The activity of the activation function 2 of the human hepatocyte nuclear factor 4 (HNF-4 alpha) is differently modulated by F domains from various origins

Hepatocyte nuclear factor 4 (HNF-4) is a member of the nuclear hormone-rece ptor superfamily, which plays an important role in the regulation of severa l genes involved in numerous metabolic pathways. HNF-4 contains a DNA-bindi ng domain located in domain C and two activation-function domains, designat ed AF-1 and AF-2, located in domains A/B and E, respectively. The seven iso forms of human HNF-4, termed alpha 1-alpha 6 and gamma, differ mainly by th eir A/B and F domains. The high sequence variability of the F domain led us to investigate whether this domain modulates the transcriptional activity of HNF-4. Using constructs having the same core receptor and different F do mains, we observed that the F domains of HNF-4 modulate the transactivating activity of the full-length HNF-4. A more precise analysis using HNF-4 alp ha AF-2 fused to GAL4 protein and various F domains demonstrated that F dom ains of isoforms alpha 3 and gamma exhibited inhibitory effects on the acti vation function AF-2 but that their inhibition behaviours were weaker than that of HNF-4 alpha 2 F domain, which has been reported previously. The pre sence of domain F results in a decreased interaction with the coactivator g lucocorticoid receptor-interacting protein 1. For a given F domain, the mod ulating effects on the full-length HNF-4 as well as on the AF-2 depended on the target promoters. Our results suggest that the presence of domain F re sults in conformation changes in HNF-4 AF-2 or in its spatial environment, which probably modify the interaction of the AF-2 activation domain with co -factors and transcription factors bound to cis-elements of the target prom oters.