A Host GPCR Signaling Network Required for the Cytolysis of Infected Cells Facilitates Release of Apicomplexan Parasites

Abstract

Summary Following intracellular replication, the apicomplexan parasites Plasmodium falciparum and Toxoplasma gondii cause host cell cytolysis to facilitate parasite release and disease progression. Parasite exit from infected cells requires the interplay of parasite-derived proteins and host actin cytoskeletal changes; however, the host proteins underlying these changes remain obscure. We report the identification of a Gαq-coupled host-signaling cascade required for the egress of both P. falciparum and T. gondii. Gαq-coupled signaling results in protein kinase C (PKC)-mediated loss of the host cytoskeletal protein adducin and weakening of the cellular cytoskeleton. This cytoskeletal compromise induces catastrophic Ca2+ influx mediated by the mechanosensitive cation channel TRPC6, which activates host calpain that proteolyzes the host cytoskeleton allowing parasite release. Reinforcing the feasibility of targeting host proteins as an antiparasitic strategy, mammalian PKC inhibitors demonstrated activity in murine models of malaria and toxoplasmosis. Importantly, an orally bioavailable PKC inhibitor prolonged survival in an experimental cerebral malaria model.

Recent insights into apicomplexan parasite egress provide new views to a kill

“…Consistent with this, atomic force microscopy revealed discontinuities in the cytoskeleton of infected erythrocytes [21]. Further work based on an RNAi interference screen of host signaling factors revealed a calcium-based signaling cascade required for egress of T. gondii and P. falciparum [22]. The pathway is proposed to involve a heterotrimeric G protein (including a Gαq component), which activates phospholipase C to generate diacylglycerol as an activator of protein kinase C. Protein kinase C phosphorylation inactivates α-adducin, causing cytoskeletal lesions.…”

Signalome-wide assessment of erythrocyte response toPlasmodiumreveals novel targets for host-directed antimalarial intervention

“…Some of the most notable changes implicated the PKC isoforms δ and θ. Several PKC isoforms have previously been reported to be activated during P. falciparum infection of erythrocytes, but the phosphorylation status of these kinases was uncharacterised 23,24 . Several phosphorylation sites of PKCδ/θ were significantly phosphorylated in trophozoite- and schizont-infected cells (Fig.…”

Protein Kinase C-Dependent Signaling Controls the Midgut Epithelial Barrier to Malaria Parasite Infection in Anopheline Mosquitoes

“…In particular, PKC-dependent signaling has been targeted aggressively for drug development in humans and selective PKC kinase inhibitors are currently in phase II clinical trials [69], [70]. Mammalian PKCs have also been implicated in the regulation of malaria parasite egress from RBCs and treatment of P. berghei- infected mice with the PKC inhibitor sotrastaurin [71], [72] significantly decreased parasitemia and increased survival of infected hosts [73]. Given that circulating levels of sotrastaurin in blood can range from ∼0.1–2.3 µM following a single treatment [74], parasites that ‘escape’ this targeted drug treatment in the human host would be ingested along with the inhibitor by mosquitoes that feed on these treated hosts.…”