title: Increased expression and altered subunit composition of proteasomes induced by continuous proteasome inhibition establish apoptosis resistance and hyperproliferation of Burkitt lymphoma cells.
abstract: The proteasome is the main protease for extralysosomal protein degradation in eukaryotic cells, and constitutes a sophisticated high molecular mass proteinase complex underlying a tightly coordinated expression and assembly of multiple subunits and subcomplexes. Here we show that continuous inhibition of proteasomal chymotrypsin-like peptidase activity by the proteasome inhibitor bortezomib induces in human Namalwa Burkitt lymphoma cells increased de novo biogenesis of proteasomes accompanied by increased expression of the proteasome maturation protein POMP, increased expression of 19S-20S-19S proteasomes, and abrogation of expression of beta 1i, beta 2i and beta 5i immunosubunits and PA28 in favor of increased expression of constitutive proteolytic beta1, beta2 and beta 5 subunits and 19S regulatory complexes. These alterations of proteasome expression and subunit composition are accompanied by an increase in proteasomal caspase-like, trypsin-like and chymotrypsin-like peptidase activities, not inhibitable by high doses of bortezomib. Cells harboring these proteasomal alterations display rapid proliferation and cell cycle progression, and acquire resistance to apoptosis induced by proteasome inhibitors, gamma-irradiation and staurosporine. This acquired apoptosis resistance is accompanied by de novo expression of anti-apoptotic Hsp27 protein and the loss of ability to accumulate and stabilize pro-apoptotic p53 protein. Thus, increased expression, altered subunit composition and increased activity of proteasomes constitute a hitherto unknown adaptive and autoregulatory feedback mechanism to allow cells to survive the lethal challenge of proteasome inhibition and to establish a hyperproliferative and apoptosis-resistant phenotype.
authors.affiliation: Institute of Immunology, Department of Transplantation Immunology, University of Heidelberg, D-69120 Heidelberg, Germany.
authors.forename: Dominik
authors.initials: D
authors.lastname: Fuchs
authors.forename: Carsten
authors.initials: C
authors.lastname: Berges
authors.forename: Gerhard
authors.initials: G
authors.lastname: Opelz
authors.forename: Volker
authors.initials: V
authors.lastname: Daniel
authors.forename: Cord
authors.initials: C
authors.lastname: Naujokat
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects*; D001897:Boronic Acids / Q000494:pharmacology; D000069286:Bortezomib; D002051:Burkitt Lymphoma / Q000201:enzymology* / Q000473:pathology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D006023:Glycoproteins / Q000378:metabolism; D055551:HSP27 Heat-Shock Proteins; D006360:Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D018832:Molecular Chaperones; D009363:Neoplasm Proteins / Q000378:metabolism; D025821:Polyubiquitin / Q000378:metabolism; D011480:Protease Inhibitors / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D061988:Proteasome Inhibitors; D021122:Protein Subunits / Q000378:metabolism; D011719:Pyrazines / Q000494:pharmacology; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D054875:Ubiquitination
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D001897:Boronic Acids; D006023:Glycoproteins; D055551:HSP27 Heat-Shock Proteins; C057725:HSPB1 protein, human; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D009363:Neoplasm Proteins; D011480:Protease Inhibitors; D061988:Proteasome Inhibitors; D021122:Protein Subunits; D011719:Pyrazines; D016159:Tumor Suppressor Protein p53; D025821:Polyubiquitin; D000069286:Bortezomib; D046988:Proteasome Endopeptidase Complex