Identification and cloning of a connective tissue growth factor-like cDNA from human osteoblasts encoding a novel regulator of osteoblast functions

We have identified and cloned a novel connective tissue growth factor-like (CTGF-L) cDNA from primary human osteoblast cells encoding a 250-amino acid single chain polypeptide, Murine CTGF-L cDNA, encoding a polypeptide of 25 1 amino acids, was obtained from a murine lung cDNA library. CTGF-L protein bears significant identity (similar to 60%) to the CCN (CTGF, Cef10/Cyr61, Nov) family of proteins. CTGF-L is composed of three distinct domains, an insulin-like growth factor binding domain, a von Willebrand Factor type C m otif, and a thrombospondin type I repeat. However, unlike CTGF, CTGF-L lack s the C-terminal domain implicated in dimerization and heparin binding. CTG F-L mRNA (similar to 1.3 kilobases) is expressed in primary human osteoblas ts, fibroblasts, ovary, testes, and heart, and a similar to 26-kDa protein is secreted from primary human osteoblasts and fibroblasts, In situ hybridi zation indicates high expression in osteoblasts forming bone, discrete alka line phosphatase positive bone marrow cells, and chondrocytes, Specific bin ding of I-125-labeled insulin-like growth factors to CTGF-L was demonstrate d by ligand Western blotting and cross-linking experiments, Recombinant hum an CTGF-L promotes the adhesion of osteoblast cells and inhibits the bindin g of fibrinogen to integrin receptors, In addition, recombinant human CTC;F -L inhibits osteocalcin production in rat osteoblast-like Ros 17/2.8 cells. Taken together, these results suggest that CTGF-L may play an important ro le in modulating bone turnover.