Gene expression signatures and small-molecule compounds link a protein kinase to Plasmodium falciparum motility

Abstract

Calcium-dependent protein kinases play a crucial role in intracellular calcium signaling in plants, some algae and protozoa. In Plasmodium falciparum, calcium-dependent protein kinase 1 (PfCDPK1) is expressed during schizogony in the erythrocytic stage as well as in the sporozoite stage. It is coexpressed with genes that encode the parasite motor complex, a cellular component required for parasite invasion of host cells, parasite motility and potentially cytokinesis. A targeted gene-disruption approach demonstrated that pfcdpk1 seems to be essential for parasite viability. An in vitro biochemical screen using recombinant PfCDPK1 against a library of 20,000 compounds resulted in the identification of a series of structurally related 2,6,9-trisubstituted purines. Compound treatment caused sudden developmental arrest at the late schizont stage in P. falciparum and a large reduction in intracellular parasites in Toxoplasma gondii, which suggests a possible role for PfCDPK1 in regulation of parasite motility during egress and invasion.

Does protein phosphorylation govern host cell entry and egress by the Apicomplexa?

“…Furthermore, Go 6983, a PKC inhibitor (PfPKB catalytic domain is closely related to PKC) is able to affect in vitro recombinant PfPKB activity and reduce the ability of P. falciparum to invade erythrocytes (Kumar et al, 2004). Consistent with a vital role in parasite development, both PKB and CDPK1 are refractory to gene disruption in P. berghei and P. falciparum (Kato et al, 2008;Solyakov et al, 2011;Tewari et al, 2010). Using a broad-range serine/threonine kinase inhibitor (staurosporine), a marked reduction of phosphorylation of PfGAP45 was observed (Jones et al, 2009).…”

“…Some of the predicted essential kinases were previously implicated in motility such as cAMPdependent protein kinase A (PKA) (Kurokawa et al, 2011;Leykauf et al, 2010), calcium-dependant protein kinase 1 (CDPK1) (Green et al, 2008;Kato et al, 2008;Winter et al, 2009), protein kinase B (PKB) (Vaid et al, 2008), and protein kinase G (PKG) (Hopp et al, 2012). These datasets therefore constitute an important resource for future hypotheses on the regulation of protein function by phosphorylation and their implications on host cell entry.…”

“…In vitro phosphorylation assays of PfGAP45 and PfMTIP identified PfCDPK1 as a potential kinase (Green et al, 2008;Kato et al, 2008;Winter et al, 2009). PfCDPK1 is localized at the periphery of the P. falciparum merozoite and is therefore correctly positioned to fulfill such a function (Green et al, 2008).…”

Signalling in malaria parasites – The MALSIG consortium

“…GAP45 is known to be phosphorylated by at least two different kinases, CDPK1 and PKB (Green et al, 2008) (Vaid et al, 2008). MTIP is also phosphorylated by CDPK1 (Kato et al, 2008) (Green et al, 2008) and recently it has been shown in T. gondii that dephosphorylation of GAP45 is a prerequisite for its association with MTIP (Gilk et al, 2009). Thus, phosphorylation/dephosphorylation appears to have a role in controlling motor function.…”

“…The best defined function of Ca 2+ as a second messenger come from studies utilizing transgenic parasites expressing a Ca 2+ reporter in P. berghei gametocytes in which cytosolic Ca 2+ mobilization occurs within seconds once cells are exposed to conditions encountered in the mosquito midgut and is critical for the initiation of gametogenesis (Billker et al, 2004 et al, 2004). PfCDPK1 was originally suggested to be exported to the parasitophorous vacuole in a myristoylation/palmitoylation-dependent manner (Moskes et al, 2004) but more recent studies suggest that it is associated with the parasite plasma membrane and has a role in merozoite egress and invasion (Green et al, 2008;Kato et al, 2008 (Green et al, 2008) and PKB phosphorylates GAP45 (Vaid et al, 2008). Clearly, Ca 2+ -dependent pathways need to be dissected to provide insights of molecular mechanisms underlying parasite development.…”