title: Platelets and DAMI megakaryocytes possess beta-secretase-like activity.
abstract: We report here the discovery of two novel human platelet and megakaryocytic DAMI cell enzymes that have beta-secretase-like activity. These activities could potentially effect cleavage of the amyloid precursor protein (APP) at the beta-amyloid peptide N-terminus, by an EC 3.4.24.15-like metalloprotease, and the N terminus-1 position, by a serine protease. Thus both enzymes may generate the amyloidogenic beta-peptide. Studies of intact and Triton X-100-lysed DAMI cells, as well as intact versus subcellular fractions of platelets, demonstrate the presence of these proteolytic activities. The resting platelet has (1) a surface serine protease, demonstrated by its ability to cleave a beta-secretase substrate and by its inhibitor sensitivity; and (2) a metalloprotease, recognized by an antibody to EC 3.4.24.15, which resides intracellularly in the alpha-granule membrane, is translocated to the surface on activation, and shows beta-secretase-like activity by cleaving the same substrate. This metalloprotease can also cleave recombinant APP to a potentially amyloidogenic fragment. Surface metalloprotease was identified in DAMI cells by flow cytometry and Western blotting with a specific anti-EC 3.4.24.15 monoclonal antibody, while activity was identified by using two beta-secretase substrates. This article is the first to document two previously unknown endoproteinases with beta-secretase-like activity in platelets and DAMI cells. These proteases are capable of effecting cleavage of APP and could therefore contribute to Abeta deposition in the cerebrovasculature.
authors.affiliation: Boston University School of Medicine, Massachusetts 02118, USA.
authors.forename: C R
authors.initials: CR
authors.lastname: Abraham
authors.forename: D C
authors.initials: DC
authors.lastname: Marshall
authors.forename: H E
authors.initials: HE
authors.lastname: Tibbles
authors.forename: K
authors.initials: K
authors.lastname: Otto
authors.forename: H J
authors.initials: HJ
authors.lastname: Long
authors.forename: A M
authors.initials: AM
authors.lastname: Billingslea
authors.forename: R
authors.initials: R
authors.lastname: Hastey
authors.forename: R
authors.initials: R
authors.lastname: Johnson
authors.forename: R E
authors.initials: RE
authors.lastname: Fine
authors.forename: S J
authors.initials: SJ
authors.lastname: Smith
authors.forename: E R
authors.initials: ER
authors.lastname: Simons
authors.forename: T A
authors.initials: TA
authors.lastname: Davies
mesh_terms: D000544:Alzheimer Disease / Q000201:enzymology*; D053829:Amyloid Precursor Protein Secretases; D016564:Amyloid beta-Protein Precursor / Q000378:metabolism; D000911:Antibodies, Monoclonal / Q000276:immunology; D016282:Aspartic Acid Endopeptidases; D001792:Blood Platelets / Q000201:enzymology*; D010450:Endopeptidases / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D008533:Megakaryocytes / Q000201:enzymology*; D008565:Membrane Proteins / Q000276:immunology; D008666:Metalloendopeptidases / Q000378:metabolism; D009282:Naphthalenesulfonates / Q000378:metabolism; D009842:Oligopeptides / Q000378:metabolism; D010455:Peptides / Q000378:metabolism; D012697:Serine Endopeptidases / Q000378:metabolism; D013379:Substrate Specificity; D013917:Thrombin / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: C095536:(4,4'-dimethylaminophenazo)benzoyl-arginyl-glycyl-valyl-valyl-asparaginyl-alanyl-seryl-seryl-arginyl-leucyl-alanyl-5-((2'-aminoethyl)amino)naphthalene-1-sulfonic acid; D016564:Amyloid beta-Protein Precursor; D000911:Antibodies, Monoclonal; D004791:Enzyme Inhibitors; D008565:Membrane Proteins; D009282:Naphthalenesulfonates; D009842:Oligopeptides; D010455:Peptides; D053829:Amyloid Precursor Protein Secretases; D010450:Endopeptidases; D012697:Serine Endopeptidases; D013917:Thrombin; D016282:Aspartic Acid Endopeptidases; C509280:BACE1 protein, human; D008666:Metalloendopeptidases