Transcriptional stimulation by hepatocyte nuclear factor-6 - Target-specific recruitment of either CREB-binding protein (CBP) or p300/CBP-associated

Transcription factors of the ONECUT class, whose prototype is HNF-6, contai n a single cut domain and a divergent homeodomain characterized by a phenyl alanine at position 48 and a methionine at position 50, The cut domain is r equired for DNA binding. The homeodomain is required either for DNA binding or for transcriptional stimulation, depending on the target gene. Transcri ptional stimulation by the homeodomain involves the F48M50 dyad, We investi gate here how HNF-6 stimulates transcription. We identify transcriptionally active domains of HNF-6 that are conserved among members of the ONECUT cla ss and show that the cut domain of HNF-6 participates to DNA binding and, v ia a LXXLL motif, to transcriptional stimulation, We also demonstrate that, on a target gene to which HNF-6 binds without requirement for the homeodom ain, transcriptional stimulation involves an interaction of HNF-6 with the coactivator CREB-binding protein (CBP). This interaction depends both on th e LXXLL motif of the cut domain and on the F48M50 dyad of the homeodomain, On a target gene for which the homeodomain is required for DNA binding, but not for transcriptional stimulation, HNF-6 interacts with the coactivator p300/CBP-associated factor but not with CBP. These data show that a transcr iption factor can act via different, sequence-specific, mechanisms that com bine distinct modes of DNA binding with the use of different coactivators.