The 5′‐untranslated sequence of the amyloid precursor protein transcript exerts post‐transcriptional control of gene expression by variable mechanisms

Abstract

The promoter of the human amyloid precursor protein (APP) gene directs cell-type specific expression with about 121 base pairs 5′ to the main transcriptional start site (+1). Transcription from this region is activated by transcription factors such as CTCF and USF. Downstream from the transcriptional start site the APP transcriptional unit contains an untranslated region (UTR) of 147 base pairs. We have here investigated the role of the APP-UTR in regulating expression from the APP promoter. For this purpose, deletions and transverse block mutations were introduced within the UTR. The constructs were analyzed by transient transfection, in vitro transcription, in vitro translation, DNase I footprinting, and mobility shift electrophoresis. The results showed that mutating sequences close to the transcriptional start site (position +1 to +25) interfered with transcriptional activity. In contrast, mutations between position +61 and +105 reduced expression in vivo in a transcriptionally independent manner. Within this domain two subdomains were identified. Mutations within one domain reduced translational activity in vitro. In contrast, mutations within a second domain eliminated a nuclear factor binding site while having no effect on translational activity. The protein that binds to the APP-UTR has not been identified but it is distinct from the thyroxin response element. In summary, two domains within the APP-UTR (position +61 to +105) affect expression from the APP promoter by independent post-transcriptional mechanisms. [Supported by NS30994].