Wnt Effector TCF4 Is Dispensable for Wnt Signaling in Human Cancer Cells.

Dusan Hrckulak,Eva Sloncova,Katerina Galuskova,Martina Vojtechova,Vladimir Korinek,Vitezslav Kriz,Lucie Janeckova,Olga Babosova,Monika Horazna,Lucie Lanikova

doi:10.3390/genes9090439

Dusan Hrckulak, Eva Sloncova + Show 8 more

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https://doi.org/10.3390/genes9090439

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Abstract

T-cell factor 4 (TCF4), together with β-catenin coactivator, functions as the major transcriptional mediator of the canonical wingless/integrated (Wnt) signaling pathway in the intestinal epithelium. The pathway activity is essential for both intestinal homeostasis and tumorigenesis. To date, several mouse models and cellular systems have been used to analyze TCF4 function. However, some findings were conflicting, especially those that were related to the defects observed in the mouse gastrointestinal tract after Tcf4 gene deletion, or to a potential tumor suppressive role of the gene in intestinal cancer cells or tumors. Here, we present the results obtained using a newly generated conditional Tcf4 allele that allows inactivation of all potential Tcf4 isoforms in the mouse tissue or small intestinal and colon organoids. We also employed the clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 system to disrupt the TCF4 gene in human cells. We showed that in adult mice, epithelial expression of Tcf4 is indispensable for cell proliferation and tumor initiation. However, in human cells, the TCF4 role is redundant with the related T-cell factor 1 (TCF1) and lymphoid enhancer-binding factor 1 (LEF1) transcription factors.

Highlights

The wingless/integrated (Wnt) signaling pathway represents one of the fundamental evolutionarily conserved signaling mechanisms controlling cell specification during embryonic development and in adult tissues
The Tcf4 positive result was noticed throughout the epithelium, with slightly less pronounced staining in the upper part of the crypts, where rapidly dividing transit amplifying (TA) cells are localized
The expression levels of intestinal alkaline phosphatase (Alpi) and cryptdins were used as markers of differentiated enterocytes or Paneth cells, respectively, and Olfm4 was used as an additional intestinal stem cells (ISCs) marker

Summary

Introduction

The wingless/integrated (Wnt) signaling pathway represents one of the fundamental evolutionarily conserved signaling mechanisms controlling cell specification during embryonic development and in adult tissues. Aberrant activation of Wnt signaling causes a number of diseases, including various types of cancer [1]. There are at least five distinct branches of Wnt signaling. The best studied is the so-called canonical Wnt pathway, with β-catenin as its key effector [2]. Nuclear β-catenin associates with DNA-binding proteins of the lymphoid enhancer-binding factor/T-cell factor (LEF/TCF) family (further referred to as TCFs). Β-Catenin converts TCFs from transcriptional repressors to activators, and TCF/β-catenin complexes upregulate the expression of Wnt target genes such as c-myc, cyclin D1, CD44, axis inhibition protein 2 (Axin2), and Sp5 transcription factor (SP5). In the absence of the Wnt stimulus, cytosolic β-catenin is marked for

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