XAB2 depletion induces intron retention in POLR2A to impair global transcription and promote cellular senescence.

Shuai Hou,Haixin Lei,Weijie Wang,Xinyue Wei,Dapeng Liang,Qi Wang,Liye Zhang,Qian Zhang,Wei Tang,Wei Guo,Baohui Zhu,Dajun Qu,Misbah Khan,Haidong Zhao,Jiaojiao Hao,Sikandar Azam,Yue Li,Siqi Zhao

doi:10.1093/nar/gkz532

Shuai Hou, Haixin Lei + Show 16 more

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https://doi.org/10.1093/nar/gkz532

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Abstract

XAB2 is a multi-functional protein participating processes including transcription, splicing, DNA repair and mRNA export. Here, we report POLR2A, the largest catalytic subunit of RNA polymerase II, as a major target gene down-regulated after XAB2 depletion. XAB2 depletion led to severe splicing defects of POLR2A with significant intron retention. Such defects resulted in substantial loss of POLR2A at RNA and protein levels, which further impaired global transcription. Treatment of splicing inhibitor madrasin induced similar reduction of POLR2A. Screen using TMT-based quantitative proteomics identified several proteins involved in mRNA surveillance including Dom34 with elevated expression. Inhibition of translation or depletion of Dom34 rescued the expression of POLR2A by stabilizing its mRNA. Immuno-precipitation further confirmed that XAB2 associated with spliceosome components important to POLR2A expression. Domain mapping revealed that TPR motifs 2–4 and 11 of XAB2 were critical for POLR2A expression by interacting with SNW1. Finally, we showed POLR2A mediated cell senescence caused by XAB2 deficiency. Depletion of XAB2 or POLR2A induced cell senescence by up-regulation of p53 and p21, re-expression of POLR2A after XAB2 depletion alleviated cellular senescence. These data together support that XAB2 serves as a guardian of POLR2A expression to ensure global gene expression and antagonize cell senescence.

Highlights

Gene expression is a fundamental and highly complex process that includes many steps, such as transcription, RNA splicing, RNA export, RNA degradation, translation and protein degradation [1]
From our previous microarray data [31], we surprisingly found that XAB2 depletion resulted in dramatic down-regulation of POLR2A mRNA (3.55-fold), the largest catalytic subunit of RNA polymerase II
XAB2 has been reported to function in several regulatory processes, such as transcription, pre-mRNA splicing and mRNA export, detailed mechanism on regulation of gene expression by XAB2 remains unclear

Summary

Introduction

Gene expression is a fundamental and highly complex process that includes many steps, such as transcription, RNA splicing, RNA export, RNA degradation, translation and protein degradation [1]. The human POLR2A gene is located on chromosome 17p13.1, encoding a protein of 1970 amino acids with an apparent molecular weight of 220 kDa, and contains a C-terminal domain (CTD) of 52 heptapeptide repeats (YSPTSPS) that are essential for its polymerase activity [8,9,10]. It is well established that POLR2A, its CTD domain, plays a key role in coordinating transcription with co-transcriptional events such as mRNA processing, thereby regulating gene expression [8,9,10,11]. It has been reported that POLR2A is significantly down-regulated in Werner syndrome patients or old human donor cells compared with young donor cells based on microarray analysis, indicating a role in cellular senescence [12].

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