Characterization of Cdkal1, a novel type 2 diabetes risk gene

CDKAL1(CDK5调节亚单位相关蛋白1样蛋白)的基因变异已被确定为2型糖尿病的风险因素。尽管有越来越多的临床证据，但CDKAL1的分子特征尚不清楚。为了研究CDKAL1的生理作用，建立了胰腺b细胞特异性CDKAL1基因敲除小鼠(CDKAL1KO)。CDKAL1 KO小鼠表现为糖耐量异常和胰岛素分泌受损。我们已经确定CDKAL1是一种哺乳动物甲硫基转移酶，它通过在细菌和哺乳动物细胞中催化N6-苏氨酰氨基甲酰腺苷(T6A)的生物合成来特异性地修饰37位的tRNA^&lt；Lys&gt；(Uuu)，从而合成2-methylthio-N6-threonylcabamoyladenosine(ms2t6A)。CDKAL1对tRNA^&lt；Lys&gt；(UUU)的修饰是准确解码Lys密码子的关键。在CDKAL1 KO b细胞中，tRNA^&lt；Lys&gt；(UUU)修饰缺失导致胰岛素原翻译错误，从而触发内质网(ER)应激反应。此外，以高脂饮食喂养的CDKAL1 KO小鼠出现了严重的糖耐量异常和内质网应激反应。根据这些结果，我们得出结论，CDKAL1对b细胞中tRNA的修饰对于维持翻译保真度至关重要，而翻译保真度有助于b细胞的动态平衡。

Genetic variations in cdkal1(Cdk5 regulatory subunit associated protein 1-like 1) have been identified as a risk for type 2 diabetes. Despite the accumulating clinical evidence, the molecular characterization of Cdkal1 is completely unknown. To investigate the physiological role of Cdkal1, pancreatic b-cell-specific Cdkal1 knockout(Cdkal1 KO) mice were generated. Cdkal1 KO mice showed glucose intolerance and impaired insulin secretion. We have identified that Cdkal1 is a mammalian methylthiotranferase, which specifically modifies tRNA^<Lys>(UUU) at position 37 by catalyzing the biosynthesis of N6-threonylcabamoyladenosine(t6A) to 2-methylthio-N6-threonylcabamoyladenosine(ms2t6A) in both bacteria and mammalian cells. Modification of tRNA^<Lys>(UUU) by Cdkal1 is critical for the accurate decoding of Lys codon. In Cdkal1 KO b-cells, deficiency of modification in tRNA^<Lys>(UUU) caused mistranslation of proinsulin and thus triggered endoplasmic reticulum(ER) stress response. Furthermore, Cdkal1 KO mice fed with a high fat diet developed severe glucose intolerance and ER stress response. From these results, we concluded that modification of tRNA by Cdkal1 in b-cells is critical to maintaining translation fidelity, which contributes to the homeostasis of b-cells.