Functional analysis of upstream common polymorphisms of the dopamine transporter gene

The human dopamine transporter (DAT, SLC6A3) has been extensively investigated because of its potential involvement in neuropsychiatric disorders. The core elements responsible for its transcription have been identified. A regulatory role for certain genomic variants upstream to the core promoter is known. Recently, other single-nucleotide polymorphisms (SNPs) have been identified in this region and are thought to be associated with schizophrenia and bipolar I disorder. Hence, we have investigated the impact of common SNPs in a 2.8-kilobase region flanking the core promoter region (-2.7 to +63 base pair) in the neuroblastoma cell line SH-SY5Y. Haplotypes generated by site-directed mutagenesis revealed varying impact of individual SNPs on promoter activity using dual luciferase assays. In silico analyses also predicted allele-specific binding of transcription factors for some of these SNPs. Though electrophoretic mobility shift assays indicated several factors that appeared to bind to specific sites within this region, allele-specific binding was not detected for any SNP apart from rs3756450. We have thus identified novel putative regulatory domains flanking the core promoter of DAT that merit further investigation.