SPECIFICITY IN RECOGNITION OF AMYLOID-BETA PEPTIDE BY THE SERPIN-ENZYME COMPLEX RECEPTOR IN HEPATOMA-CELLS AND NEURONAL CELLS

The serpin-enzyme complex (SEC) receptor was originally identified usi ng a synthetic peptide (peptide 105Y) based on the sequence of a candi date receptor-binding domain of alpha 1-antitrypsin (1-AT) and was sub sequently shown to be a receptor on the surface of hepatocytes, monocy tes, and neutrophils for recognition of alpha 1-AT-elastase and severa l other serpin-enzyme complexes (Perlmutter, D. H., Glover, G. I., Riv etna, M., Schasteen, C. S., and Fallen, R. J. (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 3753-3757). Studies of the minimal requirements for b inding to SEC receptor (SEC-R) showed that a pentapeptide FVFLM within the carboxyl-terminal tail of alpha 1-AT was sufficient for binding t o SEC-R and interacted with SEC-R in a sequence-specific manner (Josli n, G., Krause, J. E., Hershey, A. D,, Adams, S. P., Fallen, R. J., and Perlmutter, D. H. (1991) J. Biol. Chem. 266, 21897-21902). Sequence m otifs bearing homology with this pentapeptide domain were found in the amyloid-beta peptide, and amyloid-beta peptide 1-42 was shown to comp ete for binding to SEC-R on hepatoma cells (Joslin, G., Fallen, R. J., Bullock, J., Adams, S. P., and Perlmutter, D. H. (1991) J. Biol. Chem . 266, 11281-11288). In this study we examined the sequence specificit y by which amyloid-beta peptide competes for binding to SEC-R and exam ined the possibility that SEC-R is expressed in cells of neuronal orig in. The results show that amyloid-beta-(25-35) and amyloid-beta-(31-35 ) compete for binding to SEC-R as effectively as amyloid-beta-(1-39), amyloid-beta-(1-40), and amyloid-beta-(1-42). Amyloid-beta-(1-16) does not compete for binding to SEC-R. There is cross-competition for bind ing to the same site by I-125-peptide 105Y and amyloid-beta-(25-35) as well as by I-125-Y amyloid-beta-(25-35) and peptide 105Y. By deletion s and substitutions within amyloid-beta-(25-35) and generation of chim eric amyloid-beta-alpha 1-AT peptides, amyloid-beta-(31-35) is shown t o be critical for binding to the SEC receptor. However, the upstream r egion, amyloid-beta-(25-30), also contributes to recognition by SEC-R. The SEC-R is present on the surface of a neuronal cell line PC12 as w ell as that of murine cortical neurons in primary culture, and the spe cificity of neuronal SEC-R for amyloid-beta peptide is identical to th at on hepatoma cells. Finally, SEC-R mediates internalization and degr adation of amyloid beta-peptide in PC12 cells. These results provide e vidence that SEC-R plays a role in metabolism of amyloid-beta peptide in the nervous system.