Alteration of pRb/p16/cdk4 regulation in human osteosarcoma

Cell-cycle regulation depends on a fine balance between cyclin-cyclin-depen dent kinase complexes and a family of kinase inhibitors that bind cyclin-cd k complexes and block their activity. To investigate the role of mechanisms regulating cell-cycle progression in human osteosarcomas (OS), pRb/p16/cdk 4 expression was analyzed in 39 high-grade OS; 19 of these developed metast asis during follow-up. Positive reaction for functional pRB was shown by 18 /39 (46%) OS, while 21/39 (54%) were negative. A higher probability of meta stasis was seen in patients with negative pRb expression (p < 0.05). Furthe rmore, while functional pRb and D1 expression are inversely associated to m etastasis occurrence, the presence of D1/cdk4 complex in our study was rela ted to poor prognosis. We found that 10/18 pRb-positive and 14/21 pRb-negat ive tumors were p16-positive. No significant correlation was found between pRb and p16 expression. On the other hand, high cdk4 levels in p16-positive tumors as compared with p16-negative tumors resulted in a positive associa tion between p16 and cdk4 expression (Chi squared = 5.98; p = 0.01). No ext ensive p16INK4A genomic alterations were found in tumors lacking p16 protei n expression. To determine which mechanisms are involved in the down-regula tion of p16 protein, the methylation status of the p16INK4 gene was evaluat ed on the 15 p16-negative tumors: 8 samples showed 5' CpG-island methylatio n; 4/8 had a complete methylation status, while in the remaining 4 the gene was only partially methylated. These data confirm the role of the pRb/p16/ cdk4 pathway in OS development. Int. J. Cancer (Pred. Oncol.) 84:489-493, 1 999. (C) 1999 Wiley-Liss, Inc.