Uchida Chiharu, Miwa Seiichi, Kitagawa Kyoko, Hattori Takayuki, Isobe Tomoyasu, Otani Sunao, Oda Toshiaki, Sugimura Haruhiko, Kamijo Takehiko, Ookawa Keizou, Yasuda Hideyo, Kitagawa Masatoshi
Department of Biochemistry 1, Hamamatsu University School of Medicine, Hamamatsu, Shizuoka, Japan.
EMBO J. 2005 Jan 12;24(1):160-9. doi: 10.1038/sj.emboj.7600486. Epub 2004 Dec 2.
Retinoblastoma gene product (pRB) plays critical roles in regulation of the cell cycle and tumor suppression. It is known that downregulation of pRB can stimulate carcinogenesis via abrogation of the pRB pathway, although the mechanism has not been elucidated. In this study, we found that Mdm2, a ubiquitin ligase for p53, promoted ubiquitin-dependent degradation of pRB. pRB was efficiently ubiquitinated by wild-type Mdm2 in vivo as well as in vitro, but other RB family proteins were not. Mutant Mdm2 with a substitution in the RING finger domain showed dominant-negative stabilization of pRB. Both knockout and knockdown of Mdm2 caused accumulation of pRB. Moreover, Mdm2 inhibited pRB-mediated flat formation of Saos-2 cells. Downregulation of pRB expression was correlated with a high level of expression of Mdm2 in human lung cancers. These results suggest that Mdm2 regulates function of pRB via ubiquitin-dependent degradation of pRB.
视网膜母细胞瘤基因产物（pRB）在细胞周期调控和肿瘤抑制中发挥着关键作用。已知pRB的下调可通过pRB途径的废除刺激致癌作用，尽管其机制尚未阐明。在本研究中，我们发现Mdm2，一种p53的泛素连接酶，促进了pRB的泛素依赖性降解。pRB在体内和体外均被野生型Mdm2有效地泛素化，但其他RB家族蛋白则未被泛素化。在环指结构域发生替代的突变型Mdm2显示出pRB的显性负性稳定。Mdm2的敲除和敲低均导致pRB的积累。此外，Mdm2抑制了pRB介导的Saos-2细胞扁平形成。在人类肺癌中，pRB表达的下调与Mdm2的高表达水平相关。这些结果表明，Mdm2通过pRB的泛素依赖性降解来调节pRB的功能。
