1720P - Downregulation of BRCA1 protein in clear cell renal cellular carcinoma

Abstract

Background: Around 75% of renal cancer in adult kidney is clear cell renal cellular carcinoma (ccRCC). This type of cancer is characterized by lipids overacumulation and mutations in VHL (around 90% cases), BAP1 and PBRM1 genes as well as stabilization of HIF1α transcription factor. Additionally, metabolic switch to aerobic glycolysis and aberration in TCA cycle was observed in ccRCC independently on the stage of the disease. Moreover, the mTOR pathway hyperactivation and downregulation of AMPK pathway featured the ccRCC. This type of cancer is highly resistant to classical chemotherapy. BRCA1 is tumor suppressor gene, mutation in this gene is associated with breast and ovarian cancer. BRCA1 is a protein involved in DNA repair and apoptosis also interacts with BRG1 – core subunit of SWI/SNF chromatin remodeling complex. BRCA1 is transcribed from bidirectional promoter together with NBR2 – lncRNA. Interestingly, NBR2 interacts with AMPK and is downregulated in ccRCC. CTCF is a protein which binds Topologicaly Associated Domains, and CTCF binding site was found in BRCA1/NBR2 promoter region. Methods: Immunohistochemistry (IHC) on paraffin embedded clinical samples for BRCA1 and BRG1 core subunit of SWI/SNF complex, comparative transcriptomic study, co-immunoprecipitation (Co-IP) and chromatin immunoprecipitation (ChIP) method were used in this work. Results: In this study we found downregulation of BRCA1 and BRG1 proteins in ccRCC patient samples independently on stage of the disease. Interestingly, downregulation of BRG1 was more severe in samples with strong lymphocyte infiltration. By contrast, downregulation at the transcript level was observed for BRG1 encoding gene but not for BRCA1. BRG1 and CTCF co-precipitated from cancer cells, indicating the existence of co-interaction between CTCF, BRG1 and BRCA1 proteins. Additionally, overexpression of BRG1 caused increased expression of CTCF in human cells. We also found that BRG1 targets both CTCF and BRCA1 genes. Conclusions: BRCA1, BRG1 and CTCF module is dysregulated in ccRCC cells independently on Fuhrman grade and stage of the disease. This missregulation can have a brought spectrum of changes including 3D chromatin structure, transcription, epigenetic and others. Legal entity responsible for the study: Elzbieta Sarnowska Funding: This work was supported by grant from National Science Center No UMO–2013/11/B/NZ2/00132 Disclosure: All authors have declared no conflicts of interest.