Cleavage of p75 neurotrophin receptor by α-secretase and γ-secretase requires specific receptor domains

Abstract

The p75 neurotrophin receptor (p75NTR), a member of the tumor necrosis factor superfamily of receptors, undergoes multiple proteolytic cleavage events. These events are initiated by an α-secretase-mediated release of the extracellular domain followed by a γ-secretase-mediated intramembrane cleavage. However, the specific determinants of p75NTR cleavage events are unknown. Many other substrates of γ-secretase cleavage have been identified, including Notch, amyloid precursor protein, and ErbB4, indicating there is broad substrate recognition by γ-secretase. Using a series of deletion mutations and chimeric receptors of p75NTR and the related Fas receptor, we have identified domains that are essential for p75NTR proteolysis. The initial α-secretase cleavage was extracellular to the transmembrane domain. Unfortunately, deletion mutants were not capable of defining the requirements of ectodomain shedding. Although this cleavage is promiscuous with respect to amino acid sequence, its position with respect to the transmembrane domain is invariant. The generation of chimeric receptors exchanging different domains of noncleavable Fas receptor with p75NTR, however, revealed that a discrete domain above the membrane is sufficient for efficient cleavage of p75NTR. Mass spectrometric analysis confirmed the cleavage can occur with a truncated p75NTR displaying only 15 extracellular amino acids in the stalk region. © 2005 by The American Society for Biochemistry and Molecular Biology, Inc.