Promoter analysis of RPE65, the gene encoding a 61-kDa retinal pigment epithelium-specific protein

Abstract

Purpose: To identify the functional promoter region and cis-acting elements that regulate the expression of RPE65, the retinal pigment epithelium (RPE)-specific gene responsible for certain forms of autosomal recessive childhood-onset severe retinal dystrophy.

Methods: A human genomic DNA clone containing the 5'-flanking region of RPE65 was isolated and, 4.0 kb proximal to the transcription start site, was sequenced and analyzed for the presence of transcription factor-binding sites. Promoter activity was assayed by transient transfection of luciferase reporter constructs containing nested deletions of the upstream sequence in the human RPE cell lines ARPE19 and D407, as well as in the SK-Mel-28 and HeLa cell lines. Specific DNA protein-binding sites present in the 340 bp upstream of the transcription start site were identified by DNase I footprint analysis.

Results: Sequence analysis places the polymorphic marker, D1S2803, within the RPE65 upstream region and identifies a number of sequences homologous to the gene encoding the cellular retinaldehyde-binding protein. Functional analysis indicates that basal promoter activity is conferred by the sequence from -83 to +39 and is approximately equivalent in all cell lines tested, with no other control elements detected in 3.6 kb of the upstream sequence. At least eight protected regions are identified in DNase I footprint assays, including sequences corresponding to the predicted TATA box, AP-4, and nuclear factor-1 DNA protein-binding sites.

Conclusions: These findings localize the basal promoter activity of RPE65, identify potential cis-acting elements that act as positive regulators of gene expression, and suggest that additional regulatory elements are likely to be involved in restricting gene expression to the retinal pigment epithelium. Identification of promoter elements and genetic markers in the upstream sequence will enable the screening of patients with retinal degeneration for possible mutations that affect RPE65 expression.