Abstract P6-07-06: Shugoshin I signals epithelial-mesenchymal transition and promotes cell invasion in breast cancer
Authors: Jusino Shirley , Saavedra Harold I. 
Published: March 2020

Abstract
Despite being the most aggressive and poorly prognostic breast cancer subtype, there are currently no biological therapies against triple-negative (TN, or ER-PR-Her2-) breast cancers. Our laboratory is finding the sources of novel biological targets in TNBC by studying the E2F transcription factors, which are essential for cellular proliferation and maintenance of genomic stability. We recently published that the E2F transcriptional activators are overexpressed in the vast majority of TNBC and can dictate the high percentage of mitotic cells in mammary tumors. We also demonstrated that that the E2Fs control multiple mitotic regulators and maintain genomic integrity through Shugoshin I (SGO1) and BubR1. SGO1 is essential for chromosome segregation by preventing premature dissociation of the cohesion complex and sister chromatids after prophase. Until recently, SGO1 research was restricted to embryogenesis; however, recent studies have shown a role for SGO1 in tumorigenesis and epithelial-mesenchymal transition (EMT), but none have been done in breast cancer. Thus, we investigated SGO1 expression and genetic alteration in open databases such as KM-Plotter and cBioPortal and found that SGO1 is highly expressed in triple-negative breast cancer subtype and that its expression correlates with poor prognostic factors. Therefore, we decided to investigate the role of SGO1 in breast cancer EMT and cell invasion. Our hypothesis is that SGO1 modulates EMT genes, thus promoting cell invasion. To test our hypothesis, we conducted siRNA transfection to knockdown SGO1 in MDA-MB-231 and Hs578t, which are TNBC cells. After 48 hours, we evaluated mRNA levels of EMT-related genes after SGO1 depletion using RT-PCR analysis. We also evaluated the effects of SGO1 depletion in protein localization by immunofluorescence analysis. Furthermore, we evaluated the invasive behavior of MDA-MB-231 and Hs578t cells after SGO1 depletion using a Boyden Chamber Assay. Our results demonstrate that SGO1 depletion signals EMT by decreasing N-cadherin and increasing E-cadherin mRNA levels. SGO1 depletion also restores protein expression of E-cadherin in MDA-MB-231 cells. Strikingly, SGO1 depletion significantly reduces invasion in MDA-MB-231 and Hs578t cells. Our results suggest that SGO1 is a promising drug target for breast cancer metastasis since EMT and invasion are essential early steps in breast cancer metastasis. Currently, we are evaluating SGO1 expression in tissue microarrays derived from breast cancer patients (including Luminal and TNBC subtypes), in order to determine the percentage of those patients expressing Sgo1, as well as to establish important correlations with surrogate markers of prognosis (EMT, proliferation, mitosis). Our results may help establish new druggable targets in order to prevent and reduce metastasis in TNBC patients.
Citation Format: Shirley Jusino, Harold I. Saavedra. Shugoshin I signals epithelial-mesenchymal transition and promotes cell invasion in breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P6-07-06.