SNAI1-Driven Sequential EMT Changes Attributed by Selective Chromatin Enrichment of RAD21 and GRHL2.

Vignesh Sundararajan,Vin Yee Chung,Ming Tan,Qing You Pang,Tuan Zea Tan,Jieru Ye,Ruby Yun-Ju Huang

doi:10.3390/cancers12051140

Abstract

Over two decades of research on cancer-associated epithelial-mesenchymal transition (EMT) led us to ascertain the occurrence of transitional intermediate states (collectively referred to as the EMT spectrum). Among the molecular factors that drive EMT, SNAI1 plays an indispensable role in regulating other core transcription factors, and this regulation is highly context-dependent. However, molecular investigation on this context-dependent regulation is still lacking. Using two ovarian cancer cell lines, we show that SNAI1 regulation on other core EMT-TFs switches from a repressive control in highly epithelial cells to an activation signaling in intermediate epithelial cells. Upon further scrutiny, we identify that the expression of early epithelial genes PERP and ERBB3 are differentially regulated in SNAI1-induced sequential EMT changes. Mechanistically, we show that changes in PERP and ERBB3 transcript levels could be correlated to the selective enrichment loss of RAD21, a cohesin component, at the distal enhancer sites of PERP and ERBB3, which precedes that of the proximal promoter-associated sites. Furthermore, the RAD21 enrichment at the distal enhancer sites is dependent on GRHL2 expression. In a nutshell, the alteration of GRHL2-associated RAD21 enrichment in epithelial genes is crucial to redefine the transition of cellular states along the EMT spectrum.

Highlights

Metastasis remains the most devastating and enigmatic phase of cancer progression, which accounts for more than 90% of patient mortality
By using two ovarian cancer cell lines expressing SNAI1, we demonstrate that SNAI1 represses other major epithelial-to-mesenchymal transition (EMT)-TFs in epithelial (E) cell lines, whereas this regulatory pattern becomes more relaxed in an intermediate epithelial (IE) cell line
To understand the early changes induced by SNAI1, we stably overexpressed full-length SNAI1 in two ovarian cancer cell lines: one belonging to the epithelial (E) phenotype (OVCA420) and the other belonging to the intermediate epithelial (IE) phenotype (OVCA429)

Summary

Introduction

Metastasis remains the most devastating and enigmatic phase of cancer progression, which accounts for more than 90% of patient mortality. Among several mechanisms that expedite metastasis, the pivotal role of epithelial-to-mesenchymal transition (EMT) is becoming increasingly recognized. EMT is a cellular reprogramming process that enables epithelial cells to lose their key features, including intercellular adhesion junctions, to acquire mesenchymal characteristics such as cell motility and front-rear polarity [1]. EMT is accomplished through complex coordination between signaling pathways and the underlying transcriptional regulation of proteins that are critical in maintaining epithelial integrity [2,3]. Rather than a simple binary shift from an epithelial to a mesenchymal phenotype, EMT occurs as a continuum of sequential, transient dedifferentiation processes with several intermediate/transitional phenotypes [4]. During the early phases of EMT, Cancers 2020, 12, 1140; doi:10.3390/cancers12051140 www.mdpi.com/journal/cancers

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