Proteolytic processing of the amyloid precursor protein by ␣-secretase prevents formation of the amyloid -peptide (A), which is the main constituent of amyloid plaques in brains of Alzheimer disease (AD) patients. ␣-Secretase activity is decreased in AD, and overexpression of the ␣-secretase ADAM10 (a disintegrin and metalloprotease 10) in an AD animal model prevents amyloid pathology. ADAM10 has a 444-nucleotide-long, very GC-rich 5-untranslated region (5-UTR) with two upstream open reading frames. Because similar properties of 5-UTRs are found in transcripts of many genes, which are regulated by translational control mechanisms, we asked whether ADAM10 expression is translationally controlled by its 5-UTR. We demonstrate that the 5-UTR of ADAM10 represses the rate of ADAM10 translation. In the absence of the 5-UTR, we observed a significant increase of ADAM10 protein levels in HEK293 cells, whereas mRNA levels were not changed. Moreover, the 5-UTR of ADAM10 inhibits translation of a luciferase reporter in an in vitro transcription/translation assay. Successive deletion of the first half of the ADAM10 5-UTR revealed a striking increase in ADAM10 protein expression in HEK293 cells, suggesting that this part of the 5-UTR contains inhibitory elements for translation. Moreover, we detect an enhanced ␣-secretase activity and consequently reduced A levels in the conditioned medium of HEK293 cells expressing both amyloid precursor protein and a 5-UTR-ADAM10 deletion construct lacking the first half of the 5-UTR. Thus, we provide evidence that the 5-UTR of ADAM10 may have an important role for post-transcriptional regulation of ADAM10 expression and consequently A production.
Alzheimer disease (AD)4 is the most common form of dementia worldwide. The major pathological hallmarks of AD are neurofibrillary tangles and amyloid plaques (1). Amyloid plaques are composed of the amyloid- peptide (A), which is derived by proteolysis from the -amyloid precursor protein (APP) (2). Two proteases, termed -and ␥-secretase generate A. The aspartyl protease -site APP cleaving enzyme 1 (BACE1) was identified as -secretase and cleaves APP into two fragments (summarized in Ref.3). The extracellular N-terminal domain of APP, APPs, is released upon shedding by BACE1. Recently, it was reported that a N-terminal proteolytic derivative of APPs could bind to the death receptor DR6, thereby triggering axon pruning and neuronal death under conditions where trophic factors are reduced (4). The remaining membrane-bound C-terminal stub of APP is the immediate precursor for A generation by ␥-secretase (5). Alternatively, APP is also cleaved in a nonamyloidogenic pathway by ␣-secretase within the A domain, thereby preventing the formation of A (6, 7). Processing of APP by ␣-secretase generates the soluble APPs␣ ectodomain, which may have neuroprotective and neurotrophic properties (8). The resulting membrane-bound C-terminal fragment is further cleaved by ␥-secretase to produce p3, a N-terminally truncated A derivative (9).Three memb...