STAT6 is required for the anti-inflammatory activity of interleukin-4 in mouse peritoneal macrophages

Interleukin-4 (IL-4) is an anti-inflammatory cytokine which inhibits many inducible macrophage functions. The present study demonstrates that the ability of IL-4 to inhibit interferon gamma (IFNgamma)-dependent gene transcription is dependent upon STAT6. IL-4 suppressed IFNgamma-induced expression of the MIG (monokine induced by IFNgamma) gene, a C-X-C chemokine, in mouse macrophages. IFNgamma-induced expression of MIG mRNA was abolished in peritoneal macrophages from Stat1-/- mice, and the suppression of MIG mRNA by IL-4 was abolished in macrophages from Stat6-/- mice. Transient transfection assays using a reporter gene containing the MIG gene promoter or the IFNgamma-responsive element (gammaRE) from the MIG gene revealed that the IFNgamma-dependent transcription was suppressed by IL-4, although IL-4 alone had no transactivating function. IFNgamma and IL-4 activated STAT1 and STAT6, respectively, and both proteins were able to bind the gammaRE motif. Furthermore, STAT6 was associated with the co-activator CREB-binding protein in RAW264.7 cells. These observations indicate that STAT6 is necessary for the IL-4-mediated suppression of IFNgamma-induced, STAT1-dependent transcription and suggest that STAT6 may directly suppress the STAT1-dependent transcription by competing with STAT1 for occupancy of the gammaRE motif and/or by competing with limiting quantities of the transcriptional coactivator.