Evidence That Tumor Necrosis Factor α Converting Enzyme Is Involved in Regulated α-Secretase Cleavage of the Alzheimer Amyloid Protein Precursor

Abstract

The amyloid protein, A␤, which accumulates in the brains of Alzheimer patients, is derived by proteolysis of the amyloid protein precursor (APP). APP can undergo endoproteolytic processing at three sites, one at the amino terminus of the A␤ domain (␤-cleavage), one within the A␤ domain (␣-cleavage), and one at the carboxyl terminus of the A␤ domain (␥-cleavage). The enzymes responsible for these activities have not been unambiguously identified. By the use of gene disruption (knockout), we now demonstrate that TACE (tumor necrosis factor ␣ converting enzyme), a member of the ADAM family (a disintegrin and metalloprotease-family) of proteases, plays a central role in regulated ␣-cleavage of APP. Our data suggest that TACE may be the ␣-secretase responsible for the majority of regulated ␣-cleavage in cultured cells. Furthermore, we show that inhibiting this enzyme affects both APP secretion and A␤ formation in cultured cells.The amyloid protein, A␤, which accumulates in the brains of Alzheimer patients, is derived by proteolysis of the amyloid protein precursor (APP) 1 (1-3). APP can undergo endoproteolytic processing at three sites, one at the amino terminus of the A␤ domain (␤-cleavage), one within the A␤ domain (␣-cleavage), and one at the carboxyl terminus of the A␤ domain (␥-cleavage). The enzymes responsible for these activities have not been unambiguously identified.In most cells in culture, a fraction (10 -30%) of all APP undergoes ␣-cleavage (4 -7). This results in the secretion of the large extracellular domain of APP into the medium. This secreted APP (APP s ) is a major APP-related species found in cerebrospinal fluid and brain homogenates (8,9) and is thought to interact with components of the extracellular matrix and with receptors on cells. In cultured cells it has been shown that the fraction of APP that is converted to APP s can be increased by activating second messenger cascades including those involving protein kinase C, protein kinase A, mitogen-activated protein kinase, protein phosphatase 1, protein phosphatase 2B (calcineurin), and calcium (4 -6, 10 -14). In most cells in culture, activating protein kinase C causes the majority (80 -95%) of the APP to undergo ␣-cleavage ("regulated" ␣-cleavage). Stimulation of APP s formation and secretion by activating second messenger cascades is not due to the phosphorylation of APP (15, 16) but may be due to protein phosphorylation leading to alterations in the trafficking of APP (17) or in the activity of an ␣-secretase. Importantly, stimulating ␣-cleavage of APP leads to a significant decrease in A␤ formation (18 -20).The potential importance of regulated cleavage of APP is indicated by the ability of acetylcholine, a critical neurotransmitter altered in Alzheimer's disease, working through muscarinic receptors, to stimulate regulated cleavage (4,10,21,22). Activation of other metabotropic receptors also leads to activation of regulated secretion of APP (4,21,23,24). Regulated cleavage of APP appears to occur in vivo under conditions in which protein ...

Zinc and copper modulate Alzheimer Aβ levels in human cerebrospinal fluid

“…1 & 2,Table 1) probably reflects the interaction of metals with Aβ or with enzymes that cleave Aβ or process APP in the brain interstitium. Cu and Zn could promote non-amyloidogenic APP processing by metalloproteinases such as TACE and ADAM-10 [11], or promote the degradation of Aβ by interstitial metalloproteinases neprilysin and IDE. Alternatively, elevated metals could promote the sequestration of Aβ by α-2 macroglobulin [15].…”

“…Such metalloproteinases, which are also present in cerebrospinal fluid (CSF), include neprilysin [24], insulin degrading enzyme (IDE) [35] and matrix metalloproteinases (MMP2 and 3) [42]. Additionally, the normal generation of Aβ may be modulated by zinc since α-secretases, tumor necrosis factor-alpha-converting enzyme (TACE or ADAM-17) and ADAM-10 [11], are members of the cell surface zinc metalloproteinase family of disintegrin and metalloprotease (ADAM) proteins. Abnormal metal homeostasis in the brain in AD [37], may therefore impact upon the processing or catabolism of Aβ.…”

The role of cerebral amyloid accumulation in common forms of Alzheimer disease

“…Another APP secretase proteinase, α-secretase, is comprised of cell-surface metalloproteinases, a disintegrin and metalloproteinase-10 (ADAM-10) and -17 (22). These proteases cleave several known important substrates in addition to APP, including pro-TNF-α and pro-TGF-α.…”

Stimulation of cleavage of membrane proteins by calmodulin inhibitors

“…Structurally, TACE is a type I membrane protein that contains several domains in the extracellular region, including disintegrin and metalloprotease-like (ADAM) domains, characteristic of the ADAM subfamily of metalloproteases [18,19]. TACE may also participate in the cleavage of other transmembrane proteins, since cells from TACE-deficient animals fail to efficiently cleave pro-transforming growth factor α (proTGFα), L-selectin, the p75 TNFR [20] or βAPP [21]. It is possible that other proteases may be involved in the regulation of membrane-protein ectodomain cleavage.…”