Malignant progression of an HPV16-immortalized human keratinocyte cell line (HPKIA) in vitro

The DNA of human papillomavirus (HPV) types found in cervical carcinomas can immortalize primary human keratinocytes. However, in analogy to tumor progression in vivo, HPV-immortalized keratinocytes require secondary events for malignant conversion. Here, we report on an HPV16-immortalized keratinocyte cell line (HPKIA) which after gamma-irradiation and long term culturing in vitro has acquired the ability to form squamous cell carcinomas in nude mice. The HPV16 integration locus and the viral transcript pattern of HPKIA cells at different passages have remained unaltered. A difference in cytokeratin expression was noted for HPKIA-induced cysts and HPKIA-induced carcinomas. In addition to the expression of suprabasal markers such as cytokeratin 10 and involucrin, carcinomas also express cytokeratin 8 and 18. The latter cytokeratin pair is often expressed in high-grade cervical neoplasia and cervical squamous cell carcinomas. Extensive cytogenetic analyses of nontumorigenic HPKIA cells and their tumorigenic segregants has revealed no single chromosomal abnormality which is confined to all tumorigenic cells. A consistent net loss of chromosomes 3, 5, 9, 12, and 22 was evident for all malignant cells. HPKIA cells represent all stages of transformation and are thus useful for defining secondary genetic events that potentially mark malignant progression in human cells in vivo.