The expression of HPV oncogenes in transduced human foreskin keratinocyte (HFK) cells. (A) Cells were transduced by recombinant retroviruses carrying either the control vector (LXSN) or vectors encoding HPV16 E6, E7, or E6/E7. The cells were either left in serum-free medium (proliferating cells) or induced to differentiate in DMEM (with serum and high calcium). RT-PCR analysis was used to confirm the expression of the appropriate HPV oncogenes in the different cell lines (GAPDH was used as an endogenous control). (B) The effect of HPV16 E6 and E7 on the level of p53 protein. Protein extracts from transduced cells were subjected to Western blot assay for p53 or actin (the latter as loading control). Parts of representative X-ray films are shown.