title: High-throughput detection of human papillomavirus-18 L1 gene methylation, a candidate biomarker for the progression of cervical neoplasia.
abstract: The L1 gene of human papillomavirus-18 (HPV-18) is consistently hypermethylated in cervical carcinomas, but frequently hypo- or unmethylated in exfoliated cells from asymptomatic patients. In precancerous lesions, L1 is sporadically hypermethylated, correlating with the severity of the neoplasia. In order to explore the potential of using L1 methylation as a workable biomarker for carcinogenic progression of HPV-18 infections in routinely taken samples, our aim was to develop methylation-detection techniques that were sensitive and rapid without being overly complex technically. Therein, we developed a methylation-specific PCR (MSP) through the design of primer sets that specifically amplify either methylated or unmethylated HPV-18 L1 DNA within bisulfite-modified sample DNA. Amplification of unmethylated and in vitro methylated HPV-18 DNA by MSP resulted in 2500 copies of either of the two L1 DNA species being detected, a satisfactory sensitivity considering that bisulfite treatment leads to the fragmentation of about 99% of sample DNA. The primers proved specific and did not generate false positive results at concentrations exceeding the lowest limit of detection by a factor of 400. DNA from carcinomas yielded PCR signals only with the methylation-specific primers, and not with primers specific for unmethylated L1 genes. The inverse result was obtained with DNA from precursor lesions that contained only hypomethylated DNA. High-grade precursor lesions and carcinomas that contained hyper- as well as hypomethylated L1 DNA yielded PCR signals with both primers. By developing a fluorescence based real-time PCR, we quantitatively analyzed samples with in vitro methylated and unmethylated L1 DNA, and could distinguish clinical samples with hyper- and hypomethylated DNA or mixtures of both DNAs. The methylation-specific and real-time PCR techniques permitted efficient HPV-18 L1 methylation analyses and open the door for larger-scale clinical studies where the utility of methylation status to predict the progression of HPV-18 infection and HPV-18 associated lesions is assessed.
authors.affiliation: Department of Molecular Biology and Biochemistry, University of California Irvine, Irvine, CA 92697, USA.
authors.forename: Tolga
authors.initials: T
authors.lastname: Turan
authors.forename: Mina
authors.initials: M
authors.lastname: Kalantari
authors.forename: Kate
authors.initials: K
authors.lastname: Cuschieri
authors.forename: Heather A
authors.initials: HA
authors.lastname: Cubie
authors.forename: Hanne
authors.initials: H
authors.lastname: Skomedal
authors.forename: Hans-Ulrich
authors.initials: HU
authors.lastname: Bernard
mesh_terms: D015415:Biomarkers / Q000032:analysis; D036022:Capsid Proteins / Q000235:genetics; D002277:Carcinoma / Q000175:diagnosis* / Q000821:virology; D019175:DNA Methylation; D017931:DNA Primers; D018450:Disease Progression; D005260:Female; D005814:Genes, Viral; D052161:Human papillomavirus 18 / Q000235:genetics; D006801:Humans; D016133:Polymerase Chain Reaction / Q000379:methods*; D012680:Sensitivity and Specificity; D002583:Uterine Cervical Neoplasms / Q000175:diagnosis* / Q000821:virology; D014764:Viral Proteins / Q000235:genetics
chemical_list: D015415:Biomarkers; D036022:Capsid Proteins; D017931:DNA Primers; D014764:Viral Proteins; C480565:L1 protein, Human papillomavirus type 18