Dual Roles of Smad Proteins in the Conversion from Myoblasts to Osteoblastic Cells by Bone Morphogenetic Proteins

Abstract

Bone morphogenetic proteins (BMPs) induce ectopic bone formation in muscle tissue in vivo and convert myoblasts such that they differentiate into osteoblastic cells in vitro. We report here that constitutively active Smad1 induced osteoblastic differentiation of C2C12 myoblasts in cooperation with Smad4 or Runx2. In floxed Smad4 mice-derived cells, Smad4 ablation partially suppressed BMP-4-induced osteoblast differentiation. In contrast, the BMP-4-induced inhibition of myogenesis was lost by Smad4 ablation and restored by Smad4 overexpression. A nuclear zinc finger protein, E4F1, was identified as a possible component of the Smad4 complex that suppresses myogenic differentiation in response to BMP signaling. In the presence of Smad4, E4F1 stimulated the expression of Ids. Taken together, these findings suggest that the Smad signaling pathway may play a dual role in the BMP-induced conversion of myoblasts to osteoblastic cells.

Transcription factor E4F1 is essential for epidermal stem cell maintenance and skin homeostasis

“…However, the functions of E4F1 likely extend beyond the regulation of p53, however. Indeed, physical interactions between E4F1 and components of other oncogenic pathways, including RASSF1A, pRB, HMGA2, and Smad4, have been reported (7)(8)(9)(10).…”

Higher BMP receptor expression and BMP-2-induced osteogenic differentiation in tendon-derived stem cells compared with bone-marrow-derived mesenchymal stem cells

“…Constitutively activated Smad1 overexpression was reported to induce myoblast osteogenic differentiation, whereas nuclear translocation of Smad4 inhibited myoblast myogenic differentiation [34]. It is not known whether Smad proteins and MSX2 also function to inhibit osteogenic differentiation and promote TDSC tenogenic differentiation, as reported in previous studies [30,32,34]; further study is required. Other factors, such as mechanical loading [35] and local extracellular matrix environment [9], may also function to suppress TDSC osteogenesis inside the tendon midsubstance.…”

“…The Smad-dependent pathway was also reported to regulate myogenic differentiation inhibition and osteoblastic differentiation induction of myoblasts induced by BMPs [34]. Constitutively activated Smad1 overexpression was reported to induce myoblast osteogenic differentiation, whereas nuclear translocation of Smad4 inhibited myoblast myogenic differentiation [34]. It is not known whether Smad proteins and MSX2 also function to inhibit osteogenic differentiation and promote TDSC tenogenic differentiation, as reported in previous studies [30,32,34]; further study is required.…”

“…An activated form of Smad8 protein inhibited the osteogenic pathway in MSCs known to be induced by BMP-2 while promoting tenogenic differentiation [33]. The Smad-dependent pathway was also reported to regulate myogenic differentiation inhibition and osteoblastic differentiation induction of myoblasts induced by BMPs [34]. Constitutively activated Smad1 overexpression was reported to induce myoblast osteogenic differentiation, whereas nuclear translocation of Smad4 inhibited myoblast myogenic differentiation [34].…”

Regulation of neuropeptide Y Y1 receptor expression by bone morphogenetic protein 2 in C2C12 myoblasts

“…Smad expression plasmids encoding the wild-type Smad4 and constitutively active Smad1 (DVD) were provided by Dr T. Katagiri [19,20]. The plasmid DNA was transfected into cells using Lipofectamine 2000 (Invitrogen) as described previously [18].…”