Department of Biophysics and Biochemistry, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Cell. 2013 Feb 28;152(5):1106-18. doi: 10.1016/j.cell.2013.01.054.
In the mammalian circadian clockwork, CRY1 and CRY2 repressor proteins are regulated by posttranslational modifications for temporally coordinated transcription of clock genes. Previous studies revealed that FBXL3, an F-box-type E3 ligase, ubiquitinates CRYs and mediates their degradation. Here, we found that FBXL21 also ubiquitinates CRYs but counteracts FBXL3. Fbxl21(-/-) mice exhibited normal periodicity of wheel-running rhythms with compromised organization of daily activities, while an extremely long-period phenotype of Fbxl3(-/-) mice was attenuated in Fbxl3/Fbxl21 double-knockout mice. The double knockout destabilized the behavioral rhythms progressively and sometimes elicited arrhythmicity. Surprisingly, FBXL21 stabilized CRYs and antagonized the destabilizing action by FBXL3. Predominantly cytosolic distribution of FBXL21 contrasts with nuclear localization of FBXL3. These results emphasize the physiological importance of antagonizing actions between FBXL21 and FBXL3 on CRYs, and their combined actions at different subcellular locations stabilize oscillation of the circadian clock.
在哺乳动物的生物钟中，CRY1 和 CRY2 抑制蛋白通过翻译后修饰来调节时钟基因的转录，从而实现时间协调。先前的研究表明，FBXL3 是一种 F 盒型 E3 连接酶，可泛素化 CRY 并介导其降解。在这里，我们发现 FBXL21 也可泛素化 CRY，但与 FBXL3 拮抗。Fbxl21(-/-) 小鼠表现出正常的转轮节律周期性，但日常活动的组织受到损害，而 Fbxl3(-/-) 小鼠的极长周期表型在 Fbxl3/Fbxl21 双敲除小鼠中减弱。双重敲除使行为节律逐渐不稳定，有时还会引起节律失常。令人惊讶的是，FBXL21 稳定了 CRY，并拮抗了 FBXL3 的去稳定作用。FBXL21 主要分布在细胞质中，而 FBXL3 则定位于核内。这些结果强调了 FBXL21 和 FBXL3 对 CRY 的拮抗作用以及它们在不同亚细胞位置的共同作用对生物钟振荡的生理重要性。
