Mirk Regulates the Exit of Colon Cancer Cells from Quiescence
Mirk Regulates the Exit of Colon Cancer Cells from Quiescence
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DOI：
10.1074/jbc.m109.035519
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发表时间：
2009-08-21
影响因子：
4.8
通讯作者：
Friedman, Eileen
中科院分区：
文献类型：
--
作者：
Jin, Kideok;Ewton, Daina Z.;Friedman, Eileen
MERK/Dyrk1B是一种广泛表达于结肠癌的丝氨酸/苏氨酸激酶。血清饥饿诱导HD6结肠癌细胞进入静止的G0状态，其特征是DNA含量为2N，RNA含量低于G1细胞。与周期细胞相比，静止细胞显示视网膜母细胞瘤蛋白p130/Rb2的水平高16倍，它隔离E2F4以阻止进入G1，CDK抑制物p27kip1的水平高10倍，Mirk的水平高10倍。然而，Mirk的缺失并没有阻止细胞进入G0，而是使静止的HD6、SW480和Colo320结肠癌细胞获得了G1细胞的一些生化特征，包括由于细胞周转变慢而导致细胞周期蛋白D1和细胞周期蛋白D3水平升高，其CDK4/细胞周期蛋白D复合体活性增加，以及CDK4靶标p130/Rb2的磷酸化程度增加和E2F4滞留能力降低。因此，Mirk的耗尽使一些细胞能够逃离静止状态，并使从静止状态释放的细胞能够更快地穿越G1。化疗药物5-氟尿嘧啶(5-FU)可增加Mirk的活性。用5-FU处理P53突变的结肠癌细胞后，G1延长，这种延长依赖于Mirk依赖的方式，因为突变于Mirk磷酸化位点(T288A)的细胞周期蛋白D1的异位过表达缩短了G1，而野生型细胞周期蛋白D1不能。耗竭研究表明，MERK通过调节细胞周期蛋白D的转化，以及CDK抑制剂p27，独立和相加地调节肿瘤细胞从静止状态退出。
Mirk/Dyrk1B is a serine/threonine kinase widely expressed in colon cancers. Serum starvation induced HD6 colon carcinoma cells to enter a quiescent G0 state, characterized by a 2N DNA content and a lower RNA content than G1 cells. Compared with cycling cells, quiescent cells exhibited 16-fold higher levels of the retinoblastoma protein p130/Rb2, which sequesters E2F4 to block entry into G1, 10-fold elevated levels of the CDK inhibitor p27kip1, and 10-fold higher levels of Mirk. However, depletion of Mirk did not prevent entry into G0, but enabled quiescent HD6, SW480, and colo320 colon carcinoma cells to acquire some biochemical characteristics of G1 cells, including increased levels of cyclin D1 and cyclin D3 because of slower turnover, increased activity of their CDK4/cyclin D complexes, and increased phosphorylation and decreased E2F4 sequestering ability of the CDK4 target, p130/Rb2. As a result, depletion of Mirk allowed some cells to escape quiescence and enabled cells released from quiescence to traverse G1 more quickly. The kinase activity of Mirk was increased by the chemotherapeutic drug 5-fluorouracil (5-FU). Treatment of p53 mutant colon cancer cells with 5-FU led to an elongated G1 in a Mirk-dependent manner, as G1 was shortened by ectopic overexpression of cyclin D1 mutated at the Mirk phosphorylation site (T288A), but not by wild-type cyclin D1. Mirk, through regulating cyclin D turnover, and the CDK inhibitor p27, as shown by depletion studies, functioned independently and additively to regulate the exit of tumor cells from quiescence.