PAK is required for the disruption of E-cadherin adhesion by the small GTPase Rac

Journal of Cell Science, Apr 2008

Encarnación Lozano, Marieke A. M. Frasa, Katarzyna Smolarczyk, Ulla G. Knaus, Vania M. M. Braga

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PAK is required for the disruption of E-cadherin adhesion by the small GTPase Rac

Encarnacin Lozano 1 2 3 4 Marieke A. M. Frasa 2 4 Katarzyna Smolarczyk 2 4 Ulla G. Knaus 0 4 Vania M. M. Braga ) 2 4 0 Department of Immunology, The Scripps Research Institute , La Jolla, CA 92037 , USA 1 Ecology and Evolution Research Section, Faculty of Life Sciences, Imperial College London , London, SW7 2AZ , UK 2 Molecular Medicine Section, NHLI, Faculty of Medicine 3 Present address: Museo Nacional de Ciencias Naturales , CSIC, 28006 Madrid , Spain 4 cDNA contructs Full-length constitutively active Rac1 5 kinase-dead in pRK5-myc were a gift from Alan Hall (Memorial Sloane-Kettering Cancer Center , New York, NY). PAK1 Summary E-cadherin cell-cell adhesion plays a major role in the maintenance of the morphology and function of epithelial tissues. Modulation of E-cadherin function is an important process in morphogenesis and tumour de-differentiation. We have previously shown that constitutively active Rac1 induces the disassembly of E-cadherin complexes from junctions in human keratinocytes. Here, we compare this activity in three ce members of the Rac subfamily (Rac1, Rac3 and Rac1b) and en investigate the molecular mechanisms underlying Rac1ic induced destabilization of junctions. We demonstrate that Rac3 lleS smheadrieastewdiathdhResaiocn1. tRhaec1abbiilsityantoalteinrtneartfievree spwliitche vcaardiahnertinofC Rac1 but, surprisingly, Rac1b cannot induce junction fo disassembly. Thus, Rac family members differ on their lrnau cpmaoedtcehhneatrinianils-mdteoptehnprdeoreutnguthrabdwhkheeiscriohantinRdooacecystepnrootcmeilnlo-vtcoeesllvledcaisonanstisnaeccmtrseb.alsyTehionef o J - Introduction E-cadherin is one of the most important cell-cell adhesion receptors involved in tissue morphogenesis and maintenance of epithelial tissue integrity (Gumbiner, 2005). Loss of function of E-cadherin has emerged as an important event for local invasion and metastasis (Christofori and Semb, 1999). Furthermore, E-cadherin expression becomes down-regulated when epithelial cells acquire motile and invasive characteristics (i.e. during epithelial wound healing and embryonic development) (Thiery, 2003). The small GTPase Rac1 is an important modulator of the actin cytoskeleton and a key regulator of E-cadherin function (Gumbiner, 2005). Activation of Rac1 perturbs the distribution of E-cadherin at junctions in different cell types (Akhtar and Hotchin, 2001; Braga, 2000; Edme et al., 2002; Keely et al., 1997; Quinlan, 1999; Shintani et al., 2006; Yagi et al., 2007). This effect is specific because other surface receptors, such as integrins, are not removed from cell-cell contacts with the same time frame as cadherins (Braga et al., 2000). In vivo, Rac1-dependent disruption of junctions has been shown during intestinal epithelia differentiation (Stappenbeck and Gordon, 2000), salivary gland morphogenesis (Pirraglia et al., 2006) and tracheal tubulogenesis (Chihara et al., 2003). Furthermore, Rac activation is also required to perturb E-cadherin junctions after Ras activation (Braga et al., 2000; Edme et al., contractility. Instead, activation of the Rac target PAK1 is necessary for destabilization of cell-cell contacts. Inhibition of PAK1 by dominant-negative constructs or depletion of endogenous PAK1 by RNA interference efficiently blocked Rac1-induced perturbation of junctions. Interestingly, PAK1 cannot be activated by Rac1b, suggesting that this may contribute to the inability of Rac1b to disrupt cell-cell contacts in keratinocytes. As PAK1 also plays a crucial role in lamellipodia formation, our data indicate that PAK1 is at the interface between junction destabilization and increased motility during morphogenetic events. Supplementary material available online at http://jcs.biologists.org/cgi/content/full/121/7/933/DC1 2002), Csk kinase expression (Yagi et al., 2007) and HGF/scatter factor treatment (Ridley et al., 1995; Takaishi et al., 1994). Yet, these effects may be cell-type specific (Braga et al., 1999; Lozano et al., 2003). Upregulation of Rac1 protein and mRNA levels has been demonstrated in human tumours of epithelial origin, implicating Rac1 in cellular transformation (Lozano et al., 2003; Sahai and Marshall, 2002a). Two other family members, Rac3 and Rac1b, have also been found overexpressed or activated in several epithelial tumours. Rac3 is divergent from Rac1 at the C-terminal region (Haataja et al., 1997; Mira et al., 2000). Rac1b is an alternative splice variant of Rac1 (Jordan et al., 1999; Schnelzer et al., 2000) with an in-frame insertion of 19 amino acids in a region important for Rac1 interaction with regulators and effectors. Rac1b can neither induce lamellipodia nor activate the two known Rac1 effectors p21 activated kinase (PAK) and the downstream signaling pathway of Jun N-terminal kinase 1 (JNK1) (Fiegen et al., 2004; Matos et al., 2003). Yet, the functional consequences of Rac1, Rac3 and Rac1b activation are only now beginning to be unravelled (Chan et al., 2005; Matos et al., 2003). F (...truncated)


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Encarnación Lozano, Marieke A. M. Frasa, Katarzyna Smolarczyk, Ulla G. Knaus, Vania M. M. Braga. PAK is required for the disruption of E-cadherin adhesion by the small GTPase Rac, Journal of Cell Science, 2008, pp. 933-938, 121/7, DOI: 10.1242/jcs.016121