HEPATOCYTE NUCLEAR FACTOR-IV ACTIVATES MEDIUM-CHAIN ACYL-COA DEHYDROGENASE GENE-TRANSCRIPTION BY INTERACTING WITH A COMPLEX REGULATORY ELEMENT

We have recently identified a complex transcriptional regulatory eleme nt in the medium chain acyl-CoA dehydrogenase (MCAD) gene promoter reg ion that confers response to retinoids through interaction with recept ors for all-trans-retinoic acid (RARs) and 9-cis-retinoic acid (RXRs) (Raisher, B. D., Gulick, T., Zhang, Z., Strauss, A. W., Moore, D. D., and Kelly, D. P. (1992) J. Biol. Chem. 267, 20264-20269). We examined the interaction of this element (RARE(MCAD)) with hepatocyte nuclear f actor-4 (HNF-4), an orphan receptor with a tissue expression pattern s imilar to that of MCAD. Electrophoretic mobility shift assays and cotr ansfection experiments showed that HNF-4 binds with high affinity to R ARE(MCAD) to activate transcription by an RXR-independent mechanism. M utational analysis revealed that the MCAD HNF-4 response element consi sts of an imperfect direct repeat homologous to the consensus sequence for binding to the thyroid receptor/RAR/RXR subgroup of receptors and that distinct sequence requirements dictate HNF-4 binding and transac tivation. Mobility shift assays with anti-HNF-4 antiserum demonstrated that the MCAD HNF-4 response element binds endogenous rat liver HNF-4 supporting its role in the regulation of MCAD gene expression in vivo . Thus, HNF-4 activates MCAD gene transcription via a complex regulato ry element, the architecture of which carries important implications f or the structure of HNF-4 response elements in general.