Molecular cloning and characterization of mitogen-activated protein kinase 2 in Toxoplasma gondii

Not your Mother's MAPKs: Apicomplexan MAPK function in daughter cell budding

Reversible phosphorylation by protein kinases is one of the core mechanisms by which biological signals are propagated and processed. Mitogen-activated protein kinases, or MAPKs, are conserved throughout eukaryotes where they regulate cell cycle, development, and stress response. Here, we review advances in our understanding of the function and biochemistry of MAPK signaling in apicomplexan parasites. As expected for well-conserved signaling modules, MAPKs have been found to have multiple essential roles regulating both Toxoplasma tachyzoite replication and sexual differentiation in Plasmodium. However, apicomplexan MAPK signaling is notable for the lack of the canonical kinase cascade that normally regulates the networks, and therefore must be regulated by a distinct mechanism. We highlight what few regulatory relationships have been established to date, and discuss the challenges to the field in elucidating the complete MAPK signaling networks in these parasites.

Pathogenic role of mitogen activated protein kinases in protozoan parasites

Protozoan parasites with complex life cycles have high mortality rates affecting billions of human lives. Available anti-parasitic drugs are inadequate due to variable efficacy, toxicity, poor patient compliance and drug-resistance. Hence, there is an urgent need for the development of safer and better chemotherapeutics. Mitogen Activated Protein Kinases (MAPKs) have drawn much attention as potential drug targets. This review summarizes unique structural and functional features of MAP kinases and their possible role in pathogenesis of obligate intracellular protozoan parasites namely, Leishmania, Trypanosoma, Plasmodium and Toxoplasma. It also provides an overview of available knowledge concerning the target proteins of parasite MAPKs and the need to understand and unravel unknown interaction network(s) of MAPK(s).

Immunostimulatory efficacy and protective potential of putative TgERK7 protein in mice experimentally infected by Toxoplasma gondii

The extracellular signal-regulated kinases (ERKs) serve as important determinants of cellular signal transduction pathways, and hence may play important roles during infections. Previous work suggested that putative ERK7 of Toxoplasma gondii is required for efficient intracellular replication of the parasite. However, the antigenic and immunostimulatory properties of TgERK7 protein remain unknown. The objective of this study was to produce a recombinant TgERK7 protein in vitro and to evaluate its effect on the induction of humoral and T cell-mediated immune responses against T. gondii infection in BALB/c mice. Immunization using TgERK7 mixed with Freund's adjuvants significantly increased the ratio of CD3e⁺CD4⁺ T/CD3e⁺CD8a⁺ T lymphocytes in spleen and elevated serum cytokines (IFN-γ, IL-2, IL-4, IL-10, IL-12p70, IL-23, MCP-1, and TNF-α) in immunized mice compared to control mice. On the contrary, immunization did not induce high levels of serum IgG antibodies. Five predicted peptides of TgERK7 were synthesized and conjugated with KLH and used to analyze the antibody specificity in the sera of immunized mice. We detected a progressive increase in the antibody level only against TgERK7 peptide A (DEVDKHVLRKYD). Antibody raised against this peptide significantly decreased intracellular proliferation of T. gondii in vitro, suggesting that peptide A can potentially induce a protective antibody response. We also showed that immunization improved the survival rate of mice challenged with a virulent strain and significantly reduced the parasite cyst burden within the brains of chronically infected mice. Our data show that TgERK7-based immunization induced TgERK7 peptide A-specific immune responses that can impart protective immunity against T. gondii infection. The therapeutic potential of targeting ERK7 signaling pathway for future toxoplasmosis treatment is warranted.

Immune Responses Induced by pVAX/TgERK7 against Toxoplasma gondii Infection in BALB/c Mice

BACKGROUND

Toxoplasma gondii can infect all the warm-blooded vertebrates and cause serious toxoplasmosis. Extracellular signal-regulated kinase 7 in T. gondii (TgERK7) mediated the proliferation of this parasite may be a potential vaccine candidate. Thus, immune responses induced by TgERK7 were investigated in this study using a DNA vaccine strategy.

METHODS

pVAX/TgERK7 plasmid was constructed and used to immunize BALB/c mice for three times with two-week intervals. The challenge and the investigation of humoral and cellular immune responses were performed at two weeks post the last immunization, and the survival times of the infected mice were daily recorded until all of them were dead.

RESULTS

The innate immune response with higher concentrations of IFN-γ, TNF-α, IL2 and IL12p70 in sera (P < 0.05), and the adaptive immune responses were evoked by the DNA immunizations, including specific antibody, lymphocyte proliferation, and the CD3e+CD4+ and CD3e+CD8a+ T cell-mediated response effects. Interestingly, no significant difference was detected in their survival times among all the experimental groups of mice that were challenged with GT1 tachyzoites or PRU cysts (P>0.05).

CONCLUSION

The successive immunizations with pVAX/TgERK7 can provoke the innate and adaptive immune responses of BALB/c mice, whereas the DNA vaccine-induced immunological efficacy is not sufficient for complete protection the host against T. gondii infection.

Suppressors for Human Epidermal Growth Factor Receptor 2/4 (HER2/4): A New Family of Anti-Toxoplasmic Agents in ARPE-19 Cells

The effects of tyrosine kinase inhibitors (TKIs) were evaluated on growth inhibition of intracellular Toxoplasma gondii in host ARPE-19 cells. The number of tachyzoites per parasitophorous vacuolar membrane (PVM) was counted after treatment with TKIs. T. gondii protein expression was assessed by western blot. Immunofluorescence assay was performed using Programmed Cell Death 4 (PDCD4) and T. gondii GRA3 antibodies. The TKIs were divided into 3 groups; non-epidermal growth factor receptor (non-EGFR), anti-human EGFR 2 (anti-HER2), and anti-HER2/4 TKIs, respectively. Group I TKIs (nintedanib, AZD9291, and sunitinib) were unable to inhibit proliferation without destroying host cells. Group II TKIs (lapatinib, gefitinib, erlotinib, and AG1478) inhibited proliferation up to 98% equivalent to control pyrimethamine (5 μM) at 20 μM and higher, without affecting host cells. Group III TKIs (neratinib, dacomitinib, afatinib, and pelitinib) inhibited proliferation up to 98% equivalent to pyrimethamine at 1–5 μM, but host cells were destroyed at 10–20 μM. In Group I, TgHSP90 and SAG1 inhibitions were weak, and GRA3 expression was moderately inhibited. In Group II, TgHSP90 and SAG1 expressions seemed to be slightly enhanced, while GRA3 showed none to mild inhibition; however, AG1478 inhibited all proteins moderately. Protein expression was blocked in Group III, comparable to pyrimethamine. PDCD4 and GRA3 were well localized inside the nuclei in Group I, mildly disrupted in Group II, and were completely disrupted in Group III. This study suggests the possibility of a vital T. gondii TK having potential HER2/4 properties, thus anti-HER2/4 TKIs may inhibit intracellular parasite proliferation with minimal adverse effects on host cells.

Plasmodium berghei MAPK1 displays differential and dynamic subcellular localizations during liver stage development

Mitogen-activated protein kinases (MAPKs) regulate key signaling events in eukaryotic cells. In the genomes of protozoan Plasmodium parasites, the causative agents of malaria, two genes encoding kinases with significant homology to other eukaryotic MAPKs have been identified (mapk1, mapk2). In this work, we show that both genes are transcribed during Plasmodium berghei liver stage development, and analyze expression and subcellular localization of the PbMAPK1 protein in liver stage parasites. Live cell imaging of transgenic parasites expressing GFP-tagged PbMAPK1 revealed a nuclear localization of PbMAPK1 in the early schizont stage mediated by nuclear localization signals in the C-terminal domain. In contrast, a distinct localization of PbMAPK1 in comma/ring-shaped structures in proximity to the parasite's nuclei and the invaginating parasite membrane was observed during the cytomere stage of parasite development as well as in immature blood stage schizonts. The PbMAPK1 localization was found to be independent of integrity of a motif putatively involved in ATP binding, integrity of the putative activation motif and the presence of a predicted coiled-coil domain in the C-terminal domain. Although PbMAPK1 knock out parasites showed normal liver stage development, the kinase may still fulfill a dual function in both schizogony and merogony of liver stage parasites regulated by its dynamic and stage-dependent subcellular localization.

Identification of a functional prostanoid-like receptor in the protozoan parasite, Trypanosoma cruzi

Trypanosoma cruzi infection in humans and experimental animals causes Chagas disease which is often accompanied by myocarditis, cardiomyopathy, and vasculopathy. T. cruzi-derived thromboxane A2 (TXA2) modulates vasculopathy and other pathophysiological features of Chagasic cardiomyopathy. Here, we provide evidence that epimastigotes, trypomastigotes, and amastigotes of T. cruzi (Brazil and Tulahuen strains) express a biologically active prostanoid receptor (PR) that is responsive to TXA2 mimetics, e.g. IBOP. This putative receptor, TcPR, is mainly localized in the flagellar membrane of the parasites and shows a similar glycosylation pattern to that of bona fide thromboxane prostanoid (TP) receptors obtained from human platelets. Furthermore, TXA2-PR signal transduction activates T. cruzi-specific MAPK pathways. While mammalian TP is a G-protein coupled receptor (GPCR); T. cruzi genome sequencing has not demonstrated any confirmed GPCRs in these parasites. Based on this genome sequencing it is likely that TcPR is unique in these protists with no counterpart in mammals. TXA2 is a potent vasoconstrictor which contributes to the pathogenesis of Chagasic cardiovascular disease. It may, however, also control parasite differentiation and proliferation in the infected host allowing the infection to progress to a chronic state.

A method for rapid regulation of protein expression in Trypanosoma cruzi

Analysis of gene function in Trypanosoma cruzi is limited due to the absence of rapid, simple and reversible genetic tools to regulate gene and corresponding protein expression. We have designed a modified pTREX vector which uses an N-terminal fusion of a ligand-controlled destabilisation domain (ddFKBP) to a gene/protein of interest. This vector allows rapid and reversible protein expression and efficient functional analysis of proteins in different T. cruzi life cycle stages.