Molecular Cell Biology
PP2A enzyme biogenesis and monoclonal antibodies
Cells employ the phosphorylation/dephosphorylation of proteins to regulate protein function. The enzymes catalyzing these reactions, the protein kinases and phosphatases, are thus important regulators of almost all aspects of life. One of the major phosphatase enzymes in the cell is protein phosphatase 2A (PP2A), a known tumor suppressor and target of cancer causing viruses. PP2A is a family of protein serine/threonine phosphatases with prototypical multisubunit architecture,...more
Cells employ the phosphorylation/dephosphorylation of proteins to regulate protein function. The enzymes catalyzing these reactions, the protein kinases and phosphatases, are thus important regulators of almost all aspects of life. One of the major phosphatase enzymes in the cell is protein phosphatase 2A (PP2A), a known tumor suppressor and target of cancer causing viruses. PP2A is a family of protein serine/threonine phosphatases with prototypical multisubunit architecture, in which a catalytic subunit achieves substrate specificity through the interaction with regulatory subunits. The PP2A family consists of over 70 different holoenzymes that possess probably many hundred substrates in a cell. How holoenzyme assembly is regulated and what the substrates of different holoenzymes are, is largely unknown. A pathological decrease of PP2A activity has been linked to the development of human diseases such as cancer or Alzheimer. Thus, our major research goals are to understand the molecular mechanisms of PP2A regulation and to identify the substrates and processes regulated by PP2A.
Our study of PP2A biogenesis in yeast led to a model, in which the generation of the active enzyme is tightly coupled to the assembly of substrate-specific holoenzymes (Hombauer et al., 2007 PLoS Biology). This process is under surveillance of the PP2A methylesterase, PPE1, which seems to control the correct order of the PP2A biogenesis cascade. How PPE1 exerts its surveillance function and how PP2A biogenesis is regulated and by which signaling pathways, is currently investigated in the lab.
PP2A activity is decreased in Alzheimer brain tissue suggesting a potential causal role for PP2A in Alzheimer pathogenesis (Sontag et al., 2010). We are investigating in collaboration with Estelle Sontag (University of Newcastle, Australia) whether dysfunction of PP2A biogenesis might be involved in Alzheimer disease development.
PP2A substrate identification is difficult with the currently available methods due to the transient enzyme-substrate interaction during catalysis. We have adapted a novel two-hybrid system for the detection of transient PP2A interactions and are using this method for PP2A substrate validation and identification.
The second more business-oriented focus of the lab is the generation of monoclonal antibodies against human disease-linked point-mutant proteins. We show that antibodies with such exquisite specificity represent a new type of research tools for the analysis of disease mechanism (Roblek et al.,2010 PloS ONE).
In 2009 our lab established the Monoclonal Antibody Facility (MAF) and since then generated custom-tailored monoclonal antibodies for internal and external customers (please see Monoclonal Antibody Facility page).
Zuzuarregui, Aurora; Kupka, Thomas; Bhatt, Bhumika; Dohnal, Ilse; Mudrak, Ingrid; Friedmann, Christina; Schüchner, Stefan; Frohner, Ingrid E; Ammerer, Gustav; Ogris, Egon (2012). M-Track: detecting short-lived protein-protein interactions in vivo. Nature Methods. PMID: 22581371
Juanes, Maria Angeles; Khoueiry, Rita; Kupka, Thomas; Castro, Anna; Mudrak, Ingrid; Ogris, Egon; Lorca, Thierry; Piatti, Simonetta (2013). Budding Yeast Greatwall and Endosulfines Control Activity and Spatial Regulation of PP2A(Cdc55) for Timely Mitotic Progression. PLOS GENET;9(7):e1003575. PMID: 23861665
Sontag, Jean-Marie; Nunbhakdi-Craig, Viyada; Mitterhuber, Martina; Ogris, Egon; Sontag, Estelle (2010). Regulation of protein phosphatase 2A methylation by LCMT1 and PME-1 plays a critical role in differentiation of neuroblastoma cells. J NEUROCHEM. PMID: 21044074