Proteasome inhibition leads to NF-kappaB-independent IL-8 transactivation in human endothelial cells through induction of AP-1

Eur J Immunol. 2002 Aug;32(8):2208-17. doi: 10.1002/1521-4141(200208)32:8<2208::AID-IMMU2208>3.0.CO;2-2.


IL-8 is an important mediator of leukocyte trafficking and activation, participating in tumor angiogenesis, inflammatory processes and coronary atherosclerosis. Under flow conditions IL-8, in conjunction with MCP-1, triggers the firm adhesion of monocytes to the vascular endothelium. While previous studies have suggested the requirement of NF-kappaB for IL-8 secretion by endothelial cells, we investigated the possibility of IL-8 transactivation under conditions of NF-kappaB suppression. Inhibition of the proteasome by MG-132 or lactacystin completely blocked TNF-alpha-induced IkappaBalpha degradation as well as NF-kappaB activity in human arterial endothelial cells. Surprisingly, basal secretion of IL-8 protein was eight- to tenfold induced by proteasome inhibitors, while MCP-1 expression was, as expected, completely down-regulated. IL-8 was up-regulated at the transcriptional level, and promoter studies proved a more than ninefold induction of transcription factor AP-1 activity to be the cause of increased IL-8 transcription. Mutation of the AP-1 binding site in an IL-8 promoter construct completely abrogated this effect, while mutation of the NF-kappaB motif did not influence IL-8 transactivation by proteasome inhibitors. With DNA binding assays we found a seven- to eightfold induction of phosphorylated c-Jun and hence JNK kinase activity under MG-132 treatment. Induction of JNK kinase appeared independent of the cell type, even in tumor cell lines not responding to proteasome inhibitors. Since neither inactivation of p53 in wild-type p53 cells nor reintroduction of functional p53 into p53(-/-) cells affected MG-132-inducible IL-8 secretion, a direct influence of p53 on IL-8 regulation could be excluded. These results show that proteasome inhibitors can not only lead to functional AP-1 induction by enhanced c-Jun phosphorylation, but also transactivate the IL-8 gene in human endothelial cells despite complete suppression of NF-kappaB activity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cells, Cultured
  • Cysteine Endopeptidases / physiology
  • Endothelium, Vascular / cytology
  • Endothelium, Vascular / metabolism*
  • Humans
  • Interleukin-8 / genetics*
  • Interleukin-8 / metabolism
  • Multienzyme Complexes / antagonists & inhibitors*
  • Multienzyme Complexes / physiology
  • NF-kappa B / physiology*
  • Proteasome Endopeptidase Complex
  • Transcription Factor AP-1 / biosynthesis*
  • Transcriptional Activation*
  • Tumor Suppressor Protein p53 / physiology


  • Interleukin-8
  • Multienzyme Complexes
  • NF-kappa B
  • Transcription Factor AP-1
  • Tumor Suppressor Protein p53
  • Cysteine Endopeptidases
  • Proteasome Endopeptidase Complex