NLS-dependent nuclear localization of p120ctnis necessary to relieve Kaiso-mediated transcriptional repression

Abstract

IntroductionThe Armadillo catenins, β-, γ-and p120 ctn , are multifunctional proteins whose malfunction contributes to tumor progression by various means (Behrens, 1999;Van Aken et al., 2001). They are members of a larger family of Armadillo proteins that are characterized by the presence of an Armadillo domain consisting of ten or more tandem copies of a 42 amino-acid Armadillo repeat (Peifer et al., 1994). The importance of the Armadillo catenins in tumorigenesis was first credited to their involvement in the multiprotein cadherin-catenin complex, which forms the major cell-cell adhesion system in epithelial cells. Dysfunction of this complex, through defects in any of its components, correlates with the metastatic phenotype iñ 50% of human carcinomas (Behrens, 1999;Yap, 1998). The key participant in this complex is the transmembrane glycoprotein and tumor suppressor E-cadherin that mediates cell-cell adhesion by the homophilic interactions of its extracellular domain. E-cadherin is then anchored to the underlying actin cytoskeleton by the classical catenin cofactors, β-and γ-catenin, that bind E-cadherin in a mutually exclusive manner (reviewed by Nollet et al., 1999). These classical catenins bind simultaneously to a highly conserved carboxy-terminal domain of E-cadherin and to the actinbinding protein α-catenin (reviewed by Behrens, 1999;Rimm et al., 1995). Like β-and γ-catenin, the nonclassical Armadillo catenin p120 ctn binds the cytoplasmic tail of E-cadherin via its Arm domain Reynolds et al., 1992). However, β-and γ-catenin compete for binding to the distal conserved catenin-binding domain, and function by anchoring E-cadherin to the actin cytoskeleton, whereas p120 ctn binds Ecadherin at a distinct juxtamembrane domain (JMD) and does not interact with α-catenin (Daniel and Reynolds, 1995;Thoreson et al., 2000). Importantly, the JMD is implicated in E-cadherin stability (Ireton et al., 2002;Pettitt et al., 2003), modulating cadherin adhesive strength (Aono et al., 1999;Ohkubo and Ozawa, 1999;Thoreson et al., 2000;Yap et al., 1998) and regulating cytoskeletal dynamics Grosheva et al., 2001;Noren et al., 2000), and as such p120 ctn is speculated to be a key mediator of these effects. This hypothesis is supported by recent observations that p120 ctn modulates the activities of RhoA, Rac and Cdc42, which are key mediators of cytoskeletal organization Grosheva et al., 2001;Noren et al., 2000).Originally identified as a Src kinase substrate (Reynolds et al., 1989), it was the structural similarity of p120 ctn to β-catenin that led to the discovery of p120 ctn as a novel catenin component of the cadherin complex (Daniel and Reynolds, 2675The Armadillo catenin p120 ctn regulates cadherin adhesive strength at the plasma membrane and interacts with the novel BTB/POZ transcriptional repressor Kaiso in the nucleus. The dual localization of p120 ctn at cell-cell junctions and in the nucleus suggests that its nucleocytoplasmic trafficking is tightly regulated. Here we report on the identification of a specific and h...

Two conserved domains in PCIF1 mediate interaction with pancreatic transcription factor PDX‐1

“…The mechanism for nuclear import is generally unknown for nuclear POZ domain proteins. Recently, a conserved basic motif mediating nuclear localization that did not conform to consensus nuclear import signals was identified for the nuclear POZ domain protein Kaiso [23]. Interestingly, this motif bears high homology to a motif in the C-terminus of PCIF1.…”

p120 and Kaiso RegulateHelicobacter pylori-induced Expression of Matrix Metalloproteinase-7

“…We used the pGL3-4xKBS plasmid (4xKBS), which carries four tandem copies of the consensus Kaiso binding site upstream of the luciferase reporter gene (Kelly et al, 2004). Previous studies suggest that the ability to inhibit Kaiso-mediated transcriptional repression of an artificial promoter such as 4xKBS requires p120 levels greater than those endogenously present within cells (Kelly et al, 2004). Therefore, we cotransfected MKN28 cells with 4xKBS and a p120 expression vector before H. pylori coculture (Figure 6A).…”

“…The plasmids 4xKBS-pGL3 and p120-pCMV were kindly provided by Dr. Juliet M. Daniel (McMaster University) (Kelly et al, 2004). To monitor Kaisodependent gene expression, MKN28 cells were cultured in 24-well plates and cotransfected with 100 ng of 4xKBS-pGL3, 4 ng of phRL Null, and 100 ng of p120-pCMV, or 100 ng of the empty vector pCMV for 12 h by using GeneJuice (Novagen, Madison, WI) as recommended by the manufacturer's instructions.…”

“…Interactions between p120 and Kaiso can coordinately regulate genes implicated in carcinogenesis (Daniel and Reynolds, 1999;Daniel et al, 2002;Kelly et al, 2004;Kim et al, 2004;Park et al, 2005;Spring et al, 2005), and translocation of p120 to the nucleus relieves Kaiso-mediated transcriptional repression of mmp-7 (Kelly et al, 2004;Park et al, 2005;Spring et al, 2005). To determine whether H. pylori infection alters total p120 levels, MKN28 cells were cocultured with H. pylori strain 7.13 (MOI ϭ 100) or medium alone and subjected to Western blot analysis ( Figure 3A).…”

“…Having also shown that Kaiso binds the promoter region of mmp-7 and that H. pylori induces aberrant localization of p120 to the nucleus, we next sought to determine whether inhibition of Kaiso-mediated transcriptional repression was required for mmp-7 transcriptional up-regulation. We used the pGL3-4xKBS plasmid (4xKBS), which carries four tandem copies of the consensus Kaiso binding site upstream of the luciferase reporter gene (Kelly et al, 2004). Previous studies suggest that the ability to inhibit Kaiso-mediated transcriptional repression of an artificial promoter such as 4xKBS requires p120 levels greater than those endogenously present within cells (Kelly et al, 2004).…”