scholarly journals Rab11A regulates the constitutive secretory pathway during Toxoplasma gondii invasion of host cells and parasite replication

2019 ◽  
Author(s):  
Venugopal Kannan ◽  
Chehade Sylia ◽  
Werkmeister Elisabeth ◽  
Barois Nicolas ◽  
Periz Javier ◽  
...  
Keyword(s):  
Toxoplasma Gondii ◽  
Host Cell ◽  
Molecular Mechanisms ◽  
Transmembrane Protein ◽  
Small Gtpase ◽  
Host Cells ◽  
Dense Granules ◽  
Parasite Replication ◽  
Parasite Motility

SummaryToxoplasma gondii possesses an armada of secreted virulent factors that enable parasite invasion and survival into host cells. These factors are contained in specific secretory organelles, the rhoptries, micronemes and dense granules that release their content upon host cell recognition. Dense granules are secreted in a constitutive manner during parasite replication and play a crucial role in modulating host metabolic and immune responses. While the molecular mechanisms triggering rhoptry and microneme release upon host cell adhesion have been well studied, constitutive secretion remains a poorly explored aspect of T. gondii vesicular trafficking. Here, we investigated the role of the small GTPase Rab11A, a known regulator of exocytosis in eukaryotic cells. Our data revealed an essential role of Rab11A in promoting the cytoskeleton driven transport of DG and the release of their content into the vacuolar space. Rab11A also regulates transmembrane protein trafficking and localization during parasite replication, indicating a broader role of Rab11A in cargo exocytosis at the plasma membrane. Moreover, we found that Rab11A also regulates extracellular parasite motility and adhesion to host cells. In line with these findings, MIC2 secretion was altered in Rab11A-defective parasites, which also exhibited severe morphological defects. Strikingly, by live imaging we observed a polarized accumulation of Rab11A-positive vesicles and dense granules at the apical pole of extracellular motile parasites suggesting that a Rab11A-dependent apically polarized transport of cargo regulates parasite motility.

scholarly journals Ehrlichia ruminantium uses its transmembrane protein Ape to adhere to host bovine aortic endothelial cells

2021 ◽  
Author(s):  
Valerie Pinarello ◽  
Elena Bencurova ◽  
Isabel Marcelino ◽  
Olivier Gros ◽  
Carinne Puech ◽  
...  
Keyword(s):  
Endothelial Cells ◽  
Host Cell ◽  
Transmembrane Protein ◽  
Host Cells ◽  
Ehrlichia Ruminantium ◽  
Aortic Endothelial Cells ◽  
Bovine Aortic Endothelial Cells ◽  
Early Interaction ◽  
Aortic Endothelial

Ehrlichia ruminantium is an obligate intracellular bacterium, transmitted by ticks of the genus Amblyomma and responsible for heartwater, a disease of domestic and wild ruminants. High genetic diversity of E. ruminantium strains hampers the development of an effective vaccine against all strains present in the field. In order to develop strategies for the control of heartwater through both vaccine and alternative therapeutic approaches, it is important to first gain a better understanding of the early interaction of E. ruminantium and its host cell. Particularly, the mechanisms associated with bacterial adhesion remain to elucidate. Herein, we studied the role of E. ruminantium membrane protein ERGA_CDS_01230 (UniProt Q5FFA9), a probable iron transporter, in the adhesion process to host bovine aortic endothelial cells (BAEC). The recombinant version of the protein ERGA_CDS_01230, successfully produced in the Leishmania tarentolae system, is O-glycosylated. Following in vitro culture of E. ruminantium in BAEC, the expression of CDS ERGA_CDS_01230 peaks at the extracellular infectious elementary body stages. This result suggest the likely involvement of ERGA_CDS_01230, named hereafter Ape for Adhesion protein of Ehrlichia, in the early interaction of E. ruminantium with its host cells. We showed using flow cytometry and scanning electron microscopy that beads coated with recombinant ERGA_CDS_01230 (rApe) adheres to BAEC. In addition, we also abserved that rApe interacts with proteins of the cell lysate, membrane and organelle fractions. Additionally, enzymatic treatment degrading dermatan and chondroitin sulfates on the surface of BAEC is associated with a 50% reduction in the number of bacteria in the host cell after a development cycle, indicating that glycosaminoglycans seem to play a role in the adhesion of E. ruminantium to the host cell. Finally, Ape induces a humoral response in vaccinated animals. Globally, our work identifying the role of Ape in E. ruminantium adhesion to host cells makes it a gold vaccine candidate and represents a first step toward the understanding of the mechanisms of cell invasion by E. ruminantium.

scholarly journals Exit from Host Cells by the Pathogenic Parasite Toxoplasma gondii Does Not Require Motility

2007 ◽  
Vol 7 (1) ◽  
pp. 131-140 ◽  
Author(s):  
Mark D. Lavine ◽  
Gustavo Arrizabalaga
Keyword(s):  
Toxoplasma Gondii ◽  
Host Cell ◽  
Host Cells ◽  
Membrane Tension ◽  
Experimental Induction ◽  
Intracellular Parasites ◽  
Artificial Induction ◽  
Host Membrane ◽  
Parasite Motility ◽  
Parasite Egress

ABSTRACTThe process by which the intracellular parasiteToxoplasma gondiiexits its host cell is central to its propagation and pathogenesis. Experimental induction of motility in intracellular parasites results in parasite egress, leading to the hypothesis that egress depends on the parasite's actin-dependent motility. Using a novel assay to monitor egress without experimental induction, we have established that inhibiting parasite motility does not block this process, although treatment with actin-disrupting drugs does delay egress. However, using an irreversible actin inhibitor, we show that this delay is due to the disruption of host cell actin alone, apparently resulting from the consequent loss of membrane tension. Accordingly, by manipulating osmotic pressure, we show that parasite egress is delayed by releasing membrane tension and promoted by increasing it. Therefore, without artificial induction, egress does not depend on parasite motility and can proceed by mechanical rupture of the host membrane.

scholarly journals The Toxoplasma gondii Dense Granule Protein GRA7 Is Phosphorylated upon Invasion and Forms an Unexpected Association with the Rhoptry Proteins ROP2 and ROP4

2008 ◽  
Vol 76 (12) ◽  
pp. 5853-5861 ◽  
Author(s):  
Joe Dan Dunn ◽  
Sandeep Ravindran ◽  
Seon-Kyeong Kim ◽  
John C. Boothroyd
Keyword(s):  
Toxoplasma Gondii ◽  
Host Cell ◽  
Parasitophorous Vacuole ◽  
Opportunistic Pathogen ◽  
Dense Granule ◽  
Host Cells ◽  
Obligate Intracellular ◽  
Dense Granules ◽  
Obligate Intracellular Parasite ◽  
Granule Protein

ABSTRACT The obligate intracellular parasite Toxoplasma gondii infects warm-blooded animals throughout the world and is an opportunistic pathogen of humans. As it invades a host cell, Toxoplasma forms a novel organelle, the parasitophorous vacuole, in which it resides during its intracellular development. The parasite modifies the parasitophorous vacuole and its host cell with numerous proteins delivered from rhoptries and dense granules, which are secretory organelles unique to the phylum Apicomplexa. For the majority of these proteins, little is known other than their localization. Here we show that the dense granule protein GRA7 is phosphorylated but only in the presence of host cells. Within 10 min of invasion, GRA7 is present in strand-like structures in the host cytosol that contain rhoptry proteins. GRA7 strands also contain GRA1 and GRA3. Independently of its phosphorylation state, GRA7 associates with the rhoptry proteins ROP2 and ROP4 in infected host cells. This is the first report of interactions between proteins secreted from rhoptries and dense granules.

scholarly journals Lipidomic analysis of Toxoplasma gondii tachyzoites rhoptries: further insights into the role of cholesterol

2008 ◽  
Vol 415 (1) ◽  
pp. 87-96 ◽  
Author(s):  
Sébastien Besteiro ◽  
Justine Bertrand-Michel ◽  
Maryse Lebrun ◽  
Henri Vial ◽  
Jean-François Dubremetz
Keyword(s):  
Toxoplasma Gondii ◽  
Host Cell ◽  
Saturated Fatty Acids ◽  
Cholesterol Content ◽  
Host Cell Invasion ◽  
Rich Region ◽  
Lipidomic Analysis ◽  
Capillary Glc ◽  
Parasite Motility

Rhoptries are secretory organelles involved in the virulence of the human pathogen Toxoplasma gondii. In the present study we have used HPLC and capillary GLC to isolate and quantify lipids from whole Toxoplasma cells and their purified rhoptries. This comparative lipidomic analysis revealed an enrichment of cholesterol, sphingomyelin and, most of all, saturated fatty acids in the rhoptries. These lipids are known, when present in membranes, to contribute to their rigidity and, interestingly, fluorescence anisotropy measurements confirmed that rhoptry-derived membranes have a lower fluidity than membranes from whole T. gondii cells. Moreover, although rhoptries were initially thought to be highly enriched in cholesterol, we demonstrated that cholesterol is present in lower proportions, and we have provided additional evidence towards a lack of involvement of rhoptry cholesterol in the process of host-cell invasion by the parasite. Indeed, depleting the cholesterol content of the parasites did not prevent the secretion of protein-containing rhoptry-derived vesicles and the parasites could still establish a structure called the moving junction, which is necessary for invasion. Instead, the crucial role of host cholesterol for invasion, which has already been demonstrated [Coppens and Joiner (2003) Mol. Biol. Cell 14, 3804–3820], might be explained by the need of a cholesterol-rich region of the host cell we could visualize at the point of contact with the attached parasite, in conditions where parasite motility was blocked.

scholarly journals The Toxoplasma gondii Rhoptry Protein ROP4 Is Secreted into the Parasitophorous Vacuole and Becomes Phosphorylated in Infected Cells

2004 ◽  
Vol 3 (5) ◽  
pp. 1320-1330 ◽  
Author(s):  
Kimberly L. Carey ◽  
Artemio M. Jongco ◽  
Kami Kim ◽  
Gary E. Ward
Keyword(s):  
Toxoplasma Gondii ◽  
Infected Cell ◽  
Host Cell ◽  
Transmembrane Protein ◽  
Parasitophorous Vacuole ◽  
Host Cells ◽  
Cell Protein ◽  
Type I ◽  
Membrane Function ◽  
Vacuole Membrane

ABSTRACT Many intracellular pathogens are separated from the cytosol of their host cells by a vacuole membrane. This membrane serves as a critical interface between the pathogen and the host cell, across which nutrients are imported, wastes are excreted, and communication between the two cells takes place. Very little is known about the vacuole membrane proteins mediating these processes in any host-pathogen interaction. During a screen for monoclonal antibodies against novel surface or secreted proteins of Toxoplasma gondii, we identified ROP4, a previously uncharacterized member of the ROP2 family of proteins. We report here on the sequence, posttranslational processing, and subcellular localization of ROP4, a type I transmembrane protein. Mature, processed ROP4 is localized to the rhoptries, secretory organelles at the apical end of the parasite, and is secreted from the parasite during host cell invasion. Released ROP4 associates with the vacuole membrane and becomes phosphorylated in the infected cell. Similar results are seen with ROP2. Further analysis of ROP4 showed it to be phosphorylated on multiple sites, a subset of which result from the action of either host cell protein kinase(s) or parasite kinase(s) activated by host cell factors. The localization and posttranslational modification of ROP4 and other members of the ROP2 family of proteins within the infected cell make them well situated to play important roles in vacuole membrane function.

scholarly journals The Role of Potassium and Host Calcium Signaling in Toxoplasma gondii egress

2020 ◽  
Author(s):  
Stephen A. Vella ◽  
Christina A. Moore ◽  
Zhu-Hong Li ◽  
Miryam A. Hortua Triana ◽  
Evgeniy Potapenko ◽  
...  
Keyword(s):  
Toxoplasma Gondii ◽  
Host Cell ◽  
Host Cells ◽  
Mammalian Host ◽  
Cellular Functions ◽  
Obligate Intracellular ◽  
Host Cytoplasm ◽  
Host Signaling ◽  
Two Peaks

AbstractToxoplasma 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.

scholarly journals Transmembrane Insertion of the Toxoplasma gondii GRA5 Protein Occurs after Soluble Secretion into the Host Cell

1999 ◽  
Vol 10 (4) ◽  
pp. 1277-1287 ◽  
Author(s):  
Laurence Lecordier ◽  
Corinne Mercier ◽  
L. David Sibley ◽  
Marie-France Cesbron-Delauw
Keyword(s):  
Toxoplasma Gondii ◽  
Host Cell ◽  
Secretory Pathway ◽  
Transmembrane Domain ◽  
Transmembrane Protein ◽  
Parasitophorous Vacuole ◽  
Dense Granule ◽  
Soluble Form ◽  
Host Cell Membrane ◽  
Dense Granules

The intracellular parasite Toxoplasma gondii resides within a specialized compartment, the parasitophorous vacuole (PV), that resists fusion with host cell endocytic and lysosomal compartments. The PV is extensively modified by secretion of parasite proteins, including the dense granule protein GRA5 that is specifically targeted to the delimiting membrane of the PV (PVM). We show here that GRA5 is present both in a soluble form and in hydrophobic aggregates. GRA5 is secreted as a soluble form into the PV after which it becomes stably associated with the PVM. Topological studies demonstrated that GRA5 was inserted into the PVM as a transmembrane protein with its N-terminal domain extending into the cytoplasm and its C terminus in the vacuole lumen. Deletion of 8 of the 18 hydrophobic amino acids of the single predicted transmembrane domain resulted in the failure of GRA5 to associate with the PVM; yet it remained correctly packaged in the dense granules and was secreted as a soluble protein into the PV. Collectively, these studies demonstrate that the secretory pathway inToxoplasma is unusual in two regards; it allows soluble export of proteins containing typical transmembrane domains and provides a mechanism for their insertion into a host cell membrane after secretion from the parasite.

scholarly journals The “Biological Weapons” of Ehrlichia chaffeensis: Novel Molecules and Mechanisms to Subjugate Host Cells

2022 ◽  
Vol 11 ◽  
Author(s):  
Yasuko Rikihisa
Keyword(s):  
Host Cell ◽  
Signaling Pathways ◽  
Actin Polymerization ◽  
Molecular Mechanisms ◽  
Small Gtpase ◽  
Control Measures ◽  
Host Cells ◽  
Ehrlichia Chaffeensis ◽  
Intracellular Iron ◽  
Cell Functions

Ehrlichia chaffeensis is an obligatory intracellular bacterium that causes human monocytic ehrlichiosis, an emerging, potentially fatal tick-borne infectious disease. The bacterium enters human cells via the binding of its unique outer-membrane invasin EtpE to the cognate receptor DNase X on the host-cell plasma membrane; this triggers actin polymerization and filopodia formation at the site of E. chaffeensis binding, and blocks activation of phagocyte NADPH oxidase that catalyzes the generation of microbicidal reactive oxygen species. Subsequently, the bacterium replicates by hijacking/dysregulating host-cell functions using Type IV secretion effectors. For example, the Ehrlichia translocated factor (Etf)-1 enters mitochondria and inhibits mitochondria-mediated apoptosis of host cells. Etf-1 also induces autophagy mediated by the small GTPase RAB5, the result being the liberation of catabolites for proliferation inside host cells. Moreover, Etf-2 competes with the RAB5 GTPase-activating protein, for binding to RAB5-GTP on the surface of E. chaffeensis inclusions, which blocks GTP hydrolysis and consequently prevents the fusion of inclusions with host-cell lysosomes. Etf-3 binds ferritin light chain to induce ferritinophagy to obtain intracellular iron. To enable E. chaffeensis to rapidly adapt to the host environment and proliferate, the bacterium must acquire host membrane cholesterol and glycerophospholipids for the purpose of producing large amounts of its own membrane. Future studies on the arsenal of unique Ehrlichia molecules and their interplay with host-cell components will undoubtedly advance our understanding of the molecular mechanisms of obligatory intracellular infection and may identify hitherto unrecognized signaling pathways of human hosts. Such data could be exploited for development of treatment and control measures for ehrlichiosis as well as other ailments that potentially could involve the same host-cell signaling pathways that are appropriated by E. chaffeensis.

E6 and E7 oncoproteins: Potential targets of cervical cancer

2020 ◽  
Vol 27 ◽  
Author(s):  
Ramarao Malla ◽  
Mohammad Amjad Kamal
Keyword(s):  
Cervical Cancer ◽  
Drug Resistance ◽  
Host Cell ◽  
Molecular Mechanisms ◽  
Immune Therapy ◽  
Cervical Lesions ◽  
Diagnostic Strategies ◽  
E6 And E7 Oncoproteins ◽  
E6 And E7

: Cervical cancer (CC) is the fourth leading cancer in women in the age group 15-44 globally. Experimental as well as epidemiological studies identified that type16 and 18 HPV cause 70% of precancerous cervical lesions as well as cervical cancer worldwide by bringing about genetic as well as epigenetic changes in the host genome. The insertion of the HPV genome triggers various defense mechanisms including the silencing of tumor suppressor genes as well as activation of oncogenes associated with cancer metastatic pathway. E6 and E7 are small oncoproteins consisting of 150 and 100 amino acids respectively. These oncoproteins affect the regulation of the host cell cycle by interfering with p53 and pRb. Further these oncoproteins adversely affect the normal functions of the host cell by binding to their signaling proteins. Recent studies demonstrated that E6 and E7 oncoproteins are potential targets for CC. Therefore, this review discusses the role of E6 and E7 oncoproteins in metastasis and drug resistance as well as their regulation, early oncogene mediated signaling pathways. This review also uncovers the recent updates on molecular mechanisms of E6 and E7 mediated phytotherapy, gene therapy, immune therapy, and vaccine strategies as well as diagnosis through precision testing. Therefore, understanding the potential role of E6/E7 in metastasis and drug resistance along with targeted treatment, vaccine, and precision diagnostic strategies could be useful for the prevention and treatment of cervical cancer.

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