Induction of interleukin-6 expression by bone morphogenetic protein-6 in macrophages requires both SMAD and p38 signaling pathways.

Unlike the prototype transforming growth factor-β (TGF-β), bone morphogenetic protein-6 (BMP-6) activates macrophages. Here, we report that BMP-6 induces the expression of IL-6 in macrophages. Using overexpression and knockdown experiments, we demonstrate that BMP receptor type II and activin-like kinase-2 are necessary for IL-6 induction by BMP-6. At the intracellular level, both Smad and p38 signaling pathways are required for the induction of IL-6. The cross-talk between the two pathways occurs at the level of transcription factor GATA4 and Smad 1/4. These results, taken together, demonstrate a novel BMP-6 signaling mechanism in which both the Smad and non-Smad pathways directly interact to activate the transcription of a target gene.