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Mol. Cell. Biol., Jan 1998, 477-487, Vol 18, No. 1
RM Attar, H Macdonald-Bravo, C Raventos-Suarez, SK Durham and R Bravo
The transcription factor NF-kappaB is normally sequestered in the cytoplasm
by members of the IkappaB family, including IkappaB alpha, IkappaB beta,
and the recently cloned IkappaB epsilon. Upon cellular activation, these
inhibitors are rapidly phosphorylated on two amino- terminal serines,
ubiquitinated, and degraded by the 26S proteasome, releasing a functional
NF-kappaB. To determine the importance of IkappaB beta in NF-kappaB
regulation in T cells, we generated transgenic mice expressing a
constitutively active IkappaB beta mutant (mIkappaB beta) under the control
of the lck promoter. The transgene contains the two critical N-terminal
serine residues mutated to alanines and therefore no longer susceptible to
degradation upon cell activation. mIkappaB beta is unable to totally
displace IkappaB alpha from RelA-containing complexes, thus allowing a
transient activation of NF-kappaB upon T-cell stimulation. However,
mIkappaB beta completely blocks NF-kappaB activity after IkappaB alpha
degradation. In addition, as a consequence of this inhibition, ikba
expression is down regulated, along with that of other NF-kappaB-regulated
genes. These transgenic mice have a significant reduction in the peripheral
T-cell population, especially CD8+ cells. The remaining T cells have
impaired proliferation in response to phorbol 12-myristate 13-acetate plus
phytohemagglutinin or calcium ionophore but not to anti-CD3/anti-CD28
costimulation. As a result of these alterations, transgenic animals present
defects in immune responses such as delayed-type hypersensitivity and the
generation of specific antibodies against T- cell-dependent antigens. These
results show that in nonstimulated T cells, IkappaB beta cannot efficiently
displace IkappaB alpha bound to RelA-containing complexes and that
persistent NF-kappaB activity is required for proper T-cell responses in
vivo.
Copyright © 1998, American Society for Microbiology
Expression of constitutively active IkappaB beta in T cells of transgenic mice: persistent NF-kappaB activity is required for T-cell immune responses
Department of Oncology, Bristol-Myers Squibb Pharmaceutical Research Institute, Princeton, New Jersey 08543-4000, USA.
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