EVIDENCE FOR ALTERED REGULATION OF I-KAPPA-B-ALPHA DEGRADATION IN HUMAN COLONIC EPITHELIAL-CELLS

The nuclear factor kappa B (NF-kappa B) regulates the transcription of genes bearing the kappa B consensus motif, Transmigration of NF-kappa B from the cytoplasm to the nucleus is regulated by the I kappa B fam ily of inhibitory NF-kappa B-binding proteins, Dissociation of the NF- kappa B-I kappa B complex requires both phosphorylation and degradatio n of I kappa Bs. We demonstrate that IL-1 beta induces complete I kapp a B alpha degradation in Caco-2 cell lines but not in HT-29, T84, SW-4 80 transformed cell lines, or native colonic epithelial cells, A simil ar lack of I kappa B alpha degradation in HT-29 cells followed TNF-alp ha and bacterial polymer stimulation, IL-1 beta stimulated NF-kappa B nuclear translocation and NF-kappa B-dependent IL-1 beta and IL-8 expr ession in both Caco-2 and HT-29 cells as assayed by electrophoretic mo bility shift assay, immunofluorescence, kappa B-luciferase transiectio n, reverse transcriptase-PCR analysis and ELISA, In HT-29 cells stimul ated with IL-1 beta, I kappa B alpha was phosphorylated and when cyclo heximide blocked new protein synthesis. I kappa B alpha was partially degraded, NF-kappa B cytoplasmic to nuclear transmigration was incompl ete and preceded I kappa B alpha degradation in HT-29 cells, in contra st to complete coordinated NF-kappa B nuclear translocation and I kapp a B alpha degradation in Caco-2 cells. Greater sensitivity of HT-29 ce lls to a calpain inhibitor, as measured by IL-8 secretion, suggested e nhanced resistance to I kappa B alpha proteolysis. These data show tha t IL-1 beta induces NF-kappa B activity and expression of NF-kappa B-d ependent genes in colonic epithelial cells and suggest altered regulat ion of I kappa B alpha degradation compared with other cell lineages, which may result in their increased responsiveness to therapeutic bloc kade.