High-risk HPVs play a causal role in the development of cervical cancer, and their E6 oncoproteins target h-Dlg for ubiquitin-mediated proteolysis. The h-Dlg oncosuppressor is associated with cell-cell interactions, and deregulation of these structures leads to defective cell adhesion, loss of cell polarity and unregulated proliferation. We evaluated the contribution of this E6 activity in the progression to malignancy in HPV infections by analyzing h-Dlg expression in HPV-associated lesions. We analyzed h-Dlg in cervical, laryngeal, vulvar, colon and kidney histologic samples by Dlg immunohistochemistry. HPV association was ascertained by a PCR-colorimetric method. Although Dlg was certainly expressed in intraepithelial cervical, vulvar and laryngeal HPVassociated lesions, its cellular and tissue distribution patterns were altered compared to normal tissue. However, marked reduction in Dlg levels was observed in HPV-positive invasive cervical carcinomas. To elucidate whether the loss of Dlg was significant for carcinogenesis in general, we investigated Dlg expression in tumors not associated with HPV. In colon and kidney carcinomas, Dlg was expressed, albeit with a different pattern of distribution with respect to the normal tissue. The loss of Dlg may be considered a late-stage marker in cervical carcinogenesis, but alterations in its expression and localization take place during the different dysplastic stages. Dlg downregulation and/or alterations in its localization may contribute to transformation and may explain some of the characteristics of the malignant cells, such as loss of polarity and high migration ability. © 2004 Wiley-Liss, Inc. Key words: human papillomavirus; E6 protein; hDlg oncosuppressor; proteolysis; immunohistochemistryA large number of epidemiologic studies have demonstrated high-risk HPV association in almost 100% of invasive carcinomas of the uterine cervix and in the development of precursor intraepithelial neoplastic lesions. 1 The principal oncogenic effects of HPVs are mediated by the E6 and E7 proteins, which target and interfere with the function of key regulatory cellular proteins. 2 E6 oncoproteins have a great number of cellular targets involved in the regulation of cell proliferation, differentiation, apoptosis and adhesion. E6 stimulates the degradation of many of its partners, such as p53, bak, Mcm7, h-Dlg1 and h-scrib, by ubiquitin-mediated proteolysis. [3][4][5][6][7] Dlg, human homologue of Drosophila Dlg-A, was the first reported target of E6 related to cell-cell interactions and polarity. 6 Dlg 8,9 is a member of the MAGuK family of proteins, characterized by specific protein recognition domains including SH3, PDZ and homologous GuK regions. 8 -10 In Drosophila, Dlg is involved in cell growth control, maintenance of cell adhesion and polarity and functions that block cell invasion during development. 11 Dlg and another 2 related tumor suppressors, scribble and lgl, act cooperatively in regulating cell polarity and proliferation, suggesting an important connection betw...