1. ¹International Centre for Genetic Engineering and Biotechnology, Trieste, Italy
2. ²Medical Research Council Protein Phosphorylation Unit, University of Dundee, Scotland, UK
3. ³Dpto. Bioquimica y Biologia Molecular, Facultad de Veterinaria, Universidad de Extremadura, Caceres, Spain

Correspondence: Dr L Banks, International Centre for Genetic Engineering and Biotechnology, Padriciano 99, Trieste, TS 34012, Italy. E-mail: banks@icgeb.org

Received 30 June 2005; Revised 22 December 2005; Accepted 18 January 2006; Published online 13 March 2006.

Abstract

The Discs Large (Dlg) protein is intimately involved in regulating cell polarity and cell proliferation, and is targeted by the high-risk Human Papillomavirus (HPV) E6 proteins for proteasome-mediated degradation. We show here that exposure of cells to osmotic shock induces the hyperphosphorylation of Dlg and its concomitant accumulation within the cell membrane at sites of cell contact, a process that requires an intact actin filament network. In addition, hyperphosphorylation of Dlg also renders it more susceptible to degradation induced by the HPV-18 E6 oncoprotein. Mutational analysis of Dlg identifies a region within the first 185 amino acids as being important for this, with phosphorylation on residue S158 being responsible for its enhanced targeting by the E6 oncoprotein. Using specific kinase inhibitors, we show that Jun N-terminal kinase (JNK) is in part responsible for this phosphorylation, and for the subsequent Dlg accumulation at sites of cell contact. These results further support the notion of a complex phosphorylation-dependent regulation of Dlg, both with respect to its precise cellular localisation and to its susceptibility to proteasome-mediated degradation.