Biology subjects

Moreno, S. N.

Publications and source records attributed to Moreno, S. N..

3 recordsLinked to original sources

bioRxiv2024

Calcium tunneling through the entoplasmic reticulum and transfer to other organelles for optimal signaling in Toxoplasma gondii

Ca2+ signaling in cells begins with the opening of Ca2+ channels in either the plasma membrane (PM) or endoplasmic reticulum (ER), leading to a sharp increase of the physiologically low (<100 nM) cytosolic Ca2+ level. The temporal and spatial regulation of Ca{superscript 2} is crucial for the precise activation of key biological processes. In the apicomplexan parasite Toxoplasma gondii, which infects approximately one-third of the global population, Ca{superscript 2} signaling governs essential aspects of the parasites infection cycle. T. gondii relies on Ca{superscript 2} signals to regulate pathogenic traits, with several Ca{superscript 2}-signaling components playing critical roles. Ca2+ entry from the extracellular environment has been demonstrated in T. gondii for both, extracellular parasites, exposed to high Ca2+, and intracellular parasites, which acquire Ca{superscript 2} from host cells during host Ca{superscript 2} signaling events. Active egress, an essential step of the parasites infection cycle, is preceded by a large increase in cytosolic Ca2+, most likely initiated by release from intracellular stores. However, extracellular Ca2+ is also necessary to reach a cytosolic Ca2+ threshold required for timely egress. In this study, we investigated the mechanism of Ca{superscript 2} intracellular store replenishment and identified a central role for the SERCA-Ca2+-ATPase in maintaining Ca{superscript 2} homeostasis not only within the ER but also in other organelles. We demonstrate mitochondrial Ca2+ uptake, which occurs by transfer of Ca2+ from the ER, likely through membrane contact sites. Our findings suggest that the T. gondii ER plays a key role in sequestering and redistributing Ca{superscript 2} to intracellular organelles following Ca{superscript 2} influx at the PM. HIGHLIGHTSThe T. gondii ER takes up Ca2+ that enters the cytosol from the extracellular milieu. Filling of acidic stores in T. gondii depends on ER Ca{superscript 2} content. The mitochondrion of T. gondii has no direct access to extracellular Ca{superscript 2} but can take it up via transfer from the ER and/or acidic stores. The absence of SERCA activity results in reduced Ca{superscript 2} levels in the ER as well as in other organelles

cell biology↗

bioRxiv2022

De novo mapping of the apicomplexan Ca2+-responsive proteome

Apicomplexan parasites cause persistent mortality and morbidity worldwide through diseases including malaria, toxoplasmosis, and cryptosporidiosis. Ca2+ signaling pathways have been repurposed in these eukaryotic pathogens to regulate parasite-specific cellular processes governing the transition between the replicative and lytic phases of the infectious cycle. Despite the presence of conserved Ca2+-responsive proteins, little is known about how specific signaling elements interact to impact pathogenesis. We mapped the Ca2+-responsive proteome of the model apicomplexan T. gondii via time-resolved phosphoproteomics and thermal proteome profiling. The waves of phosphoregulation following PKG activation and stimulated Ca2+ release corroborate known physiological changes but identify specific proteins operating in these pathways. Thermal profiling of parasite extracts identified many expected Ca2+-responsive proteins, such as parasite Ca2+-dependent protein kinases. Our approach also identified numerous Ca2+-responsive proteins that are not predicted to bind Ca2+, yet are critical components of the parasite signaling network. We characterized protein phosphatase 1 (PP1) as a Ca2+-responsive enzyme that relocalized to the parasite apex upon Ca2+ store release. Conditional depletion of PP1 revealed that the phosphatase regulates Ca2+ uptake to promote parasite motility. PP1 may thus be partly responsible for Ca2+-regulated serine/threonine phosphatase activity in apicomplexan parasites.

microbiology↗

bioRxiv2020

The Role of Host Calcium Signaling in Toxoplasma gondii egress

Toxoplasma gondii, an obligate intracellular parasite, is capable of invading virtually any nucleated cell. Ca2+ signaling is universal and both T. gondii and its mammalian host cell will utilize Ca2+ signaling to stimulate diverse cellular functions. Egress of T. gondii from the host cell is an essential step for the infection cycle of T. gondii and a cytosolic Ca2+ increase initiates the Ca2+ signaling cascade that culminates in stimulation of motility and egress. In this work we demonstrate that intracellular T. gondii is capable of taking up Ca2+ from the host cytoplasm when this concentration is increased during host signaling events. Both intracellular and extracellular Ca2+ sources are important to reach a threshold of cytosolic Ca2+ needed for a successful egress. Two peaks of Ca2+ were observed in single parasites that egressed with the second peak resulting from Ca2+ influx. We patched infected host cells to allow a precise delivery of exact concentrations of Ca2+ for stimulating motility and egress. Using this approach, we found that low potassium concentration modulates but do not trigger host cell egress. This is the first study using whole-cell patches to study the role of ions such as K+ and Ca2+ in T. gondii egress.

microbiology↗