Oncogenic K-Ras suppresses global miRNA function

K-Ras frequently acquires gain-of-function mutations (K-RasG12D being the most common) that trigger significant transcriptomic and proteomic changes to drive tumorigenesis. However, oncogenic K-Ras-induced dysregulation of post-transcriptional regulators such as microRNAs (miRNAs) during oncogenesis is poorly understood. Here we report that K-RasG12D promotes global suppression of miRNA activity, resulting in the up-regulation of hundreds of target genes. We constructed a comprehensive profile of physiological miRNA targets in mouse colonic epithelium and tumors expressing K-RasG12D using Halo-Enhanced Argonaute Pulldown. Combining it with parallel datasets of chromatin accessibility, transcriptome, and proteome, we uncovered that K-RasG12D suppressed expression of Csnk1a1 and Csnk2a1, subsequently decreasing Ago2 phosphorylation at Ser825/829/832/835. Hypo-phosphorylated Ago2 increased binding to mRNAs while reducing its activity to repress miRNA targets. Our findings connect a potent regulatory mechanism of global miRNA activity to K-Ras in a pathophysiological context and provide a mechanistic link between oncogenic K-Ras and the post-transcriptional up-regulation of miRNA targets.K-Ras常发生功能获得性突变（其中K-RasG12D最为常见），这类突变可引发显著的转录组与蛋白质组改变，进而驱动肿瘤发生。然而，在肿瘤发生过程中，致癌性K-Ras对microRNA（miRNA）这类转录后调控因子的诱导失调机制仍不甚明晰。本研究发现，K-RasG12D可促进miRNA活性的整体抑制，进而导致数百个靶基因表达上调。我们利用Halo增强型Argonaute下拉技术（Halo-Enhanced Argonaute Pulldown），构建了表达K-RasG12D的小鼠结肠上皮及肿瘤组织中生理性miRNA靶标的综合图谱。结合染色质可及性、转录组与蛋白质组的平行数据集，我们发现K-RasG12D会抑制Csnk1a1与Csnk2a1的表达，随后降低Ago2在Ser825/829/832/835位点的磷酸化水平。低磷酸化的Ago2会增强其与mRNA的结合能力，同时削弱其抑制miRNA靶基因的活性。本研究的发现将致癌K-Ras与病理生理环境下的全局miRNA活性调控机制建立了关联，并为致癌性K-Ras与miRNA靶基因的转录后上调之间提供了机制性联系。