Hedgehog (HH) signalling is important for specific developmental processes, and aberrant, increased activity has been described in various tumours. Disturbed HH signalling has also been implicated in the hereditary syndrome, Multiple Osteochondromas. Indian Hedgehog (IHH), together with parathyroid hormone-like hormone (PTHLH), participates in the organization of growth plates in long bones. PTHLH signalling is absent in osteochondromas, benign tumours arising adjacent to the growth plate, but is reactivated when these tumours undergo malignant transformation towards secondary peripheral chondrosarcoma. We describe a gradual decrease in the expression of Patched (PTCH) and glioma-associated oncogene homologue 1 (GLI1) (both transcribed upon IHH activity), and GLI2 with increasing malignancy, suggesting that IHH signalling is inactive and PTHLH signalling is IHH independent in secondary peripheral chondrosarcomas. cDNA expression profiling and immunohistochemical studies suggest that transforming growth factor-beta (TGF-beta)-mediated proliferative signalling is active in high-grade chondrosarcomas since TGF-beta downstream targets were upregulated in these tumours. This is accompanied by downregulation of energy metabolism-related genes and upregulation of the proto-oncogene jun B. Thus, the tight regulation of growth plate organization by IHH signalling is still seen in osteochondroma, but gradually lost during malignant transformation to secondary peripheral chondrosarcoma and subsequent progression. TGF-beta signalling is stimulated during secondary peripheral chondrosarcoma progression and could potentially regulate the retained activity of PTHLH.
Copyright 2006 Pathological Society of Great Britain and Ireland.