A mechanistic insight into a proteasome-independent constitutive inhibitor kappaBalpha (IkappaBalpha) degradation and nuclear factor kappaB (NF-kappaB) activation pathway in WEHI-231 B-cells.
Inducible activation of the transcription factor NF-kappaB (nuclear factor kappaB) is classically mediated by proteasomal degradation of its associated inhibitors, IkappaBalpha (inhibitory kappaBalpha) and IkappaBbeta. However, certain B-lymphocytes maintain constitutively nuclear NF-kappaB activity (a p50-c-Rel heterodimer) which is resistant to inhibition by proteasome inhibitors. This activity in the WEHI-231 B-cell line is associated with continual and preferential degradation of IkappaBalpha, which is also unaffected by proteasome inhibitors. Pharmacological studies indicated that there was a correlation between inhibition of IkappaBalpha degradation and constitutive p50-c-Rel activity. Domain analysis of IkappaBalpha by deletion mutagenesis demonstrated that an N-terminal 36-amino-acid sequence of IkappaBalpha represented an instability determinant for constitutive degradation. Moreover, domain grafting studies indicated that this sequence was sufficient to cause IkappaBbeta, but not chloramphenicol acetyltransferase, to be rapidly degraded in WEHI-231 B-cells. However, this sequence was insufficient to target IkappaBbeta to the non-proteasome degradation pathway, suggesting that there was an additional cis-element(s) in IkappaBalpha that was required for complete targeting. Nevertheless, the NF-kappaB pool associated with IkappaBbeta now became constitutively active by virtue of IkappaBbeta instability in these cells. These findings further support the notion that IkappaB instability governs the maintenance of constitutive p50-c-Rel activity in certain B-cells via a unique degradation pathway.
Shumway
Stuart D
SD
Program in Cellular and Molecular Biology, Department of Pharmacology, University of Wisconsin, 3795 Medical Sciences Center, 1300 University Avenue, Madison, WI 53706, USA.
Miyamoto
Shigeki
S
D000818:Animals; D002154:Calpain / Q000037:antagonists & inhibitors / Q000502:physiology; D045744:Cell Line, Tumor / Q000378:metabolism; D003546:Cysteine Endopeptidases; D019281:Dimerization; D020672:I-kappa B Proteins / Q000737:chemistry / Q000502:physiology*; D008070:Lipopolysaccharides / Q000494:pharmacology; D016393:Lymphoma, B-Cell / Q000473:pathology; D046911:Macromolecular Substances; D051379:Mice; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000378:metabolism*; D052002:NF-kappa B p50 Subunit; D009363:Neoplasm Proteins / Q000502:physiology*; D011480:Protease Inhibitors / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex; D017434:Protein Structure, Tertiary; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000502:physiology; D020569:Proto-Oncogene Proteins c-rel / Q000378:metabolism; D017384:Sequence Deletion; D051020:bcl-X Protein
C494812:Bcl2l1 protein, mouse; D020672:I-kappa B Proteins; D008070:Lipopolysaccharides; D046911:Macromolecular Substances; D009097:Multienzyme Complexes; D016328:NF-kappa B; D052002:NF-kappa B p50 Subunit; D009363:Neoplasm Proteins; C000606205:Nfkbia protein, mouse; D011480:Protease Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D020569:Proto-Oncogene Proteins c-rel; D051020:bcl-X Protein; D000072000:NF-KappaB Inhibitor alpha; D002154:Calpain; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex