Biomedical subjects

Nandi Simpson

Publications and source records attributed to Nandi Simpson.

4 recordsLinked to original sources

PubMed2006

Subversion of actin dynamics by EPEC and EHEC.

During the course of infection, enteropathogenic and enterohaemorrhagic Escherichia coli (EPEC and EHEC, respectively) subvert the host cell signalling machinery and hijack the actin cytoskeleton to tighten their interaction with the gut epithelium, while avoiding phagocytosis by professional phagocytes. Much progress has been made recently in our understanding of how EPEC and EHEC regulate the pathways leading to local activation of two regulators of actin cytoskeleton dynamics, the Wiskott-Aldrich syndrome protein (N-WASP) and the Arp2/3 complex. A recent highlight is the unravelling of functions for effector proteins (particularly Tir, TccP, Map and EspG/EspG2) that are injected into the host cell by a type III secretion system.

Actin-Related Protein 2-3 Complex↗

PubMed2006

The enteropathogenic Escherichia coli type III secretion system effector Map binds EBP50/NHERF1: implication for cell signalling and diarrhoea.

Enteropathogenic Escherichia coli (EPEC) is the single most important contributor to child diarrhoea in developing countries. Nevertheless, the mechanism responsible for EPEC diarrhoea remains elusive. Using the yeast two-hybrid system to determine the target host cell protein of the EPEC type III secretion system effector Map led to identification of ezrin/radixin/moesin (ERM)-binding phosphoprotein 50 (EBP50), also known as Na+/H+ exchanger regulatory factor 1 (NHERF1). Protein interaction is mediated by the carboxy-terminal Thr-Arg-Leu (TRL) motif of Map and the PSD-95/Disk-large/ZO-1 domain 1 (PDZ1) of EBP50/NHERF1. Although EBP50/NHERF1 is recruited to site of EPEC adhesion in a Map-independent mechanism, co-immunoprecipitation and immunostaining revealed that Map binds to, induces proteolysis of, and colocalizes with EBP50/NHERF1 during infection of cultured epithelial cells. The TRL motif of Map was involved in Map-induced filopodia formation and brush border elongation on infected HeLa and Caco-2 cells respectively. As EBP50/NHERF1 regulates ion channels in the intestine we assessed the involvement of Map in diarrhoea using the Citrobacter rodentium mouse model of EPEC. We report significantly greater diarrhoea following infections with wild-type C. rodentium compared with C. rodentiumDeltamap. These results provide new insights into the mechanisms of EPEC diarrhoea.

Actins↗

PubMed2004

Identification of a novel Citrobacter rodentium type III secreted protein, EspI, and roles of this and other secreted proteins in infection.

Citrobacter rodentium is a member of a group of pathogens that colonize the lumen of the host gastrointestinal tract via attaching and effacing (A/E) lesion formation. C. rodentium, which causes transmissible colonic hyperplasia in mice, is used as an in vivo model system for the clinically significant A/E pathogens enterohemorrhagic and enteropathogenic Escherichia coli. These bacteria all contain a pathogenicity island called the locus of enterocyte effacement (LEE), which encodes a type III secretion system that is designed to deliver effector proteins into eukaryotic host cells. These effectors are involved in the subversion of host eukaryotic cell functions to the benefit of the bacterium. In this study we used mutant strains to determine the effects of the C. rodentium LEE-encoded effectors EspF, EspG, EspH, and Map on virulence in the mouse model. In addition, we identified a novel secreted protein, EspI encoded outside the LEE, whose secretion is also dependent on a functional type III secretion system. Mutant strains with each of the effectors investigated were found to be outcompeted by wild-type bacteria in mixed-infection experiments in vivo, although the effects of EspF and EspH were only subtle. In single-infection experiments, we found that EspF, EspG, and EspH are not required for efficient colonization of the mouse colon or for the production of hyperplasia. In contrast, strains producing EspI and Map had significant colonization defects and resulted in dramatically reduced levels of hyperplasia, and they exhibited very different growth dynamics in mice than the wild-type strain exhibited.

Amino Acid Sequence↗

PubMed2002

Rac regulates endothelial morphogenesis and capillary assembly.

Endothelial cells undergo branching morphogenesis to form capillary tubes. We have utilized an in vitro Matrigel overlay assay to analyze the role of the cytoskeleton and Rho GTPases during this process. The addition of matrix first induces changes in cell morphology characterized by the formation of dynamic cellular protrusions and the assembly of discrete aggregates or cords of aligned cells resembling primitive capillary-like structures, but without a recognizable lumen. This is followed by cell migration leading to the formation of a complex interconnecting network of capillary tubes with readily identifiable lumens. Inhibition of actin polymerization or actin-myosin contraction inhibits cell migration but has no effect on the initial changes in endothelial cell morphology. However, inhibition of microtubule dynamics prevents both the initial cell shape changes as well as cell migration. We find that the small GTPase Rac is essential for the matrix-induced changes in endothelial cell morphology, whereas p21-activated kinase, an effector of Rac, is required for cell motility. We conclude that Rac integrates signaling through both the actin and microtubule cytoskeletons to promote capillary tube assembly.

Actins↗