Regulation of proteolysis by cytokines in the human intestinal epithelial cell line HCT-8:: role of IFNγ

Protein metabolism contributes in the regulation of gut barrier function, which may be altered during inflammatory states. There are three major proteolytic pathways in mammalian cells: lysosomal, Ca2+-activated and ubiquitin-proteasome. The regulation of proteolytic activities during inflammation remains unknown in intestine. Intestinal epithelial cells, HCT-8, were stimulated by 1L-I beta, IFN gamma and TNF alpha each alone or in combination (Cytomix). Proteolytic activities were assessed using fluorogenic substrates and specific inhibitors, protein expressions by Western blot. Lysosomal and Ca2+-activated pathways were not significantly altered by any treatment. In contrast, the activity of ubiquitin-proteasome system was stimulated by IFN gamma and Cytomix (155, 160 versus 100, P < 0.05, respectively) but remained unaffected by IL-1 beta and TNF alpha. Free ubiquitin expression, but not ubiquitinated proteins, was enhanced by IFN gamma and Cytomix. The expression of proteasome 20S alpha 1 subunit, a constitutive proteasome 20S subunit, was not altered, beta 5 subunit expression was weakly decreased by Cytomix and inducible beta 5i subunit expression was markedly increased in response to IFN gamma and to Cytomix (202, 206 versus 100, P < 0.05, respectively). In conclusion, lysosomal, Ca2+-activated and constitutive proteasome activities were not affected by IL-10, IFN gamma and TNFa alone or in combination, in HCT-8 cells. These results suggest that IFN gamma, but not IL-1 beta and TNF alpha, increases immunoproteasome, which might contribute to enhanced antigen presentation during inflammatory bowel diseases. (c) 2006 Elsevier SAS. All rights reserved.