A regulatory axis between Epithelial Splicing Regulatory Proteins and Estrogen Receptor alpha modulates the alternative transcriptome of luminal breast cancer

The epithelial splicing regulatory proteins 1 and 2 (ESRP1/2) control the epithelial-to-mesenchymal transition (EMT) splicing program in cancer. However, their exact role in Breast Cancer (BC) remains under debate. Here, we report that ESRP1, but not ESRP2, is overexpressed in luminal BCs patients with poor prognosis and correlates with Estrogen Receptor a (ERa) mRNA levels. Analysis of ERa genome binding profiles in both cell lines and primary breast tumors showed its binding on both ESRP1 and ESRP2 promoters, and the expression of these genes strongly decreased by ERa silencing in hormone-deprived conditions (apoERa). The combined knock down of ESRP1/2 in MCF-7 cells followed by RNA-Seq, revealed the dysregulation of 754 genes expression, with a widespread alteration of alternative splicing events (ASEs) of genes involved in cell signaling, metabolism, cell growth, and EMT. Functional network analysis of ASEs that correlate with ESRP1/2 expression in ERa+ BCs showed RAC1 as the hub node in the protein-protein interactions altered by ESRP1/2 silencing. The comparison of apoERa- and ESRP-modulated ASEs revealed 63 commonly regulated events, including 27 detected both in primary BCs and endocrine resistant cell lines. Our data support a functional implication of the ERa-ESRP1/2 axis in the onset and progression of BC by controlling the splicing patterns of related genes. Overall design: MCF-7 transfected with siCTRL or siRNAs targeting ESRP1 and ESRP2