Canonical TGF\u03b2 signaling induces collective invasion in colorectal carcinogenesis through a Snail1- and Zeb1-independent partial EMT

Marion Flum,Yu-Hsiang Teng,Severin Dicks,Andreas Hecht,Melanie Boerries,Alexander Nyström,Monika Schrempp

doi:10.1038/s41388-022-02190-4

Abstract

Local invasion is the initial step towards metastasis, the main cause of cancer mortality. In human colorectal cancer (CRC), malignant cells predominantly invade as cohesive collectives and may undergo partial epithelial-mesenchymal transition (pEMT) at the invasive front. How this particular mode of stromal infiltration is generated is unknown. Here we investigated the impact of oncogenic transformation and the microenvironment on tumor cell invasion using genetically engineered organoids as CRC models. We found that inactivation of the Apc tumor suppressor combined with expression of oncogenic KrasG12D and dominant-negative Trp53R172H did not cell-autonomously induce invasion in vitro. However, oncogenic transformation primed organoids for activation of a collective invasion program upon exposure to the prototypical microenvironmental factor TGFβ1. Execution of this program co-depended on a permissive extracellular matrix which was further actively remodeled by invading organoids. Although organoids shed some epithelial properties particularly at the invasive edge, TGFβ1-stimulated organoids largely maintained epithelial gene expression while additionally implementing a mesenchymal transcription pattern, resulting in a pEMT phenotype that did not progress to a fully mesenchymal state. Notably, while TGFβ1 induced pEMT and promoted collective invasion, it abrogated self-renewal capacity of TKA organoids which correlated with the downregulation of intestinal stem cell (ISC) marker genes. Mechanistically, induction of the non-progressive pEMT required canonical TGFβ signaling mediated by Smad transcription factors (TFs), whereas the EMT master regulators Snail1 and Zeb1 were dispensable. Gene expression profiling provided further evidence for pEMT of TGFβ1-treated organoids and showed that their transcriptomes resemble those of human poor prognosis CMS4 cancers which likewise exhibit pEMT features. We propose that collective invasion in colorectal carcinogenesis is triggered by microenvironmental stimuli through activation of a novel, transcription-mediated form of non-progressive pEMT independently of classical EMT regulators.

Highlights

Metastasis - accountable for the overwhelming majority of cancerrelated deaths in solid cancers-requires that tumor cells successfully pass through a series of events summarily termed invasionmetastasis cascade [1]
To decipher the molecular and cellular basics of tumor invasion and metastasis poses a persistent challenge, and it is not clear to which extent these processes are driven by genetic changes in cancer cells and by extrinsic factors from their surroundings
Thereby, we found that the mutation of Apc, Kras, Trp53, and Smad4 was insufficient to elicit cell-intrinsic invasive behavior in organoids

Summary

Introduction

Metastasis - accountable for the overwhelming majority of cancerrelated deaths in solid cancers-requires that tumor cells successfully pass through a series of events summarily termed invasionmetastasis cascade [1]. Tumor cells can accomplish the initial step of this cascade by shedding cell-cell contacts and infiltrate adjacent stroma as individual cells, employing ameboid or mesenchymal modes of migration [2]. Most human cancers display a collective mode of invasion where tumor cells maintain intercellular interactions and migrate in groups [2]. Cells at the invasive front of such a collective may display mesenchymal features [2, 3]. Epithelial-mesenchymal transitions (EMT) are complex cellular programs that were repeatedly implicated in cancer cell invasion and metastasis [4]. In the course of EMT, cells gradually trade key epithelial characteristics such as apical-basal polarity and tight cell-cell and cell-matrix contacts for mesenchymal features, including fibroblast-like morphology, front-rear polarity, increased motility, and enhanced invasiveness. Irrespective of the upstream trigger, a central role in EMT

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