Human papillomavirus 16 E6/E7 transcript and E2 gene status in patients with cervical neoplasia

The viral transforming genes E6 and E7 of human papillomavirus (HPV) 16 cause the degradation of tumor suppressor proteins. Expression of these oncoproteins increases following the integration of viral DNA into the host cell, resulting in the disruption of the E2 open reading frame (ORF).

To detect and correlate HPV-16 oncogene transcripts and HPV-16 E2 DNA in cervical biopsies obtained from women (n = 68) with cervical neoplasia.

HPV-16 E6/E7 transcript and HPV-16 E2 DNA detection was performed on the cervical biopsies of 42 women positive for HPV-16 (36 with invasive cervical carcinoma and 6 with cervical intraepithelial neoplasia [CIN]). PCR was used to detect HPV DNA in cervical biopsies then restriction fragment length polymorphism (RFLP) was used to type the HPV DNA. Reverse-transcription (RT)-PCR for HPV-16 E6/E7 oncogene mRNA transcripts and a PCR to detect the HPV-16 E2 DNA was performed on HPV-16-positive samples.

HPV-16 E6/E7 mRNA transcripts were not detected in any of the CIN I or II biopsies, but were detected in all cases of CIN III and invasive cancer in different combinations (E6 alone, E6*I, E6*I/E6*II, E6/E6*I/E6*II) except for one patient with stage IIB cancer treated with radiotherapy. The incidence of episomal E2 DNA was high in this study with 52.4% of the samples positive for episomal E2. It was even detected in patients with advanced stage cancer with 50%, 42%, and 66.6% of samples positive in stages IIB, IIIB, and IV, respectively.

HPV-16 E6/E7 mRNA oncogene transcripts, in various combinations, were uniformly detectable in the majority of the high-grade cervical lesions examined. Intact episomal E2 DNA was seen in a high proportion of samples, even from advanced cervical lesions. Conservation of the E2 gene with concomitant expression of viral oncogenes in advanced cervical lesions may point to alternate mechanisms, other than integration, bringing about the enhanced expression of E6/E7 mRNA.

This study suggests that the detection of the HPV-16 oncogene transcripts could serve as an indicator for assessing the prognosis of patients on radiotherapy. The majority of HPV-16-positive cervical neoplastic lesions are transcriptionally active and express the oncogene transcripts. The increased occurrence of intact HPV-16 episomal E2 DNA in advanced lesions further substantiates the fact that the disruption of E2 ORF is not mandatory for increased oncogene expression. Thus, this study underscores the significance of investigating alternative mechanisms of oncogene expression in HPV-16.