Menin Maintains Cholesterol Content in Colorectal Cancer via Repression of LXR-Mediated Transcription

SIMPLE SUMMARY: Colorectal cancer (CRC) is the leading cause of cancer-related death worldwide, and new therapeutic approaches are direly needed to improve the outcomes of metastatic disease. Herein, we uncover that menin, a nuclear scaffold protein that has a myriad of tissue-specific effects on gene transcription, serves as a novel regulator of cholesterol homeostasis in CRC cell lines in vitro and in the benign colonic epithelium in vivo. Specifically, we demonstrate that menin inhibits the transcription of LXR-regulated genes, including the cholesterol exporters ABCA1 and ABCG1, leading to increased cellular cholesterol content. Conversely, menin inhibition reduces total cellular cholesterol content and sensitizes CRC to small molecule EGFR inhibitors and lipid-poor conditions. These combined findings demonstrate that menin is a key regulator of cholesterol homeostasis in both CRC and the colonic epithelium, and targeting menin may be an effective route for improving therapies for CRC. ABSTRACT: 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 from Men1(f/f);Vil1-Cre and Men1(f/f) mice 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, specifically ABCG1 and ABCA1, 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 with ABCG1 and ABCA1 upregulation, 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 assessed Men1(f/f);Vil1-Cre mice lacking menin expression in the colonic epithelium. Men1(f/f);Vil1-Cre mice were found to have no distinct baseline phenotype compared to control Men1(f/f) mice. However, similarly to CRC cell lines, Men1(f/f);Vil1-Cre mice showed an upregulation of Abcg1 and 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, including ABCA1 and ABCG1 in 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.