Three NF-kappa B sites in the I kappa B-alpha promoter are required for induction of gene expression by TNF alpha.

AUTOR(ES)

Ito, C Y

RESUMO

NF-kappa B was first identified as a postive regulator which bound to a 10 bp sequence in the first intron of the Ig kappa light chain gene. Further characterization of this transcription factor has revealed that NF-kappa B is kept from binding to its consensus sequence by its inhibitor, IkB-alpha, which retains NF-kappa B in the cytoplasm. Upon receiving various extra- and intracellular signals, I kappa B-alpha is rapidly degraded and NF-kappa B is induced to translocate into the nucleus. This process precedes the rapid induction of I kappa B-alpha mRNA and protein. To understand how I kappa B-alpha is replenished, we have cloned and sequenced the 5' flanking region of the I kappa B-alpha gene and have identified the transcription start site and three NF-kappa B sites in this region. Further characterization of these NF-kappa B sites show that they have different affinities for three specific protein complexes which we identify here to consist of various members of the Rel family. In transient assays, cotransfection with a p65 expression vector is able to activate an I kappa B-alpha promoter-CAT reporter construct and all three NF-kappa B sites are required for full activation of the I kappa B-alpha gene following stimulation with TNF-alpha. Our data confirm a transcriptional autoregulatory loop involved in maintaining appropriate NF-kappa B and I kappa B-alpha levels in the cell.

Documentos Relacionados

• Activation of NF-kappa B requires proteolysis of the inhibitor I kappa B-alpha: signal-induced phosphorylation of I kappa B-alpha alone does not release active NF-kappa B.
• Phosphorylation of human I kappa B-alpha on serines 32 and 36 controls I kappa B-alpha proteolysis and NF-kappa B activation in response to diverse stimuli.
• A proteasome inhibitor prevents activation of NF-kappa B and stabilizes a newly phosphorylated form of I kappa B-alpha that is still bound to NF-kappa B.
• In vivo control of NF-kappa B activation by I kappa B alpha.
• LMP-1 activates NF-kappa B by targeting the inhibitory molecule I kappa B alpha.