blocking autophagy prevents bortezomib-induced nf-κb activation by reducing i-κbα degradation in lymphoma cells阻断自噬可以防止bortezomib-induced nf-κb激活通过减少i-κbα淋巴瘤细胞的退化.pdfVIP

Blocking Autophagy Prevents Bortezomib-Induced NF-kB Activation by Reducing I-kBa Degradation in Lymphoma Cells Li Jia*, Ganga Gopinathan, Johanna T. Sukumar, John G. Gribben Centre for Haemato-Oncology, Barts Cancer Institute, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London, United Kingdom 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-kBa, to the autophagosome. Degradation of I-kBa results in increased NF-kB nuclear translocation and transcription activity. Since bortezomib treatment promoted I-kBa phosphorylation, ubiquitination and degradation, this suggests that the route of I- kBa degradation was not via the ubiquitin-proteasome degradation system. The autophagy inhibitor chloroquine (CQ) significantly inhibited bortezomib-induced I-kBa degradation, increased complex formation with NF-kB and reduced NF-kB 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-kBa. Inhibition of both autophagy and the proteasome has great potential to kill apoptosis- resistant lymphoma cells. Citation: Jia L, Gopinathan G, Sukumar JT, Gribben JG (2012) Blocking Autophagy Prevents Bortezomib-Induced NF-kB Activation by Reduci