CHIMERIC LIVER TRANSCRIPTION FACTORS LFB1 (HNF1) CONTAINING THE ACIDIC ACTIVATION DOMAIN OF VP16 ACT AS POSITIVE DOMINANT INTERFERING MUTANTS

The transcription factor LFB1 (HNF1) involved in the expression of liv er-specific genes is characterized by a serine/threonine-rich activati on domain whose transactivation potential differs between mammals and Xenopus. Exchanging the activation domain between the Xenopus and rat LFB1, we produced chimeric transactivators whose activities are primar ily determined by the origin of the activation domain. By replacing th e serine/threonine-rich activation domain of LFB1 with the acidic acti vation domain of VP16, we generated transcription factors that act as dominant positive interfering mutants on endogenous LFB1 in differenti ated hepatoma cells. As these LFB1/VP16 chimeras show no self-squelchi ng as observed with wild-type LFB1 and increase the activity of satura ting LFB1, we postulate that acidic and serine/threonine-rich activati on domains use different targets of the basal transcription machinery. Stable transfection of various LFB1 derivatives, including those cont aining the VP16 transactivation domain, into the dedifferentiated C2 h epatoma cell resulted in cell clones stably expressing LFB1 function. However, as in none of these clones the chromosomal albumin genes are activated, we conclude that the presence of functional LFB1 may not be sufficient to reactivate liver-specific functions lost in dedifferent iated hepatoma cells.