title: Blocking autophagy prevents bortezomib-induced NF-κB activation by reducing I-κBα degradation in lymphoma cells.
abstract: Here we show that bortezomib induces effective proteasome inhibition and accumulation of poly-ubiquitinated proteins in diffuse large B-cell lymphoma (DLBCL) cells. This leads to induction of endoplasmic reticulum (ER) stress as demonstrated by accumulation of the protein CHOP, as well as autophagy, as demonstrated by accumulation of LC3-II proteins. Our data suggest that recruitment of both ubiquitinated proteins and LC3-II by p62 directs ubiquitinated proteins, including I-κBα, to the autophagosome. Degradation of I-κBα results in increased NF-κB nuclear translocation and transcription activity. Since bortezomib treatment promoted I-κBα phosphorylation, ubiquitination and degradation, this suggests that the route of I-κBα degradation was not via the ubiquitin-proteasome degradation system. The autophagy inhibitor chloroquine (CQ) significantly inhibited bortezomib-induced I-κBα degradation, increased complex formation with NF-κB and reduced NF-κB nuclear translocation and DNA binding activity. Importantly, the combination of proteasome and autophagy inhibitors showed synergy in killing DLBCL cells. In summary, bortezomib-induced autophagy confers relative DLBCL cell drug resistance by eliminating I-κBα. Inhibition of both autophagy and the proteasome has great potential to kill apoptosis-resistant lymphoma cells.
authors.affiliation: Centre for Haemato-Oncology, Barts Cancer Institute, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London, United Kingdom. L.jia@qmul.ac.uk
authors.forename: Li
authors.initials: L
authors.lastname: Jia
authors.forename: Ganga
authors.initials: G
authors.lastname: Gopinathan
authors.forename: Johanna T
authors.initials: JT
authors.lastname: Sukumar
authors.forename: John G
authors.initials: JG
authors.lastname: Gribben
mesh_terms: D021581:Active Transport, Cell Nucleus; D000970:Antineoplastic Agents / Q000494:pharmacology; D001343:Autophagy; D001897:Boronic Acids / Q000494:pharmacology*; D000069286:Bortezomib; D016923:Cell Death; D045744:Cell Line, Tumor; D005434:Flow Cytometry / Q000379:methods; D015870:Gene Expression; D006801:Humans; D020672:I-kappa B Proteins / Q000378:metabolism*; D008223:Lymphoma / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000737:chemistry / Q000378:metabolism; D011719:Pyrazines / Q000494:pharmacology*; D025801:Ubiquitin / Q000737:chemistry
chemical_list: D000970:Antineoplastic Agents; D001897:Boronic Acids; D020672:I-kappa B Proteins; D016328:NF-kappa B; C000606204:NFKBIA protein, human; D011719:Pyrazines; D025801:Ubiquitin; D000072000:NF-KappaB Inhibitor alpha; D000069286:Bortezomib; D046988:Proteasome Endopeptidase Complex