Invasion of a suitable host hepatocyte by mosquito-transmitted Plasmodium sporozoites is an essential early step in successful malaria parasite infection. Yet, precisely how sporozoites target their host cell and facilitate productive infection remains largely unknown. Here, we found that the hepatocyte EphA2 receptor was critical for establishing a permissive intracellular replication compartment, the parasitophorous vacuole. Sporozoites productively infected hepatocytes with high EphA2 expression and deletion of EphA2 protected mice from liver infection. Lack of host EphA2 phenocopied the lack of the sporozoite proteins P52 and P36. Our data suggests that P36 engages EphA2, which is likely to be a key step to establish the permissive replication compartment.

Summary Plasmodium parasites infect the liver and replicate inside hepatocytes before they invade erythrocytes and trigger clinical malaria. Analysis of host signaling pathways affected by liver stage infection could provide critical insights into host-pathogen interactions and reveal targets for intervention. Using protein lysate microarrays we found that Plasmodium yoelii rodent malaria parasites perturb hepatocyte regulatory pathways involved in cell survival, proliferation and autophagy. Notably, the pro-death protein p53 was substantially decreased in infected hepatocytes, suggesting it could be targeted by the parasite to foster survival. Indeed, mice that express increased levels of p53 showed reduced liver stage parasite burden whereas p53 knockout mice suffered increased liver stage burden. Furthermore, boosting p53 levels using the small molecule Nutlin-3 dramatically reduced liver stage burden in vitro and in vivo. We conclude that perturbation of the hepatocyte p53 pathway critically impacts parasite survival. Thus, host pathways might constitute potential targets for host-based antimalarial prophylaxis.

Summary Productive intercellular delivery of cargo by secretory systems requires exquisite temporal and spatial choreography. Our laboratory has demonstrated that the hemolysin co-regulated secretion island I (HSI-I)-encoded type VI secretion system (H1-T6SS) of Pseudomonas aeruginosa transfers effector proteins to other bacterial cells. The activity of these effectors requires cell contact-dependent delivery by the secretion apparatus, and thus their export is highly repressed under planktonic growth conditions. Here we define regulatory pathways that orchestrate efficient secretion by this system. We identified a T6S-associated protein, TagF, as a posttranslational repressor of the H1-T6SS. Strains activated by TagF derepression or stimulation of a previously identified threonine phosphorylation pathway (TPP) share the property of secretory ATPase recruitment to the T6S apparatus, yet display different effector output levels and genetic requirements for their export. We also found that the pathways respond to distinct stimuli; we identified surface growth as a physiological cue that activates the H1-T6SS exclusively through the TPP. Coordination of posttranslational triggering with cell contact-promoting growth conditions provides a mechanism for the T6SS to avoid wasteful release of effectors.