Alterations of the p15, p16, and p18 genes in osteosarcoma

Activation of cyclin-dependent kinases (CDKs) by interaction with cyclins regulates progression through cell cycle checkpoints. This process is counterbalanced by CDK inhibitors (CDKls), which can inhibit progression through the cell cycle. Because CDKI expression acts to inhibit cellular proliferation, CDKls may have a role as tumor suppressors. One class of CDKIs, characterized by the presence of ankyrin repents, has at least four members(p15(INK4B), p16(INK4), p18, and p19). Two of these, p15(INK4B) and p16(INK4), have been mapped to chromosome 9p21, a region of frequent loss in a wide variety of cancers. Alterations of p16(INK4) have been detected in various tumors and cell lines. We analyzed p15(INK4B), p16(INK4) and p18 alterations in 52 osteosarcomas (including 11 explants), and 23 other various sarcomas. Single-stranded conformation polymorphism analysis [polymerase chain reaction (PCR-SSCP)] of the coding regions of these CDKI genes detected a missense mutation of p16(INK4) exon 1 in one soft tissue sarcoma. Southern blotting detected complete deletion of p15(INK4B) and p16(INK4) genes in osteosarcomas from 2 patients and a soft tissue sarcoma from another individual. Loss of heterozygosity (LOH) at chromosome 9p21 tvas observed with a microsatellite probe closely linked to the INK4 genes in the latter case. Deletions of both p15(INK4B) and p16(INK4) genes were detected in five of eight osteosarcoma cell lines. By contrast, no alterations of p18 were detected in any sample, Together these data suggest that alterations of the p15(INK4B) and p18(INK4) genes, but not p18, may occur in similar to 5% of sarcomas. However, deletions of the p15(INK4B) and p16(INK4) genes are frequent in osteosarcoma cell lines and probably have a role in tumor cell growth in culture. Notably, all seven detectable deletions involved both p15(INK4B) and p16(INK4) genes, suggesting that both contribute individual tumor suppressor activity.