Ookawa K, Tsuchida S, Adachi J, Yokota J
Second Department of Biochemistry, Hirosaki University School of Medicine, Aomori, Japan.
Oncogene. 1997 Mar 27;14(12):1389-96. doi: 10.1038/sj.onc.1200976.
Multiple genetic alterations, including concurrent inactivation of RB and p53, occur frequently in several human cancers. To investigate the biological significance of RB and p53 gene inactivations, a wild-type RB or p53 cDNA expression vector regulated by tetracycline was introduced by stable transfection into an osteosarcoma cell line Saos-2, in which both the RB and p53 genes were inactivated. Induction of introduced RB expression resulted in suppression of cell growth, increased percentage of cells at the G0/G1 phase, and enlargement of the cells. Furthermore, activity of alkaline phosphatase was increased and expression of fibronectin was decreased, suggesting the induction of cell differentiation by RB expression. Induction of p53 expression also resulted in significant suppression of cell growth with slight accumulation of cells at the G0/G1 and G2/M phases. The cells were detached from culture dishes and the dead cell fraction increased. Furthermore, condensation of chromatin and DNA fragmentation were observed, suggesting the induction of apoptosis by p53. These results suggest that RB and p53 play different roles in carcinogenesis of osteoblast; RB inactivation releases cells from G0/G1 arrest and suppresses cell differentiation while p53 inactivation assists the cells to proliferate by repressing both apoptosis and cell cycle arrest at G0/G1 and G2/M.
包括RB和p53同时失活在内的多种基因改变在几种人类癌症中频繁发生。为了研究RB和p53基因失活的生物学意义，通过稳定转染将受四环素调控的野生型RB或p53 cDNA表达载体导入RB和p53基因均失活的骨肉瘤细胞系Saos-2中。导入的RB表达的诱导导致细胞生长受到抑制，G0/G1期细胞百分比增加，细胞体积增大。此外，碱性磷酸酶活性增加，纤连蛋白表达降低，提示RB表达诱导细胞分化。p53表达的诱导也导致细胞生长显著受到抑制，细胞在G0/G1期和G2/M期略有积累。细胞从培养皿中脱离，死细胞比例增加。此外，观察到染色质凝聚和DNA片段化，提示p53诱导细胞凋亡。这些结果表明，RB和p53在成骨细胞致癌过程中发挥不同作用；RB失活使细胞从G0/G1期阻滞中释放出来并抑制细胞分化，而p53失活则通过抑制凋亡以及G0/G1期和G2/M期的细胞周期阻滞来协助细胞增殖。
