EFFECTS OF 12-O-TETRADECANOYLPHORBOL-13-ACETATE ON HUMAN PAPILLOMAVIRUS TYPE 16-POSITIVE KERATINOCYTES AT DIFFERENT STAGES OF TRANSFORMATION

Normal human keratinocytes grown under serum-free conditions can be tr iggered to differentiate by exposure to serum or to the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). We found that TPA treatmen t of human papillomavirus (HPV) type 16-immortalized cells in culture induced formation of cornified envelopes indicative of squamous differ entiation. Concurrent with differentiation, TPA inhibited the expressi on of HPV 16 E6 and E7 mRNA transcripts. Adaptation of the immortalize d cells to growth in serum-containing medium led to the selection of a subpopulation of HPV-transformed cells that was resistant to TPA-indu ced differentiation. in this cell line, a transient suppression of HPV transcripts was observed at 5 h, whereas in differentiation-resistant , carcinoma-derived lines, TPA had little effect on HPV oncogene expre ssion. c-myc transcripts were suppressed for the duration of exposure to TPA in only the differentiation-competent cells; c-fos and c-jun we re transiently induced in all cell lines. Transforming growth factor-a mRNAs were also increased approximately eightfold as HPV 16-immortali zed cells were induced to differentiate. These results demonstrate tha t, in HPV 16-immortalized keratinocytes, acquisition of resistance to inducers of squamous differentiation is accompanied by altered regulat ion of cell growth and gene expression. (C) 1995 Wiley-Liss, Inc.