Autoregulation of the NF-kappa B transactivator RelA (p65) by multiple cytoplasmic inhibitors containing ankyrin motifs.
RelA (p65) functions as the critical transactivating component of the heterodimeric p50-p65 NF-kappa B complex and contains a high-affinity binding site for its cytoplasmic inhibitor, I kappa B alpha. After cellular activation, I kappa B alpha is rapidly degraded in concert with the induced nuclear translocation of NF-kappa B. The present study demonstrates that tumor necrosis factor alpha-induced degradation of I kappa B alpha in human T cells is preceded by its rapid phosphorylation in vivo. However, these effects on I kappa B alpha result in nuclear mobilization of only a fraction of the entire cytoplasmic pool of RelA. Subsequent studies have revealed that (i) cytoplasmic RelA is stably associated not only with I kappa B alpha but also with other ankyrin motif-rich proteins including the products of the NF-kappa B2 (p100) and NF-kappa B1 (p105) genes; (ii) in contrast to RelA-I kappa B alpha, RelA-p100 cytoplasmic complexes are not dissociated following tumor necrosis factor alpha activation; (iii) p100 functions as a potent inhibitor of RelA-mediated transcription in vivo; (iv) the interaction of RelA and p100 involves the conserved Rel homology domain of both proteins but not the nuclear localization signal of RelA, which is required for I kappa B alpha binding; (v) p100 inhibition of RelA function requires the C-terminal ankyrin motif domain, which mediates cytoplasmic retention of RelA; and (vi) as observed with I kappa B alpha, nuclear RelA stimulates p100 mRNA and protein expression. These findings thus reveal the presence of a second inducible autoregulated inhibitory pathway that helps ensure the rapid but transient action of nuclear NF-kappa B.
Sun
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SC
Gladstone Institute of Virology and Immunology, University of California, San Francisco General Hospital 94141-9100.
Ganchi
P A
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Béraud
C
C
Ballard
D W
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Greene
W C
WC
D017487:Ankyrins / Q000235:genetics; D002451:Cell Compartmentation; D003593:Cytoplasm / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D005786:Gene Expression Regulation; D006801:Humans; D020672:I-kappa B Proteins; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000037:antagonists & inhibitors* / Q000302:isolation & purification / Q000378:metabolism*; D052002:NF-kappa B p50 Subunit; D010766:Phosphorylation; D011498:Protein Precursors / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis; D013601:T-Lymphocytes / Q000378:metabolism*; D051996:Transcription Factor RelA; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D017487:Ankyrins; D004268:DNA-Binding Proteins; D020672:I-kappa B Proteins; D016328:NF-kappa B; D052002:NF-kappa B p50 Subunit; C000606204:NFKBIA protein, human; D011498:Protein Precursors; D012333:RNA, Messenger; D051996:Transcription Factor RelA; D014409:Tumor Necrosis Factor-alpha; D000072000:NF-KappaB Inhibitor alpha