Lambda-Carrageenan Enhances the Effects of Radiation Therapy in Cancer Treatment by Suppressing Cancer Cell Invasion and Metastasis through Racgap1 Inhibition.

Radiotherapy is used extensively in cancer treatment, but radioresistance and the metastatic potential of cancer cells that survive radiation remain critical issues. There is a need for novel treatments to improve radiotherapy. Here, we evaluated the therapeutic benefit of λ-carrageenan (CGN) to enhance the efficacy of radiation treatment and investigated the underlying molecular mechanism. CGN treatment decreased viability in irradiated cancer cells and enhanced reactive oxygen species accumulation, apoptosis, and polyploid formation. Additionally, CGN suppressed radiation-induced chemoinvasion and invasive growth in 3D lrECM culture. We also screened target molecules using a gene expression microarray analysis and focused on Rac GTPase-activating protein 1 (RacGAP1). Protein expression of RacGAP1 was upregulated in several cancer cell lines after radiation, which was significantly suppressed by CGN treatment. Knockdown of RacGAP1 decreased cell viability and invasiveness after radiation. Overexpression of RacGAP1 partially rescued CGN cytotoxicity. In a mouse xenograft model, local irradiation followed by CGN treatment significantly decreased tumor growth and lung metastasis compared to either treatment alone. Taken together, these results suggest that CGN may enhance the effectiveness of radiation in cancer therapy by decreasing cancer cell viability and suppressing both radiation-induced invasive activity and distal metastasis through downregulating RacGAP1 expression.

Toxoplasma gondii RON4 binds to heparan sulfate on the host cell surface.

Toxoplasma gondii rhoptry neck protein 4 (TgRON4) is a component of the moving junction, a key structure for host cell invasion. We previously showed that host cellular ß-tubulin is a binding partner of TgRON4 in the invasion process. Here, to identify other binding partners of TgRON4 in the host cell, we examined the binding of TgRON4 to components of the host cell surface. TgRON4 binds to various mammalian cells, but this binding disappeared in glycosaminoglycan- and heparan sulfate-deficient CHO cells and after heparitinase treatment of mammalian cells. The C-terminal half of TgRON4 showed relatively strong binding to cells and heparin agarose. A glycoarray assay indicated that TgRON4 binds to heparin and modified heparin derivatives. Immunoprecipitation of T. gondii-infected CHO cell lysates showed that TgRON4 interacts with glypican 1 during Toxoplasma invasion. This interaction suggests a role for heparan sulfate in parasite invasion.

Detection and molecular characterization of Cryptosporidium and Eimeria species in Philippine bats.

The genus Cryptosporidium, which is an obligate intracellular parasite, infects various vertebrates and causes a diarrheal disease known as cryptosporidiosis. Bats are naturally infected with zoonotic pathogens; thus, they are potential reservoirs of parasites. We investigated the species and genotype distribution as well as prevalence of Cryptosporidium and Eimeria in Philippine bats. We captured and examined 45 bats; four were positive for Cryptosporidium spp. and seven were positive for Eimeria spp. We detected Cryptosporidium bat genotype II from Ptenochirus jagori. Three other Cryptosporidium sequences, detected from Rhinolophus inops, Cynopterus brachyotis, and Eonycteris spelaea, could not be classified as any known species or genotype; we therefore propose the novel genotype Cryptosporidium bat genotypes V, VI, and VII. Bat genotype V is associated with human cryptosporidiosis clade, and therefore, this genotype may be transmissible to humans. Among the Eimeria sequences, BE3 detected from Scotophilus kuhlii was classified with known bat and rodent clades; however, other sequences detected from C. brachyotis, E. spelaea, Rousettus amplexicaudatus, and R. inops could not be classified with known Eimeria species. These isolates might represent a new genotype. Our findings demonstrate that the bats of the Philippines represent a reservoir of multiple Cryptosporidium and Eimeria spp.

Lambda-carrageenan treatment exacerbates the severity of cerebral malaria caused by Plasmodium berghei ANKA in BALB/c mice.

BACKGROUND: There is an urgent need to develop and test novel compounds against malaria infection. Carrageenans, sulphated polysaccharides derived from seaweeds, have been previously shown to inhibit Plasmodium falciparum in vitro. However, they are inflammatory and alter the permeability of the blood-brain barrier, raising concerns that their use as a treatment for malaria could lead to cerebral malaria (CM), a severe complication of the disease. In this work, the authors look into the effects of the administration of λ-carrageenan to the development and severity of CM in BALB/c mice, a relatively non-susceptible model, during infection with the ANKA strain of Plasmodium berghei. METHODS: Five-week-old female BALB/c mice were infected with P. berghei intraperitoneally. One group was treated with λ-carrageenan (PbCGN) following the 4-day suppressive test protocol, whereas the other group was not treated (PbN). Another group of healthy BALB/c mice was similarly given λ-carrageenan (CGN) for comparison. The following parameters were assessed: parasitaemia, clinical signs of CM, and mortality. Brain and other vital organs were collected and examined for gross and histopathological lesions. Evans blue dye assays were employed to assess blood-brain barrier integrity. RESULTS: Plasmodium berghei ANKA-infected BALB/c mice treated with λ-carrageenan died earlier than those that received no treatment. Histopathological examination revealed that intracerebral haemorrhages related to CM were present in both groups of infected BALB/c mice, but were more numerous in those treated with λ-carrageenan than in mock-treated animals. Inflammatory lesions were also observed only in the λ-carrageenan-treated mice. These observations are consistent with the clinical signs associated with CM, such as head tilt, convulsions, and coma, which were observed only in this group, and may account for the earlier death of the mice. CONCLUSION: The results of this study indicate that the administration of λ-carrageenan exacerbates the severe brain lesions and clinical signs associated with CM in BALB/c mice infected with P. berghei ANKA.

Interaction between Theileria orientalis 23-kDa piroplasm membrane protein and heparin.

The 23-kDa piroplasm membrane protein of Theileria orientalis (p23) is an immunogenic protein expressed during the intraerythrocytic stage of the parasite; its function, however, remains unclear. To evaluate the host factor or factors that interact with p23, we examined the binding of p23 to components of the host cell surface. Recombinant p23 protein of the Ikeda genotype failed to bind to bovine red blood cells or to peripheral blood mononuclear cells, but did bind to Madin-Darby Bovine Kidney (MDBK) cells. A glycoarray assay showed that recombinant p23 proteins from the three genotypes bound to heparin, indicating that p23 is a heparin-binding Theileria surface molecule. Further analysis of heparin-binding molecules is useful for understanding attachment and invasion of T. orientalis merozoites.

Characterization and binding analysis of a microneme adhesive repeat domain-containing protein from Toxoplasma gondii.

The intracellular parasite Toxoplasma gondii invades almost all nucleated cells, and has infected approximately 34% of the world's population to date. In order to develop effective vaccines against T. gondii infection, understanding of the role of the molecules that are involved in the invasion process is important. For this purpose, we characterized T. gondii proteins that contain microneme adhesive repeats (MARs), which are common in moving junction proteins. T. gondii MAR domain-containing protein 4a (TgMCP4a), which contains repeats of 17-22 amino acid segments at the N-terminus and three putative MAR domains at the C-terminus, is localized near the rhoptry of extracellular parasites. Following infection, TgMCP4a was detected in the parasitophorous vacuole. The recombinant Fc-TgMCP4a N-terminus protein (rTgMCP4a-1/Fc) showed binding activity to the surface proteins of Vero, 293T, and CHO cells. The recombinant GST-TgMCP4a N-terminus protein (rTgMCP4a-1/GST), which exhibited binding activity, was used to pull down the interacting factors from 293T cell lysate, and subsequent mass spectrometry analysis revealed that three types of heat shock proteins (HSPs) interacted with TgMCP4a. Transfection of a FLAG fusion protein of TgMCP4a-1 (rTgMCP4a-1/FLAG) into 293T cell and the following immunoprecipitation with anti-FLAG antibody confirmed the interactions of HSC70 with TgMCP4a. The addition of rTgMCP4a-1/GST into the culture medium significantly affected the growth of the parasite. This study hints that T. gondii may employ HSP proteins of host cell to facilitate their growth.

Analyses of interactions between heparin and the apical surface proteins of Plasmodium falciparum.

Heparin, a sulfated glycoconjugate, reportedly inhibits the blood-stage growth of the malaria parasite Plasmodium falciparum. Elucidation of the inhibitory mechanism is valuable for developing novel invasion-blocking treatments based on heparin. Merozoite surface protein 1 has been reported as a candidate target of heparin; however, to better understand the molecular mechanisms involved, we characterized the molecules that bind to heparin during merozoite invasion. Here, we show that heparin binds only at the apical tip of the merozoite surface and that multiple heparin-binding proteins localize preferentially in the apical organelles. To identify heparin-binding proteins, parasite proteins were fractionated by means of heparin affinity chromatography and subjected to immunoblot analysis with ligand-specific antibodies. All tested members of the Duffy and reticulocyte binding-like families bound to heparin with diverse affinities. These findings suggest that heparin masks the apical surface of merozoites and blocks interaction with the erythrocyte membrane after initial attachment.

Characterization of the interaction between Toxoplasma gondii rhoptry neck protein 4 and host cellular ß-tubulin.

Toxoplasma rhoptry neck protein 4 (TgRON4) is a component of the moving junction macromolecular complex that plays a central role during invasion. TgRON4 is exposed on the cytosolic side of the host cell during invasion, but its molecular interactions remain unclear. Here, we identified host cellular ß-tubulin as a binding partner of TgRON4, but not Plasmodium RON4. Coimmunoprecipitation studies in mammalian cells demonstrated that the C-terminal 15-kDa region of ß-tubulin was sufficient for binding to TgRON4, and that a 17-kDa region in the proximal C-terminus of TgRON4 was required for binding to the C-terminal region of ß-tubulin. Analysis of T. gondii-infected lysates from CHO cells expressing the TgRON4-binding region showed that the C-terminal region of ß-tubulin interacted with TgRON4 at early invasion step. Our results provide evidence for a parasite-specific interaction between TgRON4 and the host cell cytoskeleton in parasite-infected cells.

Effects of dextran sulfates on the acute infection and growth stages of Toxoplasma gondii.

Toxoplasma gondii is one of the most prevalent parasites, causing toxoplasmosis in various warm-blooded animals, including humans. Because of the broad range of hosts susceptible to T. gondii, it had been postulated that a universal component of the host cell surface, such as glycosaminoglycans (GAGs), may act as a receptor for T. gondii infection. Carruthers et al. (Infect Immun 68:4005-4011, 2000) showed that soluble GAGs have also been shown to disrupt parasite binding to human fibroblasts. Therefore, we investigated the inhibitory effect of GAGs and their analogue dextran sulfate (DS) on T. gondii infection. For up to 24 h of incubation after inoculation of T. gondii, the inhibitory effect of GAGs on T. gondii infection and growth inside the host cell was weak. In contrast, DS markedly inhibited T. gondii infection. Moreover, low molecular weight DS particularly slowed the growth of T. gondii inside host cells. DS10 (dextran sulfate MW 10 kDa) was the most effective agent in these in vitro experiments and was therefore tested for its inhibitory effects in animal experiments; infection inhibition by DS10 was confirmed under these in vivo conditions. In this report, we showed that DSs, especially DS10, have the potential of a new type of drug for toxoplasmosis.

Characterization of Plasmodium falciparum cdc2-related kinase and the effects of a CDK inhibitor on the parasites in erythrocytic schizogony.

The cell cycle of Plasmodium is unique among major eukaryotic cell cycle models. Cyclin-dependent kinases (CDKs) are thought to be the key molecular switches that regulate cell cycle progression in the parasite. However, little information is available about Plasmodium CDKs. The present study was performed to investigate the effects of a CDK inhibitor, olomoucine, on the erythrocytic growth of Plasmodium falciparum. This agent inhibited the growth of the parasite at the trophozoite/schizont stage. Furthermore, we characterized the Plasmodium CDK homolog, P. falciparum cdc2-related kinase-1 (Pfcrk-1), which is a potential target of olomoucine. We synthesized a functional kinase domain of Pfcrk-1 as a GST fusion protein using a wheat germ protein expression system, and examined its phosphorylation activity. The activity of this catalytic domain was higher than that of GST-GFP control, but the same as that of a kinase-negative mutant of Pfcrk-1. After the phosphatase treatment, the labeling of [γ-(32)P]ATP was abolished. Recombinant human cyclin proteins were added to these kinase reactions, but there were no differences in activity. This report provides important information for the future investigation of Plasmodium CDKs.

Identification of mutations in TgMAPK1 of Toxoplasma gondii conferring resistance to 1NM-PP1.

Toxoplasma gondii is an important food and waterborne pathogen that causes severe disease in immunocompromised patients. Bumped kinase inhibitors (BKIs) have an antiparasitic effect on T. gondii tachyzoite growth by targeting T. gondii calmodulin-domain protein kinase 1 (TgCDPK1). To identify mutations that confer resistance to BKIs, chemical mutagenesis was performed, followed by selection in media containing either 250 or 1000 nM 1NM-PP1. Whole-genome sequence analysis of resistant clones revealed single nucleotide mutations in T. gondii mitogen-activated protein kinase 1 (TgMAPK1) at amino acids 162 (L162Q) and 171 (I171N). Plasmid constructs having the TgMAPK1 L162Q mutant sequence successfully replaced native TgMAPK1 genome locus in the presence of 1000 nM 1NM-PP1. The inhibitory effect of 1NM-PP1 on cell division observed in the parent clone was decreased in 1NM-PP1-resistant clones; however, effects on parasite invasion and calcium-induced egress were similar in both parent and resistant clones. A plasmid construct expressing the full length TgMAPK1 splicing isoform with L162Q mutation successfully complemented TgMAPK1 function in the pressure of 250 nM 1NM-PP1 in plaque assay. 1NM-PP1-resistant clones showed resistance to other BKIs (3MB-PP1 and 3BrB-PP1) with different levels. Here we identify TgMAPK1 as a novel target for 1NM-PP1 activity. This inhibitory effect is mediated through inhibition of tachyzoite cell division, and can be overcome through mutations at multiple residues in TgMAPK1.

Identification of Toxoplasma gondii cAMP dependent protein kinase and its role in the tachyzoite growth.

BACKGROUND: cAMP-dependent protein kinase (PKA) has been implicated in the asexual stage of the Toxoplasma gondii life cycle through assaying the effect of a PKA-specific inhibitor on its growth rate. Since inhibition of the host cell PKA cannot be ruled out, a more precise evaluation of the role of PKA, as well as characterization of the kinase itself, is necessary. METHODOLOGY/PRINCIPAL FINDING: The inhibitory effects of two PKA inhibitors, H89, an ATP-competitive chemical inhibitor, and PKI, a substrate-competitive mammalian natural peptide inhibitor, were estimated. In the in vitro kinase assay, the inhibitory effect of PKI on a recombinant T. gondii PKA catalytic subunit (TgPKA-C) was weaker compared to that on mammalian PKA-C. In a tachyzoite growth assay, PKI had little effect on the growth of tachyzoites, whereas H89 strongly inhibited it. Moreover, T. gondii PKA regulatory subunit (TgPKA-R)-overexpressing tachyzoites showed a significant growth defect. CONCLUSIONS/SIGNIFICANCE: Our data suggest that PKA plays an important role in the growth of tachyzoites, and the inhibitory effect of substrate-competitive inhibitor PKI on T. gondii PKA was low compared to that of the ATP competitive inhibitor H89.

1NM-PP1 treatment of mice infected with Toxoplasma gondii.

Bumped kinase inhibitors (BKIs) target analog-sensitive kinases, which the genomes of mammals rarely encode. Previously, we demonstrated that a BKI effectively suppressed the in vitro replication of Toxoplasma gondii, the causative pathogen of toxoplasmosis, by targeting T. gondii calcium-dependent protein kinase 1 (TgCDPK1) (Eukaryotic Cell, 9: 667-670). Here, we examined whether the BKI 1NM-PP1 reduced parasite replication in vivo. A high dose of 1NM-PP1, by intraperitoneal injection, just before the parasite inoculation effectively reduced the parasite load in the brains, livers, and lungs of T. gondii-infected mice, however, a low dose of 1NM-PP1 with oral administration didn't change the survival rates of infected mice.