The Malaria Parasite Cyclic GMP-Dependent Protein Kinase Plays a Central Role in Blood-Stage Schizogony

Abstract

A role for the Plasmodium falciparum cyclic GMP (cGMP)-dependent protein kinase (PfPKG) in gametogenesis in the malaria parasite was elucidated previously. In the present study we examined the role of PfPKG in the asexual blood-stage of the parasite life cycle, the stage that causes malaria pathology. A specific PKG inhibitor (compound 1, a trisubstituted pyrrole) prevented the progression of P. falciparum schizonts through to ring stages in erythrocyte invasion assays. Addition of compound 1 to ring-stage parasites allowed normal development up to 30 h postinvasion, and segmented schizonts were able to form. However, synchronized schizonts treated with compound 1 for >6 h became large and dysmorphic and were unable to rupture or liberate merozoites. To conclusively demonstrate that the effect of compound 1 on schizogony was due to its selective action on PfPKG, we utilized genetically manipulated P. falciparum parasites expressing a compound 1-insensitive PfPKG. The mutant parasites were able to complete schizogony in the presence of compound 1 but not in the presence of the broad-spectrum protein kinase inhibitor staurosporine. This shows that PfPKG is the primary target of compound 1 during schizogony and provides direct evidence of a role for PfPKG in this process. Discovery of essential roles for the P. falciparum PKG in both asexual and sexual development demonstrates that cGMP signaling is a key regulator of both of these crucial life cycle phases and defines this molecule as an exciting potential drug target for both therapeutic and transmission blocking action against malaria.

Global kinomic and phospho-proteomic analyses of the human malaria parasite Plasmodium falciparum

“…Among these 22 ePKs are 8 enzymes that we previously reported as playing a crucial role in asexual proliferation: Pfmap-2 (PF11_0147) 9 , Pfnek-1 (PFL1370w) 10 , PfCK2 (PF11_ 0096) 11 , PfTKL3 (PF13_0258) 12 , Pfcrk-3 (PFD0740w) 13 , PfCLK1 (PF14_0431) 14 , PfCLK2 (PF14_0408) 14 and PfARK1 (PF13_0258) 15 . Others have provided reverse genetics evidence for essentiality of three additional ePKs, PfCDPK1 (PFB0815w) 16 , PfPKG (PF14_ 0346) 17 and PfPCDPK5 (PF13_0211) 18 . Hence, the present study brings to 25 the number of ePKs that are highly likely to have a crucial role in the erythrocytic asexual cycle of P. falciparum (highlighted in bold in Table 1).…”

The kinomes of apicomplexan parasites

“…Compound 1 was subsequently shown to inhibit P. falciparum proliferation in vitro [44]. The effect of Compound 1 on blood-stage schizogony has recently revealed that cGMP signaling and PfPKG play a central role in both asexual and sexual development of P. falciparum [7,45]. The role of PKG in regulating the malaria parasite's life cycle progression has recently been reviewed by Hopp et al (Hopp et al in press, and see pages XX in this issue).…”

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

“…Treatment of P. falciparum ring stage with compound 1 allowed normal development up to 30 h post infection (pi), and segmented schizonts were able to form. Parasites treated only in the schizont stage became dysmorphic, were unable to rupture, and the merozoites released were not invasive (Taylor et al, 2010). Others have found that schizont treatment with compound 1 inhibited processing of the major surface protein 1 (PfMSP1) by the protease subtilisin 1 (PfSUB1), indicating that PKG acts upstream of the protease cascade (Dvorin et al, 2010).…”