Objective: This study aimed to determine the association of minichromosome maintenance proteins MCM6 and MCM7 expression with human papillomavirus (HPV) E6 and E7 mRNA expression levels, viral load and physical status in invasive cervical carcinoma. Methods: Thirty four pairs of cervical carcinoma and matched adjacent normal cervical epithelium specimens were obtained as fresh-frozen tissues. All clinical specimens were obtained with patient consent and under IRB approval. Samples were analyzed for HPV presence by PCR analysis and DNA sequencing of the L1 amplicon. mRNA expression of MCM6, MCM7, HPV E6 and E7 was analyzed by TaqMan real-time RT-PCR assay. HPV E2 and E6 DNA copy numbers were quantified by TaqMan real-time PCR assay. HPV viral load was represented by the copy number of E6 DNA per genome. Physical status was determined by the ratio between the DNA copy number of E2 and E6. Correlation of variables was statistically analyzed using Spearman's correlation method. Results: All 34 cervical carcinoma specimens were positive for high-risk HPV DNA. 32 of them infected with HPV16, HPV18 or both were analyzed. Our results showed a wide variation in expression patterns of HPV E6 and E7 mRNA (from 0.01 to 48.83) and in viral load of HPV16 and HPV18 (0.2-163 copies per genome and 3-8365 copies per genome, respectively). Mixed episomal and integrated forms of viral physical status were detected in all tumor samples with E2/E6 ratios ranged from 0.001 to 0.91. In contrast, MCM6 and MCM7 displayed consistent over-expression in the carcinoma samples with a 3.3-3.5 fold increase of mRNA relative to the matched normal cervical epithelium controls. MCM6 and MCM7 mRNA expression levels were not strongly correlated with either E6/E7 expression (R=0.481, P<0.01 for E6, and R=0.491, P<0.01 for E7) or viral load (R=0.301, P <0.05). There was no correlation between MCM6/MCM7 mRNA expression levels and HPV physical status (R=0.005, P>0.5). In addition, our previous study observed consistent elevated expression of MCM6 and MCM7 proteins in the same cohort of cervical carcinoma and cervical intraepithelial neoplasia (CIN) 2+ tissues, as evidenced by Western blot and immunohistochemistry assays (H Li, et al., Proc Amer Assoc Cancer Res 2005;46:4886). Conclusions: In the present panel of cervical specimens, elevated expression levels of MCM6 and MCM7 mRNA are not well correlated with expression levels of HPV E6 and E7 mRNA, viral load and physical status. Together with our previous findings at the protein level, MCM6 and MCM7 appear to be more reliable molecular biomarkers to identify high-grade lesions and cervical carcinoma within cervical biopsy specimens, than HPV parameters.
[Proc Amer Assoc Cancer Res, Volume 47, 2006]