Coupling of a signal response domain in I kappa B alpha to multiple pathways for NF-kappa B activation.
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.
Brockman
J A
JA
Howard Hughes Medical Institute, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0295, USA.
Scherer
D C
DC
McKinsey
T A
TA
Hall
S M
SM
Qi
X
X
Lee
W Y
WY
Ballard
D W
DW
D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers / Q000235:genetics; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D016356:Gene Products, tax / Q000378:metabolism; D015497:HIV-1 / Q000235:genetics; D015368:Human T-lymphotropic virus 1 / Q000235:genetics / Q000378:metabolism; D006801:Humans; D020672:I-kappa B Proteins; D008213:Lymphocyte Activation; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010766:Phosphorylation; D012694:Serine / Q000737:chemistry; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism; D051996:Transcription Factor RelA; D014158:Transcription, Genetic
D017931:DNA Primers; D004268:DNA-Binding Proteins; D016356:Gene Products, tax; D020672:I-kappa B Proteins; D016328:NF-kappa B; C000606204:NFKBIA protein, human; D051996:Transcription Factor RelA; D000072000:NF-KappaB Inhibitor alpha; D012694:Serine