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MBC in Press, published online ahead of print July 23, 2008
Mol. Biol. Cell 10.1091/mbc.E08-06-0558

A more recent version of this article appeared on October 1, 2008
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Submitted on June 4, 2008
Revised on July 10, 2008
Accepted on July 16, 2008

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; {dagger}Department of Biology, University of Padova, I-35121 Padova, Italy

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 identify 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 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.

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




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