Biochem. J. (2001) 357
(787–794) (Printed in Great Britain)
Constitutive shedding of the amyloid precursor protein ectodomain is up-regulated by tumour necrosis factor-a converting enzyme
Barbara E. SLACK1, Leona K. MA and Ching Ching SEAH
Department of Pathology and Laboratory Medicine, Boston University School of Medicine, 85 East Newton Street, Rm. M1007, Boston, MA 02118, U.S.A.
The amyloid precursor protein (APP) of Alzheimer's disease is a transmembrane protein that is cleaved within its extracellular domain, liberating a soluble N-terminal fragment (sAPPa). Putative mediators of this process include three members of the ADAM (a disintegrin and metalloprotease) family, ADAM9, ADAM10 and ADAM17/TACE (tumour necrosis factor-a converting enzyme). Tumour necrosis factor-a protease inhibitor (TAPI-1), an inhibitor of ADAMs, reduced constitutive and muscarinic receptor-stimulated sAPPa release in HEK-293 cells stably expressing M3 muscarinic receptors. However, the former was less sensitive to TAPI-1 (IC50 = 8.09µM) than the latter (IC50 = 3.61µM), suggesting that these processes may be mediated by different metalloproteases. Constitutive sAPPa release was increased several-fold in cells transiently transfected with TACE, and this increase was proportional to TACE expression. In contrast, muscarinic-receptor-activated sAPPa release was not altered in TACE transfectants. TACE-dependent constitutive release of co-transfected APP695 was inhibited by TAPI-1 with an IC50 of 0.92µM, a value significantly lower than the IC50s for inhibition of either constitutive or receptor-regulated sAPPa shedding mediated by endogenous secretases. The results indicate that TACE is capable of catalysing constitutive a-secretory cleavage of APP, but it is likely that additional members of the ADAM family mediate endogenous constitutive and receptor-coupled release of sAPPa in HEK-293cells.
Key words: Alzheimer's disease, ADAM proteases, disintegrins, sAPPa, a-secretase.
Abbreviations used: ADAM, a disintegrin and metalloprotease; APP, amyloid precursor protein; DMEM, Dulbecco's modified Eagle's medium; PKC, protein kinase C; sAPPa, soluble APP ectodomain released by a-secretase; TACE, tumour necrosis factor-a converting enzyme; TAPI-1, tumour necrosis factor-a protease inhibitor.
1To whom correspondence should be addressed (e-mail bslack@bu.edu).
Received 26 January 2001/13 April 2001; accepted 21 May 2001
The Biochemical Society, London ©
2001
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