Alternative splicing variants of IkappaBbeta establish differential NF-kappaB signal responsiveness in human cells

Item Type:	Article
Title:	Alternative splicing variants of IkappaBbeta establish differential NF-kappaB signal responsiveness in human cells
Creators Name:	Hirano, F. and Chung, M.R. and Tanaka, H. and Maruyama, N. and Makino, I. and Moore, D.D. and Scheidereit, C.
Abstract:	To release transcription factor NF-kappaB into the nucleus, the mammalian IkappaB molecules IkappaB alpha and IkappaB beta are inactivated by phosphorylation and proteolytic degradation. Both proteins contain conserved signal-responsive phosphorylation sites and have conserved ankyrin repeats. To confer specific physiological functions to members of the NF-kappaB/Rel family, the different IkappaB molecules could vary in their specific NF-kappaB/Rel factor binding activities and could respond differently to activation signals. We have demonstrated that both mechanisms apply to differential regulation of NF-kappaB function by IkappaB beta relative to IkappaB alpha. Via alternative RNA processing, human IkappaB beta gives rise to different protein isoforms. IkappaB beta1 and IkappaB beta2, the major forms in human cells, differ in their carboxy-terminal PEST sequences. IkappaB beta2 is the most abundant species in a number of human cell lines tested, whereas IkappaB beta1 is the only form detected in murine cells. These isoforms are indistinguishable in their binding preferences to cellular NF-kappaB/Rel homo- and heterodimers, which are distinct from those of IkappaB alpha, and both are constitutively phosphorylated. In unstimulated B cells, however, IkappaB beta1, but not IkappaB beta2, is found in the nucleus. Furthermore, the two forms differ markedly in their efficiency of proteolytic degradation after stimulation with several inducing agents tested. While IkappaB beta1 is nearly as responsive as IkappaB alpha, indicative of a shared activation mechanism, IkappaB beta2 is only weakly degraded and often not responsive at all. Alternative splicing of the IkappaB beta pre-mRNA may thus provide a means to selectively control the amount of IkappaB beta-bound NF-kappaB heteromers to be released under NF-kappaB stimulating conditions.
Keywords:	Alternative Splicing, Amino Acid Sequence, B-Lymphocytes, Cell Compartmentation, Cell Nucleus, Dimerization, DNA-Binding Proteins, Gene Expression Regulation, Genetic Transcription, Genetic Variation, I-kappa B Proteins, Molecular Sequence Data, NF-kappa B, Phosphorylation, Protein Binding, Proto-Oncogene Proteins, Proto-Oncogene Proteins c-Rel, Signal Transduction
Source:	Molecular and Cellular Biology
ISSN:	0270-7306
Publisher:	American Society for Microbiology
Volume:	18
Number:	5
Page Range:	2596-2607
Date:	May 1998
Official Publication:	http://mcb.asm.org/cgi/content/abstract/18/5/2596
PubMed:	View item in PubMed

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