Bacterial and host determinants of MAL activation upon EPEC infection: the roles of Tir, ABRA, and FLRT3

Center for Computational and Integrative Biology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, United States of America.
PLoS Pathogens (Impact Factor: 7.56). 04/2011; 7(4):e1001332. DOI: 10.1371/journal.ppat.1001332
Source: PubMed


Infection of host cells by pathogenic microbes triggers signal transduction pathways leading to a multitude of host cell responses including actin cytoskeletal re-arrangements and transcriptional programs. The diarrheagenic pathogens Enteropathogenic E. coli (EPEC) and the related Enterohemorrhagic E. coli (EHEC) subvert the host-cell actin cytoskeleton to form attaching and effacing lesions on the surface of intestinal epithelial cells by injecting effector proteins via a type III secretion system. Here we use a MAL translocation assay to establish the effect of bacterial pathogens on host cell signaling to transcription factor activation. MAL is a cofactor of Serum response factor (SRF), a transcription factor with important roles in the regulation of the actin cytoskeleton. We show that EPEC induces nuclear accumulation of MAL-GFP. The translocated intimin receptor is essential for this process and phosphorylation of Tyrosine residues 454 and 474 is important. Using an expression screen we identify FLRT3, C22orf28 and TESK1 as novel activators of SRF. Importantly we demonstrate that ABRA (actin-binding Rho-activating protein, also known as STARS) is necessary for EPEC-induced nuclear accumulation of MAL and the novel SRF activator FLRT3, is a component of this pathway. We further demonstrate that ABRA is important for structural maintenance of EPEC pedestals. Our results uncover novel components in pathogen-activated cytoskeleton signalling to MAL activation.

Download full-text


Available from: Laura M Machesky
  • [Show abstract] [Hide abstract]
    ABSTRACT: PTC3 and PTC5 are tripartite Tc (toxin complex) toxins from Photorhabdus luminescens, which consist of the binding component TcdA1, the linker component TcdB2 and the enzyme components TccC3 and TccC5, respectively. While PTC5 ADP-ribosylates Rho proteins at Gln61/63 resulting in constitutive activation of the GTPases, PTC3 ADP-ribosylates actin at Thr148 thereby inducing actin polymerization. Here, we identified amino acids involved in ADP-ribosyltransferase activity of TccC3 and TccC5 and analyzed the substrate specificity of Rho-activating TccC5. We compared the time-dependency of Rho protein activation by PTC5 in HeLa cells with the effects of Escherichia coli cytotoxic necrotizing factor 1 (CNF1), which activates Rho GTPases by deamidation of Gln61/63. Using a luciferase reporter assay, we show that PTC5 and PTC3 stimulated gene transcription via myocardin-related transcription factor A (also called MAL) and AP1. MAL activation by PTC5 involved Rho kinase and formins. Activation of AP1 by PTC5 occurred via two MAP kinase pathways involving ERK and Jun kinase, respectively.
    No preview · Article · Oct 2014 · Cellular Microbiology
  • [Show abstract] [Hide abstract]
    ABSTRACT: The hallmarks of enteropathogenic Escherichia coli (EPEC) infection are formation of attaching and effacing (A/E) lesions on mucosal surfaces and actin-rich pedestals on cultured cells, both dependent on the type III secretion system effector Tir. Following translocation into cultured cells and clustering by intimin, Tir Y474 is phosphorylated leading to recruitment of Nck, activation of N-WASP and actin polymerization via the Arp2/3 complex. A secondary, weak, actin polymerization pathway is triggered via an NPY motif (Y454). Importantly, Y454 and Y474 play no role in A/E lesion formation on mucosal surfaces following infection with the EPEC-like mouse pathogen Citrobacter rodentium. In this study we investigated the roles of Tir segments located upstream of Y451 and downstream of Y471 in C. rodentium colonization and A/E lesion formation. We also tested the role Tir residues Y451 and Y471 play in host immune responses to C. rodentium infection. We found that deletion of amino acids 382-462 or 478-547 had no impact on the ability of Tir to mediate A/E lesion formation, although deletion of amino acids 478-547 affected Tir translocation. Examination of enterocytes isolated from infected mice revealed that a C. rodentium expressing Tir_Y451A/Y471A recruited significantly less neutrophils to the colon and triggered less colonic hyperplasia on day 14 post infection, compared to infection with the wild type strain. Consistently, enterocytes isolated from mice infected with C. rodentium expressing Tir_Y451A/Y471A expressed significantly less CXCL1. These result show that Tir-induced actin remodeling plays a direct role in modulation of immune responses to C. rodentium infection. Copyright © 2015, American Society for Microbiology. All Rights Reserved.
    No preview · Article · Jun 2015 · Infection and immunity