# Toxoplasma gondii cAMP-dependent kinase PKAc3 regulation of bradyzoite formation

> **NIH NIH R21** · UNIVERSITY OF SOUTH FLORIDA · 2020 · $186,875

## Abstract

SUMMARY
 Toxoplasma gondii is a protozoan parasite that is responsible for encephalitis in people
with AIDS. Clinical disease is due to unchecked proliferation of tachyzoite forms that replicate
rapidly within nearly all nucleated cells. When infection is controlled by the immune system,
tachyzoites differentiate into bradyzoites that persist within tissue cysts. Bradyzoites may later
reactivate and cause clinical disease in immunocompromised individuals including people living
with HIV. During T. gondii replication within host cells, the parasite implements a coordinated
pattern of sequential gene expression. In response to stress, the parasite alters its metabolism,
surface antigens, and cell cycle to transition from tachyzoite to bradyzoite. Bradyzoites persist
for the lifetime of an infected host and are refractory to treatments that eliminate the tachyzoites.
cAMP signaling via cAMP-dependent kinase (PKA) is a conserved pathway that regulates
metabolism and stress responses in most eukaryotes. Using the CRISPR/Cas9 system, we
disrupted PKAc3, one of the isoforms of the catalytic subunit of the T. gondii PKA, and showed
that it is a negative regulator of the tachyzoite-bradyzoite transition. Parasite strains lacking
PKAc3 have constitutive differentiation to bradyzoite forms. We hypothesize that cAMP
signaling leads to phosphorylation of substrates by PKAc3, promoting tachyzoite growth and
repression of bradyzoite genes. We propose that the major mechanism for PKAc3 regulation of
the bradyzoite program is via modulation of tachyzoite chromatin accessibility and regulation of
the activity of repressor(s) of bradyzoite gene expression. Therefore, we plan to identify
substrates of PKAc3 that act as transcriptional repressors and chromatin structure modifiers that
regulate the bradyzoite developmental program using a combined proteomics and genetics
approach. We will use comparative phosphoproteomics to identify candidate PKAc3 substrates.
In addition, we will compare the phophoproteome and gene expression of Type I and Type II
parasites and mutants lacking PKAc3, to determine if we can identify differences in gene
expression or phosphorylation patterns that provide a mechanism for the differential ability of
Type I and Type II strains to differentiate into bradyzoite forms. Finally, to link gene expression
to PKAc3 activity, we will test the hypothesis that candidate chromatin factors and AP2 factors
regulate bradyzoite gene expression in a PKAc3 dependent manner.

## Key facts

- **NIH application ID:** 9984260
- **Project number:** 5R21AI148374-02
- **Recipient organization:** UNIVERSITY OF SOUTH FLORIDA
- **Principal Investigator:** Kami Kim
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $186,875
- **Award type:** 5
- **Project period:** 2019-08-01 → 2022-07-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9984260

## Citation

> US National Institutes of Health, RePORTER application 9984260, Toxoplasma gondii cAMP-dependent kinase PKAc3 regulation of bradyzoite formation (5R21AI148374-02). Retrieved via AI Analytics 2026-05-27 from https://api.ai-analytics.org/grant/nih/9984260. Licensed CC0.

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