Distinct Histone Post-translational Modifications during Plasmodium falciparum Gametocyte Development

Onametostat, a PfPRMT5 inhibitor, exhibits antimalarial activity to Plasmodium falciparum

Protein arginine methyltransferases (PRMTs) play critical roles in Plasmodium falciparum, a protozoan causing the deadliest form of malaria, making them potential targets for novel antimalarial drugs. Here, we screened 11 novel PRMT inhibitors against P. falciparum asexual growth and found that onametostat, an inhibitor for type II PRMTs, exhibited strong antimalarial activity with a half-maximal inhibitory concentration (IC50) value of 1.69 ± 0.04 µM. In vitro methyltransferase activities of purified PfPRMT5 were inhibited by onametostat, and a shift of IC50 to onametostat was found in the PfPRTM5 disruptant parasite line, indicating that PfPRTM5 is the primary target of onametostat. Consistent with the function of PfPRMT5 in mediating symmetric dimethylation of histone H3R2 (H3R2me2s) and in regulating invasion-related genes, onametostat treatment led to the reduction of H3R2me2s level in P. falciparum and caused the defects on the parasite's invasion of red blood cells. This study provides a starting point for identifying specific PRMT inhibitors with the potential to serve as novel antimalarial drugs.

Heterochromatin dynamics during the initial stages of sexual development in Plasmodium falciparum

Asexual replication of Plasmodium falciparum in the human blood results in exponential parasite growth and causes all clinical symptoms of malaria. However, at each round of the replicative cycle, some parasites convert into sexual precursors called gametocytes, which develop through different stages until they become infective to mosquito vectors. The genome-wide distribution of heterochromatin, a type of chromatin generally refractory to gene expression, is identical at all asexual blood stages, but is altered in stage II/III and more mature gametocytes. However, it is not known if these changes occur concomitantly with sexual conversion or at a later time during gametocyte development. Using a transgenic line in which massive sexual conversion can be conditionally induced, we show that the genome-wide distribution of heterochromatin at the initial stages of sexual development (i.e., sexual rings and stage I gametocytes) is almost identical to asexual blood stages, and major changes do not occur until stage II/III. However, we found that at loci with heterochromatin alterations, transcriptional changes associated with sexual development typically precede, rather than follow, changes in heterochromatin occupancy.

Post-Translational Modifications of Proteins of Malaria Parasites during the Life Cycle

Post-translational modifications (PTMs) are essential for regulating protein functions, influencing various fundamental processes in eukaryotes. These include, but are not limited to, cell signaling, protein trafficking, the epigenetic control of gene expression, and control of the cell cycle, as well as cell proliferation, differentiation, and interactions between cells. In this review, we discuss protein PTMs that play a key role in the malaria parasite biology and its pathogenesis. Phosphorylation, acetylation, methylation, lipidation and lipoxidation, glycosylation, ubiquitination and sumoylation, nitrosylation and glutathionylation, all of which occur in malarial parasites, are reviewed. We provide information regarding the biological significance of these modifications along all phases of the complex life cycle of Plasmodium spp. Importantly, not only the parasite, but also the host and vector protein PTMs are often crucial for parasite growth and development. In addition to metabolic regulations, protein PTMs can result in epitopes that are able to elicit both innate and adaptive immune responses of the host or vector. We discuss some existing and prospective results from antimalarial drug discovery trials that target various PTM-related processes in the parasite or host.

Histone code: a common language and multiple dialects to meet the different developmental requirements of apicomplexan parasites

Apicomplexan parasites have complex life cycles, often requiring transmission between two different hosts, facing periods of dormancy within the host or in the environment to maximize chances of transmission. To support survival in these different conditions, tightly regulated and correctly timed gene expression is critical. The modification of histones and nucleosome composition makes a significant contribution to this regulation, and as eukaryotes, the fundamental mechanisms underlying this process in apicomplexans are similar to those in model eukaryotic organisms. However, single-celled intracellular parasites face unique challenges, and regulation of gene expression at the epigenetic level provides tight control for responses that must often be rapid and robust. Here, we discuss the recent advances in understanding the dynamics of histone modifications across Apicomplexan life cycles and the molecular mechanisms that underlie epigenetic regulation of gene expression to promote parasite life cycle progression, dormancy, and transmission.

Ready for renascence in mosquito: The regulation of gene expression in Plasmodium sexual development

Malaria remains one of the most perilous vector-borne infectious diseases for humans globally. Sexual gametocyte represents the exclusive stage at which malaria parasites are transmitted from the vertebrate to the Anopheles host. The feasible and effective approach to prevent malaria transmission is by addressing the sexual developmental processes, that is, gametocytogenesis and gametogenesis. Thus, this review will comprehensively cover advances in the regulation of gene expression surrounding the transmissible stages, including epigenetic, transcriptional, and post-transcriptional control.

MYST regulates DNA repair and forms a NuA4-like complex in the malaria parasite Plasmodium falciparum

Histone lysine acetyltransferase MYST-associated NuA4 complex is conserved from yeast to humans and plays key roles in cell cycle regulation, gene transcription, and DNA replication/repair. Here, we identified a Plasmodium falciparum MYST-associated complex, PfNuA4, which contains 11 of the 13 conserved NuA4 subunits. Reciprocal pulldowns using PfEAF2, a shared component between the NuA4 and SWR1 complexes, not only confirmed the PfNuA4 complex but also identified the PfSWR1 complex, a histone remodeling complex, although their identities are low compared to the homologs in yeast or humans. Notably, both H2A.Z/H2B.Z were associated with the PfSWR1 complex, indicating that this complex is involved in the deposition of H2A.Z/H2B.Z, the variant histone pair that is enriched in the activated promoters. Overexpression of PfMYST resulted in earlier expression of genes involved in cell cycle regulation, DNA replication, and merozoite invasion, and upregulation of the genes related to antigenic variation and DNA repair. Consistently, PfMYST overexpression led to high basal phosphorylated PfH2A (γ-PfH2A), the mark of DNA double-strand breaks, and conferred protection against genotoxic agent methyl methanesulfonate (MMS), X-rays, and artemisinin, the first-line antimalarial drug. In contrast, the knockdown of PfMYST caused a delayed parasite recovery upon MMS treatment. MMS induced the gradual disappearance of PfMYST in the cytoplasm and concomitant accumulation of PfMYST in the nucleus, suggesting cytoplasm-nucleus shuttling of PfMYST. Meanwhile, PfMYST colocalized with the γ-PfH2A, indicating PfMYST was recruited to the DNA damage sites. Collectively, PfMYST plays critical roles in cell cycle regulation, gene transcription, and DNA replication/DNA repair in this low-branching parasitic protist.IMPORTANCEUnderstanding gene regulation and DNA repair in malaria parasites is critical for identifying targets for antimalarials. This study found PfNuA4, a PfMYST-associated, histone modifier complex, and PfSWR1, a chromatin remodeling complex in malaria parasite Plasmodium falciparum. These complexes are divergent due to the low identities compared to their homologs from yeast and humans. Furthermore, overexpression of PfMYST resulted in substantial transcriptomic changes, indicating that PfMYST is involved in regulating the cell cycle, antigenic variation, and DNA replication/repair. Consistently, PfMYST was found to protect against DNA damage caused by the genotoxic agent methyl methanesulfonate, X-rays, and artemisinin, the first-line antimalarial drug. Additionally, DNA damage led to the relocation of cytoplasmic PfMYST to the nucleus and colocalization of PfMYST with γ-PfH2A, the mark of DNA damage. In summary, this study demonstrated that the PfMYST complex has critical functions in regulating cell cycle, antigenic variation, and DNA replication/DNA repair in P. falciparum.

Histone globular domain epigenetic modifications: The regulators of chromatin dynamics in malaria parasite

Plasmodium species adapt a complex lifecycle with multiple phenotypes to survive inside various cell types of humans and mosquitoes. Stage-specific gene expression in the developmental stages of parasites is tightly controlled in Plasmodium species; however, the underlying mechanisms have yet to be explored. Genome organization and gene expression for each stage of the malaria parasite need to be better characterized. Recent studies indicated that epigenetic modifications of histone proteins play a vital role in chromatin plasticity. Like other eukaryotes, Plasmodium species N-terminal tail modifications form a distinct "histone code," which creates the docking sites for histone reader proteins, including gene activator/repressor complexes, to regulate gene expression. The emerging research findings shed light on various unconventional epigenetic changes in histone proteins' core/globular domain regions, which might contribute to the chromatin organization in different developmental stages of the malaria parasite. The malaria parasite lost many transcription factors during evolution, and it is proposed that the nature of local chromatin structure essentially regulates the stage-specific gene expression. This review highlights recent discoveries of unconventional histone globular domain epigenetic modifications and their functions in regulating chromatin structure dynamics in various developmental stages of malaria parasites.

Epigenetic regulation as a therapeutic target in the malaria parasite Plasmodium falciparum

Over the past thirty years, epigenetic regulation of gene expression has gained increasing interest as it was shown to be implicated in illnesses ranging from cancers to parasitic diseases. In the malaria parasite, epigenetics was shown to be involved in several key steps of the complex life cycle of Plasmodium, among which asexual development and sexual commitment, but also in major biological processes like immune evasion, response to environmental changes or DNA repair. Because epigenetics plays such paramount roles in the Plasmodium parasite, enzymes involved in these regulating pathways represent a reservoir of potential therapeutic targets. This review focuses on epigenetic regulatory processes and their effectors in the malaria parasite, as well as the inhibitors of epigenetic pathways and their potential as new anti-malarial drugs. Such types of drugs could be formidable tools that may contribute to malaria eradication in a context of widespread resistance to conventional anti-malarials.

Epigenetic Regulation and Chromatin Remodeling in Malaria Parasites

Plasmodium falciparum, the human malaria parasite, infects two hosts and various cell types, inducing distinct morphological and physiological changes in the parasite in response to different environmental conditions. These variations required the parasite to adapt and develop elaborate molecular mechanisms to ensure its spread and transmission. Recent findings have significantly improved our understanding of the regulation of gene expression in P. falciparum. Here, we provide an up-to-date overview of technologies used to highlight the transcriptomic adjustments occurring in the parasite throughout its life cycle. We also emphasize the complementary and complex epigenetic mechanisms regulating gene expression in malaria parasites. This review concludes with an outlook on the chromatin architecture, the remodeling systems, and how this 3D genome organization is critical in various biological processes.

A type II protein arginine methyltransferase regulates merozoite invasion in Plasmodium falciparum

Protein arginine methyltransferases (PRMTs) regulate many important cellular processes, such as transcription and RNA processing in model organisms but their functions in human malaria parasites are not elucidated. Here, we characterize PfPRMT5 in Plasmodium falciparum, which catalyzes symmetric dimethylation of histone H3 at R2 (H3R2me2s) and R8, and histone H4 at R3 in vitro. PfPRMT5 disruption results in asexual stage growth defects primarily due to lower invasion efficiency of the merozoites. Transcriptomic analysis reveals down-regulation of many transcripts related to invasion upon PfPRMT5 disruption, in agreement with H3R2me2s being an active chromatin mark. Genome-wide chromatin profiling detects extensive H3R2me2s marking of genes of different cellular processes, including invasion-related genes in wildtype parasites and PfPRMT5 disruption leads to the depletion of H3R2me2s. Interactome studies identify the association of PfPRMT5 with invasion-related transcriptional regulators such as AP2-I, BDP1, and GCN5. Furthermore, PfPRMT5 is associated with the RNA splicing machinery, and PfPRMT5 disruption caused substantial anomalies in RNA splicing events, including those for invasion-related genes. In summary, PfPRMT5 is critical for regulating parasite invasion and RNA splicing in this early-branching eukaryote.

Histone lactylation: a new epigenetic axis for host-parasite signalling in malaria?

Epigenetic modifications play important roles in the biology of malaria parasites. The new epigenetic mark histone lactylation, discovered only recently in humans, is also present in malaria parasites. It may have important functions as a key player in the epigenetic repertoire of Plasmodium.