Integration of human papillomavirus type 16 DNA sequences: a possible early event in the progression of genital tumors

The keratinocyte line SK-v harbors only integrated human papillomavirus type 16 (HPV 16) DNA sequences, although it originated from vulvar Bowenoid papules predominantly containing multiple copies of free HPV 16 genomes. We have cloned a fragment of cell DNA that contains the integrated HPV 16 DNA sequences and have shown that integration interrupts the HPV 16 genome in open reading frames E2 and L2 and creates a deletion of 813 base pairs. This allows the expression of open reading frames E6 and E7, as actually substantiated by Northern (RNA) blot analysis of SK-v RNAs with subgenomic HPV 16 RNA probes. Using a unique flanking cellular DNA sequence as the probe, we have shown that the integration of HPV 16 sequences had already occurred in the premalignant lesions from which the SK-v cell line was derived.