B-Myb function can be markedly enhanced by cyclin A-dependent kinase and protein truncation
B-Myb function can be markedly enhanced by cyclin A-dependent kinase and protein truncation
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DOI：
10.1038/sj.onc.1201086
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发表时间：
1997-05-22
期刊：
影响因子：
8
通讯作者：
Watson, R
中科院分区：
文献类型：
--
作者：
Lane, S;Farlie, P;Watson, R
B-Myb基因的转录是由E2 F依赖性机制调节的细胞周期，其产物B-Myb本身是进入S期所需的转录因子。以前，黑麦已经表明，B-Myb在S期特异性磷酸化，并且杆状病毒表达的细胞周期蛋白A/Cdk 2激酶可以诱导类似的修饰，使其成为不太稳定的移动的形式。我们在这里报告，细胞周期蛋白A介导的磷酸化的B-Myb与一个显着增加的反式激活功能在U-2 OS细胞。与以前的研究相反，荧光素酶报告基因的反式激活依赖于位于启动子上游的Myb结合位点。B-Myb激活功能的增强也是通过在进化中保守的结构域的下游截短C-末端获得的。通过磷酸化增强B-Myb活性并不仅仅是克服C-末端的负面影响的结果，然而，因为截短的蛋白质在较小程度上也被细胞周期蛋白A/Cdk 2激活。而野生型B-Myb反式激活活性不能增强细胞周期蛋白A/Cdk 2在NIH 3 T3细胞，截短的蛋白质是过度活跃。最后，我们发现B-Myb与cyclin A协同促进U-2 OS细胞进入S期。
Transcription of the B-Myb gene is cell cycle regulated by an E2F-dependent mechanism and its product, B-Myb, is itself a transcription factor required for S-phase entry. Previously, rye have shown that B-Myb is specifically phosphorylated during S-phase and that similar modification to a less electrophoretically mobile form could be induced by baculovirus-expressed cyclin A/Cdk2 kinase. We report here that cyclin A-mediated phosphorylation of B-Myb is associated with a marked increase in transactivation function in U-2 OS cells. In contrast to previous studies, transactivation of the luciferase reporter was dependent upon Myb binding sites located upstream of the promoter. Enhancement of B-Myb activation function was also obtained by truncation of the C-terminus just downstream of a domain conserved in evolution. Potentiation of B-Myb activity by phosphorylation was not simply a consequence of overcoming the negative effect of the C-terminus, however, as the truncated protein was to a lesser extent also activated by cyclin A/Cdk2. Whereas wild-type B-Myb transactivation activity could not be potentiated by cyclin A/Cdk2 in NIH3T3 cells, the truncated protein was hyperactive. Finally, we showed that B-Myb synergises with cyclin A to promote U-2 OS cells into S-phase.