ALTERED G(1) PHASE REGULATION IN OSTEOSARCOMA

Alterations in the normal cell cycle lead to abnormal cell proliferati on and to tumor development. To explore the role of the cyclin D/Cdk4 complex and the retinoblastoma protein (pRb) in the growth and spread of osteoblastic osteosarcoma (OS), 40 tumor samples were selected, In 17 of these cases, lung metastases occurred during follow-up, Expressi on of pRb, cyclin DI and its catalytic subunit, Cdk4, was studied by i mmunohistochemistry and immunoblotting. As controls, non-neoplastic ti ssues surrounding the tumor were used. The expression level and patter n were compared to clinical outcome. Cdk4 was over-expressed in 80% of OS, independently of clinical outcome, and showed an intense and unif orm distribution in tumor cells compared to normal cells. However, co- immunoprecipitation of Cdk4 with cyclin DI revealed low levels of cycl in D/Cdk4 complex; 20 of 40 OS examined had a negative or minimal immu nostaining for active pRb. The probability of relapse was significantl y higher in pRb-negative than in the -positive patients (p < 0.05). Th e ratio of unphosphorylated/hyperphosphorylated pRb was lower in relap sed patients than in patients with no evident disease, though the diff erence was not statistically significant, High levels of pRb/cyclin DI were found in all samples exhibiting functional pRb expression. Our r esults show that G(1) phase deregulation is involved in formation and development of OS. The expression levels of both pRb and cyclin D1 had a clear correlation with clinical outcome, suggesting that these para meters could be used as prognostic markers. (C) 1997 Wiley-Liss, Inc.