Dancing in and out of the nucleus:: p120ctn and the transcription factor Kaiso

The catenin p120 (hereafter p120(ctn)) was first identified as a Src kinase substrate and subsequently characterized as an Armadillo catenin member of the cell-cell adhesion cadherin-catenin complex. In the past decade, many studies have revealed roles for p120(ctn) in regulating Rho family GTPase activity and E-cadherin stability and turnover, events that occur predominantly at the plasma membrane or in the cytoplasm. However, the recent discovery of the nuclear BTB/POZ-ZF transcription factor Kaiso as a p120(ctn) binding partner, coupled with the detection of p120(ctn) in the nucleus of some cell lines and tumor tissues, suggested that like the classical beta-catenin, p120(ctn) undergoes nucleocytoplasmic trafficking and regulates gene expression. Indeed, p120(ctn) has a classic nuclear localization signal and does traffic to the nucleus. Moreover, nuclear p120(ctn) regulates Kaiso DNA-binding and transcriptional activity, similar to beta-catctenin's modulation of TCF/LEF transcription activity. However unlike beta-catenin, p120(ctn) does not appear to be a transcriptional activator. Hence it remains to be deten-nined whether the sole role of nuclear p 120(ctn) is regulation of Kaiso or whether p120(ctn) binds and regulates other transcription factors or nuclear proteins. (c) 2006 Elsevier B.V. All rights reserved.