P3-233: Interleukin-1 receptor II undergoes a similar set of proteolytic cleavages as the amyloid precursor protein

Abstract

Proteolytic processing of the amyloid precursor protein (APP) by α–, β–and γ–secretase controls the generation of the amyloid β peptide, which is deposited in the amyloid plaques of Alzheimer's disease (AD). Increased proteolytic processing of another membrane protein, the type II interleukin–1 receptor (IL–1R2), has been linked to the pathogenesis of AD. Importantly, increased secretion of IL1–R2, which is a decoy receptor, may prevent IL–1β to its type I receptor, which in turn has been shown to activate α–secretase cleavage of APP. Thus, increased secretion of IL1–R2 may lead to reduced IL–1β signaling and to increased Aβ–generation. We study the proteolytic processing of IL–1R2 which is so far little understood. Cell culture, Western blot, mass spectrometry, in–vitro membrane assay, molecular cloning. We show that IL–1R2 undergoes a similar set of proteolytic cleavages as APP. IL–1R2 expressed in human embryonic kidney 293 cells first undergoes ectodomain shedding in a metalloprotease–dependent manner, similar to the α–secretase cleavage of APP. Subsequently, IL–1R2 undergoes intramembrane proteolysis by γ–secretase, leading to the generation of the soluble intracellular domain of IL–1R2. Intramembrane cleavage of IL–1R2 was abolished by a highly specific inhibitor of γ–secretase, by a dominant–negative mutant of the γ–secretase subunit presenilin 1 and was absent in mouse embryonic fibroblasts deficient in presenilin 1 and 2. Transfection of the β–secretase BACE1 and its homolog BACE2 into kidney 293 cells led to increased secretion of the IL–1R2 ectodomain and to enhanced generation of an IL–1R2 C–terminal fragment, suggesting that IL–1R2 may be a novel substrate for both proteases. Importantly, BACE1 and BACE2 did not cleave several other type I membrane proteins, showing that both proteases do not contribute to general membrane protein turnover, but only cleave specific substrates. The potential cleavage of IL–1R2 by BACE1 may explain the increase in IL–1R2 secretion in moderate AD cases, since BACE1 expression is increased in AD. We show that interleukin–1 receptor II undergoes a similar set of proteolytic cleavages as the amyloid precursor protein.