Bone morphogenetic protein-6 induces the expression of inducible nitric oxide synthase in macrophages

Bone morphogenetic proteins (BMPs) are members of the transforming growth factor-β (TGF-β) superfamily. In the present study, we investigated the effect of BMPs on the production of inducible nitric oxide synthase (iNOS) in the murine macrophage cell line, RAW 264.7, and in mouse peritoneal macrophages. Among the BMPs, only BMP-6 induced iNOS expression in a time-dependent and dose-dependent manner in both cell types. Induction of iNOS was inhibited by both cycloheximide and actinomycin D, indicating that the induction of iNOS expression by BMP-6 requires new protein synthesis. Mechanistic studies revealed that the BMP-6-induced iNOS expression requires both Smads and nuclear factor-kappa B (NF-κB) signalling pathways. Furthermore, induction of interleukin-1β (IL-1β) was necessary for iNOS induction by BMP-6. These observations suggest that BMP-6 stimulates macrophages to produce iNOS through IL-1β via Smad and NF-κB signalling pathways and that BMP-6 may be an important regulator of macrophages.