MEDIATION BY NF-KAPPA-B OF CYTOKINE-INDUCED EXPRESSION OF INTERCELLULAR-ADHESION MOLECULE-1 (ICAM-1) IN AN INTESTINAL EPITHELIAL-CELL LINE,A PROCESS BLOCKED BY PROTEASOME INHIBITORS

Background/aims-The gene promoter for the intercellular adhesion molec ule ICAM-1 possesses binding sites for several transcriptional factors , including nuclear factor kappa B (NF-kappa B). The role of NF-kappa B in ICAM-1 gene regulation was therefore examined by using different proteasome inhibitors in tumour necrosis factor alpha (TNF-alpha) stim ulated IEC-6 rat intestinal epithelial cells. Methods-ICAM-1 expressio n was analysed by enzyme linked immunosorbent assay (ELISA), reverse t ranscriptase polymerase chain reaction, and immunohistochemistry. Stea dy state levels of cytoplasmic I kappa B protein were evaluated by wes tern blot, and nuclear translocation of NF-kappa B was determined by e lectrophoretic mobility shift assay and immunofluorescence staining. C ell adhesion was assayed by measuring the binding of fluorescence labe lled MOLT-4 cells. Results-TNF-alpha induced ICAM-1 mRNA and protein e xpression in IEC-6 cells, which was followed by increased adhesion of MOLT-4 lymphocytes. Blocking TNF-alpha induced I kappa B alpha degrada tion with proteasome inhibitors reduced TNF-alpha induced NF-kappa B a ctivation and ICAM-1 gene induction and notably decreased MOLT-4 cell adhesion without affecting Jun N-terminal kinase (JNK/SAPK) activity o r de novo protein synthesis. Conclusion-TNF-alpha induction of ICAM-1 expression is mediated by the transcription factor NF-kappa B and can be inhibited by blocking I kappa B alpha degradation. Thus the I kappa B/NF-kappa B system is a promising target for pharmacological modulat ion of the expression of adhesion molecules and other inflammatory gen es in the intestine.