# Regulation of host cell egress by Toxoplasma gondii

> **NIH NIH R01** · WASHINGTON UNIVERSITY · 2022 · $621,648

## Abstract

Project Summary/Abstract
Active motility by apicomplexan parasites controls host cell invasion and egress, steps that are critical to the
intracellular cycle of infection. These processes are governed by calcium-regulated secretion of adhesive
proteins from micronemes, together with the concerted action of an actin-myosin motor that lies beneath the
parasite plasma membrane. Prior studies in Toxoplasma gondii have established the importance of calcium-
dependent protein kinases and protein kinase G (PKG) in controlling microneme secretion, motility, egress,
and invasion. This cascade is tightly regulated and recent studies have also shown that the c1 isoform of
protein kinase A (PKAc1) dampens calcium signaling to shut down microneme secretion and impair motility
after invasion is complete. The balance between PKG vs. PKAc1 activities governs the decision to activate
motility and promote egress vs. to remain intracellular. Although the role of PKAc1 in blocking premature
egress is clear, neither its mechanism of regulation nor the targets that it phosphorylates in order to dampen
calcium signaling and block egress have been elucidated. PKA activity is governed by production of cyclic
AMP (cAMP) by adenylate cyclases (ACs) and its consumption by phosphodiesterases (PDEs). In preliminary
studies, we have identified candidate ACs that control cAMP levels to regulate PKA. In the proposed studies,
we will explore their functions to define how they temporally and spatially regulate PKA activity. We have also
used a protein degradation approach to create conditional knockdowns of PKA isoforms and verify that PKAc1
controls egress in type II parasites. We will use the tightly regulated conditional knockdown approach to
investigate downstream targets of PKAc1 that mediate the egress block using a combination of
phosphoproteomic studies to identify substrates and downstream validation studies to test their roles in
regulating egress. We will validate the role of specific phosphorylation sites in PKAc1 targets in suppressing
calcium signaling, motility, and egress. Collectively, the proposed studies will elucidate the molecular pathway
by which PKAc1 down regulates calcium levels, microneme secretion, and motility to prevent egress, thus
counterbalancing the activating effects of PKG. Elucidating the molecular regulation of the PKG/PKA kinases in
T. gondii will foster future studies to design inhibitors that block these pathways, thus providing new avenues
for development of therapeutics.

## Key facts

- **NIH application ID:** 10441782
- **Project number:** 1R01AI162749-01A1
- **Recipient organization:** WASHINGTON UNIVERSITY
- **Principal Investigator:** L. David Sibley
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $621,648
- **Award type:** 1
- **Project period:** 2022-06-07 → 2027-05-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10441782

## Citation

> US National Institutes of Health, RePORTER application 10441782, Regulation of host cell egress by Toxoplasma gondii (1R01AI162749-01A1). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10441782. Licensed CC0.

---

*[NIH grants dataset](/datasets/nih-grants) · CC0 1.0*