Regulated Intramembrane Proteolysis of Bri2 (Itm2b) by ADAM10 and SPPL2a/SPPL2b

• Published in: The Journal of biological chemistry 2008-01, Vol.283 (3), p.1644-1652
• Main Authors: Martin, Lucas, Fluhrer, Regina, Reiss, Karina, Kremmer, Elisabeth, Saftig, Paul, Haass, Christian
• Format: Article
• Language: English
• Subjects: ADAM Proteins - metabolism; ADAM10 Protein; Adaptor Proteins, Signal Transducing; Amyloid - metabolism; Amyloid Precursor Protein Secretases - metabolism; Aspartic Acid Endopeptidases - metabolism; Cell Line; Furin - metabolism; Humans; Intracellular Membranes - enzymology; Membrane Glycoproteins; Membrane Proteins - metabolism; Models, Biological; Protein Processing, Post-Translational; Protein Transport; Receptors, Notch - metabolism; Subcellular Fractions; Substrate Specificity
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M706661200

Presenilin, the catalytic component of the γ-secretase complex, type IV prepilin peptidases, and signal peptide peptidase (SPP) are the founding members of the family of intramembrane-cleaving GXGD aspartyl proteases. SPP-like (SPPL) proteases, such as SPPL2a, SPPL2b, SPPL2c, and SPPL3, also belong to the GXGD family. In contrast to γ-secretase, for which numerous substrates have been identified, very few in vivo substrates are known for SPP and SPPLs. Here we demonstrate that Bri2 (Itm2b), a type II-oriented transmembrane protein associated with familial British and Danish dementia, undergoes regulated intramembrane proteolysis. In addition to the previously described ectodomain processing by furin and related proteases, we now describe that the Bri2 protein, similar to γ-secretase substrates, undergoes an additional cleavage by ADAM10 in its ectodomain. This cleavage releases a soluble variant of Bri2, the BRICHOS domain, which is secreted into the extracellular space. Upon this shedding event, a membrane-bound Bri2 N-terminal fragment remains, which undergoes intramembrane proteolysis to produce an intracellular domain as well as a secreted low molecular weight C-terminal peptide. By expressing all known SPP/SPPL family members as well as their loss of function variants, we demonstrate that selectively SPPL2a and SPPL2b mediate the intramembrane cleavage, whereas neither SPP nor SPPL3 is capable of processing the Bri2 N-terminal fragment.