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Mol. Cell. Biol., Jul 1995, 3523-3530, Vol 15, No. 7
P Perez, SA Lira and R Bravo
RelA (p65) is one of the strongest activators of the Rel/NF-kappa B family.
As a first step to elucidate the mechanisms that regulate its activity in
vivo, we have generated transgenic mice overexpressing RelA in the thymus.
Although the levels of RelA were significantly increased in thymocytes of
transgenic mice, the overall NF-kappa B-binding activity in unstimulated
cells was not augmented compared with that in control thymocytes. This
could be explained by the dramatic increase of endogenous I kappa B alpha
levels observed in RelA-overexpressing cells in both cytoplasmic and
nuclear compartments. The ikba mRNA levels were not augmented by
overexpressed RelA, but I kappa B alpha inhibitor was found to be
stabilized through association with RelA. Although a fraction of RelA was
associated with cytoplasmic p105, no changes in the precursor levels were
observed. Upon stimulation of RelA- overexpressing thymocytes with phorbol
12-myristate 13-acetate and lectin (phytohemaglutinin), different kappa
B-binding complexes, including RelA homodimers, were partially released
from I kappa B alpha. Association of RelA with I kappa B alpha prevented
complete degradation of the inhibitor. No effect of phorbol 12-myristate
13- acetate-lectin treatment was detected on RelA associated with p105. Our
data indicate that cytoplasmic retention of overexpressed RelA by I kappa B
alpha is the major in vivo mechanism controlling the potential excess of
NF-kappa B activity in long-term RelA-overexpressing thymocytes.
Copyright © 1995, American Society for Microbiology
Overexpression of RelA in transgenic mouse thymocytes: specific increase in levels of the inhibitor protein I kappa B alpha
Department of Molecular Biology, Bristol-Myers Squibb Pharmaceutical Research Institute, Princeton, New Jersey 08543-4000, USA.
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