TNF receptor-associated factor-2 is involved in both IL-1 beta and TNF-alpha signaling cascades leading to NF-kappa B activation and IL-8 expression in human intestinal epithelial cells.
Cytokine signaling involves the participation of many adaptor proteins, including the docking protein TNF receptor-associated factor-2 (TRAF-2), which is believed to transmit the TNF-alpha signal through both the I kappa B/NF-kappa B and c-Jun N-terminal kinase (JNK)/stress-related protein kinase (SAPK) pathways. The physiological role of TRAF proteins in cytokine signaling in intestinal epithelial cells (IEC) is unknown. We characterized the effect of a dominant-negative TRAF-2 delivered by an adenoviral vector (Ad5dnTRAF-2) on the cytokine signaling cascade in several IEC and also investigated whether inhibiting the TRAF-2-transmitting signal blocked TNF-alpha-induced NF-kappa B and IL-8 gene expression. A high efficacy and level of Ad5dnTRAF-2 gene transfer were obtained in IEC using a multiplicity of infection of 50. Ad5dnTRAF-2 expression prevented TNF-alpha-induced, but not IL-1 beta-induced, I kappa B alpha degradation and NF-kappa B activation in NIH-3T3 and IEC-6 cells. TNF-alpha-induced JNK activation was also inhibited in Ad5dnTRAF-2-infected HT-29 cells. Induction of IL-8 gene expression by TNF-alpha was partially inhibited in Ad5dnTRAF-2-transfected HT-29, but not in control Ad5LacZ-infected, cells. Surprisingly, IL-1 beta-mediated IL-8 gene expression was also inhibited in HT-29 cells as measured by Northern blot and ELISA. We concluded that TRAF-2 is partially involved in TNF-alpha-mediated signaling through I kappa B/NF-kappa B in IEC. In addition, our data suggest that TRAF-2 is involved in IL-1 beta signaling in HT-29 cells. Manipulation of cytokine signaling pathways represents a new approach for inhibiting proinflammatory gene expression in IEC.
Jobin
C
C
Department of Medicine, Center for Gastrointestinal Biology and Disease, University of North Carolina, Chapel Hill 27599, USA. job@med.unc.edu
Holt
L
L
Bradham
C A
CA
Streetz
K
K
Brenner
D A
DA
Sartor
R B
RB
D000260:Adenoviruses, Human / Q000235:genetics / Q000276:immunology; D002472:Cell Transformation, Viral / Q000235:genetics / Q000276:immunology; D004847:Epithelial Cells / Q000276:immunology / Q000378:metabolism; D005786:Gene Expression Regulation / Q000276:immunology; D005822:Genetic Vectors / Q000138:chemical synthesis / Q000276:immunology; D019073:HT29 Cells; D006801:Humans; D007375:Interleukin-1 / Q000502:physiology*; D016209:Interleukin-8 / Q000096:biosynthesis* / Q000235:genetics; D007413:Intestinal Mucosa / Q000276:immunology / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism*; D011506:Proteins / Q000235:genetics / Q000502:physiology*; D018124:Receptors, Tumor Necrosis Factor / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology*; D047992:TNF Receptor-Associated Factor 2; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000502:physiology*
D007375:Interleukin-1; D016209:Interleukin-8; D016328:NF-kappa B; D011506:Proteins; D018124:Receptors, Tumor Necrosis Factor; D047992:TNF Receptor-Associated Factor 2; D014409:Tumor Necrosis Factor-alpha