N-RAS ONCOGENE CAUSES AP-2 TRANSCRIPTIONAL SELF-INTERFERENCE, WHICH LEADS TO TRANSFORMATION

Genetic alterations in elements of normal signal transduction mechanis ms are known to be oncogenic events often resulting in aberrant activa tion of programs of gene transcription. We have investigated the effec t of N-ras oncogene-induced tumorigenic transformation on the transcri ption factor AP-2. N-ras oncogene-induced transformation of human tera tocarcinoma cells PA-1 results in sixfold elevated AP-2 mRNA bevels. H owever, the level of AP-2-mediated trans-activation is dramatically in hibited in these cells. We show here that the high-level expression of AP-2 ultimately results in transcriptional ''self-interference''. The activation domain of AP-2, when fused to the DNA-binding domain of GA L4, is sufficient for self-interference. Non-N-ras PA-1 cells constitu tively expressing AP-2 or GAL4-AP-2 fusion protein from an SV40 promot er exhibit reduced AP-2-mediated transcriptional activation, inhibitio n of differentiation, and promotion of anchorage-independent growth, p roperties that are similar to N-ras-transformed PA-1 cells. Thus, AP-2 is placed in the N-ras signal transduction pathway, and many of the b iological effects of N-ras can be accomplished by overexpression of AP -2. This is the first evidence that inhibition of the activity of a tr anscription factor by self-interference contributes to a physiological process.