P53 MUTATION AND MDM2 AMPLIFICATION ARE RARE EVEN IN HUMAN PAPILLOMAVIRUS-NEGATIVE CERVICAL CARCINOMAS

Background. Mutation of the p53 tumor suppressor gene is the most comm only found genetic alteration in human man cancer. The E6 gene product of human papillomavirus (HPV)16 and 18 can inactivate the p53 protein by promoting its degradation. Because most HPV-positive cervical carc inoma cell lines contain wild-type p53 whereas HPV-negative cell lines have point mutations in the p53 gene, a major role in the development of HPV-negative cervical cancer has been attributed to p53. Recent st udies, however, have observed no consistent presence of p53 mutation i n HPV-negative primary cervical carcinomas, The MDM2 oncogene, which f orms an autoregulatory loop with the wild-type p53 protein, has been f ound amplified in a high percentage of human sarcomas, thus abolishing the antiproliferative function of p53. Methods. Forty-three primary c ervical carcinomas and 10 autopsy-derived distant metastases from one patient were examined for p53 mutation and MDM2 amplification. These t umors had been selected from 238 cervical cancers that had been HPV-ty ped by Southern blot hybridization and polymerase chain reaction as a representative sample for their HPV status and their clinicopathologic characteristics. Seventeen of the cases had a remarkably good or poor clinical outcome. Human papillomavirus DNA sequences had been detecte d in 30 of these 43 primary tumors and 13 were negative for HPV by bot h methods. p53 mutation in the highly conserved exons 5-8 was studied by single-strand conformation polymorphism analysis and direct sequenc ing. MDMB amplification was analyzed by Southern blot hybridization. R esults. Only two missense point mutations and one nucleotide sequence polymorphism were detected: a TAC --> TGC transition in codon 234 in e xon 7, resulting in a Tyr --> Lys substitution, a CGT --> TGT transiti on in codon 273 in exon 8, resulting in an Arg --> Cys substitution an d a polymorphism (CGA --> CGG) in codon 213 in exon 6. Both tumors rev ealing the point mutations were HPV-negative carcinomas. Amplification of the MDMB gene was observed in 1 of the 53 specimens tested. Conclu sions. In contrast to data derived from cultured cervical carcinoma ce ll lines and primary sarcomas, these results indicate that p53 mutatio n and amplification of the MDM2 oncogene are rare even in HPV-negative primary cervical carcinomas. However, to the authors; knowledge, this is the first observation of MDM2 amplification in humans outside sarc omas and neuroepithelial tumors.