title: HPV-16 oncogenes E6 and E7 are mutagenic in normal human oral keratinocytes.
abstract: The mutation frequency of pS189 shuttle vector plasmids is higher in human oral keratinocytes (NHOK) immortalized with cloned human papillomavirus-16 (HPV-16) genome than in primary normal NHOK (NHOK). To determine whether oncoproteins E6 and E7 of HPV-16 are responsible for the higher mutation frequency of the plasmids, we measured the mutation frequency in NHOK and in NHOK expressing the HPV-16 oncogenes (E6, E7, or E6 plus E7). We also measured the mutation frequency in NHOK expressing the E6 or E7 proteins of the non-oncogenic HPV-6b. The mutation frequency, either background or N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced, in NHOK expressing the HPV-16 oncoproteins (E6, E7, or E6 plus E7) was significantly higher than in NHOK. The HPV-16 oncogenes did not alter the nature of the MNNG-induced mutations (G:C-->A:T), but increased the frequency of deletions and insertions with or without MNNG. The background or MNNG-induced mutation frequency in NHOK expressing the HPV-6b E6 or E7 proteins was the same as in NHOK. NHOK and NHOK expressing HPV6b-E6 or E7 were able to arrest the cell cycle and enhance cellular p53, p21(WAF1/CIP1), and Gadd45 levels when exposed to MNNG, whereas NHOK expressing the HPV-16 E6 oncogene did not demonstrate. NHOK expressing HPV-16 E7 were able to enhance cellular p53, p21(WAF1/CIP1), and Gadd45 levels, but failed to arrest cell cycle progression when exposed to MNNG. These data indicate that HPV-16 E6 and E7 oncogenes are mutagenic in human oral keratinocytes and enhance the mutagenic effect of MNNG. However, the E6 and E7 proteins of the 'low risk' HPV-6b did not demonstrate such an ability.
authors.affiliation: Dental Research Institute, School of Dentistry, University of California, Los Angeles 90095-1668, USA.
authors.forename: X
authors.initials: X
authors.lastname: Liu
authors.forename: S
authors.initials: S
authors.lastname: Han
authors.forename: M A
authors.initials: MA
authors.lastname: Baluda
authors.forename: N H
authors.initials: NH
authors.lastname: Park
mesh_terms: D002453:Cell Cycle / Q000187:drug effects; D002471:Cell Transformation, Neoplastic; D002478:Cells, Cultured; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D015603:Keratinocytes / Q000166:cytology / Q000187:drug effects; D008769:Methylnitronitrosoguanidine / Q000494:pharmacology; D009055:Mouth / Q000166:cytology* / Q000187:drug effects; D009153:Mutagens; D009856:Oncogene Proteins, Viral / Q000235:genetics / Q000502:physiology*; D050725:Papillomavirus E7 Proteins; D010957:Plasmids; D011506:Proteins / Q000378:metabolism; D012097:Repressor Proteins; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D000097642:GADD45 Proteins
chemical_list: D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D047908:Intracellular Signaling Peptides and Proteins; D008769:Methylnitronitrosoguanidine; D009153:Mutagens; D009856:Oncogene Proteins, Viral; D050725:Papillomavirus E7 Proteins; D011506:Proteins; D012097:Repressor Proteins; D016159:Tumor Suppressor Protein p53; D000097642:GADD45 Proteins; C493956:CDKN1A protein, human; C068651:E6 protein, Human papillomavirus type 16; C059731:oncogene protein E7, Human papillomavirus type 16