Epidermal growth factor activation of NF-kappaB is mediated through IkappaBalpha degradation and intracellular free calcium.
The transcription factor NF-kappa-B is normally sequestered in the cytoplasm by its inhibitory subunit IkappaB. Most extracellular signals activate NF-kappa-B through a mechanism involving the phosphorylation and proteasome-dependent degradation of IkappaB. EGF activates NF-kappaB in A-431 carcinoma cells, which overexpress EGF receptors and in mouse embryo fibroblasts, which have a normal complement of receptors. Supershift experiments indicate that the NF-kappa-B complexes induced by EGF are composed of p50/p50 homodimers and p65/p50 heterodimers, but not c-rel. EGF stimulation enhances the degradation of IkappaBalpha, but not IkappaBbeta nor an N-terminal deletion mutant of IkappaBalpha. Treatment of cells with a proteasome inhibitor, such as ALLN or MG132, blocks EGF-mediated NF-kappaB activation, indicating that EGF-induced NF-kappa-B activation requires proteasome-dependent IkappaB degradation. Also, Bapta A/M (a cell-permeable chelator of intracellular calcium) blocks EGF-induced NF-kappa-B activation and IkappaBalpha degradation, suggesting a requirement of intracellular free Ca2+ for this growth factor response. Protein kinase C inhibition, in contrast, did not influence EGF activation of NF-kappaB.
Sun
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L
Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146, USA.
Carpenter
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G
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002450:Cell Communication; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D006801:Humans; D020672:I-kappa B Proteins; D007424:Intracellular Fluid; D051379:Mice; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D004268:DNA-Binding Proteins; D020672:I-kappa B Proteins; D016328:NF-kappa B; C000606204:NFKBIA protein, human; C000606205:Nfkbia protein, mouse; D000072000:NF-KappaB Inhibitor alpha; D004815:Epidermal Growth Factor; D002118:Calcium