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Molecular Players Involved in TGF‐β1 induced CTGF/CCN2 expression in Primary Rat Osteoblasts: SBE, TRE and SRC/ERK
Author(s) -
Arnott John A,
Sanjay Archana,
Owen Tom A,
Litvin Judith,
Safadi Fayez F,
Popoff Steven N
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.6.a972
Subject(s) - ctgf , proto oncogene tyrosine protein kinase src , microbiology and biotechnology , mapk/erk pathway , growth factor , chemistry , transforming growth factor , kinase , signal transduction , osteoblast , biology , receptor , biochemistry , in vitro
Connective tissue growth factor (CTGF/CCN2) regulates osteoblast differentiation and cell function. In osteoblasts, CTGF is induced by TGF‐β1 where it acts as a mediator of some TGF‐β1 induced biological functions. Two proximal promoter motifs, the TGF‐β response element (TRE) and the SMAD binding element (SBE), were shown to mediate the induction of CTGF by TGF‐β1 in a cell type specific fashion. To investigate if these motifs functioned in osteoblasts, we utilized CTGF promoter deletion and mutant constructs. We demonstrated the requirement of both motifs for induction of CTGF activity by TGF‐β1 in osteoblasts. Electro‐mobility assays using probes containing the TRE, SBE or both showed TGF‐β1 inducible complexes that can be ablated by mutation of the motif, confirming their role in CTGF expression by TGF‐β1. Smads and MAP kinases (JNK, p38 and ERK) are key mediators of TGF‐β1 signaling and are activated in osteoblasts by TGF‐β1. Only expression of dominant‐negative (DN) ERK showed significant inhibition of TGF‐β1 induced CTGF activity. Since the tyrosine kinase, SRC, is upstream of ERK signaling, we assessed its role in TGF‐β1 induction of CTGF. Osteoblasts that were treated with the SRC kinase inhibitor, PP2 (10μM), or the kinase‐dead SRC showed a decrease in TGF‐β1 induced CTGF activity. In conclusion, CTGF induction by TGF‐β1 in osteoblasts requires both the TRE and SBE motifs and the SRC/ERK signaling cascade.