Genetic Polymorphism in E7 Gene of Human Papillomavirus Type 16 Isolated from Uterine Cervical Cancer in Korean Women

Ahn, Chi Seok; Lee, Hyo Pyo

Abstract

Human papillomavirus (HPV)infection are now generally accepted as the most important factor for development of uterine cervical cancer and its precursor lesions. With increasing evidences that the HPV E7 encodes for oncoproteins critical for viral replication, host cell immortalization and transformation. Based on the previous reports that the high risk HPV type 16 DNA is frequently detected in specimens from Korean women with cervical cancer and that there is the sequence variation and geographical dependence of HPV 16 E7 gene in preinvasive and invasive cervical lesions, it is crucial to determine the prevalence of HPV 16 variants in uterine cervical lesions of Korean women. This study was performed to identify sequence variations of HPV 16 E7 gene and an association between HPV 16 E7 variants and uterine cervical cancer. The author has determined nucleotide sequences of the E7 gene of HPV 16 isolated from uterine cervical tissues in Korean women. HPV 16 DNAs were detected by the nested PCR in 112 (24.5%) of a total of 457 samples. By direct sequencing of PCR-HPV 16 E7 positive cases, 79 samples (70.5%) showed variant sequences, while the prototype sequence was found in only 33 samples (29.5%). Twenty-three cases (57.5%) of 40 normal cervical samples showed sequence variation. Forty-eight (77.4%) of 62 cervical cancer cases showed sequence diversity from prototype HPV 16 E7 gene. There were four types of sequence variations. A single nucleotide change at position 647 (A-->G) was found in 52 cases (65.8%) of 79 HPV 16 E7 variants. Predicted amino acid change (Asn -->Ser) was found in the HPV 16 E7 oncoproteins at amino acid position at 29. And this KE7-1 variant was commonly detected in the uterine cervical cancer compared to the normal cervix. The second most common variant, detected in 16 cases (20.3%), had three silent mutations at nucleotide positions 732 (T-->C), 789 (T-->C) and 795 (T-->G). The third variant had a single nucleotide change at position 666 (G-->A), and the fourth had a change at position 796 (T-->C). Furthermore, PCR-SSCP clearly showed distinct bands compatible with HPV 16 E7 variants as with the direct-sequencing method. PCR-SSCP was also an effective and reliable tool in detecting HPV 16 E7 variants. This study showed that there were four variant types of HPV 16 E7 in uterine cervical tissues and KE7-1 with corresponding amino acid change was the most commonly detected type in E7 variants of HPV 16 isolated from uterine cervical cancer in Korean women.