Tavella, T. A. | bioRxiv Science

bioRxiv2025

Plasmodium falciparum PP1 phosphatase is a key regulator of malaria parasite transmission

For the successful transmission of malaria parasites from humans to mosquitoes, Plasmodium falciparum gametocytes must remain in the bloodstream long enough to be taken up by a mosquito. Once ingested, they are then activated into gametes to continue the parasite life cycle in the mosquito midgut. Both persistence of gametocytes in the blood and their activation into gametes are tightly regulated by phospho-signaling. While the serine-threonine phosphatase PfPP1 is an essential enzyme for parasite asexual proliferation, its role during transmission of sexual stages remains elusive. Here, we employed a conditional depletion strategy to conduct a functional analysis of PfPP1 during gametocyte development, gamete activation and transmission to mosquitoes. We show that PfPP1 regulates the deformability and the permeability of mature gametocyte-infected erythrocytes through the dephosphorylation of PKA substrates, thus highlighting a key role for PfPP1 in modulating the host cell mechanical properties, which are crucial for gametocyte persistence in the bloodstream. We also provide evidence that PfPP1 controls crucial steps of gamete activation via stimulation of the cGMP/ PKG pathway. Collectively, these results underscore the pivotal role of PfPP1 in the transmission of P. falciparum to the mosquito during both sexual development and gamete activation. AUTHOR SUMMARYThe protein phosphatase PP1 is a major contributor to total cellular phosphatase activity in eukaryotes and plays a critical role during various cellular processes. Here, we have unraveled novel mechanisms regulated by the phosphatase PfPP1 in the human malaria parasite Plasmodium falciparum. While PfPP1 is known to be essential for the parasite asexual proliferation, in the present study we demonstrate that PfPP1 is also required during the sexual parasite stages, called gametocytes, that ensure parasite transmission from humans to mosquitoes. PfPP1 is involved in regulating the mechanical properties of the gametocyte-infected host cell, a process necessary for the persistence of gametocytes in blood circulation. Moreover, PfPP1 also contributes to the activation of gametocytes into gametes, the stages able to pursue the parasite life cycle in mosquitoes. In addition to providing insights into novel mechanisms involved in parasite transmission, this study also highlights the possibility of interfering with PfPP1 signaling pathway for blocking malarial parasite transmission.

microbiology↗

bioRxiv2020

Repurposing the Ebola and Marburg Virus Inhibitors Tilorone, Quinacrine and Pyronaridine: In vitro Activity Against SARS-CoV-2 and Potential Mechanisms

SARS-CoV-2 is a newly identified virus that has resulted in over 1.3 M deaths globally and over 59 M cases globally to date. Small molecule inhibitors that reverse disease severity have proven difficult to discover. One of the key approaches that has been widely applied in an effort to speed up the translation of drugs is drug repurposing. A few drugs have shown in vitro activity against Ebola virus and demonstrated activity against SARS-CoV-2 in vivo. Most notably the RNA polymerase targeting remdesivir demonstrated activity in vitro and efficacy in the early stage of the disease in humans. Testing other small molecule drugs that are active against Ebola virus would seem a reasonable strategy to evaluate their potential for SARS-CoV-2. We have previously repurposed pyronaridine, tilorone and quinacrine (from malaria, influenza, and antiprotozoal uses, respectively) as inhibitors of Ebola and Marburg virus in vitro in HeLa cells and of mouse adapted Ebola virus in mouse in vivo. We have now tested these three drugs in various cell lines (VeroE6, Vero76, Caco-2, Calu-3, A549-ACE2, HUH-7 and monocytes) infected with SARS-CoV-2 as well as other viruses (including MHV and HCoV 229E). The compilation of these results indicated considerable variability in antiviral activity observed across cell lines. We found that tilorone and pyronaridine inhibited the virus replication in A549-ACE2 cells with IC50 values of 180 nM and IC50 198 nM, respectively. We have also tested them in a pseudovirus assay and used microscale thermophoresis to test the binding of these molecules to the spike protein. They bind to spike RBD protein with Kd values of 339 nM and 647 nM, respectively. Human Cmax for pyronaridine and quinacrine is greater than the IC50 hence justifying in vivo evaluation. We also provide novel insights into their mechanism which is likely lysosomotropic.

pharmacology and toxicology↗