Double-stranded RNA-mediatedgene silencing of cysteine proteases (falcipain-1 and-2) of Plasmodium falciparum

Malaria remains a public health problem of enormous magnitude,affecting over 500 million people every year. Lack of success inthe past in the development of new drug/vaccines has mainlybeen attributed to poor understanding of the functions of differentparasite proteins. Recently, RNA interference (RNAi) has emergedas a simple and incisive technique to study gene functions in avariety of organisms. In this study, we report the results of RNAiby double-stranded RNA of cysteine protease genes (falcipain -1and -2) in the malaria parasite, Plasmodium falciparum. UsingRNAi directed towards falcipain genes, we demonstrate that blockingthe expression of these genes results in severe morphologicalabnormalities in parasites, inhibition of parasite growth invitro and substantial -accumulation of haemoglobinin the parasite. The inhibitory effects produced by falcipain double-stranded(ds)RNAs are reminiscent of the effects observed upon administeringE-64, a cysteine protease inhibitor. The parasites treated withfalcipain's dsRNAs also show marked reduction in the levelsof corresponding endogenous falcipain mRNAs. We also demonstratethat dsRNAs of falcipains are -broken into short interferenceRNAs approximate to 25 nucleotides in size, a characteristic of RNAi,which in turn activates sequence-specific nuclease activity in the malariaparasites. These results thus provide more evidence for the existenceof RNAi in P. falciparum and also suggest possibilities forusing RNAi as an effective tool to determine the functions of thegenes identified from the P. falciparum genome sequencing project.