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James E Casanova

Publications and source records attributed to James E Casanova.

18 recordsLinked to original sources
PubMed2006

ARAP2 effects on the actin cytoskeleton are dependent on Arf6-specific GTPase-activating-protein activity and binding to RhoA-GTP.

ARAP2 is a protein that contains both ArfGAP and RhoGAP domains. We found that it is a phosphatidylinositol (3,4,5)-trisphosphate-dependent Arf6 GAP that binds RhoA-GTP but lacks RhoGAP activity. In agreement with the hypothesis that ARAP2 mediates effects of RhoA, endogenous ARAP2 associated with focal adhesions (FAs) and reduction of ARAP2 expression, by RNAi, resulted in fewer FAs and actin stress fibers (SFs). In cells with reduced levels of endogenous ARAP2, FAs and SFs could be restored with wild-type recombinant ARAP2 but not mutants lacking ArfGAP or Rho-binding activity. Constitutively active Arf6 also caused a loss of SFs. The Rho effector ROKalpha was ineffective in restoring FAs. Conversely, overexpression of ARAP2 did not restore SFs in cells treated with a ROK inhibitor but induced punctate accumulations of paxillin. We conclude that ARAP2 is an Arf6GAP that functions downstream of RhoA to regulate focal adhesion dynamics.

ADP-Ribosylation Factor 1↗
PubMed2006

Invasion of host cells by Salmonella typhimurium requires focal adhesion kinase and p130Cas.

Salmonella typhimurium colonizes the intestinal epithelium by injecting an array of effector proteins into host cells that induces phagocytic uptake of attached bacteria. However, the host molecules targeted by these effectors remain poorly defined. Here, we demonstrate that S. typhimurium induces formation of focal adhesion-like complexes at sites of bacterial attachment and that both focal adhesion kinase (FAK) and the scaffolding protein p130Cas are required for Salmonella uptake. Entry of Salmonella into FAK(-/-) cells is dramatically impaired and can be restored to control levels by expression of wild-type FAK. Surprisingly, reconstitution of bacterial internalization requires neither the kinase domain of FAK nor activation of c-Src, but does require a C-terminal PXXP motif through which FAK interacts with Cas. Infection of Cas(-/-) cells is also impaired, and reconstitution of invasiveness requires the central Cas YXXP repeat domain. The invasion defect in Cas(-/-) cells can be suppressed by overexpression of FAK, suggesting a functional link between FAK and Cas in the regulation of Salmonella invasion. Together, these findings reveal a novel role for focal adhesion proteins in the invasion of host cells by Salmonella.

Animals↗
PubMed2006

ARNO through its coiled-coil domain regulates endocytosis at the apical surface of polarized epithelial cells.

ARNO is a guanine-nucleotide exchange protein for the ARF family of GTPases. Here we show that in polarized epithelial cells, ARNO is localized exclusively to the apical plasma membrane, where it regulates endocytosis. Expression of ARNO stimulates apical endocytosis of the polymeric immunoglobulin receptor, and coexpression of ARF6 with ARNO leads to a synergistic stimulation of apical endocytosis. Expression of a dominant negative ARF6 mutant, ARF6-T27N, antagonizes this stimulatory effect. Deletion of the N-terminal coiled-coil (CC) domain of ARNO causes the mutant ARNO to localize to both the apical and basolateral plasma membranes. Expression of the CC domain alone abolishes ARNO-induced apical endocytosis as well as co-localization of IgA-receptor complexes with ARNO and clathrin. These results suggest that the CC domain contributes to the specificity of apical localization of ARNO through association with components of the apical plasma membrane. We conclude that ARNO acts together with ARF6 to regulate apical endocytosis.

ADP-Ribosylation Factor 6↗
PubMed2006

The Arf6 GEF GEP100/BRAG2 regulates cell adhesion by controlling endocytosis of beta1 integrins.

The small GTPase Arf6 has been shown to regulate the post-endocytic trafficking of a subset of membrane proteins, including beta1 integrins, and inhibition of Arf6 function impairs both cell adhesion and motility. The activity of Arf GTPases is regulated by a large family of guanine nucleotide exchange factors (GEFs). Arf-GEP100/BRAG2 is a GEF with reported specificity for Arf6 in vitro, but it is otherwise poorly characterized. Here we report that BRAG2 exists in two ubiquitously expressed isoforms, which we call BRAG2a and BRAG2b, both of which can activate Arf6 in vivo. Depletion of endogenous BRAG2 by siRNA leads to dramatic effects in the cell periphery; one such effect is an accumulation of beta1 integrin on the cell surface and a corresponding enhancement of cell attachment and spreading on fibronectin-coated substrates. In contrast, depletion of Arf6 leads to intracellular accumulation of beta1 integrin and reduced adhesion and spreading. These findings suggest that Arf6 regulates both endocytosis and recycling of beta1 integrins and that BRAG2 functions selectively to activate Arf6 during integrin internalization.

ADP-Ribosylation Factor 6↗
PubMed2005

The DOCK180/Elmo complex couples ARNO-mediated Arf6 activation to the downstream activation of Rac1.

Cell motility requires extensions of the plasma membrane driven by reorganization of the actin cytoskeleton. Small GTPases, particularly the Rho family, are key regulators of this process. A second class of GTPases, the ADP-ribosylation factors (ARFs), have also been implicated in the regulation of the actin cytoskeleton and motility. ARF6 is intimately involved in the regulation of Rac activity; however, the mechanisms by which ARF activation leads to activation of Rac remain poorly understood. We have previously shown that expression of the ARF-GEF ARNO in MDCK cells induces robust activation of Rac, the formation of large lamellipodia, and the onset of motility. We report here that ARNO-dependent activation of Rac is mediated by a bipartite Rac GEF, the Dock180/Elmo complex. Both DOCK180 and Elmo colocalize extensively with ARNO in migrating MDCK cells. Importantly, both a catalytically inactive Dock180 mutant and an Elmo mutant that fails to couple to Dock180 block ARNO-induced Rac activation and motility. In contrast, a similar mutant of the Rac GEF beta-PIX fails to inhibit ARNO-induced Rac activation or motility. Together, these data suggest that ARNO and ARF6 coordinate with the Dock180/Elmo complex to promote Rac activation at the leading edge of migrating cells.

ADP-Ribosylation Factor 6↗
PubMed2005

WAVE2 signaling mediates invasion of polarized epithelial cells by Salmonella typhimurium.

The bacterial pathogen Salmonella penetrates the intestinal epithelium by inducing its own phagocytosis into epithelial cells. The dramatic reorganization of the actin cytoskeleton required for internalization is driven by bacterial manipulation of host signaling pathways, including activation of the Rho family GTPase Rac1 and subsequent activation of the Arp2/3 complex. However, the mechanisms linking these two events remain poorly understood. Rac1 is thought to promote activation of the Arp2/3 complex through its interaction with suppressor of cAMP receptor/WASP family verprolin-homologous (SCAR/WAVE) family proteins, but this interaction is apparently indirect. Two different Rac1 effectors have been shown to bind WAVE2: IRSp53, the SH3 domain of which binds the WAVE2 proline-rich domain, and PIR121/Sra-1, which forms a pentameric complex containing WAVE, Abi1, Nap1, and HSPC300. However, the extent to which each of these complexes contributes to Arp2/3 complex activation in the context of Salmonella infection is unclear. Here, we show that WAVE2 is necessary for efficient invasion of epithelial cells by Salmonella typhimurium. We found that although Salmonella infection strongly promotes the formation of an IRSp53/WAVE2 complex, IRSp53 is not necessary for bacterial internalization. In contrast, disruption of the PIR121/Nap1/Abi1/WAVE2/HSPC300 complex potently inhibits bacterial uptake. These results indicate that WAVE2 is an important component in signaling pathways leading to Salmonella invasion. Although infection leads to the formation of an IRSp53/WAVE2 complex, it is the association of WAVE2 with the Abi1/Nap1/PIR121/HSPC300 complex that regulates bacterial internalization.

Adaptor Proteins, Signal Transducing↗
PubMed2005

Interaction of the Salmonella-containing vacuole with the endocytic recycling system.

Upon entry of the pathogen Salmonella enterica serovar Typhimurium into host cells, the majority of bacteria reside in a membrane-bound compartment called the Salmonella-containing vacuole (SCV). Previous studies have established that the SCV transiently interacts with early endosomes but only acquires a subset of late endosomal/lysosomal proteins. However, the complete set of interactions between the SCV and the endocytic machinery has yet to be characterized. In this study, we have shown that four characterized regulators of endocytic recycling were present on the SCV after invasion. Interaction kinetics were different for each of the regulators; ARF6 and Rab4 associated immediately, but their presence was diminished 60 min post-infection, whereas syntaxin13 and Rab11 association peaked at 60 min. Using a dominant negative approach, we determined that Rab11 regulates the recycling of CD44 from the vacuole but had no effect on major histocompatibility complex (MHC) class I recycling. In contrast, syntaxin13 regulated the recycling of MHC class I but not of CD44. We also determined that maturation of the SCV, measured by the acquisition of lysosomal associated membrane protein-1, slowed when recycling was impaired. These findings suggest that protein movement through the endocytic recycling system is regulated through at least two concurrent pathways and that efficient interaction with these pathways is necessary for maturation of the Salmonella-containing vacuole. We also demonstrate the utility of using Salmonella invasion as a model of endosomal recycling events.

ADP-Ribosylation Factor 6↗
PubMed2004

Salmonella typhimurium transcytoses flagellin via an SPI2-mediated vesicular transport pathway.

Apical colonization of polarized epithelia by Salmonella typhimurium results in translocation of flagellin to the basolateral membrane domain, thus enabling activation of toll-like receptor 5 (TLR5)-mediated pro-inflammatory gene expression. Such flagellin transcytosis occurred without a change in epithelial permeability to 40 kDa FITC dextran, did not require bacterial motility and was independent of transepithelial movement of intact bacteria. Flagellin transcytosis was blocked at 20 degrees C, suggesting dependence on vesicular transport consistent with results from confocal microscopy that showed flagellin independent of bacteria inside epithelial cells. Furthermore, vesicles isolated from S. typhimurium-infected epithelia were highly enriched in flagellin. Flagellin transcytosis was dependent upon genes of Salmonella pathogenicity island (SPI)-2, which alter vesicular trafficking, but independent of SPI-1 that mediates bacterial invasion. Furthermore, such SPI-2 mutants were unable to mediate the localization of flagellin into intracellular vesicles consistent with flagellin transcytosis mediated by a S. typhimurium take-over of host vesicle trafficking pathways. As a result of their inability to transcytose flagellin, apical colonization by SPI-2 mutants induced substantially less epithelial IL-8 secretion than wild-type strains suggesting that such SPI-2 mediated transcytosis of flagellin plays a role in the pathogenesis of the mucosal inflammation characteristic of human Salmonellosis.

Animals↗
PubMed2004

The TBC (Tre-2/Bub2/Cdc16) domain protein TRE17 regulates plasma membrane-endosomal trafficking through activation of Arf6.

TBC (Tre-2/Bub2/Cdc16) domains are predicted to encode GTPase-activating proteins (GAPs) for Rab family G proteins. While approximately 50 TBC proteins are predicted to exist in humans, little is known about their substrate specificity. Here we show that TRE17 (also called Tre-2 and USP6), a founding member of the TBC family, targets the Arf family GTPase Arf6, which regulates plasma membrane-endosome trafficking. Surprisingly, TRE17 does not function as a GAP for Arf6 but rather promotes its activation in vivo. TRE17 associates directly with Arf6 in its GDP- but not GTP-bound state. Mapping experiments pinpoint the site of interaction to the TBC domain of TRE17. Forced expression of TRE17 promotes the localization of Arf6 to the plasma membrane, leading to Arf6 activation, presumably due to facilitated access to membrane-associated guanine nucleotide exchange factors (GEFs). Furthermore, TRE17 cooperates with Arf6 GEFs to induce GTP loading of Arf6 in vivo. Finally, short interfering RNA-mediated loss of TRE17 leads to attenuated Arf6 activation. These studies identify TRE17 as a novel regulator of the Arf6-regulated plasma membrane recycling system and reveal an unexpected function for TBC domains.

ADP-Ribosylation Factor 6↗
PubMed2003

ARNO and ARF6 regulate axonal elongation and branching through downstream activation of phosphatidylinositol 4-phosphate 5-kinase alpha.

In the developing nervous system, controlled neurite extension and branching are critical for the establishment of connections between neurons and their targets. Although much is known about the regulation of axonal development, many of the molecular events that regulate axonal extension remain unknown. ADP-ribosylation factor nucleotide-binding site opener (ARNO) and ADP-ribosylation factor (ARF)6 have important roles in the regulation of the cytoskeleton as well as membrane trafficking. To investigate the role of these molecules in axonogenesis, we expressed ARNO and ARF6 in cultured rat hippocampal neurons. Expression of catalytically inactive ARNO or dominant negative ARF6 resulted in enhanced axonal extension and branching and this effect was abrogated by coexpression of constitutively active ARF6. We sought to identify the downstream effectors of ARF6 during neurite extension by coexpressing phosphatidyl-inositol-4-phosphate 5-Kinase alpha [PI(4)P 5-Kinase alpha] with catalytically inactive ARNO and dominant negative ARF6. We found that PI(4)P 5-Kinase alpha plays a role in neurite extension and branching downstream of ARF6. Also, expression of inactive ARNO/ARF6 depleted the actin binding protein mammalian ena (Mena) from the growth cone leading edge, indicating that these effects on axonogenesis may be mediated by changes in cytoskeletal dynamics. These results suggest that ARNO and ARF6, through PI(4)P 5-Kinase alpha, regulate axonal elongation and branching during neuronal development.

ADP-Ribosylation Factor 6↗
PubMed2003

The guanine nucleotide exchange factor ARNO mediates the activation of ARF and phospholipase D by insulin.

BACKGROUND: Phospholipase D (PLD) is involved in many signaling pathways. In most systems, the activity of PLD is primarily regulated by the members of the ADP-Ribosylation Factor (ARF) family of GTPases, but the mechanism of activation of PLD and ARF by extracellular signals has not been fully established. Here we tested the hypothesis that ARF-guanine nucleotide exchange factors (ARF-GEFs) of the cytohesin/ARNO family mediate the activation of ARF and PLD by insulin. RESULTS: Wild type ARNO transiently transfected in HIRcB cells was translocated to the plasma membrane in an insulin-dependent manner and promoted the translocation of ARF to the membranes. ARNO mutants: DeltaCC-ARNO and CC-ARNO were partially translocated to the membranes while DeltaPH-ARNO and PH-ARNO could not be translocated to the membranes. Sec7 domain mutants of ARNO did not facilitate the ARF translocation. Overexpression of wild type ARNO significantly increased insulin-stimulated PLD activity, and mutations in the Sec7 and PH domains, or deletion of the PH or CC domains inhibited the effects of insulin. CONCLUSIONS: Small ARF-GEFs of the cytohesin/ARNO family mediate the activation of ARF and PLD by the insulin receptor.

ADP-Ribosylation Factors↗
PubMed2003

ARFs.

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GTP Phosphohydrolases↗
PubMed2003

Coordinate regulation of Salmonella enterica serovar Typhimurium invasion of epithelial cells by the Arp2/3 complex and Rho GTPases.

Salmonella enterica serovar Typhimurium can infect epithelial cells via the basolateral surface after breaching the intestinal epithelium, yet little is known about this process. Here, we show that actin polymerization driven by the Arp2/3 complex is critical to both basolateral and apical bacterial invasion of polarized MDCK cells. While there is also a dependence upon toxin B-sensitive Rho GTPases, none of the four GTPases known to be activated by S. enterica serovar Typhimurium SopE are individually required for basolateral internalization. These results underscore that the specific factors required for Salmonella invasion differ between membrane domains of polarized epithelia.

Actin-Related Protein 2↗
PubMed2002

ARF6: a newly appreciated player in G protein-coupled receptor desensitization.

The luteinizing hormone/choriogonadotropin hormone receptor (LH/CG R) signals to regulate ovulation, corpus luteum formation, and fetal survival during pregnancy. Agonist binding to the LH/CG R is poorly reversible, emphasizing the importance of a cellular mechanism to temper signaling by a potentially persistently active receptor. Like other G protein-coupled receptors (GPCRs), signaling by this receptor is modulated by its binding of an arrestin. We have identified ADP ribosylation factor 6 (ARF6) as a protein whose activation state is regulated by the LH/CG R and which functions to regulate the availability of plasma membrane-docked arrestin 2 to this receptor. We hypothesize that ARF6 might also serve GPCRs other than the LH/CG R to regulate the availability of arrestin 2 for receptor desensitization.

ADP-Ribosylation Factor 6↗
PubMed2002

GTPase signaling: bridging the GAP between ARF and Rho.

Membrane traffic and actin cytoskeleton dynamics are intimately linked, and GTPases of the Rho and ARF families may work together to regulate both. Recent studies have identified a family of GTPase activating proteins (GAPs) that contain both ARF-GAP and Rho-GAP domains, providing the first direct link between these two signaling pathways.

ADP-Ribosylation Factors↗
PubMed2002

Regulation of dendritic development by the ARF exchange factor ARNO.

Here we analyzed the role of ARF6, a member of the ADP-ribosylation factor (ARF) family of small GTPases, in dendritic arbor development in rat hippocampal neurons in culture. Overexpression of the inactive form of the GTP exchange factor ARNO (ARF nucleotide binding site opener) or inactive ARF6 enhanced dendritic branching, whereas coexpression of either Rac1 (a member of the Rho family of small GTPases known to control dendritic dynamics and growth) or active ARF6 with inactive ARNO eliminated the enhanced branching effect. These results indicate that the ARF family of small GTPases contributes to the regulation of dendritic branching, and that ARF6 activation turns on two independent pathways that suppress dendritic branching in vivo: one through Rac1 and the other through ARF6.

ADP-Ribosylation Factor 1↗
PubMed2002

Epithelial cell cytoskeleton and intracellular trafficking V. Confluence of membrane trafficking and motility in epithelial cell models.

Migration of epithelial cells occurs in a variety of important biological processes including tissue morphogenesis, wound healing, and the metastasis of epithelial tumors. In some instances, the cells remain attached to each other and migrate together as a sheet, maintaining epithelial integrity. In others (e.g., metastasis), junctional complexes are disrupted and cells migrate individually. In both cases, motility involves the extension of membranous protrusions (filopodia and lamellipodia) in the direction of movement and the transient assembly and disassembly of integrin-mediated adhesions with the extracellular matrix. The driving force for these events is provided by regulated changes in the organization of the actin cytoskeleton, which are thought to be coordinated with alterations in intracellular membrane traffic. In this themes article, I review current hypotheses about how these processes are integrated and attempt to identify fruitful areas for future research.

Animals↗