Abstract 5969: Novel tumor suppressor FRG1 reduces cancerous properties of breast cancer cell lines by regulating ERK pathway, irrespective of molecular subtypes
Authors: Mukherjee Bratati , Tiwari Ankit , Dixit Manjusha 
Published: September 2020

Abstract
Breast cancer is the most leading cause of cancer related deaths in women. Although combination of improved earlier detection and effective adjuvant therapies has dropped the breast cancer mortality, still different molecular subtypes, acquisition of quick drug resistance make it difficult to combat against this deadliest disease. So, an urging has to be compelled to inspect the additional players which are still unexplored in breast cancer.
The focus of our lab is to find out novel molecules regulating cancer development and progression. In this process, we discovered the role of FRG1 in tumorigenesis. FRG1 (FSHD Region Gene 1) is an evolutionary conserved gene which is reported to have role in muscle development, angiogenesis, RNA biogenesis, F actin bundling. In our previous study, we first time reported the association of FRG1 with cancer. In this study, our key interest is to explore the molecular mechanism behind the differential expression of FRG1 in breast cancer.
Here we started our study by exploring the expression of FRG1 in patient samples where we found reduced FRG1 expression in around 87% of breast cancer patients compared to their normal counterparts. Further, we also observed that FRG1 level was lower in triple negative breast cancer (TNBC) patients compared to Luminal A (hormone responsive) type. Similar trends of FRG1 expression was observed in Luminal A (ER+) cell line MCF7 and TNBC cell line MDAMB231. Therefore, we decided to evaluate the effect of perturbed FRG1 level in two breast cancer cell lines MCF7 (Luminal A) and MDAMB231 (TNBC). Knockdown of FRG1 in MCF7 cells led to increased cell proliferation, migration, colony formation and invasion; whereas ectopic FRG1 expression in MDAMB231 showed a reduction in these properties. Next, we investigated the signaling molecules associated with FRG1 and affected the above mentioned cellular properties. We observed low FRG1 expression in breast cancer cell line MCF7 resulted into activation of MEK/ERK pathway. Various EMT molecules like snail, slug, twist and tumor promoting cytokines such as IL1/8, growth factor like PDGFα/β was found to be up regulated in vitro due to reduction of FRG1. Similarly, FRG1 overexpression resulted into considerable downregulation of these EMT markers and cytokines. Furthermore, we found a rescue of these EMT molecules when ERK was inhibited or activated which confirmed that reduction in FRG1 in breast cancer cell lines activated ERK pathway which in turn upregulated the EMT molecules. Interestingly our data showed similar kind of trends irrespective of molecular subtypes of breast cancer cell lines. Also our study showed an activation of estrogen signaling in breast cancer due to the unliganded mechanism of estrogen receptor by FRG1.
Thus, our study first time suggests that FRG1 level is important for breast cancer progression irrespective of molecular subtypes; but further understanding and characterization of signalling mechanisms and interacting partners are required to conclusively comment on its tumor suppressive role.
Citation Format: Bratati Mukherjee, Ankit Tiwari, Manjusha Dixit. Novel tumor suppressor FRG1 reduces cancerous properties of breast cancer cell lines by regulating ERK pathway, irrespective of molecular subtypes [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5969.