Transcription of the E6 and E7 genes of human papillomavirus type 6 in anogenital condylomata is restricted to undifferentiated cell layers of the epithelium

Abstract

The E6 and E7 genes of human genital papillomaviruses (HPVs) appear to transform cells by different mechanisms. They seem to act synergistically but are not equally important when tested under diverse experimental conditions. We were therefore tempted to investigate the E6- and E7-specific transcription pattern in HPV6-infected condylomas separately, by in situ hybridization. Recent studies have identified three promoters within the E6-E7 region of HPV6 and HPV11 by applying S1, exonuclease VII, and cDNA analyses. On the basis of these data, we cloned subgenomic fragments of HPV6 into plasmid pBS to obtain riboprobes that differentiated between transcripts starting upstream of the E6 and E7 open reading frames, respectively. These different species of mRNAs were analyzed in serial thin sections of eight HPV6-positive anogenital condylomas. The E6 probe (nucleotides 7862 to 241) led to weak signals within the basal layer. In three cases, rather strong signals were confined to a few basal cells. The E7 probe (nucleotides 242 to 534) gave rise to a more pronounced labeling of all cells within the two to three lowest epidermal layers. In situ hybridization with a riboprobe for human c-fos revealed an expression pattern similar to that observed with the E7 probe. In contrast to the preferential expression of the transforming E6 and E7 genes in the lower epithelium, the major transcriptional activity of the virus was detected in the middle and upper third by probes colinear with the 3' moiety of the early region.