Molecular Pathogenesis of Cervical Carcinoma Analysis of Clonality, HPV16 Sequence Variations and Loss of Heterozygosity

Sammanfattning: A previous model of morphological pathogenesis assumed that cervical carcinoma is of monoclonal origin and progresses through multiple steps from normal epithelium via CINS into invasive carcinomas. The aim of this study was to investigate the molecular mechanism of pathogenesis of cervical neoplasia. In the clonality study, we found that 75% (6/8) of informative cases of cervical carcinoma had identical patterns of loss of heterozygosity (LOH) in the multiple synchronous lesions, while the remaining cases had different LOU patterns. In an extensively studied "golden case", the multiple carcinoma and cervical intraepithelial neoplasia (CIN) lesions could be divided into several different clonal groups by the X-chromosome inactivation patterns, HPV 16 mutations and LOH patterns. The biggest clonal family included one CIN II, one CIN III and four carcinoma samples, while four other monoclonal families of carcinoma did not include CIN lesions. These results suggested that cervical carcinoma can be either monoclonal or polygonal and contains clones developing either directly or via multiple steps. In the study of HPV types and HPV16 variations, the results confirmed that specific HPV types are the cause of cervical carcinoma but failed to support the previous opinion that HPV16 E6 variants are more malignant than the prototype. We established a novel classification called oncogene lineage of HPV16, and found that additional variations of HPV 16 oncogenes might be a weak further risk factor for cervical carcinoma. In the study of LOH, we found that interstitial deletion of two common regions of chromosome 3p, i.e., 3p2l.1-3p2l.3, and 3p22, was an early event in the development of cervical carcinoma. The results showed that the hMLH1 gene, located in 3p22 and showing LOH in 43% of the studied cases, was not involved in the development of cervical carcinoma because neither the expression level of protein nor the gene sequence was altered in these cases. In summary, a suggested model of molecular pathogenesis of cervical carcinoma is as follows. Specific types of HPV infect one or more committed stem cells in the basal layer of the epithelium. Fully efficient LOH events turn one (monoclonal origin) or more (polyclonal origin) HPV-infected stem cells into carcinoma cells without CIN steps. Less efficient LOH events would lead to CIN steps where some other unknown factors require to be added to facilitate the formation of carcinoma. In the absence of LOH events no carcinoma develops from the HPV-infected stem cells.