Human papillomavirus types in oral squamous cell carcinogenesis

The DNAs of human papillomavirus (HPV) types 4, 16 and 18 have been detected in biopsies of normal and malignant human oral mucosa by Southern blot hybridisation and polymerase chain reaction (PCR). By the former technique HPV-4, HPV-16 and HPV-18 DNAs were detected in three separate carcinomas, but only found in adjacent dysplastic and normal tissue by PCR. The PCR technique also allowed detection of HPV-16 and HPV-18 DNA in additional carcinomas and normal samples. The oral HPV-4 DNA has been molecularly cloned and extensive restriction analysis and nucleotide sequencing showed identity with the prototype HPV-4 DNA. The HPV-18 DNA detected by Southern blot hybridisation showed an altered restriction pattern in the El region of the viral genome; however direct nucleotide sequencing of PCR products from the E6 ORF showed no sequence alterations in either normal or malignant samples. HPV-16 DNA detected in one carcinoma by Southern blot hybridisation revealed altered PstI and Hpall restriction patterns as compared with the prototype viral genome. The expected 2.6kb Hpall and 1.55kb PstI bands, which overlap, were absent, and an additional band of reduced molecular weight was visible in the Hpall digest, suggesting that the oral HPV-16 genome had undergone a deletion or rearrangement. In a further two carcinoma samples positive for HPV-16 DNA by PCR, amplification of a late region fragment of the viral genome produced fragments of reduced molecular weight. When these PCR fragments were used as probes, hybridisation was observed to the 1.78kb PstI and 1.81kb Hpall-BamHI bands of HPV-16 DNA, and also (as a smear) to human genomic DNA from both tumour and normal samples. This suggests that the viral DNA in these samples had undergone recombination events with repetitive cellular sequences, perhaps as a prelude to viral integration or as a means of activating cellular genes. A keratinocyte culture (T45) derived from an oral squamous cell carcinoma was found to be non-tumorigenic in vivo. PCR analysis revealed that a proportion of cells in the culture contained HPV-16 early sequences. The establishment of HPV-positive and HPV-negative clones from this culture will provide an excellent system for studying the role of viral and cellular factors in oral squamous cell carcinogenesis