RESUMEN
The lifecycle progression of the malaria parasite Plasmodium falciparum requires precise tuning of gene expression including histone methylation. The histone methyltransferase PfSET10 was previously described as an H3K4 methyltransferase involved in var gene regulation, making it a prominent antimalarial target. In this study, we investigated the role of PfSET10 in the blood stages of P. falciparum in more detail, using tagged PfSET10-knockout (KO) and -knockdown (KD) lines. We demonstrate a nuclear localization of PfSET10 with peak protein levels in schizonts. PfSET10 deficiency reduces intraerythrocytic growth but has no effect on gametocyte commitment and maturation. Screening of the PfSET10-KO line for histone methylation variations reveals that lack of PfSET10 renders the parasites unable to mark H3K18me1, while no reduction in the H3K4 methylation status could be observed. Comparative transcriptomic profiling of PfSET10-KO schizonts shows an upregulation of transcripts particularly encoding proteins linked to red blood cell remodeling and antigenic variation, suggesting a repressive function of the histone methylation mark. TurboID coupled with mass spectrometry further highlights an extensive nuclear PfSET10 interaction network with roles in transcriptional regulation and mRNA processing, DNA replication and repair, and chromatin remodeling. The main interactors of PfSET10 include ApiAP2 transcription factors, epigenetic regulators like PfHDAC1, chromatin modulators like PfMORC and PfISWI, mediators of RNA polymerase II, and DNA replication licensing factors. The combined data pinpoint PfSET10 as a histone methyltransferase essential for H3K18 methylation that regulates nucleic acid metabolic processes in the P. falciparum blood stages as part of a comprehensive chromatin modulation network.IMPORTANCEThe fine-tuned regulation of DNA replication and transcription is particularly crucial for the rapidly multiplying blood stages of malaria parasites and proteins involved in these processes represent important drug targets. This study demonstrates that contrary to previous reports the histone methyltransferase PfSET10 of the malaria parasite Plasmodium falciparum promotes the methylation of histone 3 at lysine K18, a histone mark to date not well understood. Deficiency of PfSET10 due to genetic knockout affects genes involved in intraerythrocytic development. Furthermore, in the nuclei of blood-stage parasites, PfSET10 interacts with various protein complexes crucial for DNA replication, remodeling, and repair, as well as for transcriptional regulation and mRNA processing. In summary, this study highlights PfSET10 as a methyltransferase affecting H3K18 methylation with critical functions in chromatin maintenance during the development of P. falciparum in red blood cells.
RESUMEN
S-adenosylmethionine synthetase (SAMS) is a key enzyme for the synthesis of the lone methyl donor S-adenosyl methionine (SAM), which is involved in transmethylation reactions and hence required for cellular processes such as DNA, RNA, and histone methylation, but also polyamine biosynthesis and proteostasis. In the human malaria parasite Plasmodium falciparum, PfSAMS is encoded by a single gene and has been suggested to be crucial for malaria pathogenesis and transmission; however, to date, PfSAMS has not been fully characterized. To gain deeper insight into the function of PfSAMS, we generated a conditional gene knockdown (KD) using the glmS ribozyme system. We show that PfSAMS localizes to the cytoplasm and the nucleus of blood-stage parasites. PfSAMS-KD results in reduced histone methylation and leads to impaired intraerythrocytic growth and gametocyte development. To further determine the interaction network of PfSAMS, we performed a proximity-dependent biotin identification analysis. We identified a complex network of 1114 proteins involved in biological processes such as cell cycle control and DNA replication, or transcription, but also in phosphatidylcholine and polyamine biosynthesis and proteasome regulation. Our findings highlight the diverse roles of PfSAMS during intraerythrocytic growth and sexual stage development and emphasize that PfSAMS is a potential drug target.