Unit of Molecular Cell Biology and Transgenic Research

Dr. rer. physiol. Bernd Schröder

Tel.: +49-(0)431-880-1679 Fax: +49-(0)431-880-2218 Mail: baschroeder@biochem.uni-kiel.de

Eduard-Buchner-Haus, Otto-Hahn-Platz 9, D-24118 Kiel

Foto von Bernd Schröder
Research
 
Physiological functions of the intramembrane proteases SPPL2a and SPPL2b

The concept of regulated intramembrane proteolysis (RIP) has emerged over the last decades as a novel concept of cellular signalling. One group among the proteases being capable of cleaving substrates within the phospholipid bilayer are the signal-peptide-peptidase (SPP) and its homologues, the signal-peptide-peptidase-like proteins (SPPL2a, -2b, -2c, -3). Whereas SPPL2a is present in membranes of lysosomes/late endosomes, SPPL2b was reported to reside at the plasma membrane as well as in endosomal compartments. To date, only TNFα, Fas Ligand (FasL) and Bri2 (Itm2b) have been identified as substrates of SPPL2a/b using in vitro overexpression approaches. In agreement with the general concept of RIP it was demonstrated that the TNFα intracellular domain translocates into the nucleus after proteolytic release and influences gene expression thereby inducing the synthesis of the pro-infammatory cytokine IL12. Two of the known substrates suggest a regulatory function of SPPL2a and SPPL2b in the context of the immune system. However, a relevance of these processes and proteolytic events in a complex in vivo system has not been analysed and established yet. It was also suggested that RIPping by SPPL2a and SPPL2b may have more generalized degradative functions beyond mediating reverse signalling by TNFα or other members of this superfamily - a hypothesis being supported by the presence of SPPL orthologues in plants.
 
Fig. 1: Current model of intramembrane proteolysis by SPPL2a/b
Fig. 1: Current model of intramembrane proteolysis by SPPL2a/b.
 
In order to study functions of SPPL2a and SPPL2b in vivo, we have generated mouse lines deficient in either of the two proteases as well as mice being deficient in SPPL2a and -b. Phenotypic analysis of these mice has revealed major immunological abnormalities associated with the deficiency of SPPL2a. These in vivo approaches are combined with biochemical and cell biological experiments studying the differential processing of known and putative substrates in SPPL2a/b deficient cell lines. We are confident, that challenging these mice in infection and inflammation models will contribute to understanding the role of SPPL2a/2b-mediated intramembrane proteolysis in pathophysiology and deepen our understanding of cellular and molecular principles of inflammation. The results of these studies will help us to decide whether SPPL2a and/or -2b might even be considered as potential drug targets and if specific inhibitors of these proteases might be capable of modulating the immune system in a therapeutic way. A central objective of the project is the unbiased search for novel substrates cleaved by SPPL2a and/or –b and to ideally link the biochemical findings with the phenotypes observed in the protease deficient mice.
 
Functional characterisation of novel lysosomal membrane proteins
Lysosomes play a crucial role in the degradation and turnover of different intra- and extracellular macromolecules. Currently, extensive data are available about the proteins of the lysosomal matrix. On the contrary only a minority of the lysosomal membrane proteins has been identified and substantially characterised to date. This contrasts with the number of known and functionally described transport systems or enzymatic activities that have been shown to be associated with this membrane.
 
Fig. 2: Functions of lysosomal membrane proteins
Fig. 2: Functions of lysosomal membrane proteins
 
In a previous proteomic analysis of lysosomal membranes we have identified 16 novel enzyme and transporter proteins and 12 novel proteins of unknown functions not previously assigned to lysosomal membranes. Lysosomal localisation of several of these novel proteins could be confirmed by overexpression studies. For two of these novel proteins, “disrupted in renal carcinoma 2” (DIRC2) and “transmembrane protein 192” (TMEM192), we have performed an in-depth biochemical characterisation including validation of lysosomal localisation of the endogenous proteins as well as identification of the sequence-determinants required for lysosomal targeting. DIRC2, a member of the “major facilitator superfamily” was shown to be proteolytically processed by cathepsin L and to exhibit transport activity in a whole-cell electrophysiological assay employing a plasma membrane-localised mutant. TMEM192 a novel protein without any homology to known lysosomal membrane proteins was demonstrated to form dimers mediated by its cytosolic C-terminal tail. Further studies to unravel the molecular functions of these novel lysosomal membrane proteins are ongoing.

 

Curriculum Vitae
 
1997 – 2004 Studies of Human Medicine at the Philipps-University of Marburg and Imperial College School of Medicine, London
2004 – 2007

Ph.D. in the Institute of Physiological Chemistry, Philipps-University of Marburg
Since 2007 Postdoctoral Fellow at  Biochemical Institute, CAU Kiel

 

Selected Publications
 
19
 Bronckers, A., Güneli, N., Lüllmann-Rauch, R., Schneppenheim, J., Moraru, A.P., Himmerkus, N., Bervoets, T.J., Fluhrer, R., Everts, V., Saftig, P. and Schröder, B. (2013)
The intramembrane protease SPPL2A is critical for tooth enamel formation.
J Bone Miner Res 2013, in press.
18
 Schwake, M., Schröder, B. and Saftig, P. (2013)
Lysosomal Membrane Proteins and their central role in physiology.
Traffic 2013, in press.
17
 Schneppenheim, J., Dressel, R., Hüttl, S., Lüllmann-Rauch ,R., Engelke ,M., Dittmann, K., Wienands, J., Eskelinen, E.L., Hermans-Borgmeyer, I., Fluhrer, R., Saftig, P., and Schröder, 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.
16
 Voss, M., Fukumori, A., Kuhn, P.H., Künzel, U., Klier, B., Grammer, G., Haug-Kröper, M., Kremmer ,E., Lichtenthaler, S., Steiner, H., Schröder, B., Haass, C., and Fluhrer, R. (2012)
Foamy virus envelope protein is a substrate for signal peptide peptidase like-3 (SPPL3).
J. Biol. Chem., 287 (52), 43401-43409.
15
 Behnke, J., Schneppenheim, J., Koch-Nolte, F., Haag, F., Saftig, P., and Schröder, B. (2011)
Signal-peptide-peptidase-like 2a (SPPL2a) is targeted to lysosomes/late endsosomes by a tyrosine motif in ist C-terminal tail.
FEBS Lett, 585, 2951-2957.
14
 Savalas, L.R.T., Gasnier, B., Damme ,M., Lübke, T., Wrocklage, C., Debacker, C., Jézégou, A., Reinheckel, T., Hasilik, A., Saftig, P., and Schröder, B. (2011)
"Disrupted in renal carcinoma 2" (DIRC2) - a novel transporter of the lysosomal membrane - is proteolytically processed by cathepsin L.
Biochem. J., 439, 113-128.
13
 Behnke, J., Eskelinen, E.L., Saftig, P., and Schröder, B. (2011)
Two dileucine motifs mediate late endosomal/lysosomal targeting of Transmembrane protein 192 (TMEM192) and a C-terminal cysteine residue is responsible for disulfide bond formation in TMEM192 homodimers.
Biochem. J. 434, 219-231.
12
 Saftig, P., Schröder, B., and Blanz, J. (2010)
Lysosomal membrane proteins: life between acid and neutral conditions.
Biochem. Soc. Trans. 38, 1420-1423.
11
Schröder, B., Wrocklage, C., Hasilik, A., and Saftig, P. (2010)
The proteome of lysosomes.
Proteomics 10, 4053-4076.
10
 Schröder, B. and Saftig, P. (2010)
Molecular insights into mechanisms of intramembrane proteolysis by signal peptide peptidase (SPP).
Biochem. J. 427, 1-3.
9
 Schröder, B., Wrocklage, C., Hasilik, A., and Saftig, P. (2010)
Molecular characterisation of 'transmembrane protein 192' (TMEM192), a novel protein of the lysosomal membrane.
Biol Chem. 391, 695-704.
8
 Hasilik, A., Wrocklage, C., and Schröder, B. (2009)
Intracellular trafficking of lysosomal proteins and lysosomes.
Int. J. Clin. Pharmacol. Ther. 47 (Suppl.1), S18-33.
7
 Schieweck, O., Damme, M., Schröder, B., Hasilik, A., Schmidt, B., and Lübke, T. (2009)
NCU-G1 is a highly glycosylated integral membrane protein of the lysosome.
Biochem. J. 422, 83-90.
6
 Schröder, J., Lüllmann-Rauch, R., Himmerkus, N., Pleines,I., Nieswandt, B., Orinska, Z., Koch-Nolte ,F., Schröder, B., Bleich, M., and Saftig, P. (2008)
Deficiency of the tetraspanin CD63 associated with kidney pathology but normal lysosomal function.
Mol Cell Biol. 2009 Feb;29(4):1083-94.
5
 Beertsen, W., Willenborg, M., Everts, V., Zirogianni, A., Podschun, R., Schröder, B., Eskelinen, E.L., and Saftig, P. (2008)
Impaired phagosomal maturation in neutrophils leads to periodontitis in lysosomal-associated membrane protein-2 knockout mice.
J. Immunol. 180, 475-482.
4
 Schröder, B., Wrocklage, C., Pan, C., Jäger, R., Kösters, B., Schäfer, H., Elsässer, H.P., Mann, M., and Hasilik, A. (2007)
Integral and Associated Lysosomal Membrane Proteins.
Traffic. 8, 1676-1686.
3
 Schröder, B., Elsässer, H.P., Schmidt, B., and Hasilik, A. (2007)
Characterisation of lipofuscin-like lysosomal inclusion bodies from human placenta.
FEBS Lett. 581, 102-108.
2
 Schröder, B. and Hasilik, A. (2006)
A protocol for combined delipidation and subfractionation of membrane proteins using organic solvents.
Anal. Biochem. 357, 144-146.
1
 Melcher, R., Hillebrand, A., Bahr, U., Schröder, B., Karas, M., and Hasilik, A. (2000)
Glycosylation-site-selective synthesis of N-acetyl-lactosamine repeats in bis-glycosylated human lysozyme.
Biochem. J. 348 Pt 3, 507-515.

 

Co-Workers
 

Janna Schneppenheim
PhD Student


0431-880-1679
0431-880 2238
jschneppenheim@biochem.uni-kiel.de
 
Red Bulle Susann Hüttl
PhD Student		   Phone0431-880-3981
Fax0431-880 2238
E-Mailshuettl@biochem.uni-kiel.de
 
Red Bulle Torben Mentrup
PhD Student		   Phone0431-880-2212
Fax0431-880 2238
E-Mailtmentrup@biochem.uni-kiel.de
 
Red Bulle Sebastian Held
Laboratory Technician
   Phone0431-880-3981
Fax0431-880 2238
E-Mailsheld@biochem.uni-kiel.de
 

Alumni
 

Lalu Rudyat Telly Savalas
 
 
Red Bulle Jörg Behnke
    
 
Red Bulle Nur Güneli