate. To determine the effect of Rosco on tick CDKs, BME26 cells derived from R. microplus embryo cells were utilized in vitro inhibition assays. Cell viability decreased in the Rosco-treated groups after 24 hours of incubation in a concentration-dependent manner and this was observed up to 48 hours following incubation. To our knowledge, this is the first report on characterization of a cell cycle protein in arachnids, and the sensitivity of BME26 tick cell line to Rosco treatment suggests that CDKs are potential targets for novel drug design to control tick infestation.
Assuntos
Proteínas de Artrópodes/química , Proteína Quinase CDC2/química , Quinases Ciclina-Dependentes/química , Inibidores de Proteínas Quinases/farmacologia , Purinas/farmacologia , Rhipicephalus/efeitos dos fármacos , Trifosfato de Adenosina/química , Trifosfato de Adenosina/metabolismo , Motivos de Aminoácidos , Animais , Proteínas de Artrópodes/antagonistas & inibidores , Proteínas de Artrópodes/classificação , Proteínas de Artrópodes/metabolismo , Proteína Quinase CDC2/antagonistas & inibidores , Proteína Quinase CDC2/classificação , Proteína Quinase CDC2/metabolismo , Caspases/química , Caspases/metabolismo , Domínio Catalítico , Bovinos , Linhagem Celular , Sobrevivência Celular/efeitos dos fármacos , Quinases Ciclina-Dependentes/antagonistas & inibidores , Quinases Ciclina-Dependentes/classificação , Quinases Ciclina-Dependentes/metabolismo , Escherichia coli/química , Escherichia coli/genética , Simulação de Acoplamento Molecular , Simulação de Dinâmica Molecular , Dados de Sequência Molecular , Filogenia , Ligação Proteica , Inibidores de Proteínas Quinases/química , Purinas/química , Proteínas Recombinantes/química , Proteínas Recombinantes/classificação , Proteínas Recombinantes/metabolismo , Rhipicephalus/citologia , Rhipicephalus/enzimologia , Roscovitina , Glândulas Salivares/citologia , Glândulas Salivares/efeitos dos fármacos , Alinhamento de Sequência , Homologia Estrutural de ProteínaRESUMO
Chagas disease, or American trypanosomiasis, is a parasitic disease caused by the protozoan Trypanosoma cruzi and is transmitted by insects from the Triatominae subfamily. To identify components involved in the protozoan-vector relationship, we constructed and analyzed cDNA libraries from RNA isolated from the midguts of uninfected and T. cruzi-infected Triatoma infestans, which are major vectors of Chagas disease. We generated approximately 440 high-quality Expressed Sequence Tags (ESTs) from each T. infestans midgut cDNA library. The sequences were grouped in 380 clusters, representing an average length of 664.78 base pairs (bp). Many clusters were not classified functionally, representing unknown transcripts. Several transcripts involved in different processes (e.g., detoxification) showed differential expression in response to T. cruzi infection. Lysozyme, cathepsin D, a nitrophorin-like protein and a putative 14 kDa protein were significantly upregulated upon infection, whereas thioredoxin reductase was downregulated. In addition, we identified several transcripts related to metabolic processes or immunity with unchanged expressions, including infestin, lipocalins and defensins. We also detected ESTs encoding juvenile hormone binding protein (JHBP), which seems to be involved in insect development and could be a target in control strategies for the vector. This work demonstrates differential gene expression upon T. cruzi infection in the midgut of T. infestans. These data expand the current knowledge regarding vector-parasite interactions for Chagas disease.
Assuntos
Perfilação da Expressão Gênica , Mucosa Intestinal/metabolismo , Intestinos/parasitologia , Triatoma/genética , Triatoma/parasitologia , Trypanosoma cruzi/fisiologia , Animais , Clonagem Molecular , DNA Complementar/genética , Interações Hospedeiro-Parasita/genética , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Regulação para CimaRESUMO
The insect Triatoma infestans is a vector of Trypanosoma cruzi, the etiological agent of Chagas disease. A cDNA library was constructed from T. infestans anterior midgut, and 244 clones were sequenced. Among the EST sequences, an open reading frame (ORF) with homology to a cystatin type 2 precursor was identified. Then, a 288-bp cDNA fragment encoding mature cystatin (lacking signal peptide) named Tigutcystatin was cloned fused to a N-terminal His tag in pET-14b vector, and the protein expressed in Escherichia coli strain Rosetta gami. Tigutcystatin purified and cleaved by thrombin to remove His tag presented molecular mass of 11 kDa and 10,137 Da by SDS-PAGE and MALDI-TOF mass spectrometry, respectively. Purified Tigutcystatin was shown to be a tight inhibitor towards cruzain, a T. cruzi cathepsin L-like enzyme (K(i)=3.29 nM) and human cathepsin L (K(i)=3.78 nM). Tissue specific expression analysis showed that Tigutcystatin was mostly expressed in anterior midgut, although amplification in small intestine was also detected by semi quantitative RT-PCR. qReal time PCR confirmed that Tigutcystatin mRNA is significantly up-regulated in anterior midgut when T. infestans is infected with T. cruzi. Together, these results indicate that Tigutcystatin may be involved in modulation of T. cruzi in intestinal tract by inhibiting parasite cysteine proteases, which represent the virulence factors of this protozoan.
Assuntos
Inibidores de Cisteína Proteinase/biossíntese , Insetos Vetores/metabolismo , Insetos Vetores/parasitologia , Cistatinas Salivares/biossíntese , Triatoma/metabolismo , Triatoma/parasitologia , Trypanosoma cruzi/enzimologia , Sequência de Aminoácidos , Animais , Sequência de Bases , Clonagem Molecular , Inibidores de Cisteína Proteinase/genética , Trato Gastrointestinal/metabolismo , Insetos Vetores/genética , Masculino , Dados de Sequência Molecular , Cistatinas Salivares/genética , Triatoma/genéticaRESUMO
BACKGROUND: Hemoglobin is a rich source of biologically active peptides, some of which are potent antimicrobials (hemocidins). A few hemocidins have been purified from the midgut contents of ticks. Nonetheless, how antimicrobials are generated in the tick midgut and their role in immunity is still poorly understood. Here we report, for the first time, the contribution of two midgut proteinases to the generation of hemocidins. RESULTS: An aspartic proteinase, designated BmAP, was isolated from the midgut of Rhipicephalus (Boophilus) microplus using three chromatographic steps. Reverse transcription-quantitative polymerase chain reaction revealed that BmAP is restricted to the midgut. The other enzyme is a previously characterized midgut cathepsin L-like cysteine proteinase designated BmCL1. Substrate specificities of native BmAP and recombinant BmCL1 were mapped using a synthetic combinatorial peptide library and bovine hemoglobin. BmCL1 preferred substrates containing non-polar residues at P2 subsite and polar residues at P1, whereas BmAP hydrolysed substrates containing non-polar amino acids at P1 and P1'. CONCLUSIONS: BmAP and BmCL1 generate hemocidins from hemoglobin alpha and beta chains in vitro. We postulate that hemocidins may be important for the control of tick pathogens and midgut flora.
RESUMO
Acyl-CoA esters have many intracellular functions, acting as energy source, substrate for metabolic processes and taking part in cell signaling. The acyl-CoA-binding protein (ACBP), a highly conserved 10 kDa intracellular protein, binds long- and medium-chain acyl-CoA esters with very high affinity, directing them to specific metabolic routes and protecting them from hydrolysis. An ACBP gene sequence was identified in the genome of Rhodnius prolixus. This ACBP gene (RpACBP-1) was expressed in all analyzed tissues and quantitative PCR showed that expression was highest in posterior midgut. In this tissue, ACBP gene expression increased in the first day after blood meal ( approximately 10-fold) and then decreased to unfed levels in the seventh day after meal. Injection of serotonin (5-hydroxytryptamine; 5-HT), a neuroamine released in the hemolymph after the start of feeding, increased the expression of this gene in the midgut of unfed females, reaching levels similar to those observed in fed insects. This effect of injected 5-HT was inhibited by spiperone, an antagonist of 5-HT mammalian receptors, that was also able to block the physiological increase in RpACBP-1 expression observed after feeding. Injection of cholera toxin or dibutyryl-cAMP also resulted in the stimulation of this gene expression. These data reveal a transcriptional regulatory mechanism in R. prolixus, that is triggered by 5-HT. In this way, a novel role for 5-HT is proposed, as a regulator of ACBP gene expression and, consequently, taking part in the control of lipid metabolism.
Assuntos
Inibidor da Ligação a Diazepam/metabolismo , Regulação da Expressão Gênica/fisiologia , Rhodnius/genética , Serotonina/fisiologia , Sequência de Aminoácidos , Animais , Sequência de Bases , DNA , Feminino , Dados de Sequência Molecular , Reação em Cadeia da Polimerase Via Transcriptase ReversaRESUMO
A blood-sucking habit appeared independently several times in the course of arthropod evolution. However, from more than a million species of insects and arachnids presently living on earth, only about 14,000 species developed the capacity to feed on vertebrate blood. This figure suggests the existence of severe physiological constraints for the evolution of hematophagy, implying the selective advantage of special adaptations related to the use of blood as a food source. Digestion of vertebrate hemoglobin in the midgut of blood-feeding arthropods results in the production of large amounts of heme, a potentially cytotoxic molecule. Here we will review mechanisms by which heme can exert biological damage, together with a wide spectrum of adaptations developed by blood-feeding insects and ticks to counteract its deleterious effects. In spite of the existence of a great molecular diversity of protective mechanisms, different hematophagous organisms developed convergent solutions that may be physiologically equivalent.
Assuntos
Adaptação Fisiológica , Artrópodes/fisiologia , Heme/metabolismo , Animais , Antioxidantes/fisiologia , Artrópodes/parasitologia , Comportamento Alimentar , Hemeproteínas/fisiologia , Peroxidação de Lipídeos , Estresse OxidativoRESUMO
We have previously shown that Rhodnius prolixus' eggs and hemolymph are pink due to the presence of the hemeprotein Rhodnius heme-binding protein (RHBP). In the hemolymph it functions as an antioxidant. Nevertheless, its function in eggs has not been determined. Here we present evidence that RHBP is a source of heme for embryonic development. RHBP content decreases during embryogenesis, but the total heme content of eggs remains unchanged. Biliverdin, the product of heme degradation, is not detectable in late embryos. The activity of the heme-synthesizing pathway is low throughout embryogenesis and rises sharply after nymphs' hatching. Heme-radiolabeled eggs were produced and, at the day of hatching, nymphs were dissected. The presence of radiolabeled heme in their carcass is an indication that heme reutilization is occurring. The only animal known to reutilize heme in significant levels is the cattle tick Boophilus microplus, which cannot synthesize its own heme. Diversely, Rhodnius can synthesize its own heme but, in the context of embryogenesis, heme demand seems to be supplied by the programmed release of heme form RHBP. This behavior indicates that in Rhodnius, we might have a highly unusual profile: heme is both synthesized and reutilized.