BMAL1 shuttling controls transactivation and degradation of the CLOCK/BMAL1 heterodirner
BMAL1 shuttling controls transactivation and degradation of the CLOCK/BMAL1 heterodirner
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DOI：
10.1128/mcb.00337-06
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发表时间：
2006-10-01
影响因子：
5.3
通讯作者：
Lee, Kun Ho
中科院分区：
文献类型：
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作者：
Kwon, Ilmin;Lee, Jiwon;Lee, Kun Ho
CLOCK和BMAL 1是含有bHLH-PAS的转录因子，与E-box元件结合，对于核心生物钟组分如Per和Cry基因的表达是不可或缺的。表达的关键步骤是CLOCK和BMAL 1的异源二聚化及其在细胞核中以大约24小时的周期积累。我们在这里表明，BMAL 1的核质穿梭是必不可少的反式激活和降解的时钟/BMAL 1异源二聚体。使用连续缺失和点突变体，我们确定了一个功能性的核定位信号和Crm 1依赖的核输出信号在BMAL 1瞬时转染实验表明，异二聚化的时钟和BMAL 1加速其营业额，以及E盒依赖的时钟基因转录。此外，在胚胎小鼠成纤维细胞中，Per 2的稳健转录与CLOCK/BMAL 1异二聚体的大量降解密切相关。CRY蛋白在转录阴性阶段抑制了这一过程，并导致CLOCK/BMAL 1异源二聚体在核中积累。因此，这些发现表明，在昼夜节律周期中BMAL 1丰度的减少反映了生物钟基因的强大转录激活，而不是BMAL 1合成的抑制。
CLOCK and BMAL1 are bHLH-PAS-containing transcription factors that bind to E-box elements and are indispensable for expression of core circadian clock components such as the Per and Cry genes. A key step in expression is the heterodimerization of CLOCK and BMAL1 and their accumulation in the nucleus with an approximately 24-h periodicity. We show here that nucleocytoplasmic shuttling of BMAL1 is essential for transactivation and for degradation of the CLOCK/BMAL1 heterodimer. Using serial deletions and point mutants, we identified a functional nuclear localization signal and Crm1-dependent nuclear export signals in BMAL1 Transient-transfection experiments revealed that heterodimerization of CLOCK and BMAL1 accelerates their turnover, as well as E-box-dependent clock gene transcription. Moreover, in embryonic mouse fibroblasts, robust transcription of Per2 is tightly associated with massive degradation of the CLOCK/BMAL1 heterodimer. CRY proteins suppressed this process during the transcription-negative phase and led to nuclear accumulation of the CLOCK/BMAL1 heterodimer. Thus, these findings suggest that the decrease of BMAL1 abundance during the circadian cycle reflects robust transcriptional activation of clock genes rather than inhibition of BMAL1 synthesis.