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Mol. Cell. Biol., May 1995, 2809-2818, Vol 15, No. 5
JA Brockman, DC Scherer, TA McKinsey, SM Hall, X Qi, WY Lee and DW Ballard
The eukaryotic transcription factor NF-kappa B plays a central role in the
induced expression of human immunodeficiency virus type 1 and in many
aspects of the genetic program mediating normal T-cell activation and
growth. The nuclear activity of NF-kappa B is tightly regulated from the
cytoplasmic compartment by an inhibitory subunit called I kappa B alpha.
This cytoplasmic inhibitor is rapidly phosphorylated and degraded in
response to a diverse set of NF-kappa B-inducing agents, including T-cell
mitogens, proinflammatory cytokines, and viral transactivators such as the
Tax protein of human T-cell leukemia virus type 1. To explore these I kappa
B alpha-dependent mechanisms for NF- kappa B induction, we identified novel
mutants of I kappa B alpha that uncouple its inhibitory and
signal-transducing functions in human T lymphocytes. Specifically, removal
of the N-terminal 36 amino acids of I kappa B alpha failed to disrupt its
ability to form latent complexes with NF-kappa B in the cytoplasm. However,
this deletion mutation prevented the induced phosphorylation, degradative
loss, and functional release of I kappa B alpha from NF-kappa B in
Tax-expressing cells. Alanine substitutions introduced at two serine
residues positioned within this N-terminal regulatory region of I kappa B
alpha also yielded constitutive repressors that escaped from Tax-induced
turnover and that potently inhibited immune activation pathways for
NF-kappa B induction, including those initiated from antigen and cytokine
receptors. In contrast, introduction of a phosphoserine mimetic at these
sites rectified this functional defect, a finding consistent with a causal
linkage between the phosphorylation status and proteolytic stability of
this cytoplasmic inhibitor. Together, these in vivo studies define a
critical signal response domain in I kappa B alpha that coordinately
controls the biologic activities of I kappa B alpha and NF-kappa B in
response to viral and immune stimuli.
Copyright © 1995, American Society for Microbiology
Coupling of a signal response domain in I kappa B alpha to multiple pathways for NF-kappa B activation
Howard Hughes Medical Institute, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0295, USA.
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