Connective tissue growth factor enhances osteoblastogenesis in vitro.
Connective tissue growth factor (CTGF), a member of the CCN family of proteins, is expressed by osteoblasts, but its function in cells of the osteoblastic lineage has not been established. We investigated the effects of CTGF overexpression by transducing murine ST-2 stromal cells with a retroviral vector, where CTGF is under the control of the cytomegalovirus promoter. Overexpression of CTGF in ST-2 cells increased alkaline phosphatase activity, osteocalcin and alkaline phosphatase mRNA levels, and mineralized nodule formation. CTGF overexpression decreased the effect of bone morphogenetic protein-2 on Smad 1/5/8 phosphorylation and of Wnt 3 on cytosolic beta-catenin, indicating that the stimulatory effect on osteoblastogenesis was unrelated to BMP and Wnt signaling. CTGF overexpression suppressed Notch signaling and induced the transcription of hairy and E (spl)-1 (HES)-1, by Notch-independent mechanisms. CTGF induced nuclear factor of activated T cells (NFAT) transactivation by a calcineurin-dependent mechanism. Down-regulation of CTGF enhanced Notch signaling and decreased HES-1 transcription and NFAT transactivation. Similar effects were observed following forced CTGF overexpression, the addition of CTGF protein, or the transduction of ST-2 cells with a retroviral vector expressing HES-1. In conclusion, CTGF enhances osteoblastogenesis, possibly by inhibiting Notch signaling and inducing HES-1 transcription and NFAT transactivation.
Smerdel-Ramoya
Anna
A
Department of Research, Saint Francis Hospital and Medical Center, Hartford, Connecticut 06105-1299, USA.
Zanotti
Stefano
S
Deregowski
Valerie
V
Canalis
Ernesto
E
D000469:Alkaline Phosphatase / Q000235:genetics; D000818:Animals; D001854:Bone Marrow Cells / Q000187:drug effects / Q000502:physiology*; D055513:Connective Tissue Growth Factor; D017931:DNA Primers; D017874:Immediate-Early Proteins / Q000494:pharmacology*; D036341:Intercellular Signaling Peptides and Proteins / Q000494:pharmacology*; D051379:Mice; D015675:Osteocalcin / Q000235:genetics; D010012:Osteogenesis / Q000187:drug effects*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012269:Ribosomal Proteins / Q000235:genetics; D017154:Stromal Cells / Q000187:drug effects / Q000502:physiology*
C526318:CCN2 protein, mouse; D017931:DNA Primers; D017874:Immediate-Early Proteins; D036341:Intercellular Signaling Peptides and Proteins; D012269:Ribosomal Proteins; D015675:Osteocalcin; D055513:Connective Tissue Growth Factor; D000469:Alkaline Phosphatase