Oral Presentation Lorne Infection and Immunity 2019

Drug addiction in the human malaria parasite Plasmodium falciparum (#4)

Sarah Jackson 1 , Jack Adderley 1 , Simona John von Freyend 1 , Christian Doerig 1
  1. Monash University, Clayton, VIC, Australia

To comprehensively investigate the mobilisation of host erythrocyte signalling pathways by P. falciparum, we used an antibody microarray approach we had successfully implemented in other infection systems [1, 2].  The microarray carries >900 antibodies against human signalling proteins, the majority of which are phospho-specific, allowing the monitoring of the activation status of specific host erythrocyte kinases.  This confirmed our initial findings [3] that a PAK-MEK pathways is activated in infected cells, and identified several additional pathways that are activated by infection.

We went on to show that treatment with selective inhibitors of host erythrocyte c-MET (a receptor tyrosine kinase), B-Raf (an upstream component of MAP kinase pathways) and MEK1 (a MAP kinase activator), all of which show parasite-induced activation, leads to parasite death.  Since their supposed targets are not encoded by the parasite (which does not possess homologues of these kinases), we predicted that it would be difficult to raise resistance against these molecules.  Using a selection protocol provided by David Fidock (Columbia University), we were unable to generate lines resistant to the c-MET and B-Raf inhibitors, which supports the hypothesis that their parasiticidal effect is mediated by the predicted host cell kinase.  In contrast, parasites with 15-fold reduced susceptibility to Trametinib, the MEK inhibitor, were readily obtained, suggesting a parasite-encoded off-target.  Surprisingly, some of the Trametinib-resistant lines displayed dependency on the drug, and stop proliferating once the drug was removed.  Whole-genome sequencing identified missense mutations in the same P. falciparum gene in all clones (obtained by dilution) that display the dependency phenotype; these mutations are absent in parasite clones that are Trametinib-resistant but do not have the dependency phenotype. We are currently designing strategies for knocking-in the mutated gene into wild-type parasite, in order to verify that this confers Trametinib dependency.

A possible interpretation of these data is that MEK activation is part of a host defence mechanism, whose long-term inhibition by Trametinib removes selective pressure for the maintenance of a counter-measure by the parasite. 

This study provides an unexpected novel twist in the complex interactions between the parasite and its host erythrocyte.

  1. Haqshenas, G., Wu, J., Simpson, K. J., Daly, R. J., Netter, H. J., Baumert, T. F., and Doerig, C. (2017) Signalome-wide assessment of host cell response to hepatitis C virus. Nat Commun 8, 15158.
  2. Haqshenas, G., Terradas, G., Paradkar, P., Duchemin, J.-B., McGraw, E. and Doerig, C. (2018) A role for the Insulin receptor in the suppression of dengue virus and Zika virus in Wolbachia-infected mosquito cells. Cell Reports, in press.
  3. Sicard, A., Semblat, J. P., Doerig, C., Hamelin, R., Moniatte, M., Dorin-Semblat, D., Spicer, J. A., Srivastava, A., Retzlaff, S., Heussler, V., Waters, A. P., and Doerig, C. (2011) Activation of a PAK-MEK signalling pathway in malaria parasite-infected erythrocytes. Cell Microbiol 13, 836-845.