La is an abundant phosphoprotein that protects polymerase III transcripts from 3′-5′ exonucleolytic degradation and facilitates their folding. Consisting of the evolutionary conserved La motif (LAM) and two consecutive RNA Recognition Motifs (RRMs), La was also found to bind additional RNA transcripts or RNA domains like internal ribosome entry site (IRES), through sequence-independent binding modes which are poorly understood. Although it has been reported overexpressed in certain cancer types and depletion of its expression sensitizes cancer cells to certain chemotherapeutic agents, its role in cancer remains essentially uncharacterized. Herein, we study the effects of La overexpression in A549 lung adenocarcinoma cells, which leads to increased cell proliferation and motility. Expression profiling of several transcription and translation factors indicated that La overexpression leads to downregulation of global translation through hypophosphorylation of 4E-BPs and upregulation of IRES-mediated translation. Moreover, analysis of La localization after nutrition deprivation of the transfected cells showed a normal distribution in the nucleus and nucleoli. Although the RNA binding capacity of La has been primarily linked to the synergy between the conserved LAM and RRM1 domains which act as a module, we show that recombinant stand-alone LAM can specifically bind a pre-tRNA ligand, based on binding experiments combined with NMR analysis. We propose that LAM RNA binding properties could support the expanding and diverse RNA ligand repertoire of La, thus promoting its modulatory role, both under normal and pathogenic conditions like cancer.

La是一种丰富的磷蛋白，可保护聚合酶III转录本免受3'-5'核酸外切降解并促进其折叠。由进化保守的La基序（LAM）和两个连续的RNA识别基序（RRM）组成，La还被发现通过差的序列独立结合模式结合其他RNA转录物或RNA结构域，如内部核糖体进入位点（IRES）。了解。尽管据报道在某些癌症类型中过表达，并且表达的减少使癌细胞对某些化学治疗剂敏感，但其在癌症中的作用基本上仍未表征。本文中，我们研究了La过度表达在A549肺腺癌细胞中的作用，该作用导致细胞增殖和运动性增加。几种转录和翻译因子的表达谱表明，La的过表达通过4E-BP的低磷酸化和IRES介导的翻译的上调导致整体翻译的下调。此外，对营养缺失后的转染细胞进行La定位分析表明，其在细胞核和核仁中呈正态分布。尽管La的RNA结合能力主要与保守的LAM和充当模块的RRM1域之间的协同作用有关，但基于结合实验，我们显示重组的独立LAM可以特异性结合pre-tRNA配体NMR分析。我们建议，LAM RNA结合特性可以支持La的扩展和多样化的RNA配体库，从而促进其调控作用，