Connective tissue growth factor (CTGF/CCN2) is a downstream mediator for TGF-beta1-induced extracellular matrix production in osteoblasts.
Connective tissue growth factor (CTGF/CCN2) is a cysteine-rich, extracellular matrix (ECM) protein that acts as an anabolic growth factor to regulate osteoblast differentiation and function. Recent studies have identified CTGF as a downstream effector of transforming growth factor-beta1 (TGF-beta1) for certain functions in specific cell types. In this study, we examined the role of CTGF as a downstream mediator of TGF-beta1-induced ECM production and cell growth in osteoblasts. Using primary cultures, we demonstrated that TGF-beta1 is a potent inducer of CTGF expression in osteoblasts, and that this induction occurred at all stages of osteoblast differentiation from the proliferative through mineralization stages. TGF-beta1 treatment of osteoblasts increased the expression and synthesis of the ECM components, collagen and fibronectin. When CTGF-specific siRNA was used to prevent TGF-beta1 induction of CTGF expression, it also inhibited collagen and fibronectin production, thereby demonstrating the requirement of CTGF for their up-regulation. To examine the effects of TGF-beta1 on osteoblast cell growth, cultures were treated with TGF-beta1 during the proliferative stage. Cell number was significantly reduced and the cells exhibited a decrease in G1 cyclin expression, consistent with TGF-beta1-induced cell-cycle arrest. Cultures transfected with CTGF siRNA prior to TGF-beta1 treatment showed an even greater reduction in cell number, suggesting that TGF-beta1-induced growth arrest is independent of CTGF in osteoblasts. Collectively, these data demonstrate for the first time that CTGF is an essential downstream mediator for TGF-beta1-induced ECM production in osteoblasts, but these two growth factors function independently regarding their opposing effects on osteoblast proliferation.
Arnott
J A
JA
Department of Anatomy and Cell Biology, Temple University School of Medicine, Philadelphia, Pennsylvania 19040, USA.
Nuglozeh
E
E
Rico
M C
MC
Arango-Hisijara
I
I
Odgren
P R
PR
Safadi
F F
FF
Popoff
S N
SN
D000818:Animals; D002454:Cell Differentiation; D049109:Cell Proliferation; D002478:Cells, Cultured; D055513:Connective Tissue Growth Factor; D056746:Cyclin G; D056766:Cyclin G1; D016213:Cyclins / Q000235:genetics / Q000378:metabolism; D005109:Extracellular Matrix / Q000378:metabolism*; D016326:Extracellular Matrix Proteins / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation; D017874:Immediate-Early Proteins / Q000235:genetics / Q000502:physiology*; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000502:physiology*; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D051381:Rats; D053773:Transforming Growth Factor beta1 / Q000502:physiology*
C526316:CCN2 protein, rat; C534704:Ccng1 protein, rat; D056746:Cyclin G; D056766:Cyclin G1; D016213:Cyclins; D016326:Extracellular Matrix Proteins; D017874:Immediate-Early Proteins; D036341:Intercellular Signaling Peptides and Proteins; D034741:RNA, Small Interfering; D053773:Transforming Growth Factor beta1; D055513:Connective Tissue Growth Factor