BACKGROUND While regulated WNT activity is required for normal development and stem cell maintenance, mutations that lead to constitutive activation of the WNT pathway cause cellular transformation and drive colorectal cancer. Activation of the WNT pathway ultimately leads to the nuclear translocation of β-catenin which, in complex with TCF/LEF factors, promotes the transcription of genes necessary for growth. The proto-oncogene MYC is one of the most critical genes activated downstream the WNT pathway in colon cancer. Here, we investigate the converse regulation of the WNT pathway by MYC. METHODS We performed RNA-seq analyses to identify genes regulated in cells expressing MYC. We validated the regulation of genes in the WNT pathway including LEF1 by MYC using RT-qPCR, Western blotting, and ChIP-seq. We investigated the importance of LEF1 for the viability of MYC-expressing cells in in fibroblasts, epithelial cells, and colon cells. Bioinformatic analyses were utilized to define the expression of MYC-regulated genes in human colon cancer and metabolomics analyses were used to identify pathways regulated by LEF1 in MYC expressing cells. RESULTS MYC regulates the levels of numerous WNT-related genes, including the β-catenin co-transcription factor LEF1. MYC activates the transcription of LEF1 and is required for LEF1 expression in colon cancer cells and in primary colonic cells transformed by APC loss of function, a common mutation in colon cancer patients. LEF1 caused the retention of β-catenin in the nucleus, leading to the activation of the WNT pathway in MYC-expressing cells. Consequently, MYC-expressing cells were sensitive to LEF1 inhibition. Moreover, we describe two examples of genes induced in MYC-expressing cells that require LEF1 activity: the peroxisome proliferator activated receptor delta (PPARδ) and the Acyl CoA dehydrogenase 9 (ACAD9). CONCLUSIONS We demonstrated that MYC is a transcriptional regulator of LEF1 in colonic cells. Our work proposes a novel pathway by which MYC regulates proliferation through activating LEF1 expression which in turn activates the WNT pathway.

中文翻译：

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MYC诱导LEF1激活WNT途径并维持细胞增殖。

背景技术虽然正常发育和干细胞维持需要调节的WNT活性，但导致WNT途径组成型激活的突变会引起细胞转化并驱动结直肠癌。WNT途径的激活最终导致β-连环蛋白的核易位，其与TCF / LEF因子复合，促进生长必需的基因的转录。原癌基因MYC是结肠癌WNT途径下游激活的最关键基因之一。在这里，我们调查了MYC对WNT途径的逆向调控。方法我们进行了RNA-seq分析，以鉴定在表达MYC的细胞中调控的基因。我们使用RT-qPCR，Western印迹和ChIP-seq验证了MYC对WNT途径中基因的调节，包括LEF1。我们调查了LEF1对于成纤维细胞，上皮细胞和结肠细胞中MYC表达细胞活力的重要性。利用生物信息学分析来定义MYC调控基因在人结肠癌中的表达，并通过代谢组学分析来确定LEF1在MYC表达细胞中调控的途径。结果MYC调节了许多WNT相关基因的水平，包括β-catenin共转录因子LEF1。MYC激活LEF1的转录，这是结肠癌细胞和通过APC功能丧失转化的原代结肠细胞中LEF1表达所必需的，APC功能丧失是结肠癌患者的常见突变。LEF1导致β-catenin在细胞核中的滞留，导致MYC表达细胞中WNT途径的激活。所以，表达MYC的细胞对LEF1抑制敏感。此外，我们描述了在需要LEF1活性的MYC表达细胞中诱导的基因的两个例子：过氧化物酶体增殖物激活受体δ（PPARδ）和酰基CoA脱氢酶9（ACAD9）。结论我们证明MYC是结肠细胞中LEF1的转录调节子。我们的工作提出了一条新途径，MYC通过激活LEF1表达来调节增殖，进而激活WNT途径。