TRANSCRIPTIONAL REGULATION OF THE CHOLESTERYL ESTER TRANSFER PROTEIN GENE BY THE ORPHAN NUCLEAR HORMONE-RECEPTOR APOLIPOPROTEIN AI REGULATORY PROTEIN-1

We have defined a 105-base pair tissue-restricted promoter for the cho lesteryl ester transfer protein (CETP) gene that contains a nuclear ho rmone receptor response element essential for transcriptional activity , DNaseI protection and electrophoretic mobility shift assays showed s pecific binding of nuclear extracts from HepG2 (hepatic) and Caco-2 (i ntestinal) cells (expressing cell types) to 3 sites (designated A (-26 to -57), B (-59 to -87), and C (-93 to -118)) within the 105-base pai r minimal promoter element between -138 and -33. Mutagenesis studies i ndicated that the function of the promoter was dependent upon synergis tic interactions between transcription factors bound to these sites. M utation of site C reduced transcription by 50 and 80%, respectively, i n HepGa and Caco-2 cells, and electrophoretic mobility shift assays sh owed that nuclear hormone receptors, including ARP-1 and its homologue Ear-3/COUP-TF, were occupants of site C in both of these cell types. Overexpression of ARP-1 or Ear-3/COUP-TF with CETP promoter/chloramphe nicol acetyltransferase gene reporter plasmids repressed transcription al activity of the CETP promoter containing sequences up to -300, but activated transcription in the contest of larger constructs containing sequences up to -636. Thus ARP-1 may assume a dichotomous role as bot h a transcriptional repressor and a transcriptional activator dependen t on the promoter context. In addition, the architecture of the CETP g ene promoter suggests that its expression is under the control of mult iple transcriptional signaling pathways mediated by inducible transcri ption factors as well as nuclear hormone receptors.