Abstract P5-04-13: Splicing factorESRP1controls ER-positive breast cancer progression by altering metabolic pathway genes

Abstract Background Epithelial Splicing Regulatory Protein (ESRP1)is a key splicing factor that regulates Epithelial-to-Mesenchymal Transition (EMT) splicing program. Our previous study demonstrated that high levels of ESRP1 are associated with poor prognosis in human ER-positive (ER+) breast tumors in an independent manner of EMT process. We next explored the potential mechanisms that contribute to the role ESRP1 in endocrine therapy-resistant breast cancer. Methods Probe based-Human Transcriptome Array 2.0 (HTA; Applied Biosystems/Thermo Fisher) was performed using RNAs from control and ESRP1 knockdown cells (LCC2 versus 2C3 ESRP1 and LCC9 versus 9C2 ESRP1) of endocrine resistant breast cancer. Functional enrichment analyses were performed using the DAVID functional annotation tool (http://david.abcc.ncifcrf.gov/). To confirm the functional importance of ESRP1 on regulation of cellular metabolism, we have performed experiments that analyze the metabolic substrate flux in response to ESRP1 knockdown in resistant cells (The Seahorse XFp Cell Energy Phenotype Assay). Differentially expressed genes were validated using Western blotting assay. Results Transcriptome profiling of ESRP1in 2C3 and 9C2 knockdown models revealed differentially expressed genesusing HTA 2.0 platform. In LCC2 versus 2C3 ESRP1 knockdown, expression of 1186 genes (1263 transcripts) have been altered significantly, while 413 genes (432 transcripts) have been significantly regulated in LCC9 versus 9C2 ESRP1 knockdown with FDR<0.1 Of these significant genes, 34 downregulated and 68 upregulated (102 genes total) were shared by both 2C3 and 9C2 ESRP1 knockdowns. Using the DAVID Functional Annotation Clustering Tool, we identified the biological processes altered significantly in response to ESRP1 knockdown. The most significant annotation clusters downregulated in ESRP1 knockdown consists of fatty acid metabolism/lipid metabolism (SCD, ACACA, FASN, ACAT2, PLCH1, and HPGD), and oxireductase processes (SCD, PHGDH, FASN, DHTKD1 and HPGD. We confirmed the altered metabolic function using the Seahorse analyzer. These analyses confirmed that ESRP1 knockdown altered the glycolysis rate (extracellular acidification rate; ECAR) in both tamoxifen-resistant and fulvestrant-resistant models. In addition, ESRP1 knockdown decreased the mitochondrial respiration in tamoxifen-resistant cells, but not fulvestrant resistant cells. Using Western blotting, we validated the altered levels of fatty acid synthase (FASN) and Stearoyl-CoA desaturase 1 (SCD1), key enzymes in fatty acid metabolism. Phosphoglycerate Dehydrogenase (PHGDH), a poor prognosis marker in cancers including breast cancer, was also downregulated in response to ESRP1 knockdown. Taken together, we have demonstrated a novel functional impact of ESRP1 on the regulation of tumor growth at the functional and molecular level independent of EMT. Conclusions For the first time, we show the role of ESRP1 in altering the cellular metabolism thereby contributing to tumor growth. The study provides a molecular evidence for the role of altered metabolism in determining adverse prognosis of ER+ breast cancer via the control of ESRP1, a splicing factor. Further studies to determine the therapeutic value are underway. Citation Format: Gokmen-Polar Y, Gu Y, Gu X, Badve SS. Splicing factor ESRP1 controls ER-positive breast cancer progression by altering metabolic pathway genes [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-04-13.