Based on its localization, chondrosarcoma (CS) can be stratified as peripheral and central. Peripheral chondrosarcoma develops at the bone surface within the cartilage cap of benign osteochondromas and its genetical background is well-studied. Homozygous deletions of the EXT1 (8q24) or EXT2 (11p12-11) tumor suppressor genes are found in solitary (EXT1) and hereditary (EXT1 and 2) osteochondromas. The EXT1/EXT2 protein complex, located in the Golgi apparatus, is involved in biosynthesis of HSPGs. HSPGs function in gradient formation of Indian hedgehog (IHH) in the extracellular matrix. Central chondrosarcoma grows from the medullary cavity of bone and is the most common chondrosarcoma subtype. Similarly as in osteochondroma, enchondromas might act as benign precursor lesions. However, little is known about the genetic background of central CS. Since the role of EXT in central CS is so far unknown, we studied EXT, HSPGs and IHH in central CS. In contrast to peripheral CS, EXT1 mRNA levels in enchondromas (n=7) and central CS (grade I n=11, grade II n=7 and grade III n=9) were comparable to epiphyseal growth plates, as found by qPCR. Only two out of 34 tumors showed decreased EXT1 expression, however alterations in the 8q24 region could not be detected by hybridization of tumor DNA to a 8q tiling CGH-array. Also direct mutation scanning of EXT1 did not reveal any genetic aberrations in central CS. Immunohistochemistry for the HSPG CD44v3 revealed peri-nuclear staining in 21/30 CCS, which was shown to co-localize with the 58K Golgi protein by immunofluorescent confocal microscopy. Whereas peripheral CS shows intracellular accumulation of SDC2 by immunohistochemistry, in 50% (n=30) of central CS, SDC2 is localized in the nucleus, as well. Western blot on nuclear protein extracts of two fresh central CS samples confirmed these results. Native HS chains, bound to the HSPG core protein, were also found in the nucleus of central CS. The IHH pathway is active in central CS, since qPCR analysis showed that PTCH, SMO and GLI2 were expressed as in normal growth plates through all stages of tumor progression. This contrasts to the results found in peripheral CS, where IHH signaling is decreased upon progression, supposedly due to cytoplasmic retention of HSPGs. In conclusion, while in peripheral chondrosarcoma the EXT1/EXT2 complex is affected, causing aberrant HSPG biosynthesis, we show that in central chondrosarcoma other mechanisms are operative. EXT1 is normally expressed in central CS, while there is cellular and nuclear accumulation of HSPGs.
98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA