STAT6 mediates eotaxin-1 expression in IL-4 or TNF-α-induced fibroblasts

Eosinophils are attracted to sites of allergic inflammation by a number of chemoattractants including eotaxin-1. This chemokine can be secreted from epithelial cells and fibroblasts after IL-4 and TNF-alpha stimulation in a synergistic fashion. TNF-alpha activated gene expression at the transcriptional level in a STAT6-dependent manner, because: 1) eotaxin-1 promoter luciferase constructs were TNF-alpha inducible in STAT6-defective HEK293 cells only on cotransfection of STAT6 expression vector, an effect that was partially mediated by activation-induced binding of NF-kappaB proteins to a composite STAT6/NF-kappaB element; 2) reporter constructs defective in STAT6 DNA binding did not respond to TNF-alpha stimulation; 3) eotaxin-1 protein secretion was detected only in STAT6-transfected HEK293 cell supernatants on TNF-alpha treatment; and 4) a trans-dominant negative STAT6 protein inhibited TNF-alpha -induced eotaxin-1 secretion in primary fibroblasts. TNF-alpha inducibility of the IL-8 and monocyte chemoattractant protein-1 genes was not dependent on STAT6 expression in the same experimental systems. The inducing effect of IL-4 and IL-13 was also mediated by STAT6. The synergistic effect of IL-4 and TNF-alpha observed at the RNA and the protein level was not seen at the promoter level. The data demonstrate that both IL-4 and TNF-alpha induce eotaxin-1 expression at the level of transcription via a STAT6-mediated pathway.