The Drosophila tumour suppressor discs large (Dlg) is a cell-junction localized protein that is required for the maintenance of epithelial cyto-architecture and the negative control of cell proliferation. The mammalian homologue is likely to have a similar mode of action, and therefore functional perturbation of this protein may be linked to the development of epithelial-derived cancers. The finding that several unrelated viral oncoproteins, including the E6 protein of oncogenic human

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... iruses, bind to the human homologue of Dlg (hDlg) supports this proposition. Employing immunohistochemistry, we show that in uterine cervical squamous epithelia, prominent localization of hDlg at sites of intercellular contact occurs in cells that have left the proliferating basal cell layers and begun maturation. The presence of hDlg at sites of cell:cell contact diminishes, whilst intracellular cytoplasmic levels increase significantly in high-grade, but not low-grade, cervical neoplasias. In invasive squamous cell carcinomas, total cellular hDlg levels are greatly reduced. Our data suggest that loss of hDlg at sites of intercellular contact may be an important step in the development of epithelial cancers. Abbreviations: APC, adenomatous polyposis coli; CIN, cervical intraepithelial neoplasia; Dlg, Drosophila tumour suppressor discs large; hDlg, human homologue of Dlg; HPV, human papilloma virus; MAGUK, membraneassociated guanylate kinase; SIL, squamous intraepithelial lesions.