Molecular Cloning of the Human p120 ctn Catenin Gene (CTNND1): Expression of Multiple Alternatively Spliced Isoforms Annick Keirsebilck,* Stefan Bonne ´,* Katrien Staes,* Jolanda van Hengel,* Friedel Nollet,* Albert Reynolds,† and Frans van Roy* ,1 * Molecular Cell Biology Unit, Department of Molecular Biology, Flanders Interuniversity Institute for Biotechnology (VIB)–University of Gent, Ledeganckstraat 35, B-9000 Gent, Belgium; and †Department of Cell Biology, School of Medicine, Vanderbilt University, Nashville, Tennessee 37232 Received January 28, 1998; accepted March 30, 1998 Catenins were discovered as proteins that are linked to the cytoplasmic domain of transmembrane cad- herins. Among these junctional plaque proteins are several members of the Armadillo gene family: -cate- nin, plakoglobin, and p120 ctn . Recently it became clear that some catenins also mediate nuclear signaling. We performed a detailed analysis of the human p120 ctn gene (HGMW-approved symbol CTNND1) and its tran- scripts. The human p120 ctn gene comprises 21 exons, potentially encoding up to 32 protein isoforms as prod- ucts of alternative splicing. Human isoforms, desig- nated 1 to 4, differ from each other by the start codon used. Additional isoforms are derived from combina- tions with alternatively used exons A (exon 18) and B (20), near the end of the open reading frame, and also with exon C (11) in the middle of the open reading frame. Hence, the longest isoform is of type 1ABC and comprises 968 amino acid residues. The functional consequence of the observed multitude of p120 ctn splice variants awaits further study, but tissue-spe- cific expression was obvious. Further, we demonstrate that the exon organization, which is not simply related to the Armadillo repeat structure, is very well con- served between the p120 ctn gene and the related ARVCF gene, but not at all between these two genes and the -catenin or plakoglobin genes. The present data favor the concept that p120 ctn is the prototype of a subfamily of Armadillo proteins, comprising ARVCF, p0071, -catenin/NPRAP, and plakophilins 1 and 2, that are more related to each other than to other Ar- madillo proteins. © 1998 Academic Press INTRODUCTION The p120 catenin (p120 ctn ) is an efficient tyrosine kinase substrate implicated both in cell transformation by Src (Reynolds et al., 1989) and in ligand-induced receptor signaling through the EGF-, PDGF-, CSF-1, and Erb-B2 receptors (Downing and Reynolds, 1991; Kanner et al., 1991; McManus et al., 1995). It was previously designated p120, p120 cas , and CAS (Reyn- olds et al., 1992, 1996b; Staddon et al., 1995). Unfortu- nately, the acronym CAS, which stands for cadherin- associated Src substrate (Reynolds et al., 1994), turned out to be most confusing with identical acronyms used regularly for Crk-associated substrate, cellular apopto- sis susceptibility, etc. Hence, it was recently proposed to use the name p120 ctn (ctn = catenin) to reflect its binding as a catenin to the cytoplasmic domain of E- cadherin (Reynolds et al., 1994; Shibamoto et al., 1995; Staddon et al., 1995; Daniel and Reynolds, 1995; Reyn- olds and Daniel, 1997). Catenins were discovered as proteins that are linked (catena means chain) to the cytoplasmic domain of transmembrane cadherin proteins (Ozawa et al., 1990; Cowin, 1994). Cadherins are a family of cell– cell adhe- sion molecules essential for tight calcium-dependent adhesion between cells and playing key roles in mor- phogenesis and tissue homeostasis (Takeichi, 1991). E-Cadherin is the major cadherin molecule expressed by epithelial cells. Classic catenins comprise -catenin, -catenin, and plakoglobin (-catenin) and serve as an intracellular link between E-cadherin and the actin cytoskeleton. The conserved cytoplasmic domain of E- cadherin binds directly to -catenin or plakoglobin (McCrea and Gumbiner, 1991; Hu ¨ lsken et al., 1994), which in turn directly associate with -catenin (Hu ¨ l- sken et al., 1994). The latter catenin shares significant homology with the actin-binding protein vinculin (Her- renknecht et al., 1991; Nagafuchi et al., 1991) and is thought to link cadherin complexes to the actin cy- toskeleton either directly by interaction (Ozawa et al., 1990; Herrenknecht et al., 1991) or indirectly via -ac- tinin (Knudsen et al., 1995). The p120 ctn binds directly to E-cadherin but not to -catenin (Daniel and Reyn- olds, 1995). Its role in the complex is currently un- known. Sequence data from this article have been deposited with the EMBL/ GenBank Data Libraries under Accession No. AF062317–AF062344. 1 To whom correspondence should be addressed. Telephone: +32 (0)9 264 5017. Fax: +32 (0)9 264 5331. E-mail: F.VANROY@LMB. RUG.AC.BE. GENOMICS 50, 129 –146 (1998) ARTICLE NO. GE985325 129 0888-7543/98 $25.00 Copyright © 1998 by Academic Press All rights of reproduction in any form reserved.