Nuclear localization of the p120(ctn) Armadillo-like catenin is counteracted by a nuclear export signal and by E-cadherin expression.
The Armadillo protein p120(ctn) associates with the cytoplasmic domain of cadherins and accumulates at cell-cell junctions. Particular Armadillo proteins such as beta-catenin and plakophilins show a partly nuclear location, suggesting gene-regulatory activities. For different human E-cadherin-negative carcinoma cancer cell lines we found expression of endogenous p120(ctn) in the nucleus. Expression of E-cadherin directed p120(ctn) out of the nucleus. Previously, we reported that the human p120(ctn) gene might encode up to 32 protein isoforms as products of alternative splicing. Overexpression of p120(ctn) isoforms B in various cell lines resulted in cytoplasmic immunopositivity but never in nuclear staining. In contrast, upon expression of p120(ctn) cDNAs lacking exon B, the isoforms were detectable within both nuclei and cytoplasm. A putative nuclear export signal (NES) with a characteristic leucine-rich motif is encoded by exon B. This sequence element was shown to be required for nuclear export and to function autonomously when fused to a carrier protein and microinjected into cell nuclei. Moreover, the NES function of endogenously or exogenously expressed p120(ctn) isoforms B was sensitive to the nuclear export inhibitor leptomycin B. Expression of exogenous E-cadherin down-regulated nuclear p120(ctn) whereas activation of protein kinase C increased the level of nuclear p120(ctn). These results reveal molecular mechanisms controlling the subcellular distribution of p120(ctn).
Molecular Cell Biology Unit, Department of Molecular Biology, Flanders Interuniversity Institute for Biotechnology (VIB), University of Ghent, Ledeganckstraat 35, B-9000 Ghent, Belgium.
J
J
van Hengel
P
P
Vanhoenacker
K
K
Staes
F
F
van Roy
D000230:Adenocarcinoma; D000595:Amino Acid Sequence; D001943:Breast Neoplasms; D015820:Cadherins / Q000235:genetics / Q000502:physiology*; D051177:Catenins; D015815:Cell Adhesion Molecules / Q000032:analysis / Q000096:biosynthesis* / Q000235:genetics; D002467:Cell Nucleus / Q000502:physiology* / Q000648:ultrastructure; D003110:Colonic Neoplasms; D005091:Exons; D005260:Female; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D015388:Organelles / Q000502:physiology / Q000648:ultrastructure; D010750:Phosphoproteins / Q000032:analysis / Q000096:biosynthesis* / Q000235:genetics; D020033:Protein Isoforms / Q000032:analysis / Q000096:biosynthesis / Q000235:genetics; D011994:Recombinant Proteins / Q000032:analysis / Q000096:biosynthesis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014162:Transfection; D014407:Tumor Cells, Cultured; D000095002:Delta Catenin
D015820:Cadherins; D051177:Catenins; D015815:Cell Adhesion Molecules; D010750:Phosphoproteins; D020033:Protein Isoforms; D011994:Recombinant Proteins; D000095002:Delta Catenin; C000722347:CTNND1 protein, human