The beta-amyloid protein present in the neuritic plaques of Alzheimer's disease is cleaved from Abeta precursor protein by beta- and gamma-secretases. Following identification of beta-APP cleaving enzyme as the beta-secretase, a homologous beta-secretase 2 was described. Our goal is to characterize the regulatory region of the BACE genes. We compare functional domains within the BACE1 and BACE2 regulatory regions. Both BACE genes lack canonical TATAand CAAT boxes, but they contain distinguishing transcription start sites and transcription factor-binding sites. The BACE1 sequence (...) contains more repetitive elements than does BACE2 . Regulatory domains do not overlap strongly between the two promoter regions. The BACE1upstream sequence contains both negative and positive domains, separated from the transcription seat by a long neutral domain. The corresponding BACE2sequence consists of a weakly positive domain directly upstream of a strongly positive domain, near a functionally active domain. DNA-protein interaction was corroborated by functional data. In primary rat cortical cultures, BACE1-driven reporter protein's expression was twice that of BACE2- driven reporter. The BACE2 gene promoter relatively reduced function in neuronal cells compared with BACE1. The BACE1 gene might operate through a single transcriptional control site. BACE2 operates through dual transcriptional control sites. Two regulatory pathways might control transcription in BACE2. Thus, BACE2 is partially suppressed in normal neuronal cells and likely to be a highly regulated gene expressed in a particularly tissue-specific fashion. (shrink)

The main characteristic of Alzheimer's disease is brain deposition of the beta-amyloid peptide, generated endoproteolytically from Abeta precursor protein by beta- and gamma-secretases. A transmembrane aspartyl protease, beta-APP-cleaving enzyme , was identified as beta-secretase. Although BACE1 cleaves APP at the beta-secretase site, the role of its homolog, beta-secretase 2 is poorly understood. We report the mRNA expression profile, DNA sequence, and molecular characterization of the BACE2 gene, located on chromosome 21q22.3. The BACE2 gene expresses more strongly in peripheral tissues, although (...) BACE2 mRNA is found in the majority of brain regions, including the postcentral gyrus and temporal lobe. Characterization of 2932 bp of the BACE2 5'-flanking region , reveals the absence of canonical CCAAT and TATA boxes within 1 kb of the transcription start site . The sequence lacks significant internal repeats and has a housekeeping gene structure. Two active regions of the BACE2 promoter determine its basal expression and cell-type specificity. The proximal region likely determines general basal expression, and the distal region , cell-type specificity. Several putative transcription factor sites, particularly SP1, Oct-1, and HES-1, are predicted to be within 1 kb of the TSS. On either side of the proximal promoter region, two negative regulatory domains might reduce BACE2 expression under an induced condition. The BACE2 5'-flanking region is likely to be highly regulated and expressed in a tissue type-specific manner. (shrink)

The amyloid-beta peptide, the proteolytic fragment of Abeta precursor protein , aggregates and forms neuritic plaques, a major hallmark of Alzheimer's disease . The limiting step in generating the Abeta peptide from APP is cleavage by the beta-secretase enzyme, BACE1. Regulation of the BACE1 gene is likely to play an important role in AD etiology and treatment. We therefore studied the activity of a 4.1-kb 5'-flanking region of the BACE1 gene, both in 5'- and 3'-deletion series and through Northern blotting. (...) We show that the BACE1 promoter has regulatory activity throughout the 4.1-kb length, both positive and negative, and that this activity can be quantitatively modeled according to promoter sequence length, with the specific model depending on the presence of negative regulatory elements as the 5'- most portion of the sequence. We also examined a previously identified 141-bp proximal fragment of the BACE1 promoter and two constituent subfragments. We report that the 91-bp fragment is the most likely seat of neuronal expression of the BACE1 gene and that it is the portion of the 141-bp fragment that accounts for observed DNA-protein interactions in brain extracts. The 50-bp fragment , which showed significant reporter gene activity from the empty vector, binds nuclear proteins in a cell type-specific manner and contains the AP2 site as shown by the electrophoretic mobility shift assay. Overall, the 141-bp fragment had no strong matches within GenBank, and the 91-bp fragment is predicted to have several potential stem-loop sites. Taken together, BACE1 gene promoter activity is differentially regulated, and the 91-bp fragment represents a novel promoter region for cell type-specific regulation. This fragment might be a useful target to regulate BACE1 expression leading to Abeta production and to understand the neuropathogenesis of AD. (shrink)