Complementary antagonistic actions between C-type natriuretic peptide and the MAPK pathway through FGFR-3 in ATDC5 cells

We previously reported that C-type natriuretic peptide (CNP) stimulates endochondral ossification and corrects the reduction in body length of achondroplasia model mouse with constitutive active fibroblast growth factor receptor 3 (FGFR-3). In order to examine the interaction between CNP and FGFR-3, we studied intracellular signaling by using ATDC5 cells, a mouse chondrogenic cell line, and found that FGF2 and FGF18 markedly reduced CNP-dependent intracellular cGMP production, and that these effects were attenuated by MAPK inhibitors. Western blot analysis demonstrated that the level of GC-B, a particulate guanylyl cyclase specific for CNP, was not changed by treatment with FGFs. Conversely, CNP and 8-bromo-cGMP strongly and dose-dependently inhibited the induction of ERK phosphorylation by FGF2 and FGF18 without changing the level of FGFR-3, although they did not affect the phosphorylation of STAT-1. In the organ-cultured fetal mouse tibias, CNP and FGF18 counteracted on the longitudinal bone growth, and both the size and number of hypertrophic chondrocytes. The FGF/FGFR-3 pathway is known as the negative regulator of endochondral ossification. We found that FGFs inhibited CNP-stimulated cGMP production by disrupting the signaling pathway through GC-B while CNP antagonized the activation of the MAPK cascade by FGFs. These results suggest that the CNP/GC-B pathway plays an important role in growth plate chondrocytes and constitutes the negative cross talk between FGFs and the activity of MAPK. Our results may explain one of the molecular mechanisms of the growth stimulating action of CNP and suggest that activation of the CNP/GC-B pathway may be effective as a novel therapeutic strategy for achondroplasia.