Histone methyltransferase 1 regulates the encystation process in the parasite Giardia lamblia

Abstract

In eukaryotes, histone lysine methylation is associated with either active or repressed chromatin states, depending on the status of methylation. Even when the amino-terminus of Giardia lamblia histones diverges from other organisms, these regions contain lysine residues that are potential targets for methylation. When we examined the role of the histone methyltransferase 1 (HMT1) in the regulation of the encystation process by giardial histone methyltransferase 1 (GlHMT1) overexpression or downregulation, we observed an increase or a decrease in cyst production, respectively, compared to wild-type trophozoites. A time-lapse analysis of encystation showed that overexpression of GlHMT1 induced an earlier and faster process than in wild-type cells together with an upregulation of mRNA expression of cyst wall proteins. Subcellular localization studies indicated that GlHMT1-hemaglutinin was mainly associated with the nuclear and perinuclear region in both growing and encysting parasites, in agreement with bioinformatics analyses showing that GlHMT-1 possesses nuclear localization signals in addition to the classical SU(var)3-9, Enhancer-of-Zeste, Trithorax (SET), and post-SET domains. Altogether, these findings suggest that the function of HMT1 is critical for the success and timing of the encystation process, and reinforce the idea that epigenetic marks are critical for cyst formation in G. lamblia.

Differential protein expression and post-translational modifications in metronidazole-resistant Giardia duodenalis

“…Epigenetic regulation of transcriptional plasticity is implicated in MtzR and its stability, as the encystation–excystation process involves extensive epigenetic remodeling [ 54 ] and restores Mtz susceptibility in formerly MtzR lines [ 19 ]. The lack of a histone H1 linker in Giardia has been proposed to shift reliance to histone modifications for chromatin remodeling and gene regulation [ 91 ], with acetylation and methylation already demonstrated as regulators of chromatin state for key processes of antigen switching and encystation [ 55 , 92 ]. Although widespread changes were detected for KAc and K-MMe modifications between MtzR and MtzS lines, many of these occurred on nonhistone substrates (Fig.…”

Sirtuin GdSir2.4 participates in the regulation of rRNA transcription in the Giardia duodenalis parasite

“…TSA was used to inhibit NAD+‐independent HDACs, NAM was used to inhibit the NAD+‐dependent HDACs or sirtuins, and 3‐deazaneplanocin A (DZNep) was used to inhibit histone methyltransferases (HMTs). TSA and NAM were previously used in this parasite (Carranza et al., 2016; Lagunas‐Rangel et al., 2020), while DZNep was used to target S‐adenosyl methionine‐dependent histone methyltransferases (SAM‐HMTs) in Giardia (Lagunas‐Rangel & Bermúdez‐Cruz, 2019; Reguera et al., 2007; Salusso et al., 2017). DNA methylation was not examined in this work, as it has not been reported in this protozoan (Prucca et al., 2008).…”

“…Specifically, DZNep causes the removal of the repressive histone marks at H3K27me3 and H4K20me3, and allows the derepression of genes (Fujiwara et al., 2014). The presence of several putative histone methyltransferases in the Giardia genome, and the documented ability of Giardia 's HMT1 to promote encystation (Salusso et al., 2017), prompted us to test the effect of DZNep on this protist. Our results show that DZNep inhibits the expression of rRNA in Giardia (Figure 1)––likely by preventing a Giardia HMT from adding the repressive histone methylation marks that in generalwould decrease the expression of a potential repressor of rRNA transcription.…”

Advances in Protozoan Epigenetic Targets and Their Inhibitors for the Development of New Potential Drugs

“…They made a 3D model of GlHMT1 and compared it with the resolved structure of human ASH1 from the PDB database (3OPE), showing a coincidence at the structural level. Afterward, they found overexpression of the GlHMT1 gene during parasite differentiation [182].…”