Inactivation of the cyclin-dependent kinase inhibitor p27 upon loss of the tuberous sclerosis complex gene-2
Inactivation of the cyclin-dependent kinase inhibitor p27 upon loss of the tuberous sclerosis complex gene-2
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DOI：
10.1073/pnas.95.26.15653
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发表时间：
1998-12-22
影响因子：
11.1
通讯作者：
Hengstschläger, M
中科院分区：
文献类型：
--
作者：
Soucek, T;Yeung, RS;Hengstschläger, M
结节性硬化症是一种常染色体显性遗传病，其特点是在许多组织和器官中发生异常生长。连锁分析显示，9号染色体和16号染色体上有两个决定疾病的基因，16号染色体上的结节硬化复合体基因-2 （TSC2）编码肿瘤抑制蛋白tuberin，我们之前已经证明，TSC2的缺失足以诱导静止细胞进入细胞周期。我们发现tsc2阴性成纤维细胞表现为G(1)期缩短。尽管细胞周期蛋白E、细胞周期蛋白A、p21或Cdc25A的表达不受影响，但由于蛋白稳定性降低，tsc2阴性细胞表达的细胞周期蛋白依赖性激酶（CDK）抑制剂p27的量要低得多。在TSC2突变细胞中，p27与CDK2结合的数量减少，并伴有激酶活性升高。异位表达研究表明，在TSC2阴性细胞中转染TSC2可以逆转上述效应。高异位水平的p27在TSC2阳性细胞中具有细胞周期抑制作用，而在TSC2阴性细胞中则没有，尽管后者仍然依赖于CDK2活性。TSC2缺失诱导成纤维细胞的软琼脂生长，这一过程不能被高水平的p27所抑制。TSC2阴性细胞的两种表型，它们对异位p27活性的抗性，以及内源性p27的不稳定性，都可以通过我们的观察来解释，即核蛋白p27在TSC2缺失时错位到细胞质中。这些发现为TSC2缺失诱导细胞周期进入的分子机制提供了见解，并使人们更好地了解其肿瘤抑制功能。
Tuberous sclerosis is an autosomal dominant disorder characterized by the development of aberrant growths in many tissues and organs. Linkage analysis revealed two disease-determining genes on chromosome 9 and chromosome 16, The tuberous sclerosis complex gene-2 (TSC2) on chromosome 16 encodes the tumor suppressor protein tuberin, We have shown earlier that loss of TSC2 is sufficient to induce quiescent cells to enter the cell cycle. Here we show that TSC2-negative fibroblasts exhibit a shortened G(1) phase. Although the expression of cyclin E, cyclin A, p21, or Cdc25A is unaffected, TSC2-negative cells express much lower amounts of the cyclin dependent kinase (CDK) inhibitor p27 because of decreased protein stability. In TSC2 mutant cells the amount of p27 bound to CDK2 is diminished, accompanied with elevated kinase activity. Ectopic expression studies revealed that the aforementioned effects can be reverted by transfecting TSC2 in TSC2-negative cells, High ectopic levels of p27 have cell cycle inhibitory effects in TSC2-positive cells but not in TSC2-negative counterparts, although the latter still depend on CDK2 activity. Loss of TSC2 induces soft agar growth of fibroblasts, a process that cannot be inhibited by high levels of p27, Both phenotypes of TSC2-negative cells, their resistance to the activity of ectopic p27, and the instability of endogenous p27, could be explained by our observation that the nucleoprotein p27 is mislocated into the cytoplasm upon loss of TSC2, These findings provide insights into the molecular mechanism of how loss of TSC2 induces cell cycle entry and allow a better understanding of its tumor suppressor function.