IAI Accepts, published online ahead of print on 19 October 2009

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Infect. Immun. doi:10.1128/IAI.00252-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Requirement for formin-induced actin polymerization during spread of Shigella

Jason E. Heindl, Indrani Saran, Chae-ryun Yi, Cammie F. Lesser, and Marcia B. Goldberg^*

Division of Infectious Diseases, Massachusetts General Hospital and Harvard Medical School, Cambridge, MA 02139

^* To whom correspondence should be addressed. Email: mgoldberg1{at}partners.org.

Actin polymerization in the cytosol and at the plasma membrane is locally regulated by actin nucleators. Several microbial pathogens exploit cellular actin polymerization to spread through tissue. Movement of the enteric pathogen Shigella flexneri both within the cell body and from cell-to-cell depends on actin polymerization. During intercellular spread, actin polymerization at the bacterial surface generates protrusions of the plasma membrane, which are engulfed by adjacent cells. In the cell body, polymerization of actin by Shigella sp is dependent on N-WASP activation of the Arp2/3 complex. Here, we demonstrate that, in contrast, efficient protrusion formation and intercellular spread depends on actin polymerization that involves activation of the diaphanous formin Dia. While the Shigella virulence protein, IpgB2, can bind and activate Dia1 (3), its absence does not result in a detectable defect in Dia-dependent protrusion formation or spread. The dependence on activation of Dia during S. flexneri infection contrasts with the inhibition of this pathway observed during vaccinia infection.