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|Coordinate||126,923,594 bp (GRCm38)|
|Base Change||A ⇒ G (forward strand)|
|Gene Name||signal peptide peptidase like 2A|
|Chromosomal Location||126,890,391-126,933,235 bp (-)|
|MGI Phenotype||Mice homozygous for a knock-out allele exhibit decreased immunoglobulin prior to and after immunization and decreased splenic B cells, myeloid dendritic cells, T2 B cells and follicular B cells. Mice homozygous for a hypomorphic allele exhibit similar albeit less severe phenotypes.|
|Amino Acid Change||Serine changed to Proline|
|Institutional Source||Beutler Lab|
|Gene Model||predicted gene model for protein(s): [ENSMUSP00000028844]|
AA Change: S203P
|Predicted Effect||probably benign
PolyPhen 2 Score 0.002 (Sensitivity: 0.99; Specificity: 0.30)
|Phenotypic Category||T-independent B cell response defect- decreased TNP-specific IgM to TNP-Ficoll immunization|
|Alleles Listed at MGI|
|Mode of Inheritance||Autosomal Recessive|
|Last Updated||12/08/2016 9:55 AM by Katherine Timer|
|Record Created||11/10/2014 3:12 PM by Jin Huk Choi|
The abra phenotype was identified among G3 mice of the pedigree R1029, some of which showed a diminished T-independent antibody response to 4-hydroxy-3-nitrophenylacetyl-Ficoll (NP-Ficoll) (Figure 1).
|Nature of Mutation|
Whole exome HiSeq sequencing of the G1 grandsire identified 37 mutations. The diminished T-independent antibody response to NP-Ficoll phenotype was linked by continuous variable mapping to three genes on chromosome 2: Lrp4, Sppl2a, and Zfp335. The Sppl2a mutation is presumed causative, because the immune phenotypes observed in abra mimic those listed on MGI and another Sppl2a mutant identified in a second pedigree (see abra2). The Sppl2a mutation is a T to C transition at base pair 126,923,594 (v38) on chromosome 2, or base pair 9,669 in the GenBank genomic region NC_000068 encoding the Sppl2a gene. Linkage was found with a recessive model of inheritance (P = 1.195 x 10-5), wherein one variant homozygote departed phenotypically from 23 homozygous reference mice and 13 heterozygous mice (Figure 2).
The mutation corresponds to residue 830 in the mRNA sequence NM_023220 within exon 6 of 15 total exons.
The mutated nucleotide is indicated in red. The mutation results in a serine (S) to proline (P) substitution at position 203 (S203P) in the SPPL2A protein, and is strongly predicted by PolyPhen-2 to be benign (score = 0.002).
Sppl2a encodes SPPL2a, a signal peptide peptidase-like (SPPL) protease, and member of the GxGD intramembrane-cleaving protease family of aspartyl intramembrane-cleaving proteases (I-CLiPs) (Figure 3). SPPL proteins share several motifs, including a Tyr-Asp (YD) motif (amino acids 354-355), a GxGD motif (amino acids 413-416), and a PAL sequence (amino acids 466-468) (1-4). All three motifs contribute to SPPL proteolytic activity; the aspartate residues in the YD and GxGD motifs are required for SPPL protease activity (1;5). It is unknown how the PAL motif affects SPPL activity, but it is thought to promote the activity of the YD and GxGD motifs.
SPPL2A has nine transmembrane domains. Within the N-terminal tail is a protease-associated (PA) domain, an insert domain found in several proteases (SMART). SPPL2A has six putative N-glycosylation sites (Asn51, 61, 69, 119, 129, and 135) at the luminal N-terminus and two putative lysosomal targeting motifs at the cytoplasmic C-terminus (amino acids 498-501 [YQVM] and 506-509 [YSTN]) (6). SPPL proteins are predicted to form homodimers, which promotes their proteolytic activity.
The abra mutation results in a serine (S) to proline (P) substitution at position 203. Ser203 is within the cytoplasmic loop between transmembrane domains 1 and 2.
GxGD proteases are essential for the regulated intramembrane proteolysis (RIP) of single span type II transmembrane proteins. RIP is a sequential processing of transmembrane substrates in which there is a proteolytic cleavage of a protein’s ectodomain and then subsequent cleavage of the remaining membrane-bound fragment by an I-CLiP (Figure 4). I-CLiP-mediated cleavage promotes reverse signaling through the liberated intracellular domain (see the record for PanR1 for information about reverse signaling), and the degradation of the membrane-retained stubs.
SPPL2A cleaves TNF-α (see the record for PanR1; (7)), ITM2B (Bri2) (9), Fas ligand (FasL; see the record for riogrande) (10), CD74 (11-16), TMEM106B (14;17), and neuregulin 1 type III (18) (Table 1). TNF-α, Bri2, and FasL undergo ectodomain shedding by a protease of the ADAM (a disintegrin and metalloprotease) family (see the record for wavedx for information about ADAM17) before cleavage by SPPL2A (7;9;10).
Table 1. SPPL2A substrates.
SPPL2A-mediated processing of CD74 is essential for B cell development (11) and B cell receptor signaling in transitional B cells (14). CD74 binds to MHCII dimers in the ER of antigen-presenting cells and prevents premature peptide binding. Upon the proteolytic processing of CD74, MHCII is released. Impaired processing of CD74 leads to impaired Ag presentation by MHCII (22). CD74 also functions in the endocytic trafficking and endosomal maturation of antigen presenting cells (23;24). Dendritic cell migration (25) and the function of the proinflammatory cytokine macrophage migration inhibitory factor (26) are also CD74-dependent.
Sppl2a knockout (Sppl2a-/-) mice have a B cell developmental block during the splenic phase of B cell maturation. As a result, the frequency of mature and functionally competent B cells is reduced and the mice exhibit impaired humoral immune responses (11). In Sppl2a-deficient B cells, accumulation of the CD74 N-terminal fragment results in B cell maturation arrest at the transitional stage 1 (T1) (11). However, in Sppl2a-/- mice, B cell maturation and function improved, indicating that the B cell phenotype observed in the Sppl2a-deficient mice was due to incomplete turnover of the CD74 N-terminal fragment (11). In the Sppl2a-/- B cells, Akt activation was impaired and aberrant BCR trafficking led to reduced surface IgM and impaired BCR-associated signal transduction (14). The B cell defects in the Sppl2a-/- mice is due to an accumulation of the CD74 N-terminal fragment and subsequent aberrant endocytic membrane traffic (12;14). Bergmann and colleagues also attributed surface B cell receptor and BAFFR expression to SPPL2A expression (12). SPPL2A is required for maintaining the cellular homeostasis of ameloblasts and subsequent dental enamel formation (8). In Sppl2a-/- mice, the enamel of erupted incisors was chalky white and rapidly eroded after eruption. The mineral content in the incisors from the Sppl2a-/- mice was not homogeneous and was reduced compared to that in wild-type incisors.
An ENU-induced Sppl2a allele (named chompB) also exhibited blockade in early B cell development after the T1 stage (13). As a result of the aberrant B cell development, the chompB mice exhibited a reduced frequency of mature B cell subsets and defects in T cell-dependent antibody responses. The chompB mice also exhibited reduced frequencies of myeloid dendritic cells.
Abra mice exhibited defects in the T-independent B cell response to NP-Ficoll. The abra mice did not exhibit overt reduction in the frequency of B cells in the peripheral blood or defects in antibody responses to the T-dependent B cell antigens recombinant Semliki Forest virus (rSFV)-encoded β-galactosidase (rSFV-β-gal) or ovalbumin administered with aluminum hydroxide. Taken together, the abra mutation in Sppl2a may not confer as severe effects as those observed in other Sppl2a models, but some function was lost.
abra(F):5'- CCAGTTTCTTACCAAGCCACCTGT -3'
abra(R):5'- AGGTGACTCTTGCTGGGAGAATTCATA -3'
abra_seq(F):5'- TTCTTACCAAGCCACCTGTAGAAG -3'
abra_seq(R):5'- tgggaggcagaggcagg -3'
1. Weihofen, A., Binns, K., Lemberg, M. K., Ashman, K., and Martoglio, B. (2002) Identification of Signal Peptide Peptidase, a Presenilin-Type Aspartic Protease. Science. 296, 2215-2218.
2. Ponting, C. P., Hutton, M., Nyborg, A., Baker, M., Jansen, K., and Golde, T. E. (2002) Identification of a Novel Family of Presenilin Homologues. Hum Mol Genet. 11, 1037-1044.
3. Grigorenko, A. P., Moliaka, Y. K., Korovaitseva, G. I., and Rogaev, E. I. (2002) Novel Class of Polytopic Proteins with Domains Associated with Putative Protease Activity. Biochemistry (Mosc). 67, 826-835.
4. Martoglio, B., and Golde, T. E. (2003) Intramembrane-Cleaving Aspartic Proteases and Disease: Presenilins, Signal Peptide Peptidase and their Homologs. Hum Mol Genet. 12 Spec No 2, R201-6.
5. Krawitz, P., Haffner, C., Fluhrer, R., Steiner, H., Schmid, B., and Haass, C. (2005) Differential Localization and Identification of a Critical Aspartate Suggest Non-Redundant Proteolytic Functions of the Presenilin Homologues SPPL2b and SPPL3. J Biol Chem. 280, 39515-39523.
6. Behnke, J., Schneppenheim, J., Koch-Nolte, F., Haag, F., Saftig, P., and Schroder, B. (2011) Signal-Peptide-Peptidase-Like 2a (SPPL2a) is Targeted to lysosomes/late Endosomes by a Tyrosine Motif in its C-Terminal Tail. FEBS Lett. 585, 2951-2957.
7. Friedmann, E., Hauben, E., Maylandt, K., Schleeger, S., Vreugde, S., Lichtenthaler, S. F., Kuhn, P. H., Stauffer, D., Rovelli, G., and Martoglio, B. (2006) SPPL2a and SPPL2b Promote Intramembrane Proteolysis of TNFalpha in Activated Dendritic Cells to Trigger IL-12 Production. Nat Cell Biol. 8, 843-848.
8. Bronckers, A. L., Gueneli, N., Lullmann-Rauch, R., Schneppenheim, J., Moraru, A. P., Himmerkus, N., Bervoets, T. J., Fluhrer, R., Everts, V., Saftig, P., and Schroder, B. (2013) The Intramembrane Protease SPPL2A is Critical for Tooth Enamel Formation. J Bone Miner Res. 28, 1622-1630.
9. Martin, L., Fluhrer, R., Reiss, K., Kremmer, E., Saftig, P., and Haass, C. (2008) Regulated Intramembrane Proteolysis of Bri2 (Itm2b) by ADAM10 and SPPL2a/SPPL2b. J Biol Chem. 283, 1644-1652.
10. Kirkin, V., Cahuzac, N., Guardiola-Serrano, F., Huault, S., Luckerath, K., Friedmann, E., Novac, N., Wels, W. S., Martoglio, B., Hueber, A. O., and Zornig, M. (2007) The Fas Ligand Intracellular Domain is Released by ADAM10 and SPPL2a Cleavage in T-Cells. Cell Death Differ. 14, 1678-1687.
11. Schneppenheim, J., Dressel, R., Huttl, S., Lullmann-Rauch, R., Engelke, M., Dittmann, K., Wienands, J., Eskelinen, E. L., Hermans-Borgmeyer, I., Fluhrer, R., Saftig, P., and Schroder, B. (2013) The Intramembrane Protease SPPL2a Promotes B Cell Development and Controls Endosomal Traffic by Cleavage of the Invariant Chain. J Exp Med. 210, 41-58.
12. Bergmann, H., Yabas, M., Short, A., Miosge, L., Barthel, N., Teh, C. E., Roots, C. M., Bull, K. R., Jeelall, Y., Horikawa, K., Whittle, B., Balakishnan, B., Sjollema, G., Bertram, E. M., Mackay, F., Rimmer, A. J., Cornall, R. J., Field, M. A., Andrews, T. D., Goodnow, C. C., and Enders, A. (2013) B Cell Survival, Surface BCR and BAFFR Expression, CD74 Metabolism, and CD8- Dendritic Cells Require the Intramembrane Endopeptidase SPPL2A. J Exp Med. 210, 31-40.
13. Beisner, D. R., Langerak, P., Parker, A. E., Dahlberg, C., Otero, F. J., Sutton, S. E., Poirot, L., Barnes, W., Young, M. A., Niessen, S., Wiltshire, T., Bodendorf, U., Martoglio, B., Cravatt, B., and Cooke, M. P. (2013) The Intramembrane Protease Sppl2a is Required for B Cell and DC Development and Survival Via Cleavage of the Invariant Chain. J Exp Med. 210, 23-30.
14. Huttl, S., Klasener, K., Schweizer, M., Schneppenheim, J., Oberg, H. H., Kabelitz, D., Reth, M., Saftig, P., and Schroder, B. (2015) Processing of CD74 by the Intramembrane Protease SPPL2a is Critical for B Cell Receptor Signaling in Transitional B Cells. J Immunol. 195, 1548-1563.
15. Schneppenheim, J., Huttl, S., Kruchen, A., Fluhrer, R., Muller, I., Saftig, P., Schneppenheim, R., Martin, C. L., and Schroder, B. (2014) Signal-Peptide-Peptidase-Like 2a is Required for CD74 Intramembrane Proteolysis in Human B Cells. Biochem Biophys Res Commun. 451, 48-53.
16. Oliveira, C. C., Querido, B., Sluijter, M., de Groot, A. F., van der Zee, R., Rabelink, M. J., Hoeben, R. C., Ossendorp, F., van der Burg, S. H., and van Hall, T. (2013) New Role of Signal Peptide Peptidase to Liberate C-Terminal Peptides for MHC Class I Presentation. J Immunol. 191, 4020-4028.
17. Brady, O. A., Zhou, X., and Hu, F. (2014) Regulated Intramembrane Proteolysis of the Frontotemporal Lobar Degeneration Risk Factor, TMEM106B, by Signal Peptide Peptidase-Like 2a (SPPL2a). J Biol Chem. 289, 19670-19680.
18. Fleck, D., Voss, M., Brankatschk, B., Giudici, C., Hampel, H., Schwenk, B., Edbauer, D., Fukumori, A., Steiner, H., Kremmer, E., Haug-Kroper, M., Rossner, M. J., Fluhrer, R., Willem, M., and Haass, C. (2016) Proteolytic Processing of Neuregulin 1 Type III by Three Intramembrane-Cleaving Proteases. J Biol Chem. 291, 318-333.
19. Li-Weber, M., and Krammer, P. H. (2003) Function and Regulation of the CD95 (APO-1/Fas) Ligand in the Immune System. Semin Immunol. 15, 145-157.
20. Schwenk, B. M., Lang, C. M., Hogl, S., Tahirovic, S., Orozco, D., Rentzsch, K., Lichtenthaler, S. F., Hoogenraad, C. C., Capell, A., Haass, C., and Edbauer, D. (2014) The FTLD Risk Factor TMEM106B and MAP6 Control Dendritic Trafficking of Lysosomes. EMBO J. 33, 450-467.
21. Stagi, M., Klein, Z. A., Gould, T. J., Bewersdorf, J., and Strittmatter, S. M. (2014) Lysosome Size, Motility and Stress Response Regulated by Fronto-Temporal Dementia Modifier TMEM106B. Mol Cell Neurosci. 61, 226-240.
22. Neefjes, J., Jongsma, M. L., Paul, P., and Bakke, O. (2011) Towards a Systems Understanding of MHC Class I and MHC Class II Antigen Presentation. Nat Rev Immunol. 11, 823-836.
23. Nordeng, T. W., Gregers, T. F., Kongsvik, T. L., Meresse, S., Gorvel, J. P., Jourdan, F., Motta, A., and Bakke, O. (2002) The Cytoplasmic Tail of Invariant Chain Regulates Endosome Fusion and Morphology. Mol Biol Cell. 13, 1846-1856.
24. Landsverk, O. J., Barois, N., Gregers, T. F., and Bakke, O. (2011) Invariant Chain Increases the Half-Life of MHC II by Delaying Endosomal Maturation. Immunol Cell Biol. 89, 619-629.
25. Faure-Andre, G., Vargas, P., Yuseff, M. I., Heuze, M., Diaz, J., Lankar, D., Steri, V., Manry, J., Hugues, S., Vascotto, F., Boulanger, J., Raposo, G., Bono, M. R., Rosemblatt, M., Piel, M., and Lennon-Dumenil, A. M. (2008) Regulation of Dendritic Cell Migration by CD74, the MHC Class II-Associated Invariant Chain. Science. 322, 1705-1710.
|Science Writers||Anne Murray|
|Illustrators||Peter Jurek, Katherine Timer|
|Authors||Kuan-Wen Wang, Jin Huk Choi, Apiruck Watthanasurorot, Bruce Beutler|
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