title: Oncogenic transformation of HPV-immortalized human oral keratinocytes is associated with the genetic instability of cells.
abstract: HPV-immortalized human oral keratinocytes can convert to tumorigenic cells when exposed to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), but normal human oral keratinocytes cannot transform with a similar exposure. The different responses of these cells could be due to different genetic stability of cells. In as much as genetic stability is determined by cell cycle control and of repair of damaged DNA, we studied the effect of MNNG exposure upon cell cycle progression, expression of p53, WAF1/CIP1 and gadd45, and the mutation frequency of a shuttle vector pS189 in normal human oral keratinocytes, in HPV-immortalized oral keratinocytes, and in an oral cancer cell line expressing mutant p53. Normal cells demonstrated transient cell cycle arrest after exposure to MNNG, but the other tested cells did not. While MNNG exposure significantly increased the levels of intranuclear wt p53 protein and the expression of WAF1/CIP1 and gadd45 genes in normal cells, it did not alter them in the immortalized and cancer cells. The mutation frequency of pS189 plasmid was significantly lower in normal cells than in the other tested cells. These data indicate that malignant conversion of HPV-immortalized oral keratinocytes may, in part, be associated with the cells' genetic instability. The genetic instability may be due to cells' (1) inability to accumulate intranuclear wt p53 to a threshold level at which p53 upregulates the transcription of WAF1/CIP1 and gadd45, resulting in the loss of cell cycle control and (2) inefficient repair of DNA damage caused by genotoxic agents.
authors.affiliation: School of Dentistry, Dental Research Institute, University of California, Los Angeles 90095-1668, USA.
authors.forename: K H
authors.initials: KH
authors.lastname: Shin
authors.forename: R J
authors.initials: RJ
authors.lastname: Tannyhill
authors.forename: X
authors.initials: X
authors.lastname: Liu
authors.forename: N H
authors.initials: NH
authors.lastname: Park
mesh_terms: D002273:Carcinogens / Q000633:toxicity*; D002453:Cell Cycle / Q000187:drug effects; D002461:Cell Line, Transformed; D002467:Cell Nucleus / Q000378:metabolism; D002471:Cell Transformation, Neoplastic; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000187:drug effects* / Q000378:metabolism; D004249:DNA Damage; D005822:Genetic Vectors / Q000235:genetics; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D015603:Keratinocytes / Q000187:drug effects* / Q000378:metabolism; D008769:Methylnitronitrosoguanidine / Q000633:toxicity*; D009055:Mouth / Q000166:cytology; D027383:Papillomaviridae; D017354:Point Mutation; D011506:Proteins / Q000187:drug effects* / Q000378:metabolism; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000187:drug effects* / Q000378:metabolism; D015854:Up-Regulation; D000097642:GADD45 Proteins
chemical_list: D002273:Carcinogens; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D047908:Intracellular Signaling Peptides and Proteins; D008769:Methylnitronitrosoguanidine; D011506:Proteins; D012333:RNA, Messenger; D016159:Tumor Suppressor Protein p53; D000097642:GADD45 Proteins; C493956:CDKN1A protein, human