TGF-β drives epithelial-mesenchymal transition through δEF1-mediated downregulation of ESRP

Abstract

Epithelial-mesenchymal transition (EMT) is a crucial event in wound healing, tissue repair and cancer progression in adult tissues. We have recently shown that transforming growth factor (TGF)-β-induced EMT involves isoform switching of fibroblast growth factor receptors by alternative splicing. We performed a microarray-based analysis at single exon level to elucidate changes in splicing variants generated during TGF-β-induced EMT, and found that TGF-β induces broad alteration of splicing patterns by downregulating epithelial splicing regulatory proteins (ESRPs). This was achieved by TGF-β-mediated upregulation of δEF1 family proteins, δEF1 and SIP1. δEF1 and SIP1 each remarkably repressed ESRP2 transcription through binding to the ESRP2 promoter in NMuMG cells. Silencing of both δEF1 and SIP1, but not either alone, abolished the TGF-β-induced ESRP repression. The expression profiles of ESRPs were inversely related to those of δEF1 and SIP in human breast cancer cell lines and primary tumor specimens. Further, overexpression of ESRPs in TGF-β-treated cells resulted in restoration of the epithelial splicing profiles as well as attenuation of certain phenotypes of EMT. Therefore, δEF1 family proteins repress the expression of ESRPs to regulate alternative splicing during TGF-β-induced EMT and the progression of breast cancers.

ZEB1‐regulated inflammatory phenotype in breast cancer cells

“…S1A; Horiguchi et al ., 2012). We also obtained ChIP‐seq data in MCF7 luminal‐type breast cancer cells.…”

“…1A and data not shown). No peaks were found at the ESRP2 and CDH1 gene loci in MCF7 cells, which likely reflected the low expression of ZEB1 in luminal‐type breast cancer cells (Horiguchi et al ., 2012). One of the de novo predicted common motifs in the ZEB1‐binding regions in MDA‐231‐D cells matched the known ZEB1‐binding motif, which contained ‘CACCT’ ( q  = 0.0289) and was found in 38% of the 14 811 binding regions (Fig.…”

“…Of the basal‐type breast cancer cell lines, MDA‐231‐D and Hs578T expressed ZEB1 and ZEB2, while HCC1954‐Luc cells showed only small amounts of ZEB1 and ZEB2 proteins (Fig. S2A; Horiguchi et al ., 2012). In agreement with the immunoblot data, quantitative evaluation using RNA‐seq data in MDA‐231‐D cells suggested that the expression of ZEB2 was lower than that of ZEB1 (Fig.…”

“…We also reported that it induces isoform switching of fibroblast growth factor receptors by alternative splicing, which occurs through downregulation of the expression of epithelial splicing regulatory proteins (ESRPs) by ZEB1 and ZEB2 (Horiguchi et al ., 2012). Furthermore, the expression profiles of ZEB1 and ZEB2 are inversely correlated with those of ESRPs in human breast cancer cell lines and tumor specimens (Horiguchi et al ., 2012).…”

“…We also reported that it induces isoform switching of fibroblast growth factor receptors by alternative splicing, which occurs through downregulation of the expression of epithelial splicing regulatory proteins (ESRPs) by ZEB1 and ZEB2 (Horiguchi et al ., 2012). Furthermore, the expression profiles of ZEB1 and ZEB2 are inversely correlated with those of ESRPs in human breast cancer cell lines and tumor specimens (Horiguchi et al ., 2012). Consistent with the relationships between the EMT and cancer malignancy, high expression of ZEB1 is associated with poor prognosis of many types of cancer, including breast cancer (Chu et al ., 2013; Jang et al ., 2015).…”