Association of membrane-bound amyloid precursor protein APP with the apolipoprotein E receptor LRP

In order to identify cell surface proteins that interact with the amyloid p recursor protein (APP), we biotinylated H4 human neuroglioma cells in cultu re with a water soluble biotinylating agent, immunoprecipitated APP with an antibody specific to the intracellular domain, and probed the precipitated proteins with anti-biotin. In human neuroglioma cells overexpressing APP75 1, we found a high molecular weight protein that immunoprecipitated with AP P. This band was identified as the low density lipoprotein receptor-related protein (LRP) by three criteria: first, the band immunolabeled with anti-L RP antibodies; second, the band bound the LRP receptor associated protein, RAP; and third, this band was present in LRP-expressing fibroblasts, but no t LRP-deficient fibroblasts. In complementary experiments, we found that AP P co-precipitated with LRP, with a preference for an isoform of APP contain ing the Kunitz protease inhibitor domain. Interaction of APP and LRP on the surface of living cells was demonstrated by crosslinking APP and LRP with the water-soluble cross-linking agent BS3. APP and LRP were shown by confoc al microscopy to colocalize in perinuclear structures, but to primarily rem ain separate in vesicles and on the cell surface. We propose that full-leng th APP can transiently interact with the receptor LRP on the cell surface, affecting the processing and intracellular transport of APP. (C) 2001 Elsev ier Science B.V. All rights reserved.