Neogenin, a Receptor for Bone Morphogenetic Proteins

Abstract

Bone morphogenetic proteins (BMPs) regulate many mammalian physiologic and pathophysiologic processes. These proteins bind with the kinase receptors BMPR-I and BMPR-II, thereby activating Smad transcription factor. In this study, we demonstrate that neogenin, a receptor for netrins and proteins of the repulsive guidance molecule family, is a receptor for BMPs and modulates Smad signal transduction. Neogenin was found to bind directly with BMP-2, BMP-4, BMP-6, and BMP-7. Knockdown of neogenin in C2C12 cells resulted in the enhancement of the BMP-2-induced processes of osteoblastic differentiation and phosphorylation of Smad1, Smad5, and Smad8. Conversely, overexpression of neogenin in C2C12 cells suppressed these processes. Our results also indicated that BMP-induced activation of RhoA was mediated by neogenin. Inhibition of RhoA promoted BMP-2-induced processes of osteoblastic differentiation and phosphorylation of Smad1/ 5/8. However, treatment with Y-27632, an inhibitor of Rhoassociated protein kinase, did not modulate BMP-induced phosphorylation of Smad1/5/8. Taken together, our findings suggest that neogenin negatively regulates the functions of BMP and that this effect of neogenin is mediated by the activation of RhoA.Bone morphogenetic proteins (BMPs) 2 are a unique family belonging to the transforming growth factor-␤ superfamily. BMPs regulate various processes associated with the differentiation, growth, and death of cells (1). BMPs bind to two different serine/threonine kinase receptors and mediate their signals through Smad-dependent and Smad-independent pathways (1). The biological activities of these proteins are regulated by intracellular signaling cascades triggered by various growth factors and cytokines. In particular, the functions of BMPs are known to be modulated by small GTPase Rho. Rho and one of its effectors, ROCK, participate in a variety of biological processes such as vascular contraction, tumor invasion, and bone formation. We have previously reported that in mice, continuous infusion of the ROCK-specific inhibitor Y-27632 enhanced ectopic bone formation induced by recombinant BMP-2 (rhBMP-2) impregnated into an atelocollagen carrier, without affecting the systemic bone metabolism (2). The expression of a dominant negative mutant of ROCK in mesenchymal ST2 cells promoted osteoblastic differentiation of these cells, whereas that of a constitutively active mutant of ROCK attenuated osteoblastic differentiation; moreover, the administration of a ROCK inhibitor reversed this phenotype. These findings suggest that ROCK negatively regulates BMPinduced osteogenesis. However, the precise molecular mechanism by which Rho is involved in the BMP signals remains to be elucidated.The results of this study show that neogenin is a receptor for BMPs and uncover the missing link between the BMPs and Rho. Neogenin, a receptor for the repulsive guidance molecule (RGM) and netrins, is a single-membrane-spanning protein and a member of the Ig superfamily. Neogenin consists of four immunoglobulin-like dom...

Hyaluronan inhibits BMP‐induced osteoblast differentiation

“…In addition, recent findings indicate that the RhoA signaling pathway has important roles in bone remodeling. For example, in osteoblast survival [26], the integrity of the actin cytoskeleton as well as migration [27] and differentiation [28][29][30] are regulated by RhoA signaling. We examined the effects of HA on RhoA activation in cells.…”

The neogenin/DCC homolog UNC-40 promotes BMP signaling via the RGM protein DRAG-1 in C. elegans

“…On the one hand, neogenin positively potentiates BMP signaling to regulate the expression of hepcidin for body iron metabolism and endochondral ossification in mice Zhou et al, 2010) or human liver cells (Zhang et al, 2009). On the other hand, neogenin negatively modulates BMP2-induced osteoblastic differentiation of C2C12 cells (Hagihara et al, 2011). Neogenin also increases the secretion of soluble RGMc, which may cause downregulation of BMP signaling Zhang et al, 2007).…”

Functional Roles of Netrin-1 in Osteoblast Differentiation

“…On the other hand, this controversial result has been already reported. Hagihara et al reported that neogenin negatively regulates the functions of BMP and that this effect of neogenin is mediated by the activation of RhoA (17). However, it is conjectured that the inhibition of osteoblast differentiation by BMP via the activation of neogenin may not occur under the physiological condition.…”