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Originally published as MBC in Press, 10.1091/mbc.E08-06-0558 on July 23, 2008

Vol. 19, Issue 10, 4442-4453, October 2008

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Paracingulin Regulates the Activity of Rac1 and RhoA GTPases by Recruiting Tiam1 and GEF-H1 to Epithelial Junctions

Laurent Guillemot*, Serge Paschoud*, Lionel Jond*, Andrea Foglia*, and Sandra Citi*,{dagger}

*Department of Molecular Biology, University of Geneva, CH-1211 Geneva, Switzerland; and {dagger}Department of Biology, University of Padova, I-35121 Padova, Italy

Submitted June 4, 2008; Revised July 10, 2008; Accepted July 16, 2008
Monitoring Editor: Benjamin Margolis

Small GTPases control key cellular events, including formation of cell–cell junctions and gene expression, and are regulated by activating and inhibiting factors. Here, we characterize the junctional protein paracingulin as a novel regulator of the activity of two small GTPases, Rac1 and RhoA, through the functional interaction with their respective activators, Tiam1 and GEF-H1. In confluent epithelial monolayers, paracingulin depletion leads to increased RhoA activity and increased expression of mRNA for the tight junction protein claudin-2. During tight junction assembly by the calcium-switch, Rac1 shows two transient peaks of activity, at earlier (10–20 min) and later (3–8 h) time points. Paracingulin depletion reduces such peaks of Rac1 activation in a Tiam1-dependent manner, resulting in a delay in junction formation. Paracingulin physically interacts with GEF-H1 and Tiam1 in vivo and in vitro, and it is required for their efficient recruitment to junctions, based on immunofluorescence and biochemical experiments. Our results provide the first description of a junctional protein that interacts with GEFs for both Rac1 and RhoA, and identify a novel molecular mechanism whereby Rac1 is activated during junction formation.

This was published online ahead of print in MBC in Press (http://www.molbiolcell.org/cgi/doi/10.1091/mbc.E08-06-0558) on July 23, 2008.

Address correspondence to: Sandra Citi (sandra.citi{at}unige.ch)




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