Tumor necrosis factor reduces Plasmodium falciparum growth and activates calcium signaling in human malaria parasites

Background: Plasmodium has a complex biology including the ability to interact with host signals modulating their function through cellular machinery. Tumor necrosis factor (TNF) elicits diverse cellular responses including effects in malarial pathology and increased infected erythrocyte cytoadherence. As TNF levels are raised during P. falciparum infection we have investigated whether it has an effect on the parasite asexual stage. Methods: Flow cytometry, spectrofluorimetric determinations, confocal microscopy and PCR real time quantifications were employed for characterizing TNF induced effects and membrane integrity verified by wheat germ agglutinin staining. Results: TNF is able to decrease intracellular parasitemia, involving calcium as a second messenger of the pathway. Parasites incubated for 48h with TNF showed reduced erythrocyte invasion. Thus, TNF induced rises in intracellular calcium concentration, which were blocked by prior addition of the purinergic receptor agonists KN62 and A438079, or interfering with intra- or extracellular calcium release by thapsigargin or EGTA (ethylene glycol tetraacetic acid). Importantly, expression of PfPCNA1 which encodes the Plasmodium falciparum Proliferating-Cell Nuclear Antigen 1, decreased after P. falciparum treatment of TNF (tumor necrosis factor) or 6-Bnz cAMP (N6-Benzoyladenosine-3′,5′-cyclic monophosphate sodium salt). Conclusions: This is potentially interesting data showing the relevance of calcium in down regulating a gene involved in cellular proliferation, triggered by TNF. General significance: The data show that Plasmodium may subvert the immunological system and use TNF for the control of its proliferation within the vertebrate host

Calcium signaling in a low calcium environment: how the intracellular malaria parasite solves the problem

Malaria parasites, Plasmodia, spend most of their asexual life cycle within red blood cells, where they proliferate and mature. The erythrocyte cytoplasm has very low [Ca2+] (<100 nM), which is very different from the extracellular environment encountered by most eukaryotic cells. The absence of extracellular Ca2+ is usually incompatible with normal cell functions and survival. In the present work, we have tested the possibility that Plasmodia overcome the limitation posed by the erythrocyte intracellular environment through the maintenance of a high [Ca2+] within the parasitophorous vacuole (PV), the compartment formed during invasion and within which the parasites grow and divide. Thus, Plasmodia were allowed to invade erythrocytes in the presence of Ca2+ indicator dyes. This allowed selective loading of the Ca2+ probes within the PV. The [Ca2+] within this compartment was found to be ∼40 μM, i.e., high enough to be compatible with a normal loading of the Plasmodia intracellular Ca2+ stores, a prerequisite for the use of a Ca2+-based signaling mechanism. We also show that reduction of extracellular [Ca2+] results in a slow depletion of the [Ca2+] within the PV. A transient drop of [Ca2+] in the PV for a period as short as 2 h affects the maturation process of the parasites within the erythrocytes, with a major reduction 48 h later in the percentage of schizonts, the form that re-invades the red blood cells

Cyclic AMP and calcium interplay as second messengers in melatonin-dependent regulation of Plasmodium falciparum cell cycle

The host hormone melatonin increases cytoplasmic Ca2+ concentration and synchronizes Plasmodium cell cycle (Hotta, C.T., M.L. Gazarini, F.H. Beraldo, F.P. Varotti, C. Lopes, R.P. Markus, T. Pozzan, and C.R. Garcia. 2000. Nat. Cell Biol. 2:466–468). Here we show that in Plasmodium falciparum melatonin induces an increase in cyclic AMP (cAMP) levels and cAMP-dependent protein kinase (PKA) activity (40 and 50%, respectively)

Molecular Machinery Of Signal Transduction And Cell Cycle Regulation In Plasmodium

The regulation of the Plasmodium cell cycle is not understood. Although the Plasmodium falciparum genome is completely sequenced, about 60% of the predicted proteins share little or no sequence similarity with other eukaryotes. This feature impairs the identification of important proteins participating in the regulation of the cell cycle. There are several open questions that concern cell cycle progression in malaria parasites, including the mechanism by which multiple nuclear divisions is controlled and how the cell cycle is managed in all phases of their complex life cycle. Cell cycle synchrony of the parasite population within the host, as well as the circadian rhythm of proliferation, are striking features of some Plasmodium species, the molecular basis of which remains to be elucidated. In this review we discuss the role of indole-related molecules as signals that modulate the cell cycle in Plasmodium and other eukaryotes, and we also consider the possible role of kinases in the signal transduction and in the responses it triggers. © 2009 Elsevier B.V. All rights reserved

Combining IP3 affinity chromatography and bioinformatics reveals a novel protein-IP3 binding site on Plasmodium falciparum MDR1 transporter

Intracellular Ca2+ mobilization induced by second messenger IP3 controls many cellular events in most of the eukaryotic groups. Despite the increasing evidence of IP3-induced Ca2+ in apicomplexan parasites like Plasmodium, responsible for malaria infection, no protein with potential function as an IP3-receptor has been identified. The use of bioinformatic analyses based on previously known sequences of IP3-receptor failed to identify potential IP3-receptor candidates in any Apicomplexa. In this work, we combine the biochemical approach of an IP3 affinity chromatography column with bioinformatic meta-analyses to identify potential vital membrane proteins that present binding with IP3 in Plasmodium falciparum. Our analyses reveal that PF3D7_0523000, a gene that codes a transport protein associated with multidrug resistance as a potential target for IP3. This work provides a new insight for probing potential candidates for IP3-receptor in Apicomplexa