TL1A induces interleukin-8 (IL-8) secretion in human peripheral blood monocyte-derived macrophage in a dose- and time-dependent manner. Overexpression of its cognate receptor DR3 can induce a higher amount of IL-8 protein secretion than thin induced by TNFRI even though both receptors activate IL-8 gene transcription in a similar fashion. The underlying mechanism for the regulation of the IL-8 gene transcription by DR3 has not been investigated yet . Here, we used HEK293 cells as a model System W dissect the Possible signaling components that are involved in the regulation of DR3-mediated IL-8 gene expression. Although both DR3 and TNFRI activated TRAF2 and NF-B-K to induce IL-8 gene transcription, the kinase cascades that transduce signals for DR3- and TNFRI-induced IL-8 gene transcription are different. The axis TAKl/ASKl-MKK4/MKK7-JNK2 is responsible for DR3-mediated IL-8 gene expression whereas the axis ASKl- MKK4-JNK1/JNK2/p38MAPK is the choice for TNFRI -mediated activation of IL- 8 gene expression. This indicates that the downstream signaling pathways of DR3 and TNFRI for IL-9 secretion are divergent even though both receptors contain death-domain and induce IL-8 secretion via TRAF2. (c ) 2005 Elsevier Inc. All rights reserved.
