Identification of a p65 Peptide That Selectively Inhibits NF-κB Activation Induced by Various Inflammatory Stimuli and Its Role in Down-regulation of NF-κB-mediated Gene Expression and Up-regulation of Apoptosis

Abstract

Because of the critical role of the nuclear transcription factor NF-κB in inflammation, viral replication, carcinogenesis, antiapoptosis, invasion, and metastasis, specific inhibitors of this nuclear factor are being sought and tested as treatments. NF-κB activation is known to require p65 phosphorylation at serine residues 276, 529, and 536 before it undergoes nuclear translocation. Small protein domains, termed protein transduction domains (PTDs), which are able to penetrate cell membranes can be used to transport other proteins across the cell membrane. We have identified two peptides from the p65 subunit of NF-κB (P1 and P6 were from amino acid residues 271-282 and 525-537, respectively) that, when linked with a PTD derived from the third helix sequence of antennapedia, inhibited tumor necrosis factor (TNF)-induced NF-κB activation in vivo. Linkage to the PTD was not, however, required to suppress the binding of the p50-p65-heterodimer to the DNA in vitro. PTD-p65-P1 had no effect on TNF-induced AP-1 activation. PrD-p65-P1 suppressed NF-κB activation induced by lipopolysaccharide, interleukin-1, okadaic acid, phorbol 12-myristate 13-acetate, H 2O2, and cigarette smoke condensate as well as that induced by TNF. PTD-p65-P1 had no effect on TNF-induced inhibitory subunit of NF-κB (IκBα) phosphorylation, IκBα degradation, or IκBα kinase activation, but it blocked TNF-induced p65 phosphorylation and nuclear translocation. NF-κB-regulated reporter gene expression induced by TNF, TNF receptor 1, TNF receptor-associated death domain, TNF receptor-associated factor-2, NF-κB-inducing kinase, IκBα kinase, and p65 was also suppressed by these peptides. Suppression of NF-κB by PTD-p65-P1 enhanced the apoptosis induced by TNF and chemotherapeutic agents. Overall, our results demonstrate the identification of a p65 peptide that can selectively inhibit NF-κB activation induced by various inflammatory stimuli, down-regulate NF-κB-mediated gene expression, and up-regulate apoptosis.