Coagulation factor XIa cleaves the RHDS sequence and abolishes the cell adhesive properties of the amyloid β-protein

Abstract

Amyloid β-protein (Aβ) is the major constituent of senile plaques and cerebrovascular amyloid deposits in Alzheimer's disease and is proteolytically derived from its transmembrane parent protein the amyloid β- protein precursor (AβPP). Although the physiological role(s) of secreted AβPPs are not fully understood, several potential functions have been described including the regulation of homostatic enzymes factors XIa and IXa and a role in cell adhesion. In the present study, we investigated the proteolytic processing of AβPP by factor XIa (FXIa). Incubation of the human glioblastoma cell line U138 stably transfected to overexpress the 695 isoform of AβPP with FXIa (2.5-5 nM) resulted in proteolytic cleavage of secreted AβPP. Higher concentrations of FXIa (>25 nM) resulted in loss in cell adherence. Coincubation of FXIa with purified, recombinant Kunitz protease inhibitor domain of AβPP blocked both the proteolytic processing of AβPP and the loss of cell adhesion. The RHDS cell adhesion site of AβPP resides within residues 5-8 of the Aβ domain. Incubation of synthetic AB1-40 peptide with increasing concentrations of FXIa resulted in cleavage of Aβ between Arg5 and His6 within the cell adhesion domain of the peptide, FXIa- digested Aβ1-40 or AβPP695 lost their abilities to serve as cell adhesion substrates consistent with cleavage through this cell adhesion site. Together, these results suggest a new potential biological function for FXIa in the modulation of cell adhesion. In addition, we have shown that FXIa can proteolytically alter Aβ and therefore possibly modify its physiological and perhaps pathological properties.