Human genetic data have associated angiotensin-converting enzyme (ACE) with Alzheimer disease (AD), and purified ACE has been reported to cleave synthetic amyloid ␤-protein (A␤) in vitro. Whether deficiency in ACE activity, arising from genetic alteration or pharmacological inhibition, can decrease A␤ degradation and allow A␤ accumulation in intact cells is unknown. We cloned ACE from human neuroblastoma cells and showed that it had posttranslational processing and enzymatic activity typical of the endogenous protease. Cellular expression of ACE promoted degradation of naturally secreted A␤40 and A␤42, leading to significant clearance of both species. Using site-directed mutagenesis, we determined that both active sites within ACE contribute to A␤ clearance, and an ACE construct bearing mutations in each catalytic domain had no effect on A␤ levels. Pharmacological inhibition of ACE with a widely prescribed drug, captopril, promoted the accumulation of cell-derived A␤ in the media of ␤-amyloid precursor-protein expressing cells. Together, these results show that ACE can lower the levels of secreted A␤ in living cells and that this effect is blocked by inhibiting the protease's activity with an ACE inhibitor. This work, combined with the genetic studies, supports the hypothesis that ACE may modulate the susceptibility to and progression of AD via degradation of A␤. Our data encourage further analyses of the ACE gene for disease association and raise the question of whether currently prescribed ACE inhibitors could elevate cerebral A␤ levels in humans. An early and pathogenically important feature of Alzheimer disease (AD)2 is the progressive accumulation and deposition of the amyloid ␤-protein (A␤) in brain regions serving memory and cognition. Biochemical, cell biological, animal modeling, genetic, and emerging clinical data all suggest that A␤ is an upstream initiator of the disease process and its associated neuropathology (1-4). Although no proven diseasemodifying treatments are currently available, recent efforts to treat AD have focused on both decreasing the production of A␤ and enhancing its clearance from the brain. One little studied approach to A␤ clearance is augmenting the degradation of the peptide by various proteases expressed in the brain. Thus far, the metalloproteases neprilysin (NEP) (5), insulin-degrading enzyme (IDE) (6), and the endothelin-converting enzymes 1 and 2 (7) have each been implicated as A␤-degrading proteases in the mammalian brain. The serine protease plasmin has been implicated in A␤ degradation in vitro (8), although genetic plasmin deficiency did not promote accumulation of murine A␤ in vivo (9). Supporting a role for therapeutic regulation of A␤-degrading proteases, the overexpression of IDE or NEP in a murine model of AD decreased cerebral A␤ levels and produced significant attenuation of A␤-associated neuropathology (10).Somatic angiotensin-converting enzyme (ACE) is a zinc metalloprotease containing two homologous regions, termed the N-and C-domains, each of which is prot...

β-site APP cleaving enzyme 1 (BACE1) is a transmembrane aspartyl protease with a lumenal active site that sheds the ectodomains of membrane proteins through juxtamembrane proteolysis. BACE1 has been studied principally for its role in Alzheimer's disease as the β-secretase responsible for generating the amyloid-β protein. Emerging evidence from mouse models has identified the importance of BACE1 in myelination and cognitive performance. However, the substrates that BACE1 processes to regulate these functions are unknown, and to date only a few β-secretase substrates have been identified through candidate-based studies. Using an unbiased approach to substrate identification, we performed quantitative proteomic analysis of two human epithelial cell lines stably expressing BACE1 and identified 68 putative β-secretase substrates, a number of which we validated in a cell culture system. The vast majority were of type I transmembrane topology, although one was type II and three were GPI-linked proteins. Intriguingly, a preponderance of these proteins are involved in contact-dependent intercellular communication or serve as receptors and have recognized roles in the nervous system and other organs. No consistent sequence motif predicting BACE1 cleavage was identified in substrates versus non-substrates. These findings expand our understanding of the proteins and cellular processes that BACE1 may regulate, and suggest possible mechanisms of toxicity arising from chronic BACE1 inhibition.

Synovial sarcoma tumours contain a characteristic fusion protein, SS18-SSX, which drives disease development. Targeting oncogenic fusion proteins presents an attractive therapeutic opportunity. However, SS18-SSX has proven intractable for therapeutic intervention. Using a domain-focused CRISPR screen we identified the bromodomain of BRD9 as a critical functional dependency in synovial sarcoma. BRD9 is a component of SS18-SSX containing BAF complexes in synovial sarcoma cells; and integration of BRD9 into these complexes is critical for cell growth. Moreover BRD9 and SS18-SSX co-localize extensively on the synovial sarcoma genome. Remarkably, synovial sarcoma cells are highly sensitive to a novel small molecule degrader of BRD9, while other sarcoma subtypes are unaffected. Degradation of BRD9 induces downregulation of oncogenic transcriptional programs and inhibits tumour progression in vivo. We demonstrate that BRD9 supports oncogenic mechanisms underlying the SS18-SSX fusion in synovial sarcoma and highlight targeted degradation of BRD9 as a potential therapeutic opportunity in this disease.