ELEVATED EXPRESSION AND ACTIVITY OF MITOTIC REGULATORY PROTEINS IN HUMAN PAPILLOMAVIRUS IMMORTALIZED KERATINOCYTES

The E6 and E7 proteins of human papillomavirus (HPV) types 16 and 18 a re expressed in cell lines derived from cervical cancers and can immor talize primary human keratinocytes. Since expression of E6/E7 has been shown to induce mitotic defects and karyotype instability in primary human cells, we investigated the effect of these viral oncoproteins on the expression and activity of mitotic regulatory proteins. Primary h uman keratinocytes immortalized by the entire genome or by only the E6 /E7 genes of HPV types 16 and 18 displayed 5- to 20-fold increases in the abundance of p34(cdc2), cyclin B and cyclin A when compared with n ormal parental cells. Results obtained from normal and immortalized ce lls that were derived from identical single donors were similar to tho se from mixed donor cultures. Increased protein levels were achieved w ithout corresponding increases in mRNA, indicating alterations in tran slational and/or post-translational control. The histone H1 kinase act ivities associated with these regulatory proteins were also elevated, but to a lesser extent than the protein levels. Because p34(cdc2), cyc lin B and cyclin A regulate the entry into and exit from mitosis, incr eased expression and activity of these proteins could contribute to th e mitotic defects and chromosomal aberrations associated with HPV-indu ced immortalization.