Methylation of the long control region of HPV16 is related to the severity of cervical neoplasia.
OBJECTIVE
Oncogenic human papillomavirus (HPV) is the cause of cervical cancer. Hypermethylation of the CpG islands located at the long control region (LCR) of the HPV genome may regulate the expression of the major oncogenes E6 and E7, and may relate to cancer progression. The goal of the present study was to investigate the methylation patterns of CpG dinucleotides contained within the LCR of the HPV16 genome in a collection of clinical specimens comprising the full spectrum of cervical carcinogenesis.


METHODS
The status of LCR methylation was investigated in HPV16-infected cervical precancer and cancer cell lines, and in HPV16-infected low-grade squamous intraepithelial lesion of cervix (LSIL, n=17), high-grade squamous intraepithelial lesion (HSIL, n=21) and invasive squamous cell carcinoma (SCC, n=15) by bisulfite sequencing.


RESULTS
Among the three CpG islands of HPV16 LCR, methylation was found in three in the CaSki cell, in two upstream ones in SiHa cell, and none in the precancerous Z172 cell. Reactivation of E6 gene expression upon demethylation by 5-aza-dC and TSA treatments was noted in CaSki cells. In HPV-infected cervical specimens, progressive methylation of HPV16 LCR was noted, with rates of 5.9%, 33.3% and 53.3% in LSIL, HSIL and SCC, respectively (P<0.01). A trend toward increasing density of CpG methylation was also noted. Topologically, more methylated sites were found at the E6/E7 promoter region in SCC, compared with LSIL and HSIL.


CONCLUSIONS
The study disclosed downregulation of E6 gene transcription by LCR methylation in cervical cancer cells. Methylation of HPV 16 LCR is highly associated with severity of cervical neoplasm.
Ding
Dah-Ching
DC
Department of Obstetrics and Gynecology, Buddhist Tzu Chi General Hospital, Tzu Chi University, Hualien, Taiwan, ROC.
Chiang
Ming-Hsien
MH
Lai
Hung-Cheng
HC
Hsiung
Chao Agnes
CA
Hsieh
Chang-Yao
CY
Chu
Tang-Yuan
TY
D000328:Adult; D045744:Cell Line, Tumor; D018899:CpG Islands; D019175:DNA Methylation; D005260:Female; D052162:Human papillomavirus 16 / Q000235:genetics*; D006801:Humans; D008875:Middle Aged; D009856:Oncogene Proteins, Viral / Q000235:genetics; D050725:Papillomavirus E7 Proteins; D012097:Repressor Proteins / Q000235:genetics; D002583:Uterine Cervical Neoplasms / Q000821:virology*
C068651:E6 protein, Human papillomavirus type 16; D009856:Oncogene Proteins, Viral; D050725:Papillomavirus E7 Proteins; D012097:Repressor Proteins; C059731:oncogene protein E7, Human papillomavirus type 16