ABSTRACT

MicroRNAs (miRNAs) are post-transcriptional regulators of gene expression which act by guiding AGO (argonaute) proteins to target RNA transcripts in the RNA-induced silencing complex (RISC). This macromolecular complex includes multiple additional components (e.g., TNRC6A) that allow for interaction with enzymes mediating inhibition of translation or RNA decay. However, miRNAs also reside in low-molecular weight complexes without being engaged in target repression, and their function in this context is largely unknown. Our recent findings show that endothelial cells exposed to protective high-shear stress or MTORC inhibition activate the macroautophagy/autophagy machinery to sustain viability by promoting differential trafficking of MIR126 strands and by enabling unconventional features of MIR126-5p. Whereas MIR126-3p is degraded upon autophagy activation, MIR126-5p interacts with the RNA-binding protein MEX3A to form a ternary complex with AGO2. This complex forms on the autophagosomal surface and facilitates its nuclear localization. Once in the nucleus, MIR126-5p dissociates from AGO2 and establishes aptamer-like interactions with the effector CASP3 (caspase 3). The binding to MIR126-5p prevents dimerization and proper active site formation of CASP3, thus inhibiting proteolytic activity and limiting apoptosis. Disrupting this pathway in vivo by genetic deletion of Mex3a or by specific deficiency of endothelial autophagy aggravates endothelial apoptosis and exacerbates the progression of atherosclerosis. The direct inhibition of CASP3 by MIR126-5p reveals a non-canonical mechanism by which miRNAs can modulate protein function and mediate the autophagy-apoptosis crosstalk.

摘要

MicroRNA (miRNA) 是基因表达的转录后调节剂，其通过引导 AGO (argonaute) 蛋白靶向 RNA 诱导的沉默复合体 (RISC) 中的 RNA 转录物而发挥作用。这种大分子复合物包括多种附加成分（例如，TNRC6A），这些成分允许与介导翻译或 RNA 衰变抑制的酶相互作用。然而，miRNA 也存在于低分子量复合物中而不参与靶标抑制，它们在这种情况下的功能在很大程度上是未知的。我们最近的研究结果表明，暴露于保护性高剪切应力或 MTORC 抑制的内皮细胞通过促进MIR126 的差异运输激活巨自噬/自噬机制以维持活力链并通过启用MIR126-5p 的非常规功能。而MIR126-3p是在自体吞噬的活化降解，MIR126-5p与RNA结合蛋白MEX3A相互作用以形成三元复合物与AGO2。这种复合物在自噬体表面形成并促进其核定位。一旦进入细胞核，MIR126-5p 就会与 AGO2 分离并与效应子 CASP3（半胱天冬酶 3）建立类似适体的相互作用。与MIR126-5p的结合阻止了CASP3 的二聚化和适当的活性位点形成，从而抑制了蛋白水解活性并限制了细胞凋亡。通过基因缺失Mex3a在体内破坏该途径或通过内皮自噬的特异性缺陷加剧内皮细胞凋亡并加剧动脉粥样硬化的进展。MIR126-5p 对 CASP3的直接抑制揭示了一种非经典机制，通过该机制 miRNA 可以调节蛋白质功能并介导自噬 - 细胞凋亡串扰。