IkappaB kinase-independent IkappaBalpha degradation pathway: functional NF-kappaB activity and implications for cancer therapy.
Antiapoptotic activity of NF-kappaB in tumors contributes to acquisition of resistance to chemotherapy. Degradation of IkappaB is a seminal step in activation of NF-kappaB. The IkappaB kinases, IKK1 and IKK2, have been implicated in both IkappaB degradation and subsequent modifications of NFkappaB. Using mouse embryo fibroblasts (MEFs) devoid of both IKK1 and IKK2 genes (IKK1/2(-/-)), we document a novel IkappaB degradation mechanism. We show that this degradation induced by a chemotherapeutic agent, doxorubicin (DoxR), does not require the classical serine 32 and 36 phosphorylation or the PEST domain of IkappaBalpha. Degradation of IkappaBalpha is partially blocked by phosphatidylinositol 3-kinase inhibitor LY294002 and is mediated by the proteasome. Free NF-kappaB generated by DoxR-induced IkappaB degradation in IKK1/2(-/-) cells is able to activate chromatin based NF-kappaB reporter gene and expression of the endogenous target gene, IkappaBalpha. These results also imply that modification of NF-kappaB by IKK1 or IKK2 either prior or subsequent to its release from IkappaB is not essential for NF-kappaB-mediated gene expression at least in response to DNA damage. In addition, DoxR-induced cell death in IKK1/2(-/-) MEFs is enhanced by simultaneous inhibition of NF-kappaB activation by blocking the proteasome activity. These results reveal an additional pathway of activating NF-kappaB during the course of anticancer therapy and provide a mechanistic basis for the observation that proteasome inhibitors could be used as adjuvants in chemotherapy.
Laboratory of Genetics, The Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, CA 92037, USA.
Vinay
V
Tergaonkar
Virginie
V
Bottero
Masahito
M
Ikawa
Qiutang
Q
Li
Inder M
IM
Verma
D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D017024:Chemotherapy, Adjuvant; D002867:Chromones / Q000494:pharmacology; D003546:Cysteine Endopeptidases / Q000378:metabolism; D004247:DNA / Q000235:genetics; D004317:Doxorubicin / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm; D015870:Gene Expression; D017930:Genes, Reporter; D051550:I-kappa B Kinase; D020672:I-kappa B Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008954:Models, Biological; D009025:Morpholines / Q000494:pharmacology; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000378:metabolism; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000378:metabolism*; D009369:Neoplasms / Q000188:drug therapy; D011480:Protease Inhibitors / Q000627:therapeutic use; D046988:Proteasome Endopeptidase Complex; D017346:Protein Serine-Threonine Kinases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism; D051996:Transcription Factor RelA; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
D002867:Chromones; D020672:I-kappa B Proteins; D009025:Morpholines; D009097:Multienzyme Complexes; D016328:NF-kappa B; C000606205:Nfkbia protein, mouse; D011480:Protease Inhibitors; D017382:Reactive Oxygen Species; D051996:Transcription Factor RelA; D016159:Tumor Suppressor Protein p53; D000072000:NF-KappaB Inhibitor alpha; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D004317:Doxorubicin; D004247:DNA; D017346:Protein Serine-Threonine Kinases; C496564:Chuk protein, mouse; D051550:I-kappa B Kinase; C496562:Ikbkb protein, mouse; C496566:Ikbke protein, mouse; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex