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Mutagenesis of Key Phosphodiesterases in Toxoplasma gondii Demonstrates the Plasticity and Therapeutic Potential of Cyclic Nucleotide Signaling

ABSTRACT: Cyclic nucleotide signaling is pivotal to the asexual growth of T. gondii; however, little do we know about its counter-regulation in this parasite. We identified 18 phosphodiesterase (PDE1-18) enzymes, most of which form apicomplexan-specific clades and lack typical regulatory motifs found in mammalian PDEs. Genomic epitope-tagging in the tachyzoite stage showed the variable expression of 11 phosphodiesterases with diverse subcellular distribution. Most PDEs can degrade cAMP as well as cGMP with different affinity except for PDE2 which is cAMP-specific. In our extended work, we examined PDE1,2,7-9 for their physiological importance during the lytic cycle. Surprisingly, tachyzoites can tolerate the deletion of PDE1, 7-9 genes with no apparent impairment of the lytic cycle, suggesting remarkable plasticity in the cyclic nucleotide signaling. Co-ablation of PDE1 and PDE2 is detrimental to the parasite growth due to impairment of motility, invasion, egress and replication. The immunogold transmission electron microscopy revealed TgPDE1,2 in the cytomembranes including the inner membrane complex. Not least, we identified a number of proteins that interact with PDE1 and PDE2 and thereby regulate cAMP/cGMP signaling in tachyzoites. In summary, our work lays a strong foundation to decipher the mechanism of cyclic nucleotide signaling and exploit it for therapeutic inhibition of T. gondii.

ORGANISM(S): Cellular Organisms

SUBMITTER: Stefan Tenzer

PROVIDER: PXD032173 | JPOST Repository | Wed Feb 22 00:00:00 GMT 2023

REPOSITORIES: jPOST

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Plasticity and therapeutic potential of cAMP and cGMP-specific phosphodiesterases in Toxoplasma gondii.

Vo Kim Chi KC Ruga Liberta L Psathaki Olympia Ekaterini OE Franzkoch Rico R Distler Ute U Tenzer Stefan S Hensel Michael M Hegemann Peter P Gupta Nishith N

Computational and structural biotechnology journal 20220924

Toxoplasma gondii is a common zoonotic protozoan pathogen adapted to intracellular parasitism in many host cells of diverse organisms. Our previous work has identified 18 cyclic nucleotide phosphodiesterase (PDE) proteins encoded by the parasite genome, of which 11 are expressed during the lytic cycle of its acutely-infectious tachyzoite stage in human cells. Here, we show that ten of these enzymes are promiscuous dual-specific phosphodiesterases, hydrolyzing cAMP and cGMP. TgPDE1 ...[more]

PMID: 36382189

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Project description:Acrodysostosis represents a group of rare genetic disorders characterized by defective skeletal development and is often accompanied by intellectual disabilities. Mutations in the 3’5’cyclic AMP (cAMP)-dependent Protein Kinase (PKA) type I regulatory subunit isoform α (RIα) and phosphodiesterase (PDE) PDE4D have both been implicated in impaired PKA regulation in Acrodysostosis. How mutations on PDEs and RIα interfere with regulation of cAMP-PKA signaling is not understood. cAMP-PKA signaling can be described in two phases. In the activation phase, cAMP binding to RIα dissociates the free C-subunit. PDEs hydrolyze cAMP bound to RIα, priming the cAMP-free RIα for reassociation with the C-subunit, thereby completing one PKA activation cycle. Signal termination is thus critical for resetting PKA to its basal state and promoting adaptation to hormonal hyperstimulation. This proceeds through formation of a transient signal termination RIα:PDE complex that facilitates cAMP channeling from the cAMP-binding domain of RIα to the catalytic site of PDE. Signal termination of cAMP-PKA proceeds in three steps: Step 1) Channeling: Translocation of cAMP from the CNB of RIα to the PDE catalytic site for hydrolysis Step 2) Processivity: Binding of free cAMP from the cytosol at both CNBs of RIα and Step 3) Product (5’AMP) release from the PDE hydrolysis site through competitive displacement by a new molecule of cAMP that trigger subsequent activation cycles of PKA. We have identified the molecular basis for two acrodysostosis mutants, (PDE8 T690P) and RIα (T207A) that both allosterically impair cAMP-PKA signal termination. A combination of amide hydrogen/deuterium exchange mass spectrometry (HDXMS) and Fluorescence Polarization (FP) reveal that PDE8 T690P and RIα T207A both blocked processive hydrolysis of cAMP by interfering with competitive displacement of product 5’AMP release from the nucleotide channel at the end of each round of cAMP hydrolysis. While T690P blocked product 5’AMP release from the PDE, T207A greatly slowed release of substrate from RIα. These results highlight the role of processivity in cAMP hydrolysis by RIα:PDE termination complexes for adaptation to cAMP from GPCR hyperstimulation. Impairment of the signal termination process provides an alternate molecular basis for acrodysostosis.

Project description:Intracellular parasites reprogram the host functions for their survival and reproduction. Conversely, the infected host attempts to defend the microbial insult. The extent and relevance of parasite-mediated host response in vivo remains poorly studied. We utilized Eimeria falciformis, an obligate intracellular parasite completing its entire life cycle in the mouse intestinal epithelium, to identify and validate the host determinants of the parasite infection. The most prominent mouse genes induced during the onset of asexual (24 hrs) and sexual (144 hrs) parasite cycle include IFNg-regulated factors, e.g., immunity-related GTPases IRGA6/B6/D/M2/M3, guanylate-binding proteins GBP2/3/5/8, chemokines CxCL9-11 and several enzymes of the kynurenine pathway including indoleamine 2,3-dioxygenase 1 (IDO1). These results indicated a multifarious innate defense (tryptophan catabolism, IRG, GBP, chemokines signaling) mounted by epithelial cells, and a consequential adaptive immune response (chemokines-cytokines signaling, lymphocyte recruitment). A notable increase in the inflammation- and immunity-associated transcripts correlated with the severity of infection and influx of B-cells, T-cells and macrophages to the parasitized tissue. Indeed, parasite growth was enhanced in the animals inhibited for CxCr3, a major chemokine receptor on immune cells. Interestingly, despite a prominent induction, the mouse IRGB6 failed to recognize and disrupt the parasitophorous vacuole in the parasite cultures, implying an immune evasion by E. falciformis. Likewise, the oocyst output was impaired in IFNg-R-/- and IDO1-/- mice, which signifies a subversion of IFNg-signaling by the parasite to promote its growth. In brief, the Eimeria-rodent model shows contrasting roles of IFNg-signaling for parasite development, identifies a retinue of potential host determinants, and epitomizes its efficacy for in vivo parasite-host interaction studies. Microarray experiments were performed as dual-color hybridizations on Agilent mouse whole genome catalog 44K arrays. To compensate for dye-specific effects, a dye-reversal color-swap was applied.

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Dataset Information

Mutagenesis of Key Phosphodiesterases in Toxoplasma gondii Demonstrates the Plasticity and Therapeutic Potential of Cyclic Nucleotide Signaling

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Publications

Plasticity and therapeutic potential of cAMP and cGMP-specific phosphodiesterases in <i>Toxoplasma gondii</i>.

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