Human plasma plasminogen internalization route in Plasmodium falciparum-infected erythrocytes

Abstract

Background: The intra-erythrocytic development of the malaria parasite Plasmodium falciparum depends on the uptake of a number of essential nutrients from the host cell and blood plasma. It is widely recognized that the parasite imports low molecular weight solutes from the plasma and the consumption of these nutrients by P. falciparum has been extensively analysed. However, although it was already shown that the parasite also imports functional proteins from the vertebrate host, the internalization route through the different infected erythrocyte membranes has not yet been elucidated. In order to further understand the uptake mechanism, the study examined the trafficking of human plasminogen from the extracellular medium into P. falciparum-infected red blood cells. Methods: Plasmodium falciparum clone 3D7 was cultured in standard HEPES-buffered RPMI 1640 medium supplemented with 0.5% AlbuMAX. Exogenous human plasminogen was added to the P. falciparum culture and the uptake of this protein by the parasites was analysed by electron microscopy and Western blotting. Immunoprecipitation and mass spectrometry were performed to investigate possible protein interactions that may assist plasminogen import into infected erythrocytes. The effect of pharmacological inhibitors of different cellular physiological processes in plasminogen uptake was also tested. Results: It was observed that plasminogen was selectively internalized by P. falciparum-infected erythrocytes, with localization in plasma membrane erythrocyte and parasite's cytosol. The protein was not detected in parasitic food vacuole and haemoglobin-containing vesicles. Furthermore, in erythrocyte cytoplasm, plasminogen was associated with the parasite-derived membranous structures tubovesicular network (TVN) and Maurer's clefts. Several proteins were identified in immunoprecipitation assay and may be involved in the delivery of plasminogen across the P. falciparum multiple compartments. Conclusion: The findings here reported reveal new features regarding the acquisition of plasma proteins of the host by P. falciparum-infected erythrocytes, a mechanism that involves the exomembrane system, which is distinct from the haemoglobin uptake, clarifying a route that may be potentially targeted for inhibition studies.

Red Blood Cell BCL-xL Is Required for Plasmodium falciparum Survival: Insights into Host-Directed Malaria Therapies

“…Upon P. falciparum infection of RBCs, we have demonstrated that BCL-x L continues to localize to the host RBC cytosol but that a pool of the protein relocates either to the parasitophorous vacuole membrane, the parasite membrane, or within the parasite itself (Figure 3). P. falciparum is known to export a considerable number of proteins to its host cell, including many targeted to the RBC membrane, but only a few examples of functional human proteins have been shown to be imported by the parasite [45][46][47][48]. Further work is required to identify the exact subcellular localization of BCL-x L in iRBCs, and similar investigations should be carried out in infected hepatocytes.…”

From Myzocytosis to Cytostomal Nutrient Uptake and Transport by Intracellular Plasmodium Species

“…Mechanisms of sporozoite and merozoite invasion into hepatocytes and erythrocytes, respectively, and development within the host cell have been the subject of extensive research. In the blood stage, the mechanisms of nutrient uptake across the host red cell membrane, parasitophorous vacuole membrane (PVM) and parasite plasma membrane (PPM) have received much focus due to the trafficking of multiple parasite proteins to the host cell membrane through the Maurer’s clefts, tubovesicular membranes and other mobile membranous vesicles like the J-dots [ 2 , 3 ]. The transport of nutrients from the extracellular environment into the host erythrocyte and from the host cell cytoplasm into the parasite, although significant, have received less attention, in part, due to the challenges of investigating the trafficking pathways.…”