内部核糖体进入位点(IRES)调控细胞血清饥饿应激条件下PRDM13的翻译

Role of Internal Ribosomal Entry Site in Cellular Translation Initiation of PRDM13 under Serum Starvation

PRDM13是锌指蛋白转录抑制因子（positive regulatory domain zinc finger protein,PRDM）家族中的一员,其在细胞分化、肿瘤的发生和恶性转化中起着重要的作用。而对于PRDM13基因侧翼序列是否含有内部核糖体进入位点（internal ribosome entry site,IRES）及其功能所知甚少。本研究对PRDM13 5＇端的非翻译区（5＇UTR）进行IRES结构与功能分析,探索其在细胞血清饥饿应激条件下对PRDM13翻译的影响。实验发现,在血清饥饿的条件下,肝癌细胞Bel7402/WT中PRDM13的蛋白质水平增加,但是其mRNA水平基本没有变化。将PRDM13 5＇UTR的序列插入双顺反子的报告载体（pRL-FL）中,并且将构建的载体（pRL-PRDM13-FL）转染进细胞中,结果显示,PRDM13 5＇UTR含有IRES,且发现PRDM13 5＇UTR中的105 nt（53~157）对其IRES的功能至关重要。在帽依赖的翻译（cap-dependent translation）机制被抑制时,IRES这种机制可有效维持PRDM13蛋白合成。本研究提供了在细胞压力条件下调节PRDM13蛋白合成的一种新的解释。

Positive regulatory domain zinc finger protein（ PRDM） 13 is an important member of the PRDM family and functions in cell differentiation,as well as occurrence and transformation of malignant cancer. However,the function of putative internal ribosome entry site（ IRES） in the PRDM 13 coding sequence is still elusive. In this study,we analyzed and explored the IRES activity on PRDM 13 translation in the context of serum-starvation. The results showed that the protein expression of PRDM13 increased in Bel7402 cancer cells under serum starvation, but without prominent changes at the transcription. By inserting the PRDM13 5＇UTR sequence into a bicistronic reporter vector（ pRL-FL） and transfected into HEK293 or Bel7402 / WT cell,we determined the sequence between 53 and 157 nt was essential for the IRES function. During drug exposure,the cellular protein expression of cap-dependent translation mechanism could be inhibited. We hypothesized that PRDM13 was able to escape from such inhibition by using the IRES element for translation and maintain stable protein levels.