Roles and Cellular Localization of GBP2 and NAB2 During the Blood Stage of Malaria Parasites

The quality control and export of mRNA by RNA-binding proteins are necessary for the survival of malaria parasites, which have complex life cycles. Nuclear poly(A) binding protein 2 (NAB2), THO complex subunit 4 (THO4), nucleolar protein 3 (NPL3), G-strand binding protein 2 (GBP2) and serine/arginine-rich splicing factor 1 (SR1) are involved in nuclear mRNA export in malaria parasites. However, their roles in asexual and sexual development, and in cellular localization, are not fully understood. In this study using the rodent malaria parasite, Plasmodium berghei, we found that NAB2 and SR1, but not THO4, NPL3 or GBP2, played essential roles in the asexual development of malaria parasites. By contrast, GBP2 but not NPL3 was involved in male and female gametocyte production. THO4 was involved in female gametocyte production, but had a lower impact than GBP2. In this study, we focused on GBP2 and NAB2, which play important roles in the sexual and asexual development of malaria parasites, respectively, and examined their cellular localization. GBP2 localized to both the nucleus and cytoplasm of malaria parasites. Using immunoprecipitation coupled to mass spectrometry (IP-MS), GBP2 interacted with the proteins ALBA4, DOZI, and CITH, which play roles in translational repression. IP-MS also revealed that phosphorylated adapter RNA export protein (PHAX) domain-containing protein, an adaptor protein for exportin-1, also interacted with GBP2, implying that mRNA export occurs via the PHAX domain-containing protein pathway in malaria parasites. Live-cell fluorescence imaging revealed that NAB2 localized at the nuclear periphery. Moreover, IP-MS indicated that NAB2 interacted with transportin. RNA immunoprecipitation coupled to RNA sequencing revealed that NAB2 bound directly to 143 mRNAs, including those encoding 40S and 60S ribosomal proteins. Our findings imply that malaria parasites use an evolutionarily ancient mechanism conserved throughout eukaryotic evolution.

Plasmodium falciparum artemisinin-resistant K13 mutations confer a sexual-stage transmission advantage that can be overcome with atovaquone-proguanil

ABSTRACTContaining the spread of artemisinin (ART)-resistant Plasmodium falciparum will be assisted by improved understanding of its human-to-mosquito transmission. We compared gametocyte dynamics among field isolates containing K13 mutations conferring ART resistance and K13 wild-type parasites. In Pailin, Cambodia, the male to female gametocyte ratio was higher among K13 mutant infections compared to K13 wild-type infections. We also investigated the effects of artesunate and atovaquone-proguanil on the transmissibility of an ART-resistant K13 mutant strain, Cam3.IIR539T, in a volunteer infection study. Gametocyte production was higher after a single dose of artesunate (2 mg/kg) in volunteers infected with ART-resistant compared to ART-sensitive parasites. Despite the presence of gametocytes in volunteers infected with ART-resistant parasites, there was no infection observed in Anopheles stephensi mosquitoes after atovaquone-proguanil treatment. We report transmission determinants of ART-resistant infections that could be advantageous over ART-sensitive infections. Moreover, we show additional benefits of treating ART-resistant infections with atovaquone-proguanil treatment.

Imaging-Based High-Throughput Screening Assay To Identify New Molecules with Transmission-Blocking Potential against Plasmodium falciparum Female Gamete Formation

ABSTRACTIn response to a call for the global eradication of malaria, drug discovery has recently been extended to identify compounds that prevent the onward transmission of the parasite, which is mediated byPlasmodium falciparumstage V gametocytes. Lately, metabolic activity has been usedin vitroas a surrogate for gametocyte viability; however, as gametocytes remain relatively quiescent at this stage, their ability to undergo onward development (gamete formation) may be a better measure of their functional viability. During gamete formation, female gametocytes undergo profound morphological changes and express translationally repressed mRNA. By assessing female gamete cell surface expression of one such repressed protein, Pfs25, as the readout for female gametocyte functional viability, we developed an imaging-based high-throughput screening (HTS) assay to identify transmission-blocking compounds. This assay, designated theP. falciparumfemale gametocyte activation assay (FGAA), was scaled up to a high-throughput format (Z′ factor, 0.7 ± 0.1) and subsequently validated using a selection of 50 known antimalarials from diverse chemical families. Only a few of these agents showed submicromolar 50% inhibitory concentrations in the assay: thiostrepton, methylene blue, and some endoperoxides. To determine the best conditions for HTS, a robustness test was performed with a selection of the GlaxoSmithKline Tres Cantos Antimalarial Set (TCAMS) and the final screening conditions for this library were determined to be a 2 μM concentration and 48 h of incubation with gametocytes. TheP. falciparumFGAA has been proven to be a robust HTS assay faithful toPlasmodiumtransmission-stage cell biology, and it is an innovative useful tool for antimalarial drug discovery which aims to identify new molecules with transmission-blocking potential.