Prevalence of deletions of YY1‐binding sites in episomal HPV 16 DNA from cervical cancers

Abstract

Expression of the oncogenes E6 and E7 of human papillomavirus 16 (HPV 16) appears enhanced in pre-malignant and malignant genital tumors. We recently identified a transcriptional silencer upstream of the oncogene promoter P97, comprising 4 binding sites for the cellular YY1 protein. The analysis of the long transcriptional control regions (LCR) of episomal HPV 16 DNAs from primary tumors and lymph-node metastases of 6 patients with cervical cancer revealed deletions and point mutations of YY1 binding sites in 4 cases. To test for the activity of the P97 promoter, the mutated LCRs were cloned in a luciferase reporter gene vector. A point mutation in YY1-recognition site 4, which prevents DNA-protein interaction, did not affect promoter activity, probably due to compensation by the overlapping YY1-binding site 3. However, 5.5- to 6.5-fold increased luciferase expression was obtained under the control of 3 shortened LCRs lacking 2 to 4 YY1-binding sites. A point mutation in YY1-recognition site 2, which was previously shown to stimulate P97 3.5-fold, could be detected in the HPV 16 LCRs from both primary tumor and metastasis, indicating that the mutation is a stable characteristic of HPV 16 DNA associated with the individual cancer. These findings suggest that deletions or mutations of YY1-binding sites play a significant role in over-expression of viral oncogenes and tumor progression.