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PLoS Biol. 2018 Sep 12;16(9):e2005642. doi: 10.1371/journal.pbio.2005642. eCollection 2018 Sep.

Protein kinase A negatively regulates Ca2+ signalling in Toxoplasma gondii.

Author information

1
The Walter and Eliza Hall Institute of Medical Research, Parkville, Australia.
2
Department of Medical Biology, The University of Melbourne, Parkville, Australia.
3
School of Medicine, Tsinghua University, Beijing, China.
4
Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom.
5
Institute of Advanced Biosciences, CNRS UMR5309, INSERM U1209, Université Grenoble Alpes, Grenoble, France.
6
Research School of Biology, The Australian National University, A.C.T., Australia.
7
Department of Biochemistry and Molecular Biology, Molecular Science and Biotechnology Institute, The University of Melbourne, Parkville, Australia.

Abstract

The phylum Apicomplexa comprises a group of obligate intracellular parasites that alternate between intracellular replicating stages and actively motile extracellular forms that move through tissue. Parasite cytosolic Ca2+ signalling activates motility, but how this is switched off after invasion is complete to allow for replication to begin is not understood. Here, we show that the cyclic adenosine monophosphate (cAMP)-dependent protein kinase A catalytic subunit 1 (PKAc1) of Toxoplasma is responsible for suppression of Ca2+ signalling upon host cell invasion. We demonstrate that PKAc1 is sequestered to the parasite periphery by dual acylation of PKA regulatory subunit 1 (PKAr1). Upon genetic depletion of PKAc1 we show that newly invaded parasites exit host cells shortly thereafter, in a perforin-like protein 1 (PLP-1)-dependent fashion. Furthermore, we demonstrate that loss of PKAc1 prevents rapid down-regulation of cytosolic [Ca2+] levels shortly after invasion. We also provide evidence that loss of PKAc1 sensitises parasites to cyclic GMP (cGMP)-induced Ca2+ signalling, thus demonstrating a functional link between cAMP and these other signalling modalities. Together, this work provides a new paradigm in understanding how Toxoplasma and related apicomplexan parasites regulate infectivity.

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