The p120(ctn)-binding partner Kaiso is a new member of the POZ-zinc finger family of transcription factors implicated in development and cancer. To understand the role of Kaiso in gene regulation and p120(ctn)-mediated signaling and adhesion, we sought to identify Kaiso-specific DNA binding sequences and potential target genes. Here we demonstrate that Kaiso is a dual specificity DNA-binding protein that recognizes the specific consensus sequence TCCTGCNA as well as methyl-CpG dinucleotides. A minimal core sequence CTGCNA was identified as sufficient for Kaiso binding. Two copies of the Kaiso-binding site are present in the human and murine matrilysin promoters, implicating matrilysin as a candidate target gene for Kaiso. In electrophoretic mobility shift assays, matrilysin promoter-derived oligonucleotide probes formed a complex with GST-Kaiso fusion proteins possessing the zinc finger domain but not with fusion proteins lacking the zinc fingers. We further determined that only Kaiso zinc fingers 2 and 3 were necessary and sufficient for sequence-specific DNA binding. Interestingly, Kaiso also possesses a methyl-CpG-dependent DNA-binding activity distinct from its sequence-specific DNA binding. However, Kaiso has a higher affinity for the TCCTGCNA consensus than for the methyl-CpG sites. Furthermore, the DNA-binding ability of Kaiso with either recognition site was inhibited by p120(ctn). Kaiso thus appears to have two modes of DNA binding and transcriptional repression, both of which may be modulated by its interaction with the adhesion cofactor p120(ctn).

Gastrulation movements are critical for establishing the three principal germ layers and the basic architecture of vertebrate embryos. Although the individual molecules and pathways involved are not clearly understood, non-canonical Wnt signals are known to participate in developmental processes, including planar cell polarity and directed cell rearrangements. Here we demonstrate that the dual-specificity transcriptional repressor Kaiso, first identified in association with p120-catenin, is required for Xenopus gastrulation movements. In addition, depletion of xKaiso results in increased expression of the non-canonical xWnt11, which contributes to the xKaiso knockdown phenotype as it is significantly rescued by dominant-negative Wnt11. We further demonstrate that xWnt11 is a direct gene target of xKaiso and that p120-catenin association relieves xKaiso repression in vivo. Our results indicate that p120-catenin and Kaiso are essential components of a new developmental gene regulatory pathway that controls vertebrate morphogenesis.

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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...