Identification of a cis-acting element involved in the regulation of BACE1 mRNA alternative splicing.

beta-site APP cleaving enzyme 1 (BACE1) is the transmembrane aspartyl protease that catalyzes the first cleavage step during proteolysis of the beta-amyloid precursor protein, a process involved in the pathogenesis of Alzheimer disease. BACE1 pre-mRNA undergoes complex alternative splicing, and cis-acting elements important for its regulation have not been identified. We constructed and compared several BACE1 minigenes and found that BACE1 sequence from exon 3 through exon 5 was required for minigenes to undergo correct splicing. Minigene splicing was validated by showing specific splicing inhibition upon splice site mutation. Furthermore, we showed that mutation of the minigene at a predicted exonic splicing enhancer in exon 4 of BACE1 increased exon 4 skipping. Therefore, we have for the first time found evidence of a regulatory site involved in BACE1 alternative splicing, and these data indicate that minor sequence changes can dramatically alter BACE1 alternative splicing.