Invasion of hepatocytes by Plasmodium sporozoites requires cGMP‐dependent protein kinase and calcium dependent protein kinase 4

• Published in: Molecular microbiology 2016-10, Vol.102 (2), p.349-363
• Main Authors: Govindasamy, K., Jebiwott, S., Jaijyan, D. K., Davidow, A., Ojo, K. K., Van Voorhis, W. C., Brochet, M., Billker, O., Bhanot, P.
• Format: Article
• Language: English
• Subjects: Animals; Anopheles - parasitology; Calcium; Calcium - metabolism; Calcium-Binding Proteins - metabolism; Cyclic GMP - metabolism; Cyclic GMP-Dependent Protein Kinases - metabolism; Hep G2 Cells; Hepatocytes - metabolism; Hepatocytes - parasitology; Humans; Kinases; Motility; Parasites; Plasmodium berghei; Plasmodium berghei - enzymology; Plasmodium berghei - genetics; Plasmodium berghei - metabolism; Plasmodium falciparum - enzymology; Plasmodium falciparum - genetics; Plasmodium falciparum - metabolism; Protein Kinases - metabolism; Proteins; Protozoan Proteins - metabolism; Signal Transduction; Sporozoites - metabolism
• ISSN: 0950-382X; 1365-2958; 1365-2958
• DOI: 10.1111/mmi.13466

Summary Invasion of hepatocytes by sporozoites is essential for Plasmodium to initiate infection of the mammalian host. The parasite's subsequent intracellular differentiation in the liver is the first developmental step of its mammalian cycle. Despite their biological significance, surprisingly little is known of the signalling pathways required for sporozoite invasion. We report that sporozoite invasion of hepatocytes requires signalling through two second‐messengers – cGMP mediated by the parasite's cGMP‐dependent protein kinase (PKG), and Ca2+, mediated by the parasite's calcium‐dependent protein kinase 4 (CDPK4). Sporozoites expressing a mutated form of Plasmodium berghei PKG or carrying a deletion of the CDPK4 gene are defective in invasion of hepatocytes. Using specific and potent inhibitors of Plasmodium PKG and CDPK4, we demonstrate that PKG and CDPK4 are required for sporozoite motility, and that PKG regulates the secretion of TRAP, an adhesin that is essential for motility. Chemical inhibition of PKG decreases parasite egress from hepatocytes by inhibiting either the formation or release of merosomes. In contrast, genetic inhibition of CDPK4 does not significantly decrease the number of merosomes. By revealing the requirement for PKG and CDPK4 in Plasmodium sporozoite invasion, our work enables a better understanding of kinase pathways that act in different Plasmodium stages. Malaria infection begins with the injection of Plasmodium sporozoites into humans by a feeding mosquito. We demonstrate that two parasite kinases, PKG and CDPK4 are crucial for sporozoite motility and consequently their entry into hepatocytes. Our results have implications for understanding the role of second messenger molecules, cGMP and Ca2+ in regulating the exo‐erythrocytic cycle of Plasmodium.