Phosphoinositide metabolism links cGMP-dependent protein kinase G to essential Ca²⁺ signals at key decision points in the life cycle of malaria parasites
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Many critical events in the Plasmodium life cycle rely on the controlled release of Ca2+ from intracellular stores to activate stage-specific Ca2+-dependent protein kinases. Using the motility of Plasmodium berghei ookinetes as a signalling paradigm, we show that the cyclic guanosine monophosphate (cGMP)-dependent protein kinase, PKG, maintains the elevated level of cytosolic Ca2+ required for gliding motility. We find that the same PKG-dependent pathway operates upstream of the Ca2+ signals that mediate activation of P. berghei gametocytes in the mosquito and egress of Plasmodium falciparum merozoites from infected human erythrocytes. Perturbations of PKG signalling in gliding ookinetes have a marked impact on the phosphoproteome, with a significant enrichment of in vivo regulated sites in multiple pathways including vesicular trafficking and phosphoinositide metabolism. A global analysis of cellular phospholipids demonstrates that in gliding ookinetes PKG controls phosphoinositide biosynthesis, possibly through the subcellular localisation or activity of lipid kinases. Similarly, phosphoinositide metabolism links PKG to egress of P. falciparum merozoites, where inhibition of PKG blocks hydrolysis of phosphatidylinostitol (4,5)-bisphosphate. In the face of an increasing complexity of signalling through multiple Ca2+ effectors, PKG emerges as a unifying factor to control multiple cellular Ca2+ signals essential for malaria parasite development and transmission. Author Summary Malaria, caused by Plasmodium spp. parasites, is a profound human health problem. Plasmodium parasites progress through a complex life cycle as they move between infected humans and blood-feeding mosquitoes. We know that tight regulation of calcium ion levels within the cytosol of the parasite is critical to control multiple signalling events in their life cycle. However, how these calcium levels are controlled remains a mystery. Here, we show that a single protein kinase, the cGMP-dependent protein kinase G (PKG), controls the calcium signals that are critical at three different points of the life cycle: (1) for the exit of the merozoite form of the parasite from human erythrocytes (red blood cells), (2) for the cellular activation that happens when Plasmodium sexual transmission stages are ingested by a blood-feeding mosquito, and (3) for the productive gliding of the ookinete, which is the parasite stage that invades the mosquito midgut. We provide initial evidence that the universal role of PKG relies on the production of lipid precursors which then give rise to inositol (1,4,5)-trisphosphate (IP3), a messenger molecule that serves as a signal for the release of calcium from stores within the parasite. This signalling pathway provides a potential target to block both malaria development in the human host and transmission to the mosquito vector.
Brochet , M , Collins , M O , Smith , T K , Thompson , E , Sebastian , S , Volkmann , K , Schwach , F , Chappell , L , Gomes , A R , Berriman , M , Rayner , J C , Baker , D A , Choudhary , J & Billker , O 2014 , ' Phosphoinositide metabolism links cGMP-dependent protein kinase G to essential Ca²⁺ signals at key decision points in the life cycle of malaria parasites ' PLoS Biology , vol 12 , no. 3 , e1001806 . DOI: 10.1371/journal.pbio.1001806
© 2014 Brochet et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.