IN-VIVO PROTEIN-DNA INTERACTIONS ON A GLUCOCORTICOID RESPONSE UNIT OFA LIVER-SPECIFIC GENE - HORMONE-INDUCED TRANSCRIPTION FACTOR-BINDING TO CONSTITUTIVELY OPEN CHROMATIN

Transcription from the liver promoter of a 6-phosphofructo-2-kinase/fr uctose-2,6-bi (PFK-2) gene depends on the presence of glucocorticoids that act via a glucocorticoid response unit (GRU) located in the first intron, The promoter and the GRU are in a constitutively open chromat in configuration. To determine how glucocorticoids would affect factor binding to the GRU in absence of chromatin remodeling, we have used a combination of in vitro DNA-binding assays and in vivo genomic footpr inting in rat hepatocytes and hepatoma cells, We found that, in the ab sence of glucocorticoids, the GRU binds nuclear factor-I (NF-I), Gluco corticoid treatment modified factor binding to the NF-I site and induc ed the binding of hepatocyte nuclear factor-3 (HNF-3). Transfection as says showed that HNF-3 cooperates with the glucocorticoid receptor in stimulating transcription. In contrast with the lack of effect of gluc ococorticoids on factor binding to constitutively open GRUs of other g enes, HNF-S binding to the open PFK-2 GRU was hormone-dependent. There fore, the PFK-2 GRU behaves as a novel type of GRU.