21 February 2012

Prof Vassilis Koronakis' team have uncovered a new path by which the bacterial pathogen Salmonella triggers its uptake into intestinal cells to initiate infection. They reveal this week in Cell Host & Microbe that pathogen and host guanine nucleotide exchange factors (GEFs) cooperate to control host cell WAVE complex regulation and pathogen macropinocytosis (picture shows Salmonella (red) engulfed by macropinosome).

Eukaryotic cells contain a dynamic network of actin filaments that are assembled and disassembled to drive fundamental

Fig: Salmonella (blue) triggering Arf-enriched membrane ruffles (red)

processes such as cell migration, phagocytosis, synapse plasticity and tissue repair, and pathologies like pathogen invasion. Prof Vassilis Koronakis has recently begun to study how cellular machineries like N-WASP and the WAVE complex assemble actin filaments. By setting up a novel in vitro reconstitution of the mammalian signalling platforms at defined phospholipid membrane bilayers, he discovered that membrane recruitment and activation of the WAVE complex requires the cooperative action of two GTPases, Arf and Rac1 (previous news item - click here for information). Now, building on this discovery, he and his group - Drs Daniel Humphreys and Peter Hume and PhD student Anthony Davidson - have begun to unravel the ways by which the infamous intestinal pathogen Salmonella usurps the WAVE complex to elicit host cell membrane ruffling and pathogen invasion. How Salmonella manipulates the WAVE complex was unknown. In a new study (available here), they show that Rac1 GTPase activation by delivered Salmonella guanine nucleotide exchange factor (GEF) SopE triggered WAVE complex recruitment to the membrane but not activation, which required host Arf GTPase. Salmonella hijacked host Arf GEF ARNO to activate Arf and generate pathogen-containing invasion vacuoles. ARNO recruited and activated the WAVE complex, which was enhanced when SopE and ARNO cooperated. This synergy provides a mechanism by which pathogen and host GEFs regulate the WAVE complex for Salmonella invasion.

This novel cooperation between bacterial and host GEFs introduces a new layer of complexity in the mechanisms used by pathogens to control the host actin cytoskeleton, which has profound implications actin-dependent cellular processes in both health and disease.

• Humphreys D, Davidson AC, Hume PJ, Koronakis V (2012). Salmonella effector SopE and host GEF ARNO cooperate to recruit and activate WAVE to trigger bacterial invasion. Cell Host Microbe 11: 1-11
• Koronakis V, Hume PJ, Humphreys D, Liu T, Jensen O and McGhie EJ (2011). WAVE regulatory complex activation by cooperating GTPases Arf and Rac1. Proc Natl Acad Sci 35:14449-54
• Smith K, Humphreys D, Hume PJ, Koronakis V (2010). Enteropathogenic Escherichia coli recruits the cellular inositol phosphatase SHIP2 to regulate actin-pedestal formation. Cell Host Microbe 1: 13-24.
• Humphreys D, Hume, PJ, Koronakis V (2009). Salmonella effector SptP dephosphorylates host AAA+ ATPase VCP to promote development of its intracellular replicative niche. Cell Host Microbe, 5:225-33.

For more information contact Professor Vassilis Koronakis (vk103@cam.ac.uk). This work was funded by the Wellcome Trust and the Isaac Newton Trust