Lymphotoxin β receptor induces interleukin 8 gene expression via NF-κB and AP-1 activation

The human lymphotoxin β receptor (LTβR), a member of the tumor necrosis factor (TNF) receptor superfamily, is essential for not only the development and organization of secondary lymphoid tissues, but also for chemokine release. Even though LTβR was shown to recruit TNF-receptor-associated factor (TRAF) 2, 3, and 5, and to induce cell apoptosis or NF-κB activation, however, the downstream signaling leading to chemokine expression is not illustrated yet. In this study, we find that overexpression of LTβR in HEK293 cells increases IL-8 promoter activity and leads to IL-8 release. LTβR-induced IL-8 gene expression requires NF-κB (-80 to -71) and AP-1 (-126 to -12) binding sites located in IL-8 promoter, and NF-κB is more crucial than AP-1 for IL-8 gene expression. Reporter assay with dominant-negative mutants of TRAFs reveals that TRAF2, 3, and 5, as well as the downstream signal molecules NIK, IKKα, and IKKβ, are involved in IL-8 gene expression. LTβR-mediated IL-8 response was inhibited by the dominant-negative mutants of ASK1, MKK4, MKK7, and JNK, but not by those of MEKK1, TAK1, MEK, ERK, and p38 MAPK. This suggests that IL-8 induction by LTβR is via TRAFs-elicited signaling pathways, including NIK/IKK-dependent NF-κB activation and ASK/MKK/JNK-dependent AP-1 activation.