Cch. Li et al., INACTIVATION OF NF-KAPPA-B INHIBITOR I-KAPPA-B-ALPHA - UBIQUITIN-DEPENDENT PROTEOLYSIS AND ITS DEGRADATION PRODUCT, Biochemical and biophysical research communications, 215(1), 1995, pp. 292-301
In most cells, the inactive dimeric NF-kappa B complexes an retained i
n the cytoplasm by binding to a group of inhibitory proteins, I kappa
B. In response to extracellular stimuli, I kappa B is rapidly phosphor
ylated and degraded, thus, liberating the active NF-kappa B. To invest
igate the mechanisms involved, we have developed a cell-free system to
study the degradation of the prototype I kappa B protein, I kappa B a
lpha. In this in vitro assay, ubiquitin, proteasome-containing S100 fr
action and ATP are required for the proteolysis of I kappa B alpha. Bo
th bound and free forms of I kappa B alpha isolated from intact cells
can be degraded through this pathway. We also identified polyubiquitin
ated I kappa B alpha molecules and N-terminal truncated I kappa B alph
a degradation product(s) both in vivo and in vitro. We conclude that t
he inactivation of I kappa B alpha occurs through a series of processe
s including phosphorylation, ATP-dependent ubiquitin conjugation and p
roteasome-mediated proteolysis. (C) 1995 Academic Press, Inc.