GCN5-mediated transcription in AIDS pathogen Toxoplasma

Project: Research project

Project Details


Epigenetics and histone modifications play key roles in the pathogenic processes of protozoal parasites.
We have made several important observations regarding histone acetylation in the AIDS opportunist,
Toxoplasma gondii. Using chromatin immunoprecipitation (ChIP), we found that histone acetylation
correlates with gene expression pertinent to parasite differentiation, the process that underlies
pathogenesis. While characterizing the GCN5-family histone acetyltransferase (HAT), we discovered
that Toxoplasma harbors a second GCN5 HAT (named TgGCN5-A and -B, respectively). While both
TgGCN5s mediate the histone acetylation that we have linked to parasite differentiation, these HATs
possess unique N-terminal extensions, implying they have independent roles in regulating gene
expression. We have established that the N-terminal extensions are critical for nuclear localization and
protein-protein interactions. Furthermore, our yeast two-hybrid screen with the N-terminal extension of
TgGCN5-A has revealed unique parasite-specific interacting proteins that have domains typical of
transcription regulators. To begin addressing the cellular roles of each TgGCN5, we have attempted to
generate gene knockouts. We have established that TgGCN5-A is not required for tachyzoite
replication, but may be involved in differentiation or reactivation of latent infection. Our preliminary data
also suggests that TgGCN5-B may be essential for parasite viability. In short, GCN5-mediated histone
acetylation is not only relevant to understanding parasite differentiation, but also holds promise as a
drug target. We hypothesize that the two TgGCN5 HATs play key independent roles in Toxoplasma
pathogenesis by forming distinct complexes with novel proteins that regulate gene expression. Our
specific aims include (1) Determine the roles of TgGCN5 HATs in pathogenesis; (2) Elucidate
differences in TgGCN5 complexes by identifying proteins that bind to the unique N-terminal extensions;
(3) Define the mechanism by which each TgGCN5 is recruited to target gene promoters. The proposed
research expands our previous work and capitalizes on the novel reagents, techniques, and GCN5
transgenic parasites that we have developed. The results will have a positive impact on the field by
defining mechanisms of GCN5-mediated gene regulation and by revealing components of the parasite s
transcriptional regulatory circuitry that have significant value as potential drug targets. Thus, our results
will fundamentally advance the fields of parasitology and eukaryotic gene expression.
Effective start/end date12/1/014/30/16


  • National Institutes of Health: $380,990.00
  • National Institutes of Health: $307,838.00
  • National Institutes of Health: $354,549.00
  • National Institutes of Health: $307,838.00
  • National Institutes of Health: $377,180.00
  • National Institutes of Health: $377,180.00


  • Medicine(all)
  • Immunology and Microbiology(all)

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