scholarly journals ARHGAP25, a novel Rac GTPase-activating protein, regulates phagocytosis in human neutrophilic granulocytes

Blood ◽  
2012 ◽  
Vol 119 (2) ◽  
pp. 573-582 ◽  
Author(s):  
Roland Csépányi-Kömi ◽  
Gábor Sirokmány ◽  
Miklós Geiszt ◽  
Erzsébet Ligeti
Keyword(s):  
Actin Cytoskeleton ◽  
Rho Gtpases ◽  
Active Form ◽  
Cell Types ◽  
Small Gtpases ◽  
Negative Regulator ◽  
Phagocytic Cells ◽  
Rac Gtpase

Members of the Rac/Rho family of small GTPases play an essential role in phagocytic cells in organization of the actin cytoskeleton and production of toxic oxygen compounds. GTPase-activating proteins (GAPs) decrease the amount of the GTP-bound active form of small GTPases, and contribute to the control of biologic signals. The number of potential Rac/RhoGAPs largely exceeds the number of Rac/Rho GTPases and the expression profile, and their specific role in different cell types is largely unknown. In this study, we report for the first time the properties of full-length ARHGAP25 protein, and show that it is specifically expressed in hematopoietic cells, and acts as a RacGAP both in vitro and in vivo. By silencing and overexpressing the protein in neutrophil model cell lines (PLB-985 and CosPhoxFcγR, respectively) and in primary macrophages, we demonstrate that ARHGAP25 is a negative regulator of phagocytosis acting probably via modulation of the actin cytoskeleton.

scholarly journals Rho GTPases as Key Molecular Players within Intestinal Mucosa and GI Diseases

Cells ◽  
2021 ◽  
Vol 10 (1) ◽  
pp. 66
Author(s):  
Rashmita Pradhan ◽  
Phuong A. Ngo ◽  
Luz d. C. Martínez-Sánchez ◽  
Markus F. Neurath ◽  
Rocío López-Posadas
Keyword(s):  
Intestinal Mucosa ◽  
Rho Gtpases ◽  
Current Knowledge ◽  
Cell Types ◽  
Effector Proteins ◽  
Special Focus ◽  
Specific Cell ◽  
Rho Proteins

Rho proteins operate as key regulators of the cytoskeleton, cell morphology and trafficking. Acting as molecular switches, the function of Rho GTPases is determined by guanosine triphosphate (GTP)/guanosine diphosphate (GDP) exchange and their lipidation via prenylation, allowing their binding to cellular membranes and the interaction with downstream effector proteins in close proximity to the membrane. A plethora of in vitro studies demonstrate the indispensable function of Rho proteins for cytoskeleton dynamics within different cell types. However, only in the last decades we have got access to genetically modified mouse models to decipher the intricate regulation between members of the Rho family within specific cell types in the complex in vivo situation. Translationally, alterations of the expression and/or function of Rho GTPases have been associated with several pathological conditions, such as inflammation and cancer. In the context of the GI tract, the continuous crosstalk between the host and the intestinal microbiota requires a tight regulation of the complex interaction between cellular components within the intestinal tissue. Recent studies demonstrate that Rho GTPases play important roles for the maintenance of tissue homeostasis in the gut. We will summarize the current knowledge on Rho protein function within individual cell types in the intestinal mucosa in vivo, with special focus on intestinal epithelial cells and T cells.

scholarly journals Abr and Bcr, Two Homologous Rac GTPase-Activating Proteins, Control Multiple Cellular Functions of Murine Macrophages

2006 ◽  
Vol 27 (3) ◽  
pp. 899-911 ◽  
Author(s):  
Young Jin Cho ◽  
Jess M. Cunnick ◽  
Sun-Ju Yi ◽  
Vesa Kaartinen ◽  
John Groffen ◽  
...  
Keyword(s):  
Ectopic Expression ◽  
Small Gtpases ◽  
Cellular Functions ◽  
Rac Gtpase ◽  
Mutant Proteins ◽  
Genetic Ablation ◽  
Murine Macrophages ◽  
Gtpase Activating Proteins

ABSTRACT Small GTPases of the Rho family are key regulators of phagocytic leukocyte function. Abr and Bcr are homologous, multidomain proteins. Their C-terminal domain has GTPase-activating protein (GAP) activity that, in vitro, is specific for Rac and Cdc42. To address the in vivo relevance of these entire proteins, of which little is known, the current study examined the effect of the genetic ablation of Abr and Bcr in murine macrophages. The concomitant loss of Abr and Bcr induced multiple alterations of macrophage cellular behavior known to be under the control of Rac. Macrophages lacking both Abr and Bcr exhibited an atypical, elongated morphology that was reproduced by the ectopic expression of GAP domain mutant Abr and Bcr in a macrophage cell line and of constitutively active Rac in primary macrophages. A robust increase in colony-stimulating factor 1 (CSF-1)-directed motility was observed in macrophages deficient for both proteins and, in response to CSF-1 stimulation, Abr and Bcr transiently translocated to the plasma membrane. Phagocytosis of opsonized particles was also increased in macrophages lacking both proteins and correlated with sustained Rac activation. Bcr and Abr GAP mutant proteins localized around phagosomes and induced distinct phagocytic cup formation. These results identify Abr and Bcr as the only GAPs to date that specifically negatively regulate Rac function in vivo in primary macrophages.

scholarly journals Pseudomonas aeruginosa Cytotoxin ExoU Is Injected into Phagocytic Cells during Acute Pneumonia

2010 ◽  
Vol 78 (4) ◽  
pp. 1447-1456 ◽  
Author(s):  
Maureen H. Diaz ◽  
Alan R. Hauser
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Immune Cells ◽  
Type Iii Secretion ◽  
Cell Types ◽  
Secretion System ◽  
Host Cells ◽  
Phagocytic Cells ◽  
Acute Pneumonia

ABSTRACT ExoU, a cytotoxin translocated into host cells via the type III secretion system of Pseudomonas aeruginosa, is associated with increased mortality and disease severity. We previously showed that impairment of recruited phagocytic cells allowed survival of ExoU-secreting P. aeruginosa in the lung. Here we analyzed types of cells injected with ExoU in vivo using translational fusions of ExoU with a β-lactamase reporter (ExoU-Bla). Cells injected with ExoU-Bla were detectable in vitro but not in vivo, presumably due to the rapid cytotoxicity induced by the toxin. Therefore, we used a noncytotoxic ExoU variant, designated ExoU(S142A)-Bla, to analyze injection in vivo. We determined that phagocytic cells in the lung were frequently injected with ExoU(S142A). Early during infection, resident macrophages constituted the majority of cells into which ExoU was injected, but neutrophils and monocytes became the predominant types of cells into which ExoU was injected upon recruitment into the lung. We observed a modest preference for injection into neutrophils over injection into other cell types, but in general the repertoire of injected immune cells reflected the relative abundance of these cells in the lung. Our results indicate that phagocytic cells in the lung are injected with ExoU and support the hypothesis that ExoU-mediated impairment of phagocytes has a role in the pathogenesis of pneumonia caused by P. aeruginosa.

scholarly journals Phosphatase PP2C6 negatively regulates phosphorylation status of Pti1b kinase, a regulator of flagellin-triggered immunity in tomato

2019 ◽  
Author(s):  
Fabian Giska ◽  
Gregory B. Martin
Keyword(s):  
Immune Responses ◽  
Plant Immunity ◽  
Active Form ◽  
Control Plant ◽  
Negative Regulator ◽  
Response To Treatment ◽  
Positive Regulators ◽  
Molecular Patterns

AbstractPlant immune responses, including the production of reactive oxygen species (ROS), are triggered when pattern recognition receptors (PRR) become activated upon detection of microbe-associated molecular patterns (MAMPs). Receptor-like cytoplasmic kinases are key components of PRR-dependent signaling pathways. In tomato two such kinases, Pti1a and Pti1b, are important positive regulators of the plant immune response. However, it is unknown how these kinases control plant immunity at the molecular level, and how their activity is regulated. To investigate these issues, we used mass spectrometry to search for interactors of Pti1b in Nicotiana benthamiana leaves and identified a protein phosphatase, PP2C6. An in vitro pull-down assay and in vivo split luciferase complementation assay verified this interaction. Pti1b was found to autophosphorylate on threonine-233 and this phosphorylation was abolished in the presence of PP2C6. An arginine-to-cysteine substitution at position 240 in the Arabidopsis MARIS kinase was previously reported to convert it into a constitutive-active form. The analogous substitution in Pti1b made it resistant to PP2C6 phosphatase activity, although it still interacted with PP2C6. Treatment of N. benthamiana leaves with the MAMP flg22 induced threonine phosphorylation of Pti1b. Expression of PP2C6, but not a phosphatase-inactive variant of this protein, in N. benthamiana leaves greatly reduced ROS production in response to treatment with MAMPs flg22 or csp22. The results indicate that PP2C6 acts as a negative regulator by dephosphorylating the Pti1b kinase, thereby interfering with its ability to activate plant immune responses.

Simvastatin inhibits Wnt/β-catenin pathway in uterine leiomyoma

Endocrinology ◽  
2021 ◽  
Author(s):  
Malak El Sabeh ◽  
Subbroto Kumar Saha ◽  
Sadia Afrin ◽  
Mostafa A Borahay
Keyword(s):  
Uterine Leiomyoma ◽  
Reproductive Tract ◽  
Controlled Trial ◽  
Active Form ◽  
Cell Types ◽  
Female Reproductive Tract ◽  
Benign Tumors ◽  
Therapeutic Effects

Abstract The Wnt/β-catenin pathway is upregulated in uterine leiomyomas, the most common benign tumors in the female reproductive tract. Simvastatin is an anti-hyperlipidemic drug, and previous in vitro and in vivo reports showed it may have therapeutic effects in treating leiomyomas. The objective of this study is to examine the effects of simvastatin on the Wnt/β-catenin signaling pathway in leiomyoma. We treated primary and immortalized human leiomyoma cells with simvastatin and examined its effects using RT-qPCR, Western Blotting, and immunocytochemistry. We also examined the effects using human leiomyoma tissues from an ongoing, randomized controlled trial where women with symptomatic leiomyoma received simvastatin (40mg) or placebo for 3 months prior to their surgery. The results of this study reveal that simvastatin significantly reduced the expression of Wnt4 and its co-receptor LRP5. After simvastatin treatment, levels of total β-catenin and its active form, non-phosphorylated β-catenin, were reduced in both cell types. Additionally, simvastatin reduced the expression of Wnt4 and total β-catenin, as well as non-phosphorylated β-catenin protein expression in response to estrogen and progesterone. Simvastatin also inhibited the expression of c-Myc, a downstream target of the Wnt/β-catenin pathway. The effect of simvastatin on non-phosphorylated-β-catenin, the key regulator of the Wnt/β-catenin pathway, was recapitulated in human leiomyoma tissue. These results suggest that simvastatin may have a beneficial effect on uterine leiomyoma through suppressing the overactive Wnt/β-catenin pathway.

Cell motility: can Rho GTPases and microtubules point the way?

2001 ◽  
Vol 114 (21) ◽  
pp. 3795-3803 ◽  
Author(s):  
Torsten Wittmann ◽  
Clare M. Waterman-Storer
Keyword(s):  
Actin Cytoskeleton ◽  
Cell Motility ◽  
Rho Gtpases ◽  
Molecular Mechanisms ◽  
Rho Gtpase ◽  
Cell Types ◽  
Small Gtpases ◽  
Cell Polarization ◽  
Microtubule Cytoskeleton ◽  
Filament Bundles

Migrating cells display a characteristic polarization of the actin cytoskeleton. Actin filaments polymerise in the protruding front of the cell whereas actin filament bundles contract in the cell body, which results in retraction of the cell’s rear. The dynamic organization of the actin cytoskeleton provides the force for cell motility and is regulated by small GTPases of the Rho family, in particular Rac1, RhoA and Cdc42. Although the microtubule cytoskeleton is also polarized in a migrating cell, and microtubules are essential for the directed migration of many cell types, their role in cell motility is not well understood at a molecular level. Here, we discuss the potential molecular mechanisms for interplay of microtubules, actin and Rho GTPase signalling in cell polarization and motility. Recent evidence suggests that microtubules locally modulate the activity of Rho GTPases and, conversely, Rho GTPases might be responsible for the initial polarization of the microtubule cytoskeleton. Thus, microtubules might be part of a positive feedback mechanism that maintains the stable polarization of a directionally migrating cell.

scholarly journals PP2C phosphatase Pic1 negatively regulates the phosphorylation status of Pti1b kinase, a regulator of flagellin-triggered immunity in tomato

2019 ◽  
Vol 476 (11) ◽  
pp. 1621-1635 ◽  
Author(s):  
Fabian Giska ◽  
Gregory B. Martin
Keyword(s):  
Immune Responses ◽  
Plant Immunity ◽  
Active Form ◽  
Control Plant ◽  
Negative Regulator ◽  
Response To Treatment ◽  
Positive Regulators ◽  
Molecular Patterns

Abstract Plant immune responses, including the production of reactive oxygen species (ROS), are triggered when pattern recognition receptors (PRRs) become activated upon detection of microbe-associated molecular patterns (MAMPs). Receptor-like cytoplasmic kinases are key components of PRR-dependent signaling pathways. In tomato, two such kinases, Pti1a and Pti1b, are important positive regulators of the plant immune response. However, it is unknown how these kinases control plant immunity at the molecular level and how their activity is regulated. To investigate these issues, we used mass spectrometry to search for interactors of Pti1b in Nicotiana benthamiana leaves and identified a PP2C protein phosphatase, referred to as Pic1. An in vitro pull-down assay and in vivo split-luciferase complementation assay verified this interaction. Pti1b was found to autophosphorylate on threonine-233, and this phosphorylation was abolished in the presence of Pic1. An arginine-to-cysteine substitution at position 240 in the Arabidopsis MARIS kinase was previously reported to convert it into a constitutive-active form. The analogous substitution in Pti1b made it resistant to Pic1 phosphatase activity, although it still interacted with Pic1. Treatment of N. benthamiana leaves with the MAMP flg22 induced threonine phosphorylation of Pti1b. The expression of Pic1, but not a phosphatase-inactive variant of this protein, in N. benthamiana leaves greatly reduced ROS production in response to treatment with MAMPs flg22 or csp22. The results indicate that Pic1 acts as a negative regulator by dephosphorylating the Pti1b kinase, thereby interfering with its ability to activate plant immune responses.

Hypotonicity induces membrane protrusions and actin remodeling via activation of small GTPases Rac and Cdc42 in Rat-1 fibroblasts

2003 ◽  
Vol 285 (4) ◽  
pp. C935-C944 ◽  
Author(s):  
Iris Carton ◽  
Diane Hermans ◽  
Jan Eggermont
Keyword(s):  
Actin Cytoskeleton ◽  
Rho Gtpases ◽  
Cell Types ◽  
Small Gtpases ◽  
Dominant Negative ◽  
Cell Swelling ◽  
Toxin B ◽  
Rhodamine Phalloidin ◽  
Actin Reorganization ◽  
Membrane Protrusions

An important consequence of cell swelling is the reorganization of the F-actin cytoskeleton in different cell types. We demonstrate in this study by means of rhodamine-phalloidin labeling and fluorescence microscopy that a drastic reorganization of F-actin occurs in swollen Rat-1 fibroblasts: stress fibers disappear and F-actin patches are formed in peripheral extensions at the cell border. Moreover, we demonstrate that activation of both Rac and Cdc42, members of the family of small Rho GTPases, forms the link between the hypotonic stimulation and F-actin reorganization. Indeed, inhibition of the small GTPases RhoA, Rac, and Cdc42 (by Clostridium difficile toxin B) prevents the hypotonicity-induced reorganization of the actin cytoskeleton, whereas inhibition of RhoA alone (by C. limosum C3 exoenzyme) does not preclude this rearrangement. Second, a direct activation and translocation toward the actin patches underneath the plasma membrane is observed for endogenous Rac and Cdc42 (but not for RhoA) during cell swelling. Finally, transfection of Rat-1 fibroblasts with constitutively active RhoA, dominant negative Rac, or dominant negative Cdc42 abolishes the swelling-induced actin reorganization. Interestingly, application of cRGD, a competitor peptide for fibronectin-integrin association, induces identical membrane protrusions and changes in the F-actin cytoskeleton that are also inhibited by C. difficile toxin B and dominant negative Rac or Cdc42. Moreover, cRGD also induces a redistribution of endogenous Rac and Cdc42 to the newly formed submembranous F-actin patches. We therefore conclude that hypotonicity and cRGD remodel the F-actin cytoskeleton in Rat-1 fibroblasts in a Rac/Cdc42-dependent way.

scholarly journals Favipiravir and Ivermectin Showed in Vitro Synergistic Antiviral Activity against SARS-CoV-2

2021 ◽  
Author(s):  
Kunlakanya Jitobaom ◽  
Chompunuch Boonarkart ◽  
Suwimon Manopwisedjaroen ◽  
Nuntaya Punyadee ◽  
Suparerk Borwornpinyo ◽  
...  
Keyword(s):  
Antiviral Activity ◽  
Synergistic Effects ◽  
Active Form ◽  
Cell Types ◽  
Vero Cells ◽  
Clear Cut ◽  
Clinical Benefits ◽  
Repurposed Drugs

Abstract Despite the urgent need for effective antivirals against SARS-CoV-2 to mitigate the catastrophic impact of the COVID-19 pandemic, there are still no proven effective and widely available antivirals for COVID-19 treatment. Favipiravir and Ivermectin are among common repurposed drugs, which have been provisionally used in some countries. There have been clinical trials with mixed results, and therefore, it is still inconclusive whether they are effective or should be dismissed. It is plausible that the lack of clear-cut clinical benefits was due to the finding of only marginal levels of in vivo antiviral activity. An obvious way to improve the activity of antivirals is to use them in synergistic combinations. Here we show that Favipiravir and Ivermectin had the synergistic effects against SARS-CoV-2 in Vero cells. The combination may provide better efficacy in COVID-19 treatment. In addition, we found that Favipiravir had an additive effect with Niclosamide, another repurposed anti-parasitic drug with anti-SARS-CoV-2 activity. However, the anti-SARS-CoV-2 activity of Favipiravir was drastically reduced when tested in Calu-3 cells. This suggested that this cell type might not be able to metabolize Favipiravir into its active form, and that this deficiency in some cell types may affect in vivo efficacy of this drug.

scholarly journals PhaC and PhaR Are Required for Polyhydroxyalkanoic Acid Synthase Activity in Bacillus megaterium

2001 ◽  
Vol 183 (14) ◽  
pp. 4235-4243 ◽  
Author(s):  
Gabriel J. McCool ◽  
Maura C. Cannon
Keyword(s):  
Bacillus Megaterium ◽  
Inclusion Bodies ◽  
Active Form ◽  
Cell Types ◽  
Pha Synthase ◽  
Class Iii ◽  
Polyhydroxyalkanoic Acid ◽  
Genes Encoding

ABSTRACT Polyhydroxyalkanoic acids (PHAs) are a class of polyesters stored in inclusion bodies and found in many bacteria and in some archaea. The terminal step in the synthesis of PHA is catalyzed by PHA synthase. Genes encoding this enzyme have been cloned, and the primary sequence of the protein, PhaC, is deduced from the nucleotide sequences of more than 30 organisms. PHA synthases are grouped into three classes based on substrate range, molecular mass, and whether or not there is a requirement for phaE in addition to thephaC gene product. Here we report the results of an analysis of a PHA synthase that does not fit any of the described classes. This novel PHA synthase from Bacillus megaterium required PhaC (PhaCBm) and PhaR (PhaRBm) for activity in vivo and in vitro. PhaCBm showed greatest similarity to the PhaCs of class III in both size and sequence. Unlike those in class III, the 40-kDa PhaE was not required, and furthermore, the 22-kDa PhaRBm had no obvious homology to PhaE. Previously we showed that PhaCBm, and here we show that PhaRBm, is localized to inclusion bodies in living cells. We show that two forms of PHA synthase exist, an active form in PHA-accumulating cells and an inactive form in nonaccumulating cells. PhaC was constitutively produced in both cell types but was more susceptible to protease degradation in the latter type. Our data show that the role of PhaR is posttranscriptional and that it functions directly or indirectly with PhaCBm to produce an active PHA synthase.

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