Identification of the human papillomavirus type 18 E6 and E6 proteins in nuclear protein fractions from human cervical carcinoma cells grown in the nude mouse or in vitro.

We recently reported the transcription patterns of human papillomavirus (HPV) type 18 sequences in human cervical carcinoma cell lines. The open reading frames (ORFs) E6* and E6 represent the 5'-terminal cistrons in HPV18 mRNAs. ORF E6* was assumed to be specific for HPV types associated with genital carcinomas. To identify the predicted gene product, ORF E6* from a HeLa cDNA clone was expressed as an MS2 fusion protein in Escherichia coli. The C-terminal 23 amino acid residues were chemically synthesized. A panel of monoclonal antibodies was generated, recognizing E6* and E6* plus E6, respectively. In human cervical carcinoma cell lines grown in vitro these monoclonal antibodies specifically immunoprecipitate the putative Mr 17,000 and 18,000 HPV18 E6 proteins in nuclear protein fractions. In a HPV18 DNA containing human cervical carcinoma established in nude mice, these monoclonal antibodies specifically immunoprecipitate a polypeptide with a molecular weight of 6500 as predicted for the HPV18 ORF E6* gene product in a nuclear protein fraction.