Association of the human papillomavirus type 11 E1-E4 protein with cornified cell envelopes derived from infected genital epithelium

The cornified cell envelope (CCE) is an insoluble matrix of covalently linked proteins assembled in differentiating keratinocytes, providing a barrier against external insults. CCEs derived from HPV Ii-infected tissue are fragile compared to those derived from healthy epithelium. To study a possible role for the E1(boolean AND)E4 protein, HPV Ii-infected epithelium was examined for the distribution of this protein and three CCE proteins. CCEs were then purified from genital epithelium, fragmented, washed to remove nonassociated proteins, and analyzed for E1(boolean AND)E4 protein. In HPV Ii-infected tissue, the E1(boolean AND)E4 protein was detected in the region of the CCE in differentiated keratinocytes. Loricrin and cytokeratin 10 (K10) were absent in E1(boolean AND)E4-positive cells, and E1(boolean AND)E4 protein was not detected in cells containing these proteins. E1(boolean AND)E4 protein was detected in immunoblots as a 10- to 11-kDa doublet in extracts of intact CCEs from infected tissue and in extracts of CCE fragments prepared without using reducing agents. Extraction with reducing agents eliminated E1(boolean AND)E4 detection, suggesting that disulfide bonding was involved in the association with CCE fragments. In addition, cyanogen bromide degradation experiments, immunofluorescence, and immunoelectron microscopy provided evidence that E1(boolean AND)E4 protein was associated with CCE fragments by covalent bonds other than disulfide bonds. We conclude that E1(boolean AND)E4 protein expression is associated with profound alterations in detection of loricrin and K10 in HPV 11-infected genital epithelium. The E1(boolean AND)E4 protein copurified with CCEs derived from infected epithelium and could he identified in CCE fragments, suggesting a possible role for E1(boolean AND)E4 in the development of CCE abnormalities. (C) 2000 Academic Press.