Regulation of a progenitor gene program by SOX4 is essential for mammary tumor proliferation

M Guy Roukens,Danielle Seinstra,Simon De Neck,Jacco Van Rheenen,Bart Westendorp,Alain De Bruin,Luca Braccioli,Cornelieke Pals,Paul J Coffer,Michal Mokry,Evelyne Beerling,Antoine A Khalil,Cynthia L Frederiks,Laura Bornes

doi:10.1038/s41388-021-02004-z

Abstract

In breast cancer the transcription factor SOX4 has been shown to be associated with poor survival, increased tumor size and metastasis formation. This has mostly been attributed to the ability of SOX4 to regulate Epithelial-to-Mesenchymal-Transition (EMT). However, SOX4 regulates target gene transcription in a context-dependent manner that is determined by the cellular and epigenetic state. In this study we have investigated the loss of SOX4 in mammary tumor development utilizing organoids derived from a PyMT genetic mouse model of breast cancer. Using CRISPR/Cas9 to abrogate SOX4 expression, we found that SOX4 is required for inhibiting differentiation by regulating a subset of genes that are highly activated in fetal mammary stem cells (fMaSC). In this way, SOX4 re-activates an oncogenic transcriptional program that is regulated in many progenitor cell-types during embryonic development. SOX4-knockout organoids are characterized by the presence of more differentiated cells that exhibit luminal or basal gene expression patterns, but lower expression of cell cycle genes. In agreement, primary tumor growth and metastatic outgrowth in the lungs are impaired in SOX4KO tumors. Finally, SOX4KO tumors show a severe loss in competitive capacity to grow out compared to SOX4-proficient cells in primary tumors. Our study identifies a novel role for SOX4 in maintaining mammary tumors in an undifferentiated and proliferative state. Therapeutic manipulation of SOX4 function could provide a novel strategy for cancer differentiation therapy, which would promote differentiation and inhibit cycling of tumor cells.

Highlights

An underlying aspect of cellular plasticity in tumorigenesis is the re-activation of developmental pathways by tumor cells [1, 2], of which perhaps the best characterized is epithelial-tomesenchymal-transition (EMT)
In this study RNA-sequencing data demonstrated that SOX4 is required to regulate a fetal mammary stem cell gene program which is abundant in cell cycle genes
We show that SOX4 mediates breast tumor-progression through maintenance of fetal mammary stem cells (fMaSC) gene expression

Summary

Introduction

An underlying aspect of cellular plasticity in tumorigenesis is the re-activation of developmental pathways by tumor cells [1, 2], of which perhaps the best characterized is epithelial-tomesenchymal-transition (EMT). EMT has been suggested to be of major importance for the metastatic cascade by facilitating detachment from the primary tumors and invasion into the surrounding stroma. As most secondary tumors exhibit epithelial characteristics this suggested that tumor cells require to undergo the reversal of EMT, mesenchymal-to-epithelial transition (MET) for efficient metastatic outgrowth. Reverting EMT in circulating tumor cells was shown to promote metastatic outgrowth in animal models [5,6,7]. Metastatic outgrowths regain E-cadherin levels before they can grow out to macrometastases [8, 9]. These studies indicate that EMT is dynamically regulated during metastasis formation and that mesenchymal cells are unable to sustain tumor growth

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Results

Conclusion