Effects of Fibroblast Growth Factor 1 (FGF‐1) on CCN2 Gene Expression in Chondrocytic Cells

Cartilage and bone are developed by chondrocytes and osteoblasts differentiated from mesenchymal stem cells under the multiple interactions of extracellular signaling molecules. Among such molecules, CCN family protein 2 (CCN2) plays a critical role in the development and regeneration of the cartilage and bone to promote proliferation, differentiation and chondrocyte maturation as well as matrix remodeling during chondrogenesis. CCN2 interacts with several growth factors involved in endochondral ossification, which include fibroblast growth factor 1 (FGF‐1) showing a specific binding with this CCN2. However, the role of FGF‐1 in chondrocyte metabolism has not been investigated well. Therefore, in this study, we evaluated the effect of FGF‐1 on chondrocytes and its role on CCN2 regulation. The effect of FGF‐1 on CCN2 in human chondrocytic HCS‐2/8 cells and the cellular phenotype was estimated by the gene expression of chondrocytic markers. Addition of FGF‐1 to chondrocytic cell culture drastically repressed the mRNA levels of CCN2, with significant repression of other chondrocytic markers in those cells. The ELISA experiments revealed consistent results, in which the protein level of CCN2 was drastically down‐regulated by the addition of FGF‐1. Next, reporter gene assay was used to examine whether the CCN2 regulation by FGF‐1 is mediated by genetic elements involved in the proximal promoter, or not. However, the negative effect of FGF‐1 on CCN2 promoter activity appears to have been too weak to account for the observed decrease at mRNA and protein levels. Another reporter gene assay was performed with a plasmid containing multiple post‐transcriptional regulatory elements in the 3′‐untranslated region of the CCN2 gene. Surprisingly, FGF‐1 has no effect on these elements. Degradation fate of CCN2 mRNA after the addition of actinomycin D was tested, in the presence or absence of FGF‐1, showing unexpected results. Suspecting a regulation at a chromatin level, the effect of a histone deacetylase inhibitor, valproic acid (VPA), on the FGF‐1 function was evaluated, but VPA did not prevent the repressive effect of FGF‐1 on CCN2 gene expression. Further investigation is underway, suspecting a transcriptional regulation through a silencer located outside of the proximal promoter region. Support or Funding Information Japan Society for the Promotion of Science (JSPS) This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .