Induction of LEF1 by MYC activates the WNT pathway and maintains cell proliferation

Abstract

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. Graphical Abstract

Cooperation Between Distinct Cancer Driver Genes Underlies Intertumor Heterogeneity in Hepatocellular Carcinoma

“…MYC overexpression has been shown to lead to LEF1 transcription, which in turn promotes b-catenin translocation to the nucleus, where it is active. 26 However, in our mouse models, b-catenin could be found in the nucleus, even in the context of low levels of MYC, which suggests a different mechanism, possibly involving suppression of bcatenin-mediated transcription. Expressed independently, MYC promotes proliferation and dedifferentiation, which is observed at the transcriptional and histologic level, while b-catenin is associated with differentiation.…”

Wnt Activation After Inhibition Restores Trabecular Meshwork Cells Toward a Normal Phenotype

“…Nevertheless, as expected, an upregulation in phosphorylated β-catenin accompanied with increased phosphorylation of GSK3β demonstrates Wnt inhibition. [39][40][41] Inhibition of pGSK3β, with LY2090314, and subsequent activation of canonical Wnt/β-catenin signaling was confirmed through overexpression of AXIN2 42 and LEF1 33 regardless of prior Wnt inhibition; this was accompanied by significant repression of Wnt inhibitors, sFRP1 and DKK1. This is important when we consider our findings from a prior study 21 where cells remained in a disruptive state, despite removal of Wnt inhibitor, prolonging a pathologic phenotype.…”

“…2 B). AXIN2 32 and lymphoid enhancer-binding factor 1 ( LEF1 ), 33 transcriptional target genes for Wnt, were used as markers of Wnt signaling activation. The mRNA expression of both genes were significantly upregulated with Wnt activation after inhibition (6.7-fold, P < 0.001 and 3.7-fold, P < 0.001, respectively) and with activation only (6.35-fold, P < 0.001 and 3.8-fold P < 0.001, respectively) ( Fig.…”

Knockdown of ectodysplasin‑A receptor‑associated adaptor protein exerts a tumor‑suppressive effect in tongue squamous cell carcinoma cells

“…MYC is related to cell growth arrest and proliferation, thereby contributing to tumorigenesis (58). A previous study showed that knocking down MYC resulted in a reduction in the viability of colon cancer cells (59). In addition, a study indicated that the expression of MYC target genes was inhibited in response to the downregulation of Gcn5 histone acetyltransferase activity, contributing to apoptosis of lymphoma cells (60).…”