Indian hedgehog signaling pathway differences between swarm rat chondrosarcoma and native rat chondrocytes

Indian Hedgehog (Ihh)--Parathyroid related protein (PTHrP) and Fibroblast Growth Factor 3 (FGFR3) signaling pathways are important in regulating endochondral bone formation. In the growth plate, Ihh and PTHrP are involved in a feedback loop to increase proliferation and delay differentiation of chondrocytes. Fibroblast Growth Factor Receptor 3 (FGFR3) conversely decreases proliferation and hastens differentiation with an agonist. Since proliferation is the hallmark of chondrosarcoma cells, we hypothesized that Ihh/PTHrP and FGF3R pathways may be dysfunctional on these cells. Therefore, we sought to investigate the role of these signaling pathways in the Swarm rat chondrosarcoma cells utilizing expression and functional studies. Semiquantitative RT-PCR analysis demonstrated difference in expression between normal growth plate chondrocytes and chondrosarcoma cells (JWS). JWS had an increased mRNA expression of FGF2 and FGFR3 suggesting a mechanism to reverse the proliferative rate of the cells. Immunohistochemical analysis showed increased staining for FGFR3 and patched-1 (Ihh receptor) in JWS compared to the rat tibia growth plate (p = 0.O004 and 0.02 respectively). In vitro functional experiments demonstrated that the use of FGF2, a FGFR3 receptor agonist, dramatically decreased the proliferative rate of Swarm chondrosarcoma cells (LTC). Cyclopamine, a hedgehog inhibitor, did not have a significant effect on their proliferative rate. However, when cyclopamine was used on normal chondrocytes, it effectively decreased the proliferative rate of these cells, suggesting abnormalities in this pathway in the chondrosarcoma cells. In conclusion, our investigation describes dissimilarity in the Indian Hedgehog and FGFR3 signaling pathways between the rat chondrosarcoma cells and native rat chondrocytes. Understanding the underlying mechanisms may provide a target for future therapy for chondrosarcoma.