Expression and function of CCN2-derived circRNAs in chondrocytes.

Cellular communication network factor 2 (CCN2) molecules promote endochondral ossification and articular cartilage regeneration, and circular RNAs (circRNAs), which arise from various genes and regulate gene expression by adsorbing miRNAs, are known to be synthesized from CCN2 in human vascular endothelial cells and other types of cells. However, in chondrocytes, not only the function but also the presence of CCN2-derived circRNA remains completely unknown. In the present study, we investigated the expression and function of CCN2-derived circRNAs in chondrocytes. Amplicons smaller than those from known CCN2-derived circRNAs were observed using RT-PCR analysis that could specifically amplify CCN2-derived circRNAs in human chondrocytic HCS-2/8 cells. The nucleotide sequences of the PCR products indicated novel circRNAs in the HCS-2/8 cells that were different from known CCN2-derived circRNAs. Moreover, the expression of several Ccn2-derived circRNAs in murine chondroblastic ATDC5 cells was confirmed and observed to change alongside chondrocytic differentiation. Next, one of these circRNAs was knocked down in HCS-2/8 cells to investigate the function of the human CCN2-derived circRNA. As a result, CCN2-derived circRNA knockdown significantly reduced the expression of aggrecan mRNA and proteoglycan synthesis. Our data suggest that CCN2-derived circRNAs are expressed in chondrocytes and play a role in chondrogenic differentiation. Production and role of CCN2-derived RNAs in chondrocytes.

RFX1-mediated CCN3 induction that may support chondrocyte survival under starved conditions.

Cellular communication network factor (CCN) family members are multifunctional matricellular proteins that manipulate and integrate extracellular signals. In our previous studies investigating the role of CCN family members in cellular metabolism, we found three members that might be under the regulation of energy metabolism. In this study, we confirmed that CCN2 and CCN3 are the only members that are tightly regulated by glycolysis in human chondrocytic cells. Interestingly, CCN3 was induced under a variety of impaired glycolytic conditions. This CCN3 induction was also observed in two breast cancer cell lines with a distinct phenotype, suggesting a basic role of CCN3 in cellular metabolism. Reporter gene assays indicated a transcriptional regulation mediated by an enhancer in the proximal promoter region. As a result of analyses in silico, we specified regulatory factor binding to the X-box 1 (RFX1) as a candidate that mediated the transcriptional activation by impaired glycolysis. Indeed, the inhibition of glycolysis induced the expression of RFX1, and RFX1 silencing nullified the CCN3 induction by impaired glycolysis. Subsequent experiments with an anti-CCN3 antibody indicated that CCN3 supported the survival of chondrocytes under impaired glycolysis. Consistent with these findings in vitro, abundant CCN3 production by chondrocytes in the deep zones of developing epiphysial cartilage, which are located far away from the synovial fluid, was confirmed in vivo. Our present study uncovered that RFX1 is the mediator that enables CCN3 induction upon cellular starvation, which may eventually assist chondrocytes in retaining their viability, even when there is an energy supply shortage.

Bipartite regulation of cellular communication network factor 2 and fibroblast growth factor 1 genes by fibroblast growth factor 1 through histone deacetylase 1 and fork head box protein A1.

Fibroblast growth factor 1 (FGF-1) is the first FGF family member, and it induces proliferation of fibroblasts and other types of the cells. However, recent studies are uncovering unexpected functions of this molecule. Our previous study redefined this growth factor as a catabolic molecule produced in cartilage upon metabolic insult. Indeed, FGF-1 was found to repress the gene expression of cellular communication network factor 2 (CCN2), which protects and regenerates cartilage, amplifying its own production through positive feedback regulation. In the present study, we investigated the molecular mechanism of this bipartite CCN2 repression and FGF1 activation by FGF-1 in chondrocytes. Repression of CCN2 and induction of FGF1 in human chondrocytic cells were both partly abolished by valproic acid, an inhibitor of histone deacetylase 1 (HDAC1), indicating the involvement of chromatin remodeling by histone acetylation in this system. In contrast, RNA degradation analysis suggested no contribution of post-transcriptional regulation of the mRNA stability to the effects conferred by FGF-1. Suspecting a regulation by a specific transcription factor, we next sought a candidate in silico from a large dataset. As a result, we found fork head box protein A1 (FOXA1) as the transcription factor that bound to both CCN2 and FGF1 loci. Functional analysis demonstrated that FOXA1 silencing significantly attenuated the CCN2 repression and FGF1 induction caused by FGF1. These findings collectively indicate that the bipartite regulation by FGF-1 is enabled by the combination of chromatin remodeling by HDACs and transcriptional modulation by FOXA1 with unknown transcriptional coactivators of opposite functionalities.

Regulation of cellular communication network factor 2 (CCN2) in breast cancer cells via the cell-type dependent interplay between CCN2 and glycolysis.

OBJECTIVES: Anti-osteoclastic treatments for breast cancer occasionally cause medication-related osteonecrosis of the jaw. Moreover, elevated glycolytic activity, which is known as the Warburg effect, is usually observed in these breast cancer cells. Previously, we found that cellular communication network factor 2 (CCN2) production and glycolysis enhanced each other in chondrocytes. Here, we evaluated the interplay between CCN2 and glycolysis in breast cancer cells, as we suspected a possible involvement of CCN2 in the Warburg effect in highly invasive breast cancer cells. METHODS: Two human breast cancer cell lines with a distinct phenotype were used. Glycolysis was inhibited by using 2 distinct compounds, and gene silencing was performed using siRNA. Glycolysis and the expression of relevant genes were monitored via colorimetric assays and quantitative RT-PCR, respectively. RESULTS: Although CCN2 expression was almost completely silenced when treating invasive breast cancer cells with a siRNA cocktail against CCN2, glycolytic activity was not affected. Notably, the expression of glycolytic enzyme genes, which was repressed by CCN2 deficiency in chondrocytes, tended to increase upon CCN2 silencing in breast cancer cells. Inhibition of glycolysis, which resulted in the repression of CCN2 expression in chondrocytic cells, did not alter or strongly enhanced CCN2 expression in the invasive and non-invasive breast cancer cells, respectively. CONCLUSIONS: High CCN2 expression levels play a critical role in the invasion and metastasis of breast cancer. Thus, a collapse in the intrinsic repressive machinery of CCN2 due to glycolysis may induce the acquisition of an invasive phenotype in breast cancer cells.