Dual role of tumor suppressor p53 in regulation of DNA replication and oncogene E6-promoter activity of epidermodysplasia verruciformis-associated human papillomavirus type 8

Abstract

Human papillomavirus 8 (HPV8) is a representative of Epidermodysplasia verruciformis (EV)-associated viruses. Transient assays in the human skin keratinocyte cell line RTS3b have shown that its replication depends in trans on expression of the viral proteins E1 and E2, similarly to other HPVs. Using deletion mutants and cloned subfragments of the noncoding region (NCR) of HPV8 we identified a 65-bp sequence in the 3' part of the NCR to be necessary and sufficient to support replication in cis. The origin of replication (ori) of HPV8 is composed of the sequence motifs "CCAAC" (nt 57-73) and M29 (nt 84-112), which are highly conserved among the majority of EV HPVs. Analysis of M29 revealed an unconventional binding site of the E2 protein and an overlapping DNA recognition site of the tumor suppressor protein p53. Both these factors competitively bind to M29. In transient replication assays p53 acted as a potent inhibitor of ori activity, most probably in a DNA-binding-dependent fashion. The minimal ori sequences are also functionally critical for the E6 oncogene promoter P(175). In contrast to its effect on replication, p53 stimulated promoter activity depending on its interaction with M29. Our observations suggest that p53 is involved in controlling the balance between DNA replication and gene expression of HPV8.