Pa. Paganetti et al., AMYLOID PRECURSOR PROTEIN TRUNCATED AT ANY OF THE GAMMA-SECRETASE SITES IS NOT CLEAVED TO BETA-AMYLOID, Journal of neuroscience research, 46(3), 1996, pp. 283-293
beta A4 secretion occurs upon processing of amyloid protein precursor
(APP) by beta-secretase (N-terminus of beta A4) and gamma-secretase (C
-terminus), To determine the sequence of these activities and the proc
essing intermediate of beta A4, we expressed several truncated APP mol
ecules in human HEK-293 cells, Immunofluorescence and biotinylation st
udies indicated that full-length APP or APP lacking the cytosolic doma
in both were located intracellularly, associated with the cell surface
and secreted, APPs truncated after amino acid 40, 42, or 43 of beta A
4 were not inserted into cell membranes, were found intracellularly bu
t not on the cell surface, and were efficiently secreted into the cult
ure medium, The secretion of APP truncated at amino acid 40 of beta A4
occurred without proteolytic processing, Neither beta A4 nor P3 (the
product of the alpha-secretase) was secreted from any of the APP molec
ules truncated at the gamma-secretase sites, In sharp contrast to this
, when the C-terminal 100 amino acids of APP were expressed (APP trunc
ated at the N-terminus of beta A4), a robust beta A4 secretion was obs
erved, Thus, the C-terminal fragment of APP produced by beta-secretase
activity is likely to be the processing intermediate of beta A4. (C)
1996 Wiley-Liss, Inc.