Abstract
The HIPPI (HIP-1 protein interactor) protein is a multifunctional protein that is involved in the regulation of apoptosis. The interaction partners of HIPPI include HIP-1 (Huntingtin-interacting protein-1), Apoptin, Homer1c, Rybp/DEDAF, and BAR (bifunctional apoptosis regulator). In search for other binding partners of HIPPI, we performed a yeast two hybrid screen and identified BLOC1S2 (Biogenesis of lysosome-related organelles complex-1 subunit 2) as a novel HIPPI-interacting protein. In co-immunoprecipitation assays, BLOC1S2 specifically associates with HIPPI, but not with HIP-1. To study the expression of BLOC1S2 on the protein level, we generated a mouse monoclonal antibody specific for BLOC1S2 and a multiple tissue array comprising 70 normal and cancer tissue samples of diverse origin. BLOC1S2 protein is widely expressed in normal tissue as well as in malignant tumors with a tendency towards lower expression levels in certain subtypes of tumors. On the subcellular level, BLOC1S2 is expressed in an organellar-like pattern and co-localizes with mitochondria. Over-expression of BLOC1S2 in the presence or absence of HIPPI does not induce apoptosis. However, BLOC1S2 and HIPPI sensitize NCH89 glioblastoma cells to the pro-apoptotic actions of staurosporine and the death ligand TRAIL by enhancing caspase activation, cytochrome c release, and disruption of the mitochondrial membrane potential. Given its interaction with HIPPI and its pro-apoptotic activity, BLOC1S2 might play an important functional role in cancer and neurodegenerative diseases.
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Acknowledgments
This work was supported by a grant from the Deutsche Krebshilfe to W.R. (German Cancer Aid, Max Eder Program), a fellowship from the Heinrich F.C. Behr Foundation to G.G., the Tissue Bank of the National Center for Tumor Diseases (NCT) Heidelberg, and grants from the National Institutes of Health, CA69381 and AG15393, to J.C.R. We thank Sarah Messnard for expert technical assistance, Christel Herold-Mende for providing NCH89 glioblastoma cells, and Frank Stenner-Liewen for generation of the pcDNA3-FLAG-HIPPI plasmid.
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Gdynia, G., Lehmann-Koch, J., Sieber, S. et al. BLOC1S2 interacts with the HIPPI protein and sensitizes NCH89 glioblastoma cells to apoptosis. Apoptosis 13, 437–447 (2008). https://doi.org/10.1007/s10495-007-0176-3
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DOI: https://doi.org/10.1007/s10495-007-0176-3