Regulated intramembrane proteolysis of Bri2 (Itm2b) by ADAM10 and SPPL2a/SPPL2b
ABSTRACT Presenilin, the catalytic component of the gamma-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 gamma-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 gamma-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.
- SourceAvailable from: Janna Schneppenheim[Show abstract] [Hide abstract]
ABSTRACT: Signal-peptide-peptidase-like 2A (SPPL2a), an aspartyl intramembrane protease, has been implicated in the proteolysis of TNF-alpha, Fas Ligand and Bri2. Here, we show that endogenous SPPL2a - in agreement with overexpression studies - is localised in membranes of lysosomes/late endosomes. Furthermore, we have analysed the molecular determinants for lysosomal sorting of SPPL2a by creating chimaeric constructs between SPPL2a and its plasma membrane localised homologue SPPL2b. Lysosomal transport of SPPL2a critically depends on its cytosolic carboxyterminal tail. A canonical tyrosine-based sorting motif of the YXXø type at position 498 is sufficient to direct SPPL2a to lysosomal/late endosomal compartments. This motif accounts for the differential localisation of the homologous proteases SPPL2a and SPPL2b and thereby influences the access to substrates and biological function of SPPL2a.FEBS letters 09/2011; 585(19):2951-7. DOI:10.1016/j.febslet.2011.08.043 · 3.34 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Two different mutated forms of BRI2 protein are linked with familial British and Danish dementias, which present neuropathological similarities with Alzheimer's disease. BRI2 is a type II transmembrane protein that is trafficked through the secretory pathway to the cell surface and is processed by furin and ADAM10 (a disintegrin and metalloproteinase domain 10) to release secreted fragments of unknown function. Its apparent molecular mass (42-44 kDa) is significantly higher than that predicted by the number and composition of amino acids (30 kDa) suggesting that BRI2 is glycosylated. In support, bioinformatics analysis indicated that BRI2 bears the consensus sequence Asn-Thr-Ser (residues 170-173) and could be N-glycosylated at Asn170. Given that N-glycosylation is considered essential for protein folding, processing and trafficking, we examined whether BRI2 is N-glycosylated. Treatment of HEK293 (human embryonic kidney) cells expressing BRI2 with the N-glycosylation inhibitor tunicamycin or mutation of Asn170 to alanine reduced its molecular mass by ~2 kDa. These data indicate that BRI2 is N-glycosylated at Asn170. To examine the effect of N-glycosylation on BRI2 trafficking at the cell surface, we performed biotinylation and (35)S methionine pulse-chase experiments. These experiments showed that mutation of Asn170 to alanine reduced BRI2 trafficking at the cell surface and its steady state levels at the plasma membrane. Furthermore, we obtained data indicating that this mutation did not affect cleavage of BRI2 by furin or ADAM10. Our results confirm the theoretical predictions that BRI2 is N-glycosylated at Asn170 and show that this post-translational modification is essential for its expression at the cell surface but not for its proteolytic processing.Glycobiology 07/2011; 21(10):1382-8. DOI:10.1093/glycob/cwr097 · 3.75 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Presenilin is the catalytic component of gamma-secretase, a complex aspartyl protease and a founding member of intramembrane-cleaving proteases. gamma-Secretase is involved in the pathogenesis of Alzheimer's disease and a top target for therapeutic intervention. However, the protease complex processes a variety of transmembrane substrates, including the Notch receptor, raising concerns about toxicity. Nevertheless, gamma-secretase inhibitors and modulators have been identified that allow Notch processing and signaling to continue, and promising compounds are entering clinical trials. Molecular and biochemical studies offer a model for how this protease hydrolyzes transmembrane domains in the confines of the lipid bilayer. Progress has also been made toward structure elucidation of presenilin and the gamma-secretase complex by electron microscopy as well as by studying cysteine-mutant presenilins. The signal peptide peptidase (SPP) family of proteases are distantly related to presenilins. However, the SPPs work as single polypeptides without the need for cofactors and otherwise appear to be simple model systems for presenilin in the gamma-secretase complex. SPP biology, structure, and inhibition will also be discussed.Biological Chemistry 08/2010; 391(8):839-47. DOI:10.1515/BC.2010.086 · 2.69 Impact Factor