Hsu, D.-W. | Search bioRxiv

bioRxiv2020

Methylation-directed Acetylation of Histone H3 Regulates Developmental Sensitivity to Histone Deacetylase Inhibition

BackgroundTreatment of cells with hydroxamate-based lysine deacetylase inhibitors (KDACis) such as Trichostatin A (TSA) can induce biological effects such as differentiation or apoptosis of cancer cells, and a number of related compounds have been approved for clinical use. TSA treatment induces rapid initial acetylation of histone 3 (H3) proteins which are already modified by tri-methylation on lysine 4 (H3K4me3) while acetylation of bulk histones, lacking this mark, is delayed. Sgf29, a subunit of the SAGA acetyltransferase complex, interacts with H3K4me3 via a tandem tudor domain (TTD) and has been proposed to target the acetyltransferase activity to H3K4me3. However the importance of acetylation of this pool of H3 in the biological consequences of KDACi treatment is not known. ResultsWe investigated the role of H3K4me3-directed acetylation in the mechanism of action of TSA on inhibiting development of the eukaryotic social amoeba Dictyostelium discoideum. Loss of H3K4me3 in strains with mutations in the gene encoding Set1 or the histone proteins confers resistance to TSA-induced inhibition of development and delays accumulation of histone acetylation on H3K9 and K14. A candidate orthologue of Sgf29 in Dictyostelium has been identified which specifically recognizes the H3K4me3 modification via its tandem Tudor domain (TTD). Disruption of the gene encoding Sgf29 delayed accumulation of H3K9Ac, abolished targeted H3K4me3-directed H3Ac and led to developmental resistance to TSA, which is dependent on a functional TTD. TSA resistance also results from overexpression of Sgf29. ConclusionPreferential acetylation of H3K4me3 histones, regulated by Sgf29 via its TTD, is important in developmental sensitivity to TSA. Levels of H3K4me3 or Sgf29 will provide useful biomarkers for sensitivity to this class of chemotherapeutic drug.

pharmacology and toxicology↗

bioRxiv2019

Plant A20/AN1 proteins coordinate different immune responses including RNAi pathway for antiviral immunity

Salicylic acid (SA)-mediated immunity plays important roles in combating virus in plants. Two plant stress associated protein (SAPs) containing dual A20/AN1 zinc-finger domain were found to play important roles in SA-mediated immunity; however, detailed mechanisms remain elusive. In this study, another orchid homolog gene of Pha13, Pha21, was analyzed. Pha21 confers antiviral immunity in both transgenic orchid and Arabidopsis overexpressing Pha21. Expression of Pha21 is early-induced by SA treatment, and is involved in the expression of the orchid homolog of the master regulator NPR1. Pha21 but not Pha13 is involved in the expression of key RNAi-related genes, Dicer-like nuclease 4 (DCL4) and Argonaut 1 (AGO1) in orchids. The involvement of SAPs in expression of orchid DCL4 and AGO1 is not limited to orchid, as AtSAP5 also plays essential role in the expression of Arabidopsis DCL4 and AGO1. However, unlike Pha13 and AtSAP5, Pha21 does not play positive role in the expression of orchid homolog gene of RNA-dependent RNA polymerase 1 (RdR1), an important gene in RNAi pathway. Pha21 can be found localized in the nucleus, and confers self-E3 ligase and ubiquitin binding activities. Functional domain analysis revealed that both A20 and AN1 domains of Pha21 are required for decreasing virus accumulation, and the AN1 domain plays a more important role in the expression of orchid DCL4. Collectively, our data suggests SA regulated SAPs play important roles in antiviral immunity and is involved in delicate regulation of key genes in RNAi-mediated pathway.\n\nIMPORTANCESalicylic acid (SA)-mediated antiviral immunity plays an important role to protect plants from virus infection; however, the detailed mechanisms remain elusive. We previously demonstrated that two plant A20/AN1 proteins, orchid Pha13 and Arabidopsis AtSAP5, function similarly and serve as an important hub to regulate SA-mediated antiviral immunity. In this study, we identified another orchid A20/AN1 protein, Pha21, which is involved in SA-mediated antiviral immunity. In contrast to Pha13 and AtSAP5, Pha21 plays minor negative roles in the expression of PhaRdR1 (orchid homolog of RNA-dependent RNA polymerase 1). However, Pha21 and AtSAP5, but not Pha13, are involved in the expression of important players in RNAi pathway, Dicer-like nuclease 4 (DCL4) and Argonaut 1 (AGO1), in orchid and Arabidopsis. Our data demonstrates that plant A20/AN1 proteins are conserved players in SA-mediated antiviral resistance among plants, and provide links between the A20/AN1 proteins and the RNAi pathway.

plant biology↗