Toxoplasma gondii Inhibits Covalent Modification of Histone H3 at the IL-10 Promoter in Infected Macrophages

Infection of macrophages with the protozoan parasite Toxoplasma gondii results in inhibition of a large panel of LPS-responsive cytokines, including TNF-α, while leaving others such as IL-10 intact. Recent studies provide evidence that the parasite interferes with chromatin remodeling at the TNF-α promoter that is normally associated with LPS stimulation, but that is not required for TLR4 induction of IL-10. Here, we examined the effect of Toxoplasma on IL-10 induced by simultaneous signaling through TLR4 and FcγR, a combined stimulus that triggers histone H3 covalent modification at the IL-10 promoter resulting in high level IL-10 cytokine production. We show that the parasite inhibits high level IL-10 production and prevents histone H3 Ser¹⁰ phosphorylation and Lys^9/14 acetylation at the IL-10 promoter. These results provide compelling evidence that T. gondii targets the host cell chromatin remodeling machinery to down-regulate cytokine responses in infected macrophages.     

Ellagic acid inhibits adipocyte differentiation through coactivator-associated arginine methyltransferase 1-mediated chromatin modification

Chromatin remodeling is a key mechanism in adipocyte differentiation. However, it is unknown whether dietary polyphenols are epigenetic effectors for adiposity control. Ellagic acid (EA) is a naturally occurring polyphenol in numerous fruits and vegetables. Recently, EA-containing foods have been reported to reduce adiposity. In the present study, we sought to determine whether EA inhibits adipogenesis by modifying chromatin remodeling in human adipogenic stem cells (hASCs). qPCR microarray of chromatin modification enzymes revealed that 10 μmol/L of EA significantly inhibits histone deacetylase (HDAC)9 down-regulation. In addition, EA was associated with up-regulation of HDAC activity and a marked reduction of histone acetylation levels. However, chemical inhibition of HDAC activity or depletion of HDAC9 by siRNA were not sufficient to reverse the antiadipogenic effects of EA. Intriguingly, EA treatment was also associated with reduced histone 3 arginine 17 methylation levels (H3R17me2), implying the inhibitory role of EA in coactivator-associated arginine methyltransferase 1 (CARM)1 activity during adipogenesis. Boosting CARM1 activity by delivering cell-penetrating peptides of CARM1 not only recovered H3R17me2 but also restored adipogenesis evidenced by H3 acetylation at lysine 9, HDAC9 down-regulation, PPARγ expression and triglyceride accumulation. Taken together, our data suggest that reduced CARM1 activity by EA results in a decrease of H3R17me2 levels, which may interrupt consecutive histone remodeling steps for adipocyte differentiation including histone acetylation and HDAC9 dissociation from chromatin. Our work provides the mechanistic insights into how EA, a polyphenol ubiquitously found in fruits and vegetables, attenuates human adipocyte differentiation by altering chromatin remodeling.     

Role of Jade-1 in the histone acetyltransferase (HAT) HBO1 complex

Regulation of global chromatin acetylation is important for chromatin remodeling. A small family of Jade proteins includes Jade-1L, Jade-2, and Jade-3, each bearing two mid-molecule tandem plant homology domain (PHD) zinc fingers. We previously demonstrated that the short isoform of Jade-1L protein, Jade-1, is associated with endogenous histone acetyltransferase (HAT) activity. It has been found that Jade-1L/2/3 proteins co-purify with a novel HAT complex, consisting of HBO1, ING4/5, and Eaf6. We investigated a role for Jade-1/1L in the HBO1 complex. When overexpressed individually, neither Jade-1/1L nor HBO1 affected histone acetylation. However, co-expression of Jade-1/1L and HBO1 increased acetylation of the bulk of endogenous histone H4 in epithelial cells in a synergistic manner, suggesting that Jade1/1L positively regulates HBO1 HAT activity. Conversely, small interfering RNA-mediated depletion of endogenous Jade resulted in reduced levels of H4 acetylation. Moreover, HBO1-mediated H4 acetylation activity was enhanced severalfold by the presence of Jade-1/1L in vitro. The removal of PHD fingers affected neither binding nor mutual Jade-1-HBO1 stabilization but completely abrogated the synergistic Jade-1/1L- and HBO1-mediated histone H4 acetylation in live cells and in vitro with reconstituted oligonucleosome substrates. Therefore, PHDs are necessary for Jade-1/1L-induced acetylation of nucleosomal histones by HBO1. In contrast to Jade-1/1L, the PHD zinc finger protein ING4/5 failed to synergize with HBO1 to promote histone acetylation. The physical interaction of ING4/5 with HBO1 occurred in the presence of Jade-1L or Jade-3 but not with the Jade-1 short isoform. In summary, this study demonstrates that Jade-1/1L are crucial co-factors for HBO1-mediated histone H4 acetylation.     

Chaperone control of the activity and specificity of the histone H3 acetyltransferase Rtt109

Acetylation of Saccharomyces cerevisiae histone H3 on K56 by the histone acetyltransferase (HAT) Rtt109 is important for repairing replication-associated lesions. Rtt109 purifies from yeast in complex with the histone chaperone Vps75, which stabilizes the HAT in vivo. A whole-genome screen to identify genes whose deletions have synthetic genetic interactions with rtt109Delta suggests Rtt109 has functions in addition to DNA repair. We show that in addition to its known H3-K56 acetylation activity, Rtt109 is also an H3-K9 HAT, and we show that Rtt109 and Gcn5 are the only H3-K9 HATs in vivo. Rtt109's H3-K9 acetylation activity in vitro is enhanced strongly by Vps75. Another histone chaperone, Asf1, and Vps75 are both required for acetylation of lysine 9 on H3 (H3-K9ac) in vivo by Rtt109, whereas H3-K56ac in vivo requires only Asf1. Asf1 also physically interacts with the nuclear Hat1/Hat2/Hif1 complex that acetylates H4-K5 and H4-K12. We suggest Asf1 is capable of assembling into chromatin H3-H4 dimers diacetylated on both H4-K5/12 and H3-K9/56.