title: Secretory protein with RING finger domain (SPRING) specific to Trypanosoma cruzi is directed, as a ubiquitin ligase related protein, to the nucleus of host cells.
abstract: While some intracellular bacterial and viral proteins secreted into host cell possess ubiquitin ligase (E3) activity for their profit, it has not been reported whether intracellular parasites secrete such molecules. We identified a gene that encodes a protein containing a secretory signal peptide and a RING finger domain in the intracellular protozoan parasite, Trypanosoma cruzi. This gene was specific to T. cruzi and was designated spring (secretory protein with RING finger domain). An in vitro ubiquitination assay showed that SPRING possessed E3 activity in a RING finger domain-dependent manner. SPRING could utilize human ubiquitin-activating enzymes (E2), UbcH5 and UbcH13. Although SPRING was found to be a secretory protein, the signal peptide-cleaved mature form of SPRING was localized in the nucleus of host cells, indicating that SPRING may function in the host cell nuclei. Yeast two-hybrid screening identified 52 putative SPRING interactors in HeLa cells, suggesting that SPRING affects the stability or function of a number of host proteins. Furthermore, a co-immunoprecipitation assay showed that breast cancer-associated protein 3 interacted with SPRING, as well as being ubiquitinated by SPRING in vitro. These findings are the first to show that this protozoan parasite secretes an ubiquitin ligase-related protein into host cells.
authors.affiliation: Department of Molecular and Cellular Parasitology, Juntendo University School of Medicine, Hongo, Bunkyo-ku, Tokyo, Japan. muneaki@juntendo.ac.jp
authors.forename: Muneaki
authors.initials: M
authors.lastname: Hashimoto
authors.forename: Eri
authors.initials: E
authors.lastname: Murata
authors.forename: Takashi
authors.initials: T
authors.lastname: Aoki
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D015153:Blotting, Western; D002467:Cell Nucleus / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D047468:Immunoprecipitation; D009363:Neoplasm Proteins / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism; D016133:Polymerase Chain Reaction; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D054829:RING Finger Domains / Q000235:genetics / Q000502:physiology*; D014349:Trypanosoma cruzi / Q000201:enzymology* / Q000502:physiology; D020798:Two-Hybrid System Techniques; D044763:Ubiquitin-Conjugating Enzymes / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: C471621:AKIP1 protein, human; D048868:Adaptor Proteins, Signal Transducing; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D015800:Protozoan Proteins; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases