Takahiro Tougan1, Jyotheeswara R Edula2,3, Masayuki Morita4, Eizo Takashima4, Hajime Honma5, Takafumi Tsuboi4, Toshihiro Horii6. 1. Research Centre for Infectious Disease Control, Research Institute for Microbial Diseases, Osaka University, 3-1 Yamadaoka, Suita, Osaka, 565-0871, Japan. ttougan@biken.osaka-u.ac.jp. 2. Department of Molecular Protozoology, Research Institute for Microbial Diseases, Osaka University, 3-1 Yamadaoka, Suita, Osaka, 565-0871, Japan. 3. Cell and Developmental Biology Section, Division of Biological Sciences, University of California, San Diego, 9500 Gilman Dr, La Jolla, CA, 92093, USA. 4. Division of Malaria Research, Proteo-Science Centre, Ehime University, 3 Bunkyo-cho, Matsuyama, Ehime, 790-8577, Japan. 5. Department of International Affairs and Tropical Medicine, Tokyo Women's Medical University, 8-1 Kawada-cho, Shinjuku-ku, Tokyo, 162-8666, Japan. 6. Department of Malaria Vaccine Development, Research Institute for Microbial Diseases, Osaka University, 3-1 Yamadaoka, Suita, Osaka, 565-0871, Japan.
Abstract
BACKGROUND: The malaria parasite Plasmodium falciparum is a protozoan that develops in red blood cells (RBCs) and requires various host factors. For its development in RBCs, nutrients not only from the RBC cytosol but also from the extracellular milieu must be acquired. Although the utilization of host nutrients by P. falciparum has been extensively analysed, only a few studies have reported its utilization of host serum proteins. Hence, the aim of the current study was to comprehensively identify host serum proteins taken up by P. falciparum parasites and to elucidate their role in pathogenesis. METHODS: Plasmodium falciparum was cultured with human serum in vitro. Uptake of serum proteins by parasites was comprehensively determined via shotgun liquid chromatography-mass spectrometry/mass spectrometry and western blotting. The calcium ion concentration in serum was also evaluated, and coagulation activity of the parasite lysate was assessed. RESULTS: Three proteins, vitamin K-dependent protein S, prothrombin, and vitronectin, were selectively internalized under sufficient Ca2+ levels in the culture medium. The uptake of these proteins was initiated before DNA replication, and increased during the trophozoite and schizont stages, irrespective of the assembly/disassembly of actin filaments. Coagulation assay revealed that prothrombin was activated and thereby induced blood coagulation. CONCLUSIONS: Serum proteins were taken up by parasites under culture conditions with sufficient Ca2+ levels. This uptake phenomenon was associated with their pathogenicity.
BACKGROUND: The malaria parasite Plasmodium falciparum is a protozoan that develops in red blood cells (RBCs) and requires various host factors. For its development in RBCs, nutrients not only from the RBC cytosol but also from the extracellular milieu must be acquired. Although the utilization of host nutrients by P. falciparum has been extensively analysed, only a few studies have reported its utilization of host serum proteins. Hence, the aim of the current study was to comprehensively identify host serum proteins taken up by P. falciparum parasites and to elucidate their role in pathogenesis. METHODS:Plasmodium falciparum was cultured with human serum in vitro. Uptake of serum proteins by parasites was comprehensively determined via shotgun liquid chromatography-mass spectrometry/mass spectrometry and western blotting. The calcium ion concentration in serum was also evaluated, and coagulation activity of the parasite lysate was assessed. RESULTS: Three proteins, vitamin K-dependent protein S, prothrombin, and vitronectin, were selectively internalized under sufficient Ca2+ levels in the culture medium. The uptake of these proteins was initiated before DNA replication, and increased during the trophozoite and schizont stages, irrespective of the assembly/disassembly of actin filaments. Coagulation assay revealed that prothrombin was activated and thereby induced blood coagulation. CONCLUSIONS: Serum proteins were taken up by parasites under culture conditions with sufficient Ca2+ levels. This uptake phenomenon was associated with their pathogenicity.