Actin Pedestal Formation by Enteropathogenic Escherichia coli Is Regulated by IQGAP1, Calcium, and Calmodulin

Matthew D Brown,Lynn Bry,Zhigang Li,David B Sacks

doi:10.1074/jbc.m803477200

Matthew D Brown, Lynn Bry + Show 2 more

Open Access

https://doi.org/10.1074/jbc.m803477200

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Abstract

During infection, enteropathogenic Escherichia coli (EPEC) injects effector proteins into the host cell to manipulate the actin cytoskeleton and promote formation of actin pedestals. IQGAP1 is a multidomain protein that participates in numerous cellular functions, including Rac1/Cdc42 and Ca(2+)/calmodulin signaling and actin polymerization. Here we report that IQGAP1, Ca(2+), and calmodulin modulate actin pedestal formation by EPEC. Infection with EPEC promotes both the interaction of IQGAP1 with calmodulin and the localization of IQGAP1 and calmodulin to actin pedestals while reducing the interaction of IQGAP1 with Rac1 and Cdc42. IQGAP1-null fibroblasts display a reduced polymerization of actin in response to EPEC. In addition, antagonism of calmodulin or chelation of intracellular Ca(2+) reduces EPEC-dependent actin polymerization. Furthermore, IQGAP1 specifically interacts with Tir in vitro and in cells. Together these data identify IQGAP1, Ca(2+), and calmodulin as a novel signaling complex regulating actin pedestal formation by EPEC.

Highlights

translocated intimin receptor (Tir) and induces phosphorylation of a critical tyrosine residue at position 474 by the tyrosine kinase c-Fyn [3]
IQGAP1 Localizes to enteropathogenic Escherichia coli (EPEC)-induced Actin Pedestals—A large body of work has shown that several actin regulatory proteins of the host cell are required for EPEC to form actin pedestals
To determine whether IQGAP1, a well characterized regulator of the actin cytoskeleton [15,16,17], participates in EPEC pathogenesis, we first examined the localization of IQGAP1 during the formation of actin pedestals by EPEC

Summary

Introduction

Tir and induces phosphorylation of a critical tyrosine residue at position 474 by the tyrosine kinase c-Fyn [3]. To examine the time course of IQGAP1 localization to actin pedestals, HeLa cells were infected with GFP EPEC for 1, 2, or 3 h before fixing and staining cells for actin (red) and endogenous IQGAP1 (blue) (Fig. 1B). We previously reported that IQGAP1 is required for efficient host cell invasion by Salmonella through modulation of Rac1, Cdc42, and actin polymerization [22].

Results

Conclusion