STAT3 regulates NF- B recruitment to the IL-12p40 promoter in dendritic cells

Interleukin-10–deficient (IL-10 / ) mice develop an IL-12–mediated intestinal inflammation in the absence of endogenous IL-10. The molecular mechanisms of the dysregulated IL-12 responses in IL-10 / mice are poorly understood. In this study, we investigated the role of nuclear factor– B (NFB) and signal transducers and activators of transcription 3 (STAT3) in lipopolysaccharide (LPS)–induced IL12p40 gene expression in bone marrow derived–dendritic cells (BMDCs) isolated from wild-type (WT) and IL-10 / mice. We report higher IL-12p40 mRNA accumulation and protein secretion in LPSstimulated BMDCs isolated from IL-10 / compared with WT mice. LPS-induced NFB signaling is similar in IL-10 / and WT BMDCs as measured by I B phosphorylation and degradation, RelA phosphorylation and nuclear translocation, and NFB transcriptional activity, with no down-regulatory effects of exogenous IL10. Chromatin immunoprecipitation demonstrated enhanced NFB (cRel, RelA) binding to the IL-12p40 promoter in IL10 / but not WT BMDCs. Interestingly, LPS induced STAT3 phosphorylation in WT but not IL-10 / BMDCs, a process blocked by IL-10 receptor blocking antibody. Adenoviral gene delivery of a constitutively active STAT3 but not control green fluorescence protein (GFP) virus blocked LPS-induced IL-12p40 gene expression and cRel recruitment to the IL-12p40 promoter. In conclusion, dysregulated LPSinduced IL-12p40 gene expression in IL10 / mice is due to enhanced NFB recruitment to the IL-12p40 promoter in the absence of activated STAT3. (Blood. 2005;105:689-696)