Garcinol Inhibits GCN5-Mediated Lysine Acetyltransferase Activity and Prevents Replication of the Parasite Toxoplasma gondii

Abstract

Lysine acetylation is a critical posttranslational modification that influences protein activity, stability, and binding properties. The acetylation of histone proteins in particular is a well-characterized feature of gene expression regulation. In the protozoan parasite Toxoplasma gondii, a number of lysine acetyltransferases (KATs) contribute to gene expression and are essential for parasite viability. The natural product garcinol was recently reported to inhibit enzymatic activities of GCN5 and p300 family KATs in other species. Here we show that garcinol inhibits TgGCN5b, the only nuclear GCN5 family KAT known to be required for Toxoplasma tachyzoite replication. Treatment of tachyzoites with garcinol led to a reduction of global lysine acetylation, particularly on histone H3 and TgGCN5b itself. We also performed transcriptome sequencing (RNA-seq), which revealed increasing aberrant gene expression coincident with increasing concentrations of garcinol. The majority of the genes that were most significantly affected by garcinol were also associated with TgGCN5b in a previously reported chromatin immunoprecipitation assay with microarray technology (ChIP-chip) analysis. The dysregulated gene expression induced by garcinol significantly inhibits Toxoplasma tachyzoite replication, and the concentrations used exhibit no overt toxicity on human host cells. Garcinol also inhibits Plasmodium falciparum asexual replication with a 50% inhibitory concentration (IC 50 ) similar to that for Toxoplasma. Together, these data support that pharmacological inhibition of TgGCN5b leads to a catastrophic failure in gene expression control that prevents parasite replication.

Chemical and Biological Aspects of Garcinol and Isogarcinol: Recent Developments

“…Garcinol treatment led to decreased levels of acetylated histone H3 of TgGCN5b and to an inhibition of replication (IC 50 =1.7 μM). Similar replication inhibitory effects were observed for the malaria parasite Plasmodium falciparum (IC 50 =1.69 μM for chloroquine‐sensitive HB3 strains, and IC 50 =2.05 μM for chloroquine‐resistant Dd2 strains; inhibition of erythrocytic asexual replication) …”

“…Similar replication inhibitory effects were observed for the malaria parasite Plasmodium falciparum (IC 50 = 1.69 μM for chloroquine-sensitive HB3 strains, and IC 50 = 2.05 μM for chloroquine-resistant Dd2 strains; inhibition of erythrocytic asexual replication). [63]…”

“…Inhibition of PCAF and GCN5 Bacillus anthracis [62] Antidote for LT intoxication Reduction of stress-fiber formation Candida albicans [15] Induction of apoptosis, inhibition of biofilm formation -Toxoplasma gondii [63] Inhibition of replication Inhibition of TgGCN5b…”

Bromodomains in Protozoan Parasites: Evolution, Function, and Opportunities for Drug Development

“…We may be able to add infections caused by protozoan parasites to this list, as genetic studies have shown that most parasite bromodomain proteins are crucial for viability and virulence. Some studies have already begun to examine the effects of bromodomain inhibitors against these protozoan parasites, and these complement previous work showing the antiparasitic activities of KAT and KDAC inhibitors (55)(56)(57)(58)(59)(60)(61)(62)(63).…”

Review of Experimental Compounds Demonstrating Anti-Toxoplasma Activity

“…Host cell toxicity remains a concern with compound 34; the TD 50 for human host cells is less than 10 times greater than the IC 50 for T. gondii, but compound 35 seems to fare better on host cells with a TD 50 of Ͼ10 M in HS68 cells (74,77) (Table 1). Garcinol, derived from the Garcinia indica fruit, is another compound that affects histone acetylation, targeting a family of lysine acetyltransferases (KAT) enzymes required for T. gondii tachyzoites to replicate successfully (78). Additionally, other (nonhistone) substrates of these compounds may be affected, contributing to the overall host cell toxicity and to the efficacy of the compound against the parasite (79).…”