OR30-3 Direct and VGLL1-Mediated Gene Regulation by GRHL2 During Mesenchymal to Epithelial Transition in Breast Cancer

Abstract

Abstract The transcription factor (TF) GRHL2 controls normal epithelial differentiation in different tissues. It is expressed in all breast cancer subtypes except those with a mesenchymal phenotype (claudin-low subtype), where its ectopic expression leads to induction of a mesenchymal-epithelial transition (MET) (1). Here we explored the mechanisms by which GRHL2 induces MET in claudin-low breast cancer cell lines using a combination of ChIP-seq and RNAseq analyses upon modulation of GRHL2 expression in mesenchymal and epithelial cell lines. Direct DNA binding by GRHL2 was enriched in proximity of genes positively regulated in mesenchymal cell lines, which include several epithelial TFs as well as an array of epithelial genes. Biotinylation and mass spectrometry analysis of membrane proteins confirmed surfaceome remodeling via induction of membrane proteins with roles in cell-cell contacts and adhesion. Repression of mesenchymal genes was mediated in part by direct induction of miRNAs targeting mesenchymal transcription factors. In addition, GRHL2 strongly induced expression of the cofactor VGLL1, whose expression is high in the triple-negative (TNBC) basal-like subtype. VGLL1 overexpression in mesenchymal cell lines and suppression in basal-like TNBC cells confirmed its role in mediating part of GRHL2 signaling, in particular via interaction with and modulation of TEAD transcription factors. In addition, GRHL2 also interacted with VGLL1 upon its induction in mesenchymal cells, recruiting it to some of its binding motifs, suggesting a multilayered cross-talk between GRHL2 and TEAD factors. Together, our results indicate that GRHL2 acts as a master regulator in the induction of TNBC epithelial differentiation via direct upregulation of epithelial transcription factors, miRNAs and TEAD cofactor VGLL1, resulting in both upregulation of epithelial genes and suppression of mesenchymal genes.(1) Cieply B. et al., Cancer Res. 2013 Oct. 1;73 (20): 6299-309 Presentation: Tuesday, June 14, 2022 10:15 a.m. - 10:30 a.m.