I kappa B beta-related proteins in normal and transformed colonic epithelial cells

The transcription factor nuclear factor-kappa B (NF-kappa B) regulates gene s that can influence cell proliferation, apoptosis, and inflammatory respon ses. Since these events can contribute to carcinogenesis, we examined the e xpression of NF-kappa B inhibitory proteins (I kappa Bs) in normal and tran sformed colonic epithelial cells. Immunohistochemical analysis of the mouse colon revealed a high level of I kappa B beta expression in epithelial cel ls relative to the rest of the tissue, whereas I kappa B alpha was found pr imarily in cells of the lamina propria. Mouse colon tumors showed a similar cell-specific staining pattern. Immunoblot analysis of I kappa B beta from mouse colonocytes and the human HT-29 colon cancer cell line indicated tha t most of the I kappa B beta in these cells was similar to the C-terminal-t runcated I kappa B beta 2 isoform. Cell fractionation studies were consiste nt with I kappa B beta being a major regulator of p65-p50 NF-kappa B comple xes in HT-29 cells. Interestingly, two larger proteins specifically recogni zed by I kappa B beta antibodies (p106 and p112)were found in HT-29 cells a nd in colon tissue of carcinogen-exposed mice. The p106 and p112 proteins b ound to NF-kappa B, and their levels changed during the transient interleuk in-1 beta activation of NF-kappa B in HT-29 cells. Evidence was obtained in dicating that p106 and p112 are stably ubiquitinated forms of I kappa B bet a. We propose that deficiencies in the proteasomal degradation of I kappa B beta lead to p106 and p112 accumulation, which in turn alter NF-kappa B re gulation in colon cancer cells. Mel. Carcinog. 29:25-36, 2000. (C) 2000 Wil ey-Liss, Inc.