title: Bioassays to monitor Taspase1 function for the identification of pharmacogenetic inhibitors.
abstract: BACKGROUND
  Threonine Aspartase 1 (Taspase1) mediates cleavage of the mixed lineage leukemia (MLL) protein and leukemia provoking MLL-fusions. In contrast to other proteases, the understanding of Taspase1's (patho)biological relevance and function is limited, since neither small molecule inhibitors nor cell based functional assays for Taspase1 are currently available.
  
  
  RESULTS
  Efficient cell-based assays to probe Taspase1 function in vivo are presented here. These are composed of glutathione S-transferase, autofluorescent protein variants, Taspase1 cleavage sites and rational combinations of nuclear import and export signals. The biosensors localize predominantly to the cytoplasm, whereas expression of biologically active Taspase1 but not of inactive Taspase1 mutants or of the protease Caspase3 triggers their proteolytic cleavage and nuclear accumulation. Compared to in vitro assays using recombinant components the in vivo assay was highly efficient. Employing an optimized nuclear translocation algorithm, the triple-color assay could be adapted to a high-throughput microscopy platform (Z'factor = 0.63). Automated high-content data analysis was used to screen a focused compound library, selected by an in silico pharmacophor screening approach, as well as a collection of fungal extracts. Screening identified two compounds, N-[2-[(4-amino-6-oxo-3H-pyrimidin-2-yl)sulfanyl]ethyl]benzenesulfonamide and 2-benzyltriazole-4,5-dicarboxylic acid, which partially inhibited Taspase1 cleavage in living cells. Additionally, the assay was exploited to probe endogenous Taspase1 in solid tumor cell models and to identify an improved consensus sequence for efficient Taspase1 cleavage. This allowed the in silico identification of novel putative Taspase1 targets. Those include the FERM Domain-Containing Protein 4B, the Tyrosine-Protein Phosphatase Zeta, and DNA Polymerase Zeta. Cleavage site recognition and proteolytic processing of these substrates were verified in the context of the biosensor.
  
  
  CONCLUSIONS
  The assay not only allows to genetically probe Taspase1 structure function in vivo, but is also applicable for high-content screening to identify Taspase1 inhibitors. Such tools will provide novel insights into Taspase1's function and its potential therapeutic relevance.
authors.affiliation: Institute for Molecular Biology, Centre for Medical Biotechnology (ZMB), University Duisburg-Essen, Essen, Germany.
authors.forename: Shirley K
authors.initials: SK
authors.lastname: Knauer
authors.forename: Verena
authors.initials: V
authors.lastname: Fetz
authors.forename: Jens
authors.initials: J
authors.lastname: Rabenstein
authors.forename: Sandra
authors.initials: S
authors.lastname: Friedl
authors.forename: Bettina
authors.initials: B
authors.lastname: Hofmann
authors.forename: Samaneh
authors.initials: S
authors.lastname: Sabiani
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Schröder
authors.forename: Lena
authors.initials: L
authors.lastname: Kunst
authors.forename: Eugen
authors.initials: E
authors.lastname: Proschak
authors.forename: Eckhard
authors.initials: E
authors.lastname: Thines
authors.forename: Thomas
authors.initials: T
authors.lastname: Kindler
authors.forename: Gisbert
authors.initials: G
authors.lastname: Schneider
authors.forename: Rolf
authors.initials: R
authors.lastname: Marschalek
authors.forename: Roland H
authors.initials: RH
authors.lastname: Stauber
authors.forename: Carolin
authors.initials: C
authors.lastname: Bier
mesh_terms: D016475:3T3 Cells; D000818:Animals; D001681:Biological Assay / Q000379:methods*; D015374:Biosensing Techniques; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D002470:Cell Survival; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D004353:Drug Evaluation, Preclinical; D010450:Endopeptidases / Q000378:metabolism*; D006801:Humans; D051379:Mice; D010597:Pharmacogenetics / Q000379:methods*; D011480:Protease Inhibitors / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D011480:Protease Inhibitors; D010450:Endopeptidases; C480823:taspase1, human