Multileveled reduction of p21 expression by Linc-ASEN represses cellular senescence [ChIRP-seq]

Long noncoding RNAs regulating diverse cellular processes implicate in many diseases. Here, we report the identification of a novel long intergenic noncoding RNA, Linc-ASEN, expressed in prematurely senescent cells, that associates with UPF1 and represses cellular senescence by reducing p21 production transcriptionally and post-transcriptionally. The Linc-ASEN-UPF1 complex suppressed p21 transcription by recruiting Polycomb Repressive Complex 1 (PRC1) and PRC2 to the p21 locus, and thereby preventing binding of the transcriptional activator p53 on the p21 promoter. Moreover, the Linc-ASEN-UPF1 complex repressed p21 expression post-transcriptionally by lowering p21 mRNA stability in association with DCP1A. Accordingly, Linc-ASEN levels were found inversely correlated with p21 mRNA levels in tumor tissues from patient-derived xenograft mice, in various human cancer tissues, and in aged mice tissues. Our studies reveal that Linc-ASEN prevents cellular senescence by reducing the transcription and stability of p21 mRNA in concert with UPF1, and suggest that Linc-ASEN might be a potential therapeutic target in processes influenced by senescence, including cancer. Overall design: Analysis of genome wide binding sites of Linc-ASEN via ChIRP-seq in MCF7 breast cancer cells.

长链非编码RNA（long noncoding RNAs, lncRNAs）可调控多种细胞进程，与诸多疾病的发生发展密切相关。本研究成功鉴定出一种新型基因间长链非编码RNA（long intergenic noncoding RNA, lincRNA）Linc-ASEN，该分子在早衰细胞中表达，可与UPF1蛋白结合，并通过在转录与转录后水平减少p21的生成，进而抑制细胞衰老。
Linc-ASEN与UPF1形成的复合体可将多梳抑制复合体1（Polycomb Repressive Complex 1, PRC1）与多梳抑制复合体2（Polycomb Repressive Complex 2, PRC2）招募至p21基因位点，通过阻断转录激活因子p53与p21启动子的结合，抑制p21的转录。此外，Linc-ASEN-UPF1复合体还可通过与DCP1A结合降低p21 mRNA的稳定性，在转录后层面抑制p21的表达。
进一步研究发现，在患者来源异种移植小鼠的肿瘤组织、多种人类癌症组织以及衰老小鼠组织中，Linc-ASEN的表达水平与p21 mRNA的水平呈负相关。
本研究揭示，Linc-ASEN可通过与UPF1协同作用，降低p21 mRNA的转录水平与稳定性，从而抑制细胞衰老；同时提示Linc-ASEN或许可作为衰老相关进程（包括癌症）中的潜在治疗靶点。
总体实验设计：在MCF7乳腺癌细胞中通过染色质RNA纯化测序（Chromatin Isolation by RNA Purification sequencing, ChIRP-seq）分析Linc-ASEN的全基因组结合位点。