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Altered expression of K13 disrupts DNA replication and repair in Plasmodium falciparum

ABSTRACT: Background: Plasmodium falciparum has evolved resistance to the artemisinin component of the frontline antimalarial treatment Artemisinin-based Combination Therapy in South East Asia. Millions of lives will be at risk if resistance spreads to Africa. Single non-synonymous mutations in the propeller region of PF3D7_1343700, “K13”are implicated in resistance. In this work, we use transcriptional profiling to characterize a laboratory-generated k13 insertional mutant previously demonstrated to have increased sensitivity to artemisinins to explore the functional role of k13. Results: A set of RNA-seq and microarray experiments confirmed that the expression profile of k13 is specifically altered during the early ring and early trophozoite stages of the mutant intraerythrocytic development cycle. The down-regulation of k13 in this mutant during the early ring stage is associated with a transcriptome shift towards a more trophozoite-like state. To discover the specific downstream effect of k13 dysregulation, we developed a new computational method to search for differential gene expression while accounting for the temporal sequence of transcription. We found that the strongest biological signature of the transcriptome shift is an up-regulation of DNA replication and repair genes during the early ring developmental stage and a down-regulation of DNA replication and repair genes during the early trophozoite stage; by contrast, the expressions of housekeeping genes are unchanged. This effect, due to k13 dysregulation, is antagonistic, such that k13 levels are negatively correlated with DNA replication and repair gene expression. Conclusion: Because a hypothesized mode of action of artemisinins is oxidative stress our results support a role for k13 as a stress response regulator, consistent with the role of its human homolog Keap1, that regulates DNA replication and repair genes in response to oxidative stress.

ORGANISM(S): Plasmodium falciparum

PROVIDER: GSE119231 | GEO | 2018/10/25

REPOSITORIES: GEO

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Project description:Plasmodium falciparum, the most pathogenic human malaria parasite, infects millions of human beings and causes a serious public health threat. Currently, the most potent anti-malarial drugs are artemisinin and its derivatives1,2. Artemisinin is a sesquiterpene lactone with an endoperoxide bridge3. The activation of artemisinin requires the cleavage of the endoperoxide bridge in the presence of iron sources4. Once activated, artemisinins are converted into highly reactive carbon-centered radicals5,6 that attack macromolecules through alkylation and propagate a series of damages, eventually leading to parasite death7,8. Even though several parasite proteins have been reported as the targets of artemisinin9,10, the exact mechanism of artemisinin action is still controversial and its high potency and specificity against the malaria parasite could not be fully accounted. Here, we have developed an unbiased chemical proteomics approach to directly probe the mechanism of action of artemisinin in P. falciparum in situ. An alkyne-tagged artemisinin analogue coupled with biotin enables selective purification and identification of 124 artemisinin covalent-binding protein targets, many of which are involved in essential biological processes of the parasite. In vitro assays confirm the specific artemisinin binding and inhibition of selected targets. Such a broad targeting spectrum disrupts the biochemical landscape of the parasite and causes its death. Furthermore, using the alkyne-tagged artemisinin coupled with a fluorescent dye to monitor its protein binding, we showed that heme, rather than free ferrous iron, is predominantly responsible for artemisinin activation. The extremely high level of heme released from the hemoglobin digestion by the parasite make artemisinin exceptionally potent against late-stage parasites (trophozoite and schizont stages) compared to parasites at early ring stage, which have low level of heme, mainly from endogenous synthesis. The ‘blood eating’ nature of the parasite with the release of large amounts of heme confers artemisinin with extremely high specificity against the parasites, with minimum side effects towards healthy red blood cells. Taken together, our results established a unifying model to explain the action and specificity of artemisinin in parasite killing. Our findings could facilitate the development of better alternative strategies to treat malaria in times of emerging artemisinin resistance11,12.

Project description:Control of malaria is threatened by emerging parasite resistance to artemisinin drug (ART) therapies. The molecular details of how Plasmodium malaria parasites response to ART and how this relates to resistance is not clear. To determine how parasites respond to ART by altering gene expression, we performed a transcriptomic study of dihydroartemisinin (DHA) response in P. falciparum K1 strain and in P. berghei ANKA strain. Microarray data from DHA-treated P. falciparum trophozoite stage parasites were compared with data from other ART treatments. Genes with consistent changes in expression were identified, which includes notably down-regulation of cytosolic ribosomal protein genes. RNA-seq data revealed a similar pattern of transcriptomic change, although the pattern was much clearer in that more than one-third of P. falciparum trophozoite genes are differentially expressed with greater statistical support for down-regulation of ribosomal protein genes. The poor overlap of differentially-expressed genes between microarray and RNA-seq and less-well defined patterns for the former suggests that the accuracy of microarray is limited by technological bias. The trophozoite response to DHA is overall âring-likeâ and less âtrophozoite-likeâ, which is consistent with previous findings that Plasmodium can enter a quiescent ring-like state to resist ART. RNA-seq data from DHA-treated P. falciparum rings reveal a more muted response, although there is considerable overlap of differentially expressed genes with DHA-treated trophozoites. In contrast, P. falciparum schizonts are unresponsive to DHA, suggesting that the protective response acts mainly to arrest parasite development through the G2/M checkpoint. The transcriptional response of P. berghei to DHA treatment in vivo in infected mice is strikingly similar to the P. falciparum in vitro ring and trophozoite responses, in which ribosomal protein genes are notably down-regulated. These results suggest Plasmodium species respond to DHA in the same way. This knowledge could be applied to outwit the parasite to deliver more effective artemisinin therapies, and maybe hinder the development of drug resistance. Two condition drug-treatment experiment, Dihydroartemisinin vs. Vehicle control treatment with matched reference untreated controls. Biological replicates: 5 independently grown and harvested experimental culture replicates. One replicate of treatment/reference time-point per array.

Project description:Control of malaria is threatened by emerging parasite resistance to artemisinin drug (ART) therapies. The molecular details of how Plasmodium malaria parasites response to ART and how this relates to resistance is not clear. To determine how parasites respond to ART by altering gene expression, we performed a transcriptomic study of dihydroartemisinin (DHA) response in P. falciparum K1 strain and in P. berghei ANKA strain. Microarray data from DHA-treated P. falciparum trophozoite stage parasites were compared with data from other ART treatments. Genes with consistent changes in expression were identified, which includes notably down-regulation of cytosolic ribosomal protein genes. RNA-seq data revealed a similar pattern of transcriptomic change, although the pattern was much clearer in that more than one-third of P. falciparum trophozoite genes are differentially expressed with greater statistical support for down-regulation of ribosomal protein genes. The poor overlap of differentially-expressed genes between microarray and RNA-seq and less-well defined patterns for the former suggests that the accuracy of microarray is limited by technological bias. The trophozoite response to DHA is overall “ring-like” and less “trophozoite-like”, which is consistent with previous findings that Plasmodium can enter a quiescent ring-like state to resist ART. RNA-seq data from DHA-treated P. falciparum rings reveal a more muted response, although there is considerable overlap of differentially expressed genes with DHA-treated trophozoites. In contrast, P. falciparum schizonts are unresponsive to DHA, suggesting that the protective response acts mainly to arrest parasite development through the G2/M checkpoint. The transcriptional response of P. berghei to DHA treatment in vivo in infected mice is strikingly similar to the P. falciparum in vitro ring and trophozoite responses, in which ribosomal protein genes are notably down-regulated. These results suggest Plasmodium species respond to DHA in the same way. This knowledge could be applied to outwit the parasite to deliver more effective artemisinin therapies, and maybe hinder the development of drug resistance.

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Altered expression of K13 disrupts DNA replication and repair in Plasmodium falciparum

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