Abstract GMM-055: BMI1 AND RING1A ARE INVOLVED IN H2A UBIQUITINATION AT SITES OF PLATINUM-INDUCED DAMAGE

Abstract

Abstract Ovarian cancer is the 5th leading cause of death among women with the five year survival rate for ovarian cancer patients being only 46%. The standard of care for treatment of ovarian cancer patients is debulking surgery followed by platinum-taxane based chemotherapy. However, the major obstacle in the treatment of these patients with platinum based agents is development of chemoresistance. The platinum agents, cisplatin and carboplatin damage DNA by forming adducts with adjacent guanines, a high density of which are found in the promoter CpG islands of genes. Aberrant promoter DNA hypermethylation of genes and their subsequent transcriptional repression has been associated with development of cisplatin resistance. However, the mechanism of initiation of this aberrant DNA methylation and subsequent transcriptional repression is not known. Our overall hypothesis is that platinum induced DNA damage or repair of the damage leads to recruitment of repressive proteins to sites of damage. These repressive proteins transiently repress transcription in vicinity of damage to promote repair. However, similar to our findings with enzyme induced double strand breaks, repressive proteins may be retained at some key loci causing persistent transcriptional repression and gene silencing contributing to the development of platinum resistance. Our preliminary data demonstrates that BMI1, a member of polycomb repressive complex 1, localizes to sites of damage after cisplatin treatment. We also observe mono-ubiquitination of H2AX after cisplatin treatment and we hypothesize that this ubiquitination is occurring on K119. Mono-ubiquitination of H2A/H2AX at K119 has been associated with transcriptional repression and gene silencing during development and differentiation and also during repair of ionizing radiation and enzyme induced double strand breaks. Our data suggests that knockdown of RING1A reduces the cisplatin induced H2AX ubiquitination. We are currently determining which repair pathways and/or proteins result in recruitment of BMI1, RING1A to sites of damage. Importantly, after acute cisplatin treatment we also observe a reduction in expression of candidate genes which are known to be methylated in cisplatin resistant cells. We plan to determine if RING1A mediated ubiquitination is responsible for reduction in expression of target genes after acute cisplatin treatment and their methylation in cisplatin resistant cells. Understanding the mechanism of platinum induced gene silencing will enable us to design therapies to avert the development of drug resistant ovarian cancers. Citation Format: Shruthi Sriramkumar, Heather M. O'Hagan. BMI1 AND RING1A ARE INVOLVED IN H2A UBIQUITINATION AT SITES OF PLATINUM-INDUCED DAMAGE [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr GMM-055.