Transcriptional repression by a conserved intronic sequence in the nicotinic receptor α3 subunit gene

Abstract

The genes encoding the nicotinic acetylcholine receptor α3, α5, and β4 subunits are genomically clustered. These genes are co-expressed in a variety of cells in the peripheral and central nervous systems. Their gene products assemble in a number of stoichiometries to generate several nicotinic receptor subtypes that have distinct pharmacological and physiological properties. Signaling through these receptors is critical for a variety of fundamental biological processes. Despite their importance, the transcriptional mechanisms underlying their coordinated expression remain to be completely elucidated. By using a bioinformatics approach, we identified a highly conserved intronic sequence within the fifth intron of the α3 subunit gene. Reporter gene analysis demonstrated that this sequence, termed "α3 intron 5," inhibits the transcriptional activities of the α3 and β4 subunit gene promoters. This repressive activity is position- and orientation-independent. Importantly, repression occurs in a cell type-specific manner, being present in cells that do not express the receptor genes or expresses them at very low levels. Electrophoretic mobility shift assays demonstrate that nuclear proteins specifically interact with α3 intron 5 at two distinct sites. We propose that this intronic repressor element is important for the restricted expression patterns of the nicotinic receptor α3 and β4 subunit genes. © 2007 by The American Society for Biochemistry and Molecular Biology, Inc.