THE HUMAN PAPILLOMAVIRUS E6 E7 GENES INDUCE DISCORDANT CHANGES IN THEEXPRESSION OF CELL-GROWTH REGULATORY PROTEINS/

The E6/E7 oncoproteins of human papillomavirus (HPV) types 16 and 18 a re responsible for the efficient immortalization of human genital kera tinocytes and we have recently reported that such immortalized cells d isplay alterations in the expression of cyclin A, cyclin a, and cdc-2, To determine whether these alterations were the consequence of E6/E7 protein expression or whether they resulted from the process of cellul ar immortalization, we multiply-infected primary genital keratinocytes with a retrovirus expressing the HPV-18 E6/E7 genes and examined the cells for acute, pre-immortalization changes in several critical cell growth regulatory proteins including cyclin A, cyclin B, cdc-2, p53 an d c-myc, In addition, we simultaneously evaluated the expression of th e E6/E7, bcl-2 and involucrin genes to determine whether there were ac companying alterations in the expression of viral genes or in cellular genes related to cell apoptosis and the state of keratinocyte differe ntiation. The cell cycle regulating proteins (cyclin A, cyclin B, cdc- 2 and p53) change significantly within days after retroviral infection , Cyclin B and cdc-2 increase over 4-fold by three passages and remain relatively constant thereafter through passage 21, whereas the levels of p53 protein decrease 25% by passage three. Increases in the expres sion of cyclin A, cyclin a and cdc-2, and decreases in p53 are therefo re among the earliest observable changes in cell regulatory proteins f ollowing E6/E7 gene expression and may be important contributors to th e development of cell immortalization, The expressions of viral E6/E7 genes, c-myc, bcl-2 and involucrin exhibit progressive changes with in creased passage numbers until passage 21, presumably reflecting the se lective outgrowth of immortalized cells.