Isolation and characterization of the rat huntingtin promoter

Huntington's disease (HD) is a neurodegenerative disorder caused by a (CAG)(>37) repeat expansion in a novel gene of unknown function. Although the huntingtin gene is expressed in neuronal and non-neuronal tissues, the disease affects nerve cells of selected regional areas of the central nervous system. To gain insight into the regulation of the HD gene we analysed 1348 bp of the rat huntingtin promoter region. This region lacks a TATA and a CAAT box, is rich in GC content and has several consensus sequences for binding sites for SP1, PEA3, Sif and H2A. The stretch between nucleotides -56 and -206 relative to the first ATG is highly conserved between human and rodents and it harbours several potential binding sites for transcription factors. We analysed deletion mutants fused with the chloramphenicol acetyltransferase reporter gene in transfected, HD-expressing neuronal (NS20Y, NG108-15) and non-neuronal Chinese hamster ovary cell lines. Hence these cells should contain the: required trans-acting factors necessary for HD gene expression. Partial deletion of the evolutionarily conserved part of the promoter significantly decreases the activity in both neuronal and non-neuronal cells, indicating that the core promoter activity is located between nucleotides -332 and -15. DNase I footprinting and electrophoretic mobility-shift assays were used to define the nucleotide positions and binding affinity of DNA-protein interactions.