Hypoxia causes the activation of nuclear factor kappa B through the phosphorylation of I kappa B alpha on tyrosine residues.
The response of mammalian cells to stress is controlled by transcriptional regulatory proteins such as nuclear factor kappa B (NF-kappa B) to induce a wide variety of early response genes. In this report, we show that exposure of cells to hypoxia (0.02% O2) results in I kappa B alpha degradation, increased NF-kappa B DNA binding activity, and transactivation of a reporter gene construct containing two NF-kappa B DNA binding sites. Pretreatment of cells with protein tyrosine kinase inhibitors and the dominant negative allele of c-Raf-1 (Raf 301) inhibited I kappa B alpha degradation, NF-kappa B binding, and transactivation of kappa B reporter constructs by hypoxia. To demonstrate a direct link between changes in the phosphorylation pattern of I kappa B alpha with NF-kappa B activation, we immunoprecipitated I kappa B alpha after varying times of hypoxic exposure and found that its tyrosine phosphorylation status increased during hypoxic exposure. Inhibition of the transfer of tyrosine phosphoryl groups onto I kappa B alpha prevented I kappa B alpha degradation and NF-kappa B binding. In comparison to other activators of NF-kappa B such as phorbol myristate acetate or tumor necrosis factor, we did not detect changes in the tyrosine phosphorylation status of I kappa B alpha following treatment with either of these agents. These results suggest that tyrosine phosphorylation of I kappa B alpha during hypoxia is an important proximal step which precedes its dissociation and degradation from NF-kappa B.
Koong
A C
AC
Cancer Biology Research Laboratory, Stanford University School of Medicine, California 94305-5468.
Chen
E Y
EY
Giaccia
A J
AJ
D001483:Base Sequence; D015687:Cell Hypoxia / Q000502:physiology*; D002467:Cell Nucleus / Q000502:physiology; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000235:genetics / Q000502:physiology; D006801:Humans; D020672:I-kappa B Proteins; D007700:Kinetics; D008969:Molecular Sequence Data; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D016759:Oncogene Protein p65(gag-jun) / Q000235:genetics; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000502:physiology; D013601:T-Lymphocytes / Q000378:metabolism / Q000502:physiology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D015533:Transcriptional Activation / Q000235:genetics; D014178:Translocation, Genetic / Q000235:genetics; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D014443:Tyrosine / Q000378:metabolism*
D004268:DNA-Binding Proteins; D020672:I-kappa B Proteins; D016328:NF-kappa B; C000606204:NFKBIA protein, human; D016759:Oncogene Protein p65(gag-jun); D014409:Tumor Necrosis Factor-alpha; D000072000:NF-KappaB Inhibitor alpha; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D013755:Tetradecanoylphorbol Acetate