Cancers 2022, 14, 4478. https://doi.org/10.3390/cancers14184478 www.mdpi.com/journal/cancers Article Downregulation of the Tumor Suppressor TFF1 Is Required during Induction of Colon Cancer Progression by L1 Arka Saha 1 , Nancy Gavert 1 , Thomas Brabletz 2 and Avri Ben‐Ze’ev 1, * 1 Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot 7610001, Israel 2 Department of Experimental Medicine I, Nikolaus‐Feibiger‐Center for Molecular Medicine, University of Erlangen‐Nuernberg, 91054 Erlangen, Germany * Correspondence: avri.ben‐zeev@weizmann.ac.il Simple Summary: Aberrant activation of Wnt/β‐catenin signaling and the subsequent induction of downstream target genes is a hallmark of colorectal cancer (CRC) development. Previously, we found that overexpression of the immunoglobulin‐like cell adhesion receptor L1CAM (L1), a target of the Wnt/β‐catenin pathway, confers enhanced proliferation, motility, tumorigenesis, and liver metastasis in CRC cells. Transcriptomic and proteomic analyses revealed changes in both pro‐tu‐ morigenic and potential tumor‐suppressor genes in L1‐overexpressing CRC cells. We wished to identify such tumor suppressor/s, and found that trefoil family factor 1 (TFF1) was involved in L1‐ mediated CRC progression. TFF1 overexpression suppressed the growth, motility and tumorigene‐ sis of L1‐expressing CRC cells by inhibiting the NF‐κB pathway. In human CRC tissue, TFF1‐posi‐ tive staining was evident in goblet cells of the normal mucosa, while in CRC tissue, TFF1 expression was lost in >50% of the tumor samples. Our results support a tumor‐suppressor role of TFF1 in human CRC, and we suggest that TFF1 could be used for CRC detection and as a novel therapeutic target in L1‐mediated CRC. Abstract: The immunoglobulin family cell adhesion receptor L1 is induced in CRC cells at the inva‐ sive front of the tumor tissue, and confers enhanced proliferation, motility, tumorigenesis, and liver metastasis. To identify putative tumor suppressors whose expression is downregulated in L1‐ex‐ pressing CRC cells, we blocked the L1–ezrin–NF‐κB signaling pathway and searched for genes in‐ duced under these conditions. We found that TFF1, a protein involved in protecting the mucus epithelial layer of the colon, is downregulated in L1‐expressing cells and displays characteristics of a tumor suppressor. Overexpression of TFF1 in L1‐transfected human CRC cells blocks the pro‐ tumorigenic and metastatic properties conferred by L1 by suppressing NF‐κB signaling. Immuno‐ histochemical analyses revealed that human CRC tissue samples often lose the expression of TFF1, while the normal mucosa displays TFF1 in goblet cells. Identifying TFF1 as a tumor suppressor in CRC cells could provide a novel marker for L1‐mediated CRC development and a potential target for therapy. Keywords: TFF1; L1; cancer cell adhesion and invasion; colon cancer; metastasis 1. Introduction Hyperactivation of the Wnt/β‐catenin signaling pathway and the subsequent induc‐ tion of β‐catenin/TCF target genes is a hallmark of CRC development [1]. We previously identified members of the immunoglobulin‐like family of cell adhesion receptors NrCAM and L1 as targets of the Wnt/β‐catenin pathway in CRC cells [2,3]. We reported that L1 is localized exclusively at the invading front of human CRC tissue [3]. Overexpression of L1 in CRC cells results in enhanced proliferation, motility and tumorigenesis, and promotes the metastasis of CRC cells to the liver in a mouse model [3,4]. A key downstream signal‐ ing mechanism involved in L1‐mediated tumorigenesis is an L1–ezrin–NF‐κB pathway Citation: Saha, A.; Gavert, N.; Brabletz, T.; Ben‐Ze’ev, A. Downregulation of the Tumor Suppressor TFF1 is Required during Induction of Colon Cancer Progression by L1. Cancers 2022, 14, 4478. https://doi.org/10.3390/ cancers14184478 Academic Editors: Cinzia Allegrucci and Paloma Ordóñez‐Morán Received: 17 August 2022 Accepted: 12 September 2022 Published: 15 September 2022 Publisher’s Note: MDPI stays neu‐ tral with regard to jurisdictional claims in published maps and institu‐ tional affiliations. Copyright: © 2022 by the authors. Li‐ censee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and con‐ ditions of the Creative Commons At‐ tribution (CC BY) license (https://cre‐ ativecommons.org/licenses/by/4.0/).