A γ-secretase-like intramembrane cleavage of TNFα by the GxGD aspartyl protease SPPL2b

Adolf Butenandt Institute, Department of Biochemistry, Laboratory for Alzheimer's and Parkinson's Disease Research, Ludwig Maximilians University, 80336 Munich, Germany.
Nature Cell Biology (Impact Factor: 19.68). 09/2006; 8(8):894-6. DOI: 10.1038/ncb1450
Source: PubMed


Gamma-secretase and signal peptide peptidase (SPP) are unusual GxGD aspartyl proteases, which mediate intramembrane proteolysis. In addition to SPP, a family of SPP-like proteins (SPPLs) of unknown function has been identified. We demonstrate that SPPL2b utilizes multiple intramembrane cleavages to liberate the intracellular domain of tumor necrosis factor alpha (TNFalpha) into the cytosol and the carboxy-terminal counterpart into the extracellular space. These findings suggest common principles for regulated intramembrane proteolysis by GxGD aspartyl proteases.

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    • "The intramembrane protease Signal-peptide-peptidase-like 2a (SPPL2a) resides in lysosomes and late endosomes [1] and has been implicated in the processing of type 2 transmembrane proteins [2] including TNFa [3] [4], the Fas ligand [5], the Bri2 protein [6] and the invariant chain (CD74) of the MHCII complex [7]. Among these, only the latter has been confirmed in vivo. "
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    ABSTRACT: The invariant chain (CD74) mediates targeting of the MHCII complex to endosomal compartments, where CD74 undergoes degradation allowing MHCII to acquire peptides. We demonstrated recently that intramembrane proteolysis of the final membrane-bound N-terminal fragment (NTF) of CD74 is catalysed by Signal-peptide-peptidase-like 2a (SPPL2a) and that this process is indispensable for development and function of B lymphocytes in mice. In SPPL2a-/- mice, homeostasis of these cells is disturbed by the accumulation of the unprocessed CD74 NTF. So far, evidence for this essential role of SPPL2a is restricted to mice. Nevertheless, inhibition of SPPL2a has been suggested as novel approach to target B cells for treating autoimmunity. Here, we characterize human B cell lines with a homozygous microdeletion on chromosome 15. We demonstrate that this deletion disrupts the SPPL2a genomic locus and leads to loss of SPPL2a transcript. Lymphoblastoid cell lines from patients with this deletion exhibit absence of SPPL2a at the protein level and show an accumulation of the CD74 NTF comparable to B cells from SPPL2a-/- mice. By this means, we present evidence that the role of SPPL2a in CD74 proteolysis is conserved in human B cells and provide support for modulation of SPPL2a activity as a therapeutic concept.
    Biochemical and Biophysical Research Communications 08/2014; 451(1). DOI:10.1016/j.bbrc.2014.07.051 · 2.30 Impact Factor
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    • "It is also well documented that membrane-bound TNF or FasL are shed by cleavage with metalloproteases (TACE, ADAM10), leaving behind on the expressing cell the transmembrane segment and intracellular domain of the ligands. The transmembrane domain is thereafter processed by signal peptide peptidase-like aspartyl proteases that release in the producing cell the intracellular domains of TNF or FasL that can migrate and signal in the nucleus [36], [37], [38], [39]. The mechanism by which atacicept promoted CNS inflammation in patients with relapsing-remitting multiple sclerosis remains unknown. "
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    ABSTRACT: Myeloid cells express the TNF family ligands BAFF/BLyS and APRIL, which exert their effects on B cells at different stages of differentiation via the receptors BAFFR, TACI (Transmembrane Activator and CAML-Interactor) and/or BCMA (B Cell Maturation Antigen). BAFF and APRIL are proteins expressed at the cell membrane, with both extracellular and intracellular domains. Therefore, receptor/ligand engagement may also result in signals in ligand-expressing cells via so-called "reverse signalling". In order to understand how TACI-Fc (atacicept) technically may mediate immune stimulation instead of suppression, we investigated its potential to activate reverse signalling through BAFF and APRIL. BAFFR-Fc and TACI-Fc, but not Fn14-Fc, reproducibly stimulated the ERK and other signalling pathways in bone marrow-derived mouse macrophages. However, these effects were independent of BAFF or APRIL since the same activation profile was observed with BAFF- or APRIL-deficient cells. Instead, cell activation correlated with the presence of high molecular mass forms of BAFFR-Fc and TACI-Fc and was strongly impaired in macrophages deficient for Fc receptor gamma chain. Moreover, a TACI-Fc defective for Fc receptor binding elicited no detectable signal. Although these results do not formally rule out the existence of BAFF or APRIL reverse signalling (via pathways not tested in this study), they provide no evidence in support of reverse signalling and point to the importance of using appropriate specificity controls when working with Fc receptor-expressing myeloid cells.
    PLoS ONE 04/2013; 8(4):e61350. DOI:10.1371/journal.pone.0061350 · 3.23 Impact Factor
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    • "Upon stimulation, the TNF alpha-converting enzyme ADAM17 cleaves the extracellular domain of tmTNF, which releases the soluble TNF (sTNF) [1]. The newly generated membrane-bound moiety of TNF is further cleaved within its intramembrane region by signal peptide peptidase-like 2b (SPPL2b), leading to the generation of an intracellular domain (ICD) of TNF [2]. Soluble TNF signals through two distinct cell surface receptors, TNFR1 and TNFR2. "
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    ABSTRACT: The pleiotropic pro-inflammatory cytokine Tumour Necrosis Factor alpha (TNF) is synthesised as a transmembrane protein that is subject to palmitoylation. In this study, the roles of this acylation on TNF-mediated biological effects were investigated. We found that the lipid raft partitioning of TNF is regulated by its palmitoylation. Furthermore, we demonstrated that this palmitoylation process interferes with the cleavage / degradation of TNF intracellular fragments but is not involved in the regulation of its ectodomain shedding. Moreover, we found that the palmitoylation of TNF hinders the binding of soluble TNF to TNFR1 and regulates the integration / retention of TNFR1 into lipid rafts. Finally, we demonstrate that the transmembrane forms of wild-type and palmitoylation-defective TNF interact differently with TNFR1 and regulate differently NFκB activity, Erk1/2 phosphorylation and Interleukin-6 synthesis, strongly suggesting that palmitoylation of TNF is involved in the regulation of TNFR1 signalling. An evidence for the physiological intervention of this regulation is provided by the fact that, in macrophages, the binding of endogenous soluble TNF to TNFR1 is enhanced by inhibition of palmitoylation. Therefore, our data introduce the new concept that palmitoylation of TNF is one of the means by which TNF-producing cells regulate their sensitivity to soluble TNF.
    Biochimica et Biophysica Acta 11/2012; 1833(3). DOI:10.1016/j.bbamcr.2012.11.009 · 4.66 Impact Factor
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