Chen Xuedan, Li Juan, Guan Xingying, Bai Yun, Wang Kai
Department of Medical Genetics, Department of Basic Medicine, Army Medical University, Chongqing 400038, China.
Jinfeng Laboratory, Chongqing 400038, China.
Heliyon. 2024 Jun 13;10(12):e32857. doi: 10.1016/j.heliyon.2024.e32857. eCollection 2024 Jun 30.
Long noncoding RNA (lncRNA) cancer susceptibility 9 (CASC9) has been found to be overexpressed and functions as an oncogene in many cancer types. We investigated the molecular mechanism underlying CASC9 overexpression in esophageal squamous cell carcinoma (ESCC). Transcripts containing exons 2 and 6 and exons 4 and 6 showed the highest CASC9 expression levels in ESCC, no transcripts were detected in the normal esophageal epithelial Het1A cell line. The Long Interspersed Nuclear Element-1 (LINE1 or L1) element in the genome was found to participate in the evolution of lncRNA CASC9, the antisense promoter (ASP) of L1 provides the -regulatory elements necessary for CASC9 activation, and the antisense chain of L1 participates in the formation of exons of CASC9. The activation of the antisense promoter was due to the aberrant hypomethylation of L1 elements. An active enhancer element was identified in the downstream region of CASC9 gene by ChIP-seq and ChIP-qPCR. The interaction between ASP and the enhancer elements was confirmed by chromosome conformation capture (3C). Thus, our results suggest that the L1 ASP activation due to aberrant hypomethylation and downstream enhancer interaction plays a key role in the overexpression of lncRNA CASC9 in ESCC.
长链非编码RNA（lncRNA）癌症易感性9（CASC9）已被发现在多种癌症类型中过表达，并作为一种癌基因发挥作用。我们研究了食管鳞状细胞癌（ESCC）中CASC9过表达的分子机制。包含外显子2和6以及外显子4和6的转录本在ESCC中显示出最高的CASC9表达水平，在正常食管上皮Het1A细胞系中未检测到转录本。发现基因组中的长散在核元件1（LINE1或L1）元件参与lncRNA CASC9的进化，L1的反义启动子（ASP）提供了CASC9激活所需的调控元件，并且L1的反义链参与了CASC9外显子的形成。反义启动子的激活是由于L1元件的异常低甲基化。通过ChIP-seq和ChIP-qPCR在CASC9基因的下游区域鉴定出一个活性增强子元件。通过染色体构象捕获（3C）证实了ASP与增强子元件之间的相互作用。因此，我们的结果表明，由于异常低甲基化和下游增强子相互作用导致的L1 ASP激活在ESCC中lncRNA CASC9的过表达中起关键作用。
