BIOTEC - Biotechnology Center TU Dresden

Major challenges in biology are to understand the complexity of biological systems and to predict how their dynamics can be tuned in different cell types in order to fulfill a specific function in a given tissue or be perturbed by somatic mutations or drugs affecting single components of these biological systems. An example of a complex biological system is illustrated by protein sorting and membrane traffic in the biosynthetic and endocytic pathways of mammalian cells, which govern the biogenesis and the integrity of organelles. Our scientific interest is to gain a comprehensive understanding of the mechanics of post-Golgi traffic leading to lysosome biogenesis, its means of regulation during cell differentiation and to understand how this regulation contributes to tissue specialization, as observed in the bone digesting osteoclasts. These multinucleated cells acquire during their differentiation the capability of building up resorbtion lacunae that can be viewed as extra-cellular lysosomes. These multi-nucleated cells, together with the bone rebuilding osteoblasts, contribute to bone homeostasis. Using functional genomics and proteomics, our goals are also to translate a key aspect of cell biology into the physiology of the bone tissue and its pathology.

Capitalizing on our progress, our research follows three major directions in membrane and bone biology.

• One focus of our group is to gain a comprehensive understanding of lysosomes biogenesis. We rely on the combination of biological and biophysical techniques applied to in vitro and in vivo systems to understand basic aspects of membrane traffic, in particular how coat assembly, actin polymerization and membrane fusion are coordinated. Second, we rely on high-throughput RNA interference-based functional screens to identify new components and to understand how lysosome biogenesis is regulated.

• Another focus is the cell biology of osteoclasts. Whereas it is critical to obtain a large comprehensive view of signaling cascades regulating osteoclast differentiation, a process that we can now investigate using RNA interference-based functional screens, it is also important to have a deeper molecular understanding of how osteoclasts function in bone degradation. Of particular interest is actin dynamics (podosome formation), a process regulated by the Src kinase, and membrane/actin cytoskeleton interactions. During bone degradation, several intracellular compartments involved in secretion of hydrolytic enzymes required for bone digestion or uptake and transcytosis of digested bone material are concentrated around the podosome/actin-rich sealing zone of osteoclasts.

• An important aspect in bone remodeling, i.e. cycles of destruction and rebuilding occurring continuously throughout live, is the coordinated action of the bone digesting osteoclasts and the bone rebuilding osteoblasts. It is now clear that signaling molecules expressed by osteoblasts control osteoclastogenesis. Using co-culture systems, we have accumulated evidence that osteoclasts could control some aspects of osteoblast-mediated bone rebuilding. We now want to investigate further these interesting possibilities using appropriate mouse model systems.

Anitei M, Stange C, Parshina I, Baust T, Scheck A, Raposo G, Kirchhausen T, Hoflack B. (2010) Protein complexes containing CYFIP/Sra/PIR121 coordinate Arf1 and Rac1 signalling during clathrin-AP-1-coated carrier biogenesis at the TGN.Nat Cell Biol. 2010 Apr;12(4):330-40. Epub 2010 Mar 14. Erratum in: Nat Cell Biol. 2010 May;12(5):520. PMID: 20228810  MEDLINE

Heckel T, Czupalla C, Expirto Santo AI, Anitei M, Arantzazu Sanchez-Fernandez M, Mosch K, Krause E, Hoflack B. (2009) Src-dependent repression of ARF6 is required to maintain podosome-rich sealing zones in bone-digesting osteoclasts.Proc Natl Acad Sci U S A. 2009 Feb 3;106(5):1451-6. Epub 2009 Jan 21.PMID: 19164586 MEDLINE

Sanchez-Fernandez MA, Gallois A, Riedl T, Jurdic P, Hoflack B. (2008) Osteoclasts control osteoblast chemotaxis via PDGF-BB/PDGF receptor beta signaling. PLoS One. 2008;3(10):e3537. Epub 2008 Oct 27.PMID: 18953417 MEDLINE

Baust T, Anitei M, Czupalla C, Parshyna I, Bourel L, Thiele C, Krause E, Hoflack B. (2008) Protein networks supporting AP-3 function in targeting lysosomal membrane proteins. Mol Biol Cell. 2008 May;19(5):1942-51. Epub 2008 Feb 20.PMID: 18287518 MEDLINE

Baust T., Czupalla C., Krause E., Bourel-Bonnet L., Hoflack B. (2006) Proteomic analysis of AP-1A coats selectively assembled on liposomes. Proc. Natl. Acad. Sci. USA 103: 3159-3164.

Czupalla C, Mansukoski H, Riedl T, Thiel D, Krause E, Hoflack B. (2006) Proteomic Analysis of Lysosomal Acid Hydrolases Secreted by Osteoclasts: Implications for Lytic Enzyme Transport and Bone Metabolism. Mol Cell Proteomics 1:134-143.

Czupalla C, Mansukoski H, Pursche T, Krause E, Hoflack B. (2005) Comparative study of protein and mRNA expression during osteoclastogenesis. Proteomics. 15:3868-75.

Waguri S, Dewitte F, Le Borgne R, Rouille Y, Uchiyama Y, Dubremetz JF, Hoflack B. (2003) Visualization of TGN to endosome trafficking through fluorescently labeled MPR and AP-1 in living cells. Mol Biol Cell. 1:142-55.

Rohn WM, Rouille Y, Waguri S, Hoflack B. (2000) Bi-directional trafficking between the trans-Golgi network and the endosomal/lysosomal system (review). J. Cell Sci., 113: 2093-2101.

Rouille Y, Rohn W, Hoflack B. (2000) Targeting of lysosomal proteins (review). Semin. Cell Dev. Biol., 11: 165-171.

Le Borgne R, Hoflack B. (1998) Mechanisms of protein sorting and coat assembly: insights from the clathrin-coated vesicle pathway (review). Curr. Opin. Cell Biol., 10: 499-503.

All current group members are listed on the Staff Page.