CDK8-Cyclin C Mediates Nutritional Regulation of Developmental Transitions through the Ecdysone Receptor in Drosophila.
CDK8-Cyclin C Mediates Nutritional Regulation of Developmental Transitions through the Ecdysone Receptor in Drosophila.
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DOI：
10.1371/journal.pbio.1002207
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发表时间：
2015-07
期刊：
影响因子：
9.8
通讯作者：
Ji JY
中科院分区：
文献类型：
--
作者：
Xie XJ;Hsu FN;Gao X;Xu W;Ni JQ;Xing Y;Huang L;Hsiao HC;Zheng H;Wang C;Zheng Y;Xiaoli AM;Yang F;Bondos SE;Ji JY
类固醇激素蜕皮激素及其受体（EcR）在协调节肢动物的发育转变中起着关键作用。然而，EcR整合营养和发育线索以正确激活转录的机制仍然知之甚少。在这里，我们表明，ECR依赖的转录，因此，在果蝇的发育时间，是由CDK 8和它的监管伙伴细胞周期蛋白C（CycC），和CDK 8的水平受营养的可用性。我们观察到cdk 8和cycC突变体类似于EcR突变体，并且在这两种突变体中EcR靶基因均系统性下调。事实上，EcR-超气门（USP）异二聚体结合多线染色体和EcR靶基因启动子的能力也降低了。与EcR和USP共免疫沉淀的蛋白质的质谱分析鉴定了多个介体亚基，包括CDK 8和CycC。一致地，CDK 8-CycC与EcR-USP在体内相互作用;特别地，CDK 8和Med 14可以直接与EcR的AF 1结构域相互作用。这些结果表明，CDK 8-CycC可能作为转录辅因子的ECR依赖性转录。在幼虫-蛹转变期间，CDK 8蛋白的水平与EcR和USP水平正相关，但与固醇调节元件结合蛋白（SREBP）的活性负相关，该蛋白是细胞内脂质稳态的主要调节剂。同样，饥饿的早期三龄幼虫早熟增加CDK 8，EcR和USP的水平，但下调SREBP活性。相反，重新喂养饥饿的幼虫强烈降低CDK 8水平，但增加SREBP活性。重要的是，这些变化与幼虫-蛹转变的时间相关。综上所述，这些结果表明，CDK 8-CycC链接营养摄入发育过渡（EcR活性）和脂肪代谢（SREBP活性）在幼虫蛹过渡。在果蝇的幼虫-蛹转变过程中，CDK 8-CycC通过激活蜕皮激素受体依赖性转录来帮助将营养摄入与发育联系起来，并通过抑制SREBP激活的基因表达来帮助将营养摄入与脂肪代谢联系起来。节肢动物估计占地球上动物物种的80%以上。幼年节肢动物具有坚硬的外骨骼，为了生长，它们必须定期通过蜕皮脱落厚厚的外壳。类固醇激素蜕皮激素在调节发育转变的时间方面起着至关重要的作用，但蜕皮激素及其受体EcR在整合营养和发育线索后如何正确激活转录仍然未知。我们的两个果蝇突变体，cdk 8和cycC的发育遗传分析表明，他们是致命的prepupal阶段，异常积累的脂肪和严重延迟的幼虫蛹过渡。正如我们之前报道的，CDK 8-CycC通过直接灭活SREBP来抑制脂肪积累，SREBP是一种控制脂肪生成基因表达的主转录因子，这解释了cdk 8和cycC突变体中的异常脂肪积累。我们发现，CDK 8和CycC所需的EcR结合到其靶基因，作为转录辅因子的EcR依赖的基因表达。EcR靶基因的表达在cdk 8和cycC突变体中受到损害，并支持延迟的孕化表型。饥饿的幼虫喂养过早上调CDK 8和EcR，过早下调SREBP活性，并导致早期pupariation，而重新喂养饥饿的幼虫有相反的效果。综上所述，这些结果表明，CDK 8和CycC在协调营养摄入与脂肪代谢中发挥重要作用，直接抑制SREBP依赖的基因表达和调节发育时序，通过激活EcR依赖的转录在果蝇。
The steroid hormone ecdysone and its receptor (EcR) play critical roles in orchestrating developmental transitions in arthropods. However, the mechanism by which EcR integrates nutritional and developmental cues to correctly activate transcription remains poorly understood. Here, we show that EcR-dependent transcription, and thus, developmental timing in Drosophila, is regulated by CDK8 and its regulatory partner Cyclin C (CycC), and the level of CDK8 is affected by nutrient availability. We observed that cdk8 and cycC mutants resemble EcR mutants and EcR-target genes are systematically down-regulated in both mutants. Indeed, the ability of the EcR-Ultraspiracle (USP) heterodimer to bind to polytene chromosomes and the promoters of EcR target genes is also diminished. Mass spectrometry analysis of proteins that co-immunoprecipitate with EcR and USP identified multiple Mediator subunits, including CDK8 and CycC. Consistently, CDK8-CycC interacts with EcR-USP in vivo; in particular, CDK8 and Med14 can directly interact with the AF1 domain of EcR. These results suggest that CDK8-CycC may serve as transcriptional cofactors for EcR-dependent transcription. During the larval–pupal transition, the levels of CDK8 protein positively correlate with EcR and USP levels, but inversely correlate with the activity of sterol regulatory element binding protein (SREBP), the master regulator of intracellular lipid homeostasis. Likewise, starvation of early third instar larvae precociously increases the levels of CDK8, EcR and USP, yet down-regulates SREBP activity. Conversely, refeeding the starved larvae strongly reduces CDK8 levels but increases SREBP activity. Importantly, these changes correlate with the timing for the larval–pupal transition. Taken together, these results suggest that CDK8-CycC links nutrient intake to developmental transitions (EcR activity) and fat metabolism (SREBP activity) during the larval–pupal transition. During the larval-pupal transition in Drosophila, CDK8-CycC helps to link nutrient intake to development by activating ecdysone receptor-dependent transcription and to fat metabolism by inhibiting SREBP-activated gene expression. Arthropods are estimated to account for over 80% of animal species on earth. Characterized by their rigid exoskeletons, juvenile arthropods must periodically shed their thick outer cuticles by molting in order to grow. The steroid hormone ecdysone plays an essential role in regulating the timing of developmental transitions, but exactly how ecdysone and its receptor EcR activates transcription correctly after integrating nutritional and developmental cues remains unknown. Our developmental genetic analyses of two Drosophila mutants, cdk8 and cycC, show that they are lethal during the prepupal stage, with aberrant accumulation of fat and a severely delayed larval–pupal transition. As we have reported previously, CDK8-CycC inhibits fat accumulation by directly inactivating SREBP, a master transcription factor that controls the expression of lipogenic genes, which explains the abnormal fat accumulation in the cdk8 and cycC mutants. We find that CDK8 and CycC are required for EcR to bind to its target genes, serving as transcriptional cofactors for EcR-dependent gene expression. The expression of EcR target genes is compromised in cdk8 and cycC mutants and underpins the retarded pupariation phenotype. Starvation of feeding larvae precociously up-regulates CDK8 and EcR, prematurely down-regulates SREBP activity, and leads to early pupariation, whereas re-feeding starved larvae has opposite effects. Taken together, these results suggest that CDK8 and CycC play important roles in coordinating nutrition intake with fat metabolism by directly inhibiting SREBP-dependent gene expression and regulating developmental timing by activating EcR-dependent transcription in Drosophila.