Keynote Conference - Interevent

Symp#5 Host Parasite Interaction
Chair Wanderley de Souza
Wanderley de Souza
Federal University of Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil
Introductory Notes
Dephosphorylation of eIF5A is Required for Translation Arrest at the Stationary Growth Phase of Trypanosoma cruzi
Chung, J.*; Rocha, A. A.*, Tonelli, R. R.;,Castilho, B. A., and Sérgio Schenkman.
Departamento de Microbiologia, Imunologia e Parasitologia, Universidade Federal de São Paulo, São Paulo, Brazil
* Both authors contributed equally
The protein known as eukaryotic initiation factor 5A (eIF5A) has an elusive role in the translation elongation. It has a unique and
essential hypusine modification on a conserved lysine residue in most eukaryotes. In addition, this protein is modified by
phosphorylations with unknown functions. Here we found that a phosphorylated state of eIF5A from Trypanosoma cruzi (TceIF5A),
the protozoan that causes Chagas’ disease, predominates in exponentially growing cells and extensive dephosphorylation occurs in
cells reaching the stationary growth phase. The phosphorylation was shown to occur mainly at Ser 2, then at Ser 47, homologous to
yeast eIF5A. In addition, a novel phosphorylation site was identified at Tyr 21. In exponential cells, TceIF5A is partially associated with
polysomes, compatible with its function as an elongation factor and become relatively enriched in polysomal fractions at stationary at
stationary phase. TceIF5A overexpression increases the rate of cell proliferation, protein synthesis, and the relative amount of
polysomes. When Ser 2 is replaced by Asp, but not by Ala, in the overexpressors, the cells still show an increased protein synthesis
and growth rate. However, the presence of Asp causes cell damage when cultures reach the stationary phase. Wild type, or Ala, but
not Asp replacing Ser 2 forms of TceIF5A causes protein synthesis arrest and are enriched in polysomal content at the stationary
phase. We conclude that dephosphorylation of eIF5A has a key role in arresting the protein synthesis under unfavorable conditions,
indicating that eIF5A phosphorylation/dephosphorylation might control its association with polysomes during translation elongation.
Ion Regulation in the Malaria Parasite: The Target of a New Generation of Antimalarials
Kiaran Kirk
Research School of Biology, The Australian National University, Canberra, ACT, 0200, Australia
The intraerythrocytic malaria parasite induces novel channels in the membrane of its host erythrocyte. These channels mediate the
uptake of essential nutrients but, at the same time, allow a net influx of Na + ions, resulting in an elevated Na + concentration in the
host cell compartment. The intraerythrocytic malaria parasite itself maintains an intracellular Na + concentration some ten-fold less
than that in its host cell, extruding Na + via a Na + -ATPase on its plasma membrane. Bioinformatic analysis of the genome of the human
malaria parasite Plasmodium falciparum reveals that the most likely candidate for the parasite’s Na + ATPase is a protein known as
PfATP4.
The spiroindolones are a new class of compound that inhibit the in vitro growth of the human malaria parasite, Plasmodium
falciparum, at nanomolar concentrations. One of the spiroindolones is now in Phase IIa clinical trials, and is the first molecule with a
novel mechanism of action to enter Phase IIa studies for malaria in the last 20 years. Prolonged exposure of P. falciparum parasites to
sub-lethal concentrations of spiroindolones leads to the emergence of spiroindolone-resistant parasites, with the resistance
attributable to mutations in PfATP4. In this talk I will introduce the cell physiology of the intracellular malaria parasite and present
evidence that the spiroindolones exert their antimalarial effect by inhibiting Na + extrusion via PfATP4, thereby disrupting Na +
regulation in the intracellular parasite.
Why coinfect cells with non-viral pathogens?
Michel Rabinovitch
Universidade Federal de São Paulo – Escola Paulista de Medicina, Departamento de Microbiologia, Imunologia e Parasitologia, São
Paulo, Brazil e-mail: michel.rabinovitch3@gmail.com
Coinfection of E. coli bacteria with mutant bacteriophages in the 1940s spurred the development of molecular virology. Beginning in
the 1960s, virologists, among them alumni of the CSHL Phage Course, coinfected mammalian cells with virus mutants, strains or
species and developed the basic procedures and concepts of viral genetics. The AIDS pandemic of the 1980s begot cell coinfections of
HIV and non-viral pathogens. In the 1990s, impressive horizontal gene exchanges were detected between pathogens sheltered in
free-living protozoa. In contrast, there are few reports–briefly reviewed in the presentation-of mammalian cells coinfected with
bacteria or protozoa. Initially, the model permitted the targeting of pathogens to intracellular compartments they normally don’t
occupy, thanks to C. burnetii’s exceptionally large and hospitable parasitophorous vacuoles. Vacuolar colocalization will probably be
rare in the world of coinfections. We believe that coinfection, apart from its ludic quality, may uncover unexpected, and hopefully
interesting, interactions involving (for instance), antagonism via secreted toxins or antibiotics, competition for cell derived nutrients,
quorum sensing effects, exploitable modulation of host cell gene expression and transduction cascades. We thus argue that
coinfection with non-viral-pathogens could provide an added tool for mono-infection-entrenched cellular microbiologists. However,
whereas mono-infections may reflect a dialogue – by proxy - between two genomes, the neo-coinfector may be confronted with a
livelier dialogue involving three – genomes, besides the potential participation of a fourth, the host cell mitochondrial genome. One
problem remains: given the number of available microorganisms, how is one to select the most promising pair for coinfection?
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