Apically-located P4-ATPase1-Lem1 complex internalizes phosphatidylserine and regulates motility-dependent invasion and egress in Toxoplasma gondii

The membrane asymmetry regulated by P4-ATPases is crucial for the functioning of eukaryotic cells. The underlying spatial translocation or flipping of specific lipids is usually assured by respective P4-ATPases coupled to conforming non-catalytic subunits. Our previous work has identified five P4-ATPases (TgP4-ATPase1-5) and three non-catalytic partner proteins (TgLem1-3) in the intracellular protozoan pathogen, Toxoplasma gondii. However, their flipping activity, physiological relevance and functional coupling remain unknown. Herein, we demonstrate that TgP4-ATPase1 and TgLem1 work together to translocate phosphatidylserine (PtdSer) during the lytic cycle of T. gondii. Both proteins localize in the plasma membrane at the invasive (apical) end of its acutely-infectious tachyzoite stage. The genetic knockout of P4-ATPase1 and conditional depletion of Lem1 in tachyzoites severely disrupt the asexual reproduction and translocation of PtdSer across the plasma membrane. Moreover, the phenotypic analysis of individual mutants revealed a requirement of lipid flipping for the motility, egress and invasion of tachyzoites. Not least, the proximity-dependent biotinylation and reciprocal immunoprecipitation assays demonstrated the physical interaction of P4-ATPase1 and Lem1. Our findings disclose the mechanism and significance of PtdSer flipping during the lytic cycle and identify the P4-ATPase1-Lem1 heterocomplex as a potential drug target in T. gondii.

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

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 and TgPDE9, with a Km of 18 μM and 31 μM, respectively, are primed to hydrolyze cGMP, whereas TgPDE2 is highly specific to cAMP (Km, 14 μM). Immuno-electron microscopy revealed various subcellular distributions of TgPDE1, 2, and 9, including in the inner membrane complex, apical pole, plasma membrane, cytosol, dense granule, and rhoptry, indicating spatial control of signaling within tachyzoites. Notably, despite shared apical location and dual-catalysis, TgPDE8 and TgPDE9 are fully dispensable for the lytic cycle and show no functional redundancy. In contrast, TgPDE1 and TgPDE2 are individually required for optimal growth, and their collective loss is lethal to the parasite. In vitro phenotyping of these mutants revealed the roles of TgPDE1 and TgPDE2 in proliferation, gliding motility, invasion and egress of tachyzoites. Moreover, our enzyme inhibition assays in conjunction with chemogenetic phenotyping underpin TgPDE1 as a target of commonly-used PDE inhibitors, BIPPO and zaprinast. Finally, we identified a retinue of TgPDE1 and TgPDE2-interacting kinases and phosphatases, possibly regulating the enzymatic activity. In conclusion, our datasets on the catalytic function, physiological relevance, subcellular localization and drug inhibition of key phosphodiesterases highlight the previously-unanticipated plasticity and therapeutic potential of cyclic nucleotide signaling in T. gondii.

Nicotinamide Mononucleotide Alleviates Cardiomyopathy Phenotypes Caused by Short-Chain Enoyl-Coa Hydratase 1 Deficiency

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ECHS1 hydrates medium- and short-chain enoyl CoAs and catalyzes the oxidation of fatty acids and branched-chain amino acids.

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The mechanism driving ECHS1 deficiency–associated cardiomyopathy was investigated using conventional biochemistry and molecular biology methods, including immunoprecipitation and polymerase chain reaction.

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Echs1 heterogeneous knockout mice displayed cardiac dysfunction as evaluated by echocardiography.

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ECHS1 deficiency causes cardiomyopathy by enhancing p300-mediated H3K9ac.

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ECHS1 deficiency–induced cardiomyopathy can be prevented using an intervention approach targeting H3K9ac.

Short-chain enoyl-CoA hydratase 1 (ECHS1) deficiency plays a role in cardiomyopathy. Whether ECHS1 deficiency causes or is only associated with cardiomyopathy remains unclear. By using Echs1 heterogeneous knockout (Echs1^+/-) mice, we found that ECHS1 deficiency caused cardiac dysfunction, as evidenced by diffuse myocardial fibrosis and upregulated fibrosis-related genes. Mechanistically, ECHS1 interacts with the p300 nuclear localization sequence, preventing its nuclear translocation in fibroblasts. ECHS1 deficiency promotes p300 nuclear translocation, leading to increased H3K9 acetylation, a known risk factor for cardiomyopathy. Nicotinamide mononucleotide–mediated acetylation targeting suppressed ECHS1 deficiency–induced cardiomyopathy phenotypes in Echs1^+/- mice. Thus, enhancing p300-mediated H3K9ac is a potential interventional approach for preventing ECHS1 deficiency–induced cardiomyopathy.

The protozoan parasite Toxoplasma gondii encodes a gamut of phosphodiesterases during its lytic cycle in human cells

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Toxoplasma genome harbors at least 18 phosphodiesterases encoded by distinct genes.

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Most parasite PDEs lack regulatory modules and are quite divergent from their human orthologs.

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Acutely-infectious tachyzoite stage of T. gondii expresses 11 PDEs with varied localizations.

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PDE8 and PDE9 are closely-related dual-substrate specific proteins residing in the apical pole.

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Homology modeling of PDE8 and PDE9 reveals a conserved 3D topology and substrate pocket.

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PDE9 is dispensable in tachyzoites, signifying a functional redundancy with PDE8.

Cyclic nucleotide signaling is pivotal to the asexual reproduction of Toxoplasma gondii, however little do we know about the phosphodiesterase enzymes in this widespread obligate intracellular parasite. Here, we identified 18 phosphodiesterases (TgPDE1-18) in the parasite genome, most of which form apicomplexan-specific clades and lack archetypal regulatory motifs often found in mammalian PDEs. Genomic epitope-tagging in the tachyzoite stage showed the expression of 11 phosphodiesterases with diverse subcellular distributions. Notably, TgPDE8 and TgPDE9 are located in the apical plasma membrane to regulate cAMP and cGMP signaling, as suggested by their dual-substrate catalysis and structure modeling. TgPDE9 expression can be ablated with no apparent loss of growth fitness in tachyzoites. Likewise, the redundancy in protein expression, subcellular localization and predicted substrate specificity of several other PDEs indicate significant plasticity and spatial control of cyclic nucleotide signaling during the lytic cycle. Our findings shall enable a rational dissection of signaling in tachyzoites by combinatorial mutagenesis. Moreover, the phylogenetic divergence of selected Toxoplasma PDEs from human counterparts can be exploited to develop parasite-specific inhibitors and therapeutics.

Tumor stroma-derived factors skew monocyte to dendritic cell differentiation toward a suppressive CD14+ PD-L1+ phenotype in prostate cancer

Tumor-associated stromal myofibroblasts are essential for the progression and metastatic spread of solid tumors. Corresponding myeloid cell infiltration into primary tumors is a negative prognostic factor in some malignancies. The aim of this study was to define the exact role of stromal myofibroblasts and stromal factors in early prostate carcinoma (PCa) regulating monocyte infiltration and differentiation into dendritic cells (DCs). Epithelial and stromal primary cultures were generated from PCa biopsies and their purity confirmed. Stromal cells produced significantly more of the (C-C) motif chemokine ligand 2 (CCL2), interleukin 6 (IL-6) and transforming growth factor β (TGFβ) than epithelial cells. Monocyte chemoattraction was predominantly due to stromal-derived factors, mainly CCL2. DCs generated in the presence of stromal (but not epithelial) factors upregulated CD209, but failed to downregulate the monocyte marker CD14 in a signal transducer and activator of transcription 3 (STAT3)-dependent manner. Monocytes exposed to stromal factors did not produce detectable amounts of IL-10, however, upon lipopolysaccharide stimulation, stromal factor generated dendritic cells (sDC) produced significantly more IL-10 and less IL-12 than their conventional DC counterparts. sDC failed to cross-present tumor-antigen to CD8⁺ T cells and suppressed T-cell proliferation. Most importantly, sDC expressed significantly elevated levels of programmed cell death ligand-1 (PD-L1) in a primarily STAT3 and IL-6-dependent manner. In parallel with our findings in vitro, tumor-infiltrating CD14⁺ cells in situ were found to express both PD-L1 and CD209, and a higher percentage of tumor-associated CD3⁺ T cells expressed programmed cell death-1 (PD-1) molecules compared to T cells in blood. These results demonstrate a hitherto undescribed, fundamental contribution of tumor-associated stromal myofibroblasts to the development of an immunosuppressive microenvironment in early PCa.