| Human papillomavirus (HPV) E6 is a multifunctional protein that, along with E7, is probably essential for the life cycle of all HPV genotypes, and the carcinogenesis associated with high risk genotypes. The functions of E6 are mediated through its protein-protein interactions that result in the disruption of various regulators of cell growth and apoptosis. These studies focus on characterization of the associations between high risk E6 and the novel interaction partner PATJ, a protein that was identified in a yeast two-hybrid screen, and the established interaction partner Dlg. PATJ and Dlg belong to a class of membrane-associated proteins that contain multiple PDZ protein-protein interaction domains and regulate the development of cell polarity and differentiation. Through its high risk-specific PDZ binding site, high risk E6 types bind and decrease the accumulation of a total of six such PDZ proteins. Similarly, the association with PATJ is demonstrated here to occur with high risk types 16 and 18, but not low risk types 6 and 11, in a PDZ binding motif-dependent manner. Like Dlg, the accumulation and stability of PATJ are reduced in the presence of high risk E6 types. Interestingly, these effects on PATJ were also observed for 18 E6 * I, an alternatively spliced isoform, suggesting that other high risk E6 isoforms may affect PDZ proteins. Unlike the mechanism of degradation of many E6 targets, the ubiquitin ligase E6AP is not required for the 18 E6-dependent decrease of Dlg and PATJ. Studies addressing the role of the SCFbetaTrCP ubiquitin ligase complex revealed that the mechanisms controlling Dlg stability in the presence and absence of 18 E6 are distinct. The membrane localization of the PDZ protein partners of E6 is critical for, at least, certain aspects of their functions. Expression of GFP-tagged 18.E6 affected the subcellular localization of Dlg, but not PATJ and Scrib, in the polarizable MDCK cell line. In agreement with data from other cell types, transient expression of 18 E6 resulted in the decreased accumulation of all three PDZ proteins. |
