Interleukin-13 upregulates eotaxin expression in airway epithelial cells by a STAT6-dependent mechanism

Interleukin (IL)-13 is a T helper 2-derived cytokine that has recently been implicated in allergic airway responses. We hypothesized that IL-13 may re gulate expression of eotaxin in airway epithelium, We found that IL-13 upre gulated eotaxin messenger RNA and protein synthesis in the airway epithelia l cell line BEAS-2B; this effect showed synergy with tumor necrosis factor (TNF)-alpha and also was inhibited by the glucocorticoid budesonide. To est ablish the mechanisms of eotaxin upregulation by IL-13, cells were transfec ted with an eotaxin promoter-luciferase reporter plasmid and transcription was activated by IL-13 (1.7-fold) and TNF-alpha (2.8-fold). The combination of IL-13 and TNF-cu additively activated the promoter constructs (4.1-fold ). Activation of signal transducer and activator of transcription (STAT) 6 by IL-13 was confirmed by nuclear protein binding to a DNA probe derived fr om the eotaxin promoter. Activation of eotaxin transcription by IL-13 and t he additive effect with TNF-ol were lost in plasmids mutated at a putative STAT6 binding site. Cotransfection with a wild-type STAT6 expression vector significantly enhanced activation of the eotaxin promoter after IL-13 stim ulation (6-fold induction). A significant increase of eotaxin protein secre tion in the supernatant of STAT6 wild-type-transfected cells was observed a fter IL-13 stimulation, Cotransfection with a dominant negative STAT6 mutan t expression vector inhibited activation of the eotaxin promoter by IL-13. These results indicate that IL-13 stimulates eotaxin expression in airway e pithelial cells and that STAT6 plays a pivotal role in this response.