BRCA1 Mutation Leads to Deregulated Ubc9 Levels which Triggers Proliferation and Migration of Patient-Derived High Grade Serous Ovarian Cancer and Triple Negative Breast Cancer Cells

Rao Vn,You S,Singh K

doi:10.19070/2572-7613-160006

Abstract

Women who carry a germline mutation in BRCA1 gene typically develop triple negative breast cancers (TNBC) and high grade serous ovarian cancers (HGSOC). Previously, we reported that wild type BRCA1 proteins, unlike the disease-associated mutant BRCA1 proteins to bind the sole sumo E2-conjugating enzyme Ubc9. In this study, we have used clinically relevant cell lines with known BRCA1 mutations and report the in-vivo association of BRCA1 and Ubc9 in normal mammary epithelial cells but not in BRCA1 mutant HGSOC and TNBC cells by immunofluorescence analysis. BRCA1-mutant HGSOC/TNBC cells and ovarian tumor tissues showed increased expression of Ubc9 compared to BRCA1 reconstituted HGSOC, normal mammary epithelial cells and matched normal ovarian tissues. Knockdown of Ubc9 expression resulted in decreased proliferation and migration of BRCA1 mutant TNBC and HGSOC cells. This is the first study demonstrating the functional link between BRCA1 mutation, high Ubc9 expression and increased migration of HGSOC and TNBC cells. High Ubc9 expression due to BRCA1 mutation may trigger an early growth and transformation advantage to normal breast and ovarian epithelial cells resulting in aggressive cancers. Future work will focus on studying whether Ubc9 expression could show a positive correlation with BRCA1 linked HGSOC and basal like TNBC phenotype.

Highlights

Women who have mutations in the BRCA1 gene have an increased lifetime risk of developing hereditary breast and ovarian cancers
Using these cells we have studied the in vivo association of BRCA1 with Ubc9, expression of Ubc9 in these BRCA1 mutant triple negative breast cancers (TNBC) and high grade serous carcinoma (HGSOC) cell lines and tumor tissues
Loss of association of BRCA1 and Ubc9 in BRCA1 mutant HGSOC and TNBC cells Wild Type BRCA1 but not the disease associated mutants have been shown to bind in vitro to SUMO E2 conjugating enzyme Ubc9 and this is responsible for both ER-alpha activation and tumor suppression of breast and ovarian cancer cells [31, 34]. To examine whether this occurs in vivo, we have studied the association of BRCA1 and Ubc9 in normal mouse mammary epithelial cells MCF10A and a basal-like TNBC cell line HCC1937 obtained from a patient with germ line BRCA1 mutation using immunofluorescence analysis

Summary

Introduction

Women who have mutations in the BRCA1 gene have an increased lifetime risk of developing hereditary breast and ovarian cancers. BRCA1 mutations are responsible for up to 10% of the epithelial ovarian cancers (EOC) and 15% of breast cancers [1, 2]. The most common and aggressive histotype of epithelial ovarian cancer (EOC), high grade serous carcinoma (HGSOC) is associated with germ line BRCA1 mutations with a lifetime risk of 40–60% [4]. A high percentage of BRCA1-associated hereditary and sporadic breast cancers are triple negative and are more likely to occur among pre-menopausal women of African American descent [6]. For women of African American descent there is a low survival rate for individuals that have advanced EOC or TNBC due to lack of treatment for advanced epithelial ovarian cancer and no targeted treatment for TNBC. There is a critical need for better targeted therapies for these high grade TNBC and ovarian cancers [7,8,9]

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Conclusion