INVESTIGATING THE ROLE OF cAMP SIGNALLING CONSERVATION DURING MALARIA PARASITE INVASION

The essential nature of host cell signalling during Plasmodium merozoite invasion makes it an attractive target for novel intervention methods for the disease. At this stage, the exact mechanism of this signalling process has not been elucidated but preliminary studies have indicated that calcium signalling is a critical and conserved part of this signalling cascade across the different Plasmodium species during their invasion into human erythrocytes. In P. falciparum, the responsible ligand-receptor pair triggering calcium influx has been identified as PfRh5 and Basigin respectively, but this information is lacking in other species. The absence of a PfRH5 orthologue in other Plasmodium species and the lack of dependence of Basigin as an erythrocyte receptor indicates that these parasites have evolved other ligand-receptor interactions that mediate this signal. In eukaryotic cells, the induction of calcium signalling is tightly regulated and involves extracellular stimulus, cell surface molecular interaction and signal transduction for the activation of calcium channels on the cell surface. Thus, this mechanism may involve the GPCRs, G-proteins, adenylyl cyclases, intracellular kinases like PKA and PKC. How the malaria parasite manipulates these host cell pathways during invasion is not known. We have established in our preliminary studies that PfRH5 binding to Basigin induces a transient host cell cAMP flux that is critical for the subsequent calcium influx. This suggests the involvement of GPCR signalling pathway that leads to the activation of adenylyl cyclase and the observed cAMP spike. Here we propose to compare and contrast the activation of cAMP in a parasite (P. falciparum) that uses PfRH5-Basigin and one (P. knowlesi) that uses a different but so far unknown mechanism to trigger this signal. Therefore, the focus of this proposal is to understand the specific host signalling mechanism across these two Plasmodium species by firstly identifying the parasite ligands and receptors interactions that leads to the activation of GPCRs and G-protein signalling pathways. As G-protein activation leads to the activation of cAMP, this proposal would like to understand the specific role of different molecular players required for this induction. As at this stage the parasite ligand -erythrocyte receptor combination that is responsible for triggering the equivalent signalling cascade in P. knowlesi is not known, the second aim focuses on the identification of these critical ligand receptor interactions. With this information, we then will aim to identify the molecular players that trigger the cAMP and subsequent calcium signalling in P. knowlesi. Successful completion of these aims will provide new fundamental insights on how parasites manipulate the host cell signalling processes and provide new information for the future development of novel therapeutic intervention approaches. Moreover, this study will provide new insights into the general understanding of the processes that control the erythrocyte signalling mechanisms.