Roles of Bone Morphogenetic Protein Type I Receptors and Smad Proteins in Osteoblast and Chondroblast Differentiation

Abstract

The biological effects of type I serine/threonine kinase receptors and Smad proteins were examined using an adenovirus-based vector system. Constitutively active forms of bone morphogenetic protein (BMP) type I receptors (BMPR-IA and BMPR-IB; BMPR-I group) and those of activin receptor-like kinase (ALK)-1 and ALK-2 (ALK-1 group) induced alkaline phosphatase activity in C2C12 cells. Receptor-regulated Smads (R-Smads) that act in the BMP pathways, such as Smad1 and Smad5, also induced the alkaline phosphatase activity in C2C12 cells. BMP-6 dramatically enhanced alkaline phosphatase activity induced by Smad1 or Smad5, probably because of the nuclear translocation of R-Smads triggered by the ligand. Inhibitory Smads, i.e., Smad6 and Smad7, repressed the alkaline phosphatase activity induced by BMP-6 or the type I receptors. Chondrogenic differentiation of ATDC5 cells was induced by the receptors of the BMPR-I group but not by those of the ALK-1 group. However, kinase-inactive forms of the receptors of the ALK-1 and BMPR-I groups blocked chondrogenic differentiation. Although R-Smads failed to induce cartilage nodule formation, inhibitory Smads blocked it. Osteoblast differentiation induced by BMPs is thus mediated mainly via the Smad-signaling pathway, whereas chondrogenic differentiation may be transmitted by Smad-dependent and independent pathways.

Activin receptor‐like kinase 1 inhibits human microvascular endothelial cell migration: Potential roles for JNK and ERK

“…Recombinant adenoviral vectors expressing the constitutively active form of ALK1 (AdALK1ca, mutation of glutamine 201 into aspartic acid) tagged with an influenza virus hemagglutinin (HA) epitope or Smad6 tagged with Flag (AdSmad6, generated by Dr. M. Fujii and kindly given to us by Dr. K. Miyazono, University of Tokyo, Tokyo, Japan) (Fujii et al, 1999) were used for infection. A recombinant adenovirus expressing bacterial b-galactosidase (Adb-gal) was used as a control.…”

The BMP signaling and in vivo bone formation

“…In contrast, Smad6 heterodimerizes with Hoxc8 and represses BMP-2-induced gene transcription (Bai et al, 2000). Smads 1 and 5 are two Smad proteins which have been shown to play an important role in osteoblast differentiation in C2C12 myoblast/osteoblast precursor cells and other osteoblastic cell lines (Yamamoto et al, 1997;Fujii et al, 1999). In addition to Smads, BMPs also activate non-Smad signaling pathways such as mitogen-activated protein kinase (MAPK) family of molecules including ERK1/2 and p38 (Guicheux et al, 2003;Reilly et al, 2005).…”

Activation of Smad signaling enhances collagenase-3 (MMP-13) expression and invasion of head and neck squamous carcinoma cells

“…Adenovirus for antisense ribozyme against MMP-13 (RAdMMP-13AsRZ) has been described before (Ala-aho et al, 2004). Adenoviruses for Smad3DN (RAdSmad3DN) (Pardali et al, 2000), Smad7 (RAdSmad7) (Fujii et al, 1999), constitutively active ALK5 (RAdCA-ALK5) (Fujii et al, 1999), and kinase-defective ALK5 (RAdKD-ALK5) (Fujii et al, 1999) were kindly provided by Dr Aristidis Moustakas (Ludwig Institute for Cancer Research, Uppsala, Sweden). Recombinant adenovirus RAdLacZ, which contains the Escherichia coli b-galactosidase gene under the control of the CMV IE promoter, and empty control virus RAd66 were kindly provided by Dr Gavin WG Wilkinson (University of Cardiff, UK) (Wilkinson and Akrigg, 1992).…”