Role of RGM coreceptors in bone morphogenetic protein signaling

Peter J Halbrooks¹ , Ru Ding² , John M Wozney² and Gerard Bain²

¹Quality Control Technical Services Laboratory, Genzyme Corporation, Framingham MA, 01701, USA

²Women's Health and Musculoskeletal Biology, Wyeth Discovery Research, Cambridge, MA, 02140, USA

author email corresponding author email

Journal of Molecular Signaling 2007, 2:4doi:10.1186/1750-2187-2-4


Published:	5 July 2007

Abstract

Background

The repulsive guidance molecule (RGM) proteins, originally discovered for their roles in neuronal development, have been recently identified as co-receptors in the bone morphogenetic protein (BMP) signaling pathway. BMPs are members of the TGFβ superfamily of signaling cytokines, and serve to regulate many aspects of cellular growth and differentiation.

Results

Here, we investigate whether RGMa, RGMb, and RGMc play required roles in BMP and TGFβ signaling in the mouse myoblast C2C12 cell line. These cells are responsive to BMPs and are frequently used to study BMP/TGFβ signaling pathways. Using siRNA reagents to specifically knock down each RGM protein, we show that the RGM co-receptors are required for significant BMP signaling as reported by two cell-based BMP activity assays: endogenous alkaline phosphatase activity and a luciferase-based BMP reporter assay. Similar cell-based assays using a TGFβ-induced luciferase reporter show that the RGM co-receptors are not required for TGFβ signaling. The binding interaction of each RGM co-receptor to each of BMP2 and BMP12 is observed and quantified, and equilibrium dissociation constants in the low nanomolar range are reported.

Conclusion

Our results demonstrate that the RGMs play a significant role in BMP signaling and reveal that these molecules cannot functionally compensate for one another.