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Published 2 February 2004. doi:10.1083/jcb.200306032
The Rockefeller University Press, 0021-9525 $8.00
JCB, Volume 164, Number 3, 407-416
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Article

Clustering of Nck by a 12-residue Tir phosphopeptide is sufficient to trigger localized actin assembly



Kenneth G. Campellone1, Susannah Rankin2, Tony Pawson3, Marc W. Kirschner2, Donald J. Tipper1, and John M. Leong1

1 Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, Worcester, MA 01655
2 Department of Cell Biology, Harvard Medical School, Boston, MA 02115
3 Programme in Molecular Biology and Cancer, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario M5G 1X5, Canada

Address correspondence to John M. Leong, Dept. of Molecular Genetics and Microbiology, University of Massachusetts Medical School, 55 Lake Ave. North, Worcester, MA 01655. Tel.: (508) 856-4059. Fax: (508) 856-5920. email: John.Leong{at}umassmed.edu

Enteropathogenic Escherichia coli (EPEC) translocates effector proteins into mammalian cells to promote reorganization of the cytoskeleton into filamentous actin pedestals. One effector, Tir, is a transmembrane receptor for the bacterial surface adhesin intimin, and intimin binding by the extracellular domain of Tir is required for actin assembly. The cytoplasmic NH2 terminus of Tir interacts with focal adhesion proteins, and its tyrosine-phosphorylated COOH terminus binds Nck, a host adaptor protein critical for pedestal formation. To define the minimal requirements for EPEC-mediated actin assembly, Tir derivatives were expressed in mammalian cells in the absence of all other EPEC components. Replacement of the NH2 terminus of Tir with a viral membrane-targeting sequence promoted efficient surface expression of a COOH-terminal Tir fragment. Artificial clustering of this fusion protein revealed that the COOH terminus of Tir, by itself, is sufficient to initiate a complete signaling cascade leading to pedestal formation. Consistent with this finding, clustering of Nck by a 12-residue Tir phosphopeptide triggered actin tail formation in Xenopus egg extracts.

Key Words: actin pedestals; type III effector; N-WASP; EPEC; tyrosine phosphorylation

Abbreviations used in this paper: EPEC, enteropathogenic Escherichia coli; LEE, locus of enterocyte effacement; MEF, mouse embryonic fibroblast; TirFL, full-length Tir.


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