Preferential translation of p53 target genes

The transcription factor p53 exerts its tumour suppressive effect through transcriptional activation of numerous target genes controlling cell cycle arrest, apoptosis, cellular senescence and DNA repair. In addition, there is evidence that p53 influences the translation of specific mRNAs, including translational inhibition of ribosomal protein synthesis and translational activation of MDM2. A challenge in the analysis of translational control is that changes in mRNA abundance exert a kinetic (passive) effect on ribosome densities. In order to separate these passive effects from active regulation of translation efficiency in response to p53 activation, we conducted a comprehensive analysis of translational regulation by comparative analysis of mRNA levels and ribosome densities upon DNA damage induced by neocarzinostatin in wild-type and TP53^−/− HCT116 colorectal carcinoma cells. Thereby, we identified a specific group of mRNAs that are preferentially translated in response to p53 activation, many of which correspond to p53 target genes including MDM2, SESN1 and CDKN1A. By subsequent polysome profile analysis of SESN1 and CDKN1A mRNA, we could demonstrate that p53-dependent translational activation relies on a combination of inducing the expression of translationally advantageous isoforms and <i>trans</i>-acting mechanisms that further enhance the translation of these mRNAs.

转录因子p53通过转录激活一系列调控细胞周期阻滞、细胞凋亡、细胞衰老及DNA修复的靶基因，发挥其抑癌作用。此外，已有研究表明p53可影响特定信使RNA（mRNA）的翻译过程，包括抑制核糖体蛋白合成的翻译以及激活MDM2的翻译。翻译调控分析的一项核心挑战在于，信使RNA（mRNA）丰度的变化会对核糖体密度产生动力学（被动）效应。为将此类被动效应与p53激活后翻译效率的主动调控区分开来，我们针对野生型及TP53^−/− HCT116结直肠癌细胞，在新制癌菌素诱导DNA损伤的条件下，通过比较分析其mRNA水平与核糖体密度，对翻译调控展开了全面研究。借此，我们鉴定出一组在p53激活后优先被翻译的特定mRNA群体，其中多数对应p53靶基因，包括MDM2、SESN1及CDKN1A。通过后续对SESN1与CDKN1A mRNA的多聚核糖体谱分析，我们证实p53依赖的翻译激活依赖于两种机制的协同：一是诱导具有翻译优势的同工型的表达，二是进一步增强此类mRNA翻译的反式（trans）作用机制。