BMPER, a Novel Endothelial Cell Precursor-Derived Protein, Antagonizes Bone Morphogenetic Protein Signaling and Endothelial Cell Differentiation

Abstract

The development of endothelial cell precursors is essential for vasculogenesis. We screened for differentially expressed transcripts in endothelial cell precursors in developing mouse embryoid bodies. We cloned a complete cDNA encoding a protein that contains an amino-terminal signal peptide, five cysteine-rich domains, a von Willebrand D domain, and a trypsin inhibitor domain. We termed this protein BMPER (bone morphogenetic protein [BMP]-binding endothelial cell precursor-derived regulator). BMPER is specifically expressed in flk-1-positive cells and parallels the time course of flk-1 induction in these cells. In situ hybridization in mouse embryos demonstrates dorsal midline staining and staining of the aorto-gonadal-mesonephric region, which is known to host vascular precursor cells. BMPER is a secreted protein that directly interacts with BMP2, BMP4, and BMP6 and antagonizes BMP4-dependent Smad5 activation. In Xenopus embryos, ventral injection of BMPER mRNA results in axis duplication and downregulation of the expression of Xvent-1 (downstream target of Smad signaling). In an embryoid body differentiation assay, BMP4-dependent differentiation of endothelial cells in embryoid bodies is also antagonized by BMPER. Taken together, our data indicate that BMPER is a novel BMP-binding protein that is expressed by endothelial cell precursors, has BMP-antagonizing activity, and may play a role in endothelial cell differentiation by modulating local BMP activity.

ACKNOWLEDGMENTS

We are indebted to Barbara Pohl for the Xenopus BMP4 construct and M. Kato for the Smad5 reporter construct (3GC2). We thank Rebecca Rapaport for technical advice with ES cell differentiation and Dave Roberts for help with in situ hybridization.

M.M. is a postdoctoral fellow supported by the Deutsche Forschungsgemeinschaft. F.L.C. is supported by the American Heart Association. C.P. is an established investigator of the American Heart Association and a Burroughs Wellcome Fund clinician scientist in translational research. This work was supported by National Institutes of Health grants HL 61656, HL 03658, and HL 072347 to C.P.