Background and Aims: Menin is a nuclear scaffold protein that regulates gene transcription in an oftentimes tissue-specific manner. Our previous work showed that menin is over-expressed in colorectal cancer (CRC); however, the full spectrum of menin function in colonic neoplasia remains unclear. Herein, we aimed to uncover novel menin-regulated pathways important for colorectal carcinogenesis. Methods: RNA-Seq analysis identified that menin regulates LXR-target gene expressions in CRC cell lines. Isolated colonic epithelium fromMen1f/f;Vil1-Cre andMen1f/fmice was used to validate the results in vivo. Cholesterol content was quantified via an enzymatic assay. Results: RNA-Seq analysis in the HT-29 CRC cell line identified that menin inhibition upregulated LXR-target genes, specificallyABCG1andABCA1, with protein products that promote cellular cholesterol efflux. Similar results were noted across other CRC cell lines and with different methods of menin inhibition. Consistent withABCG1andABCA1upregulation, and similarly to LXR agonists, menin inhibition reduced the total cellular cholesterol in both HT-29 and HCT-15 cells. To confirm the effects of menin inhibition in vivo, we assessedMen1f/f;Vil1-Cre mice lacking menin expression in the colonic epithelium.Men1f/f;Vil1-Cre mice were found to have no distinct baseline phenotype compared to controlMen1f/fmice. However, similarly to CRC cell lines,Men1f/f;Vil1-Cre mice showed an upregulation ofAbcg1and a reduction in total cellular cholesterol. Promoting cholesterol efflux, either via menin inhibition or LXR activation, was found to synergistically suppress CRC cell growth under cholesterol-depleted conditions and when administered concomitantly with small molecule EGFR inhibitors. Conclusions: Menin represses the transcription of LXR-target genes, includingABCA1andABCG1in the colonic epithelium and CRC. Menin inhibition conversely upregulates LXR-target genes and reduces total cellular cholesterol, demonstrating that menin inhibition may be an important mechanism for targeting cholesterol-dependent pathways in colorectal carcinogenesis.
背景与目的：Menin是一种核支架蛋白，常以组织特异性方式调控基因转录。我们先前的研究表明，menin在结直肠癌中过度表达，但其在结肠肿瘤发生中的完整功能谱尚不明确。本研究旨在揭示menin调控的、对结直肠癌发生至关重要的新通路。方法：通过RNA测序分析发现，menin在结直肠癌细胞系中调控LXR靶基因的表达。利用从Men1f/f;Vil1-Cre和Men1f/f小鼠分离的结肠上皮细胞进行体内验证。采用酶学法测定胆固醇含量。结果：在HT-29结直肠癌细胞系中，RNA测序分析显示抑制menin可上调LXR靶基因（特别是ABCG1和ABCA1），其编码蛋白产物能促进细胞胆固醇外流。在其他结直肠癌细胞系及采用不同menin抑制方法时均观察到类似结果。与ABCG1和ABCA1上调一致，且类似于LXR激动剂的作用，menin抑制降低了HT-29和HCT-15细胞的总细胞胆固醇水平。为验证menin抑制在体内的作用，我们评估了结肠上皮细胞中menin表达缺失的Men1f/f;Vil1-Cre小鼠。与对照Men1f/f小鼠相比，Men1f/f;Vil1-Cre小鼠未表现出明显的基础表型差异。然而，与结直肠癌细胞系类似，Men1f/f;Vil1-Cre小鼠显示出Abcg1上调及总细胞胆固醇降低。研究发现，在胆固醇耗竭条件下，或与小分子EGFR抑制剂联合给药时，通过menin抑制或LXR激活促进胆固醇外流，能协同抑制结直肠癌细胞生长。结论：Menin在结肠上皮和结直肠癌中抑制LXR靶基因（包括ABCA1和ABCG1）的转录。相反，menin抑制可上调LXR靶基因并降低总细胞胆固醇，表明menin抑制可能是靶向结直肠癌发生中胆固醇依赖通路的重要机制。
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