Detection and characterization of human papillomavirus type 45 DNA in the cervical carcinoma cell line MS751

This study identified and characterized human papillomavirus type 45 (HPV-45) DNA in the MS751 cervical carcinoma cell line, correcting the previous misidentification as HPV-18. Using Southern blot analysis, molecular cloning, and DNA sequencing, researchers isolated a 9.5 kilobase genomic fragment containing partially deleted HPV-45 sequences integrated at a single chromosomal location. The integrated viral genome lacks several regions (3' E1, E2, E4, E5, L2, and 5' L1 open reading frames) but retains functional E6 and E7 oncogenes. Northern blot analysis demonstrated that only E6-E7 sequences are expressed as polyadenylated mRNA species, likely as virus-cell fusion transcripts. The sequence identity between MS751 HPV-45 and the original HPV-45 isolate was 98%, with notable amino acid differences in the E7 protein that may affect biological properties. The disruption of the E1 gene during integration likely uncouples the E2 repressor, potentially upregulating expression of viral oncoproteins E6 and E7, contributing to cellular transformation.

Key findings

• MS751 cells contain HPV-45 DNA, not HPV-18 as previously thought, due to cross-hybridization between closely related HPV types
• The integrated HPV-45 genome is partially deleted, missing E1, E2, E4, E5, L2, and portions of L1 open reading frames
• Only E6 and E7 viral genes are expressed as polyadenylated mRNA in MS751 cells
• The E7 protein from MS751 HPV-45 contains three amino acid substitutions compared to the original HPV-45 isolate, potentially affecting transforming potential