Abstract PR02: Cyclin E1 deregulation occurs early during fallopian tube tumorigenesis and promotes secretory cell transformation

Abstract

Abstract The fallopian tube has been implicated as the dominant site of origin for high-grade serous ovarian carcinoma. However, the molecular pathogenesis of fallopian tube-derived serous cancer is poorly understood and there are few experimental studies examining the transformation of human fallopian tube cells. Recent genomic analyses have identified CCNE1 (Cyclin E1) gene amplification as a potential oncogenic driver of high-grade serous ovarian carcinoma development. Here, we examine the oncogenic role of Cyclin E1 in serous carcinogenesis, first by characterizing its expression in both late-stage and early-stage human tumor samples, and secondly, by generating an experimental model of Cyclin E1-mediated transformation using primary human fallopian tube secretory epithelial cells. Using fluorescent in situ hybridization and immunohistochemical analyses, we show that Cyclin E1 is strongly expressed in a subset of late-stage high-grade serous carcinomas harboring CCNE1 amplification and that aberrant Cyclin E1 expression can occur very early during serous tumorigenesis, evident in non-invasive tubal carcinoma and putative precursor lesions. To examine the effects of constitutive Cyclin E1 expression in untransformed cells, we immortalized human fallopian tube secretory epithelial cells with TERT (telomerase reverse transcriptase) and mutant TP53R175H (representing early genetic alterations in serous tumorigenesis), followed by overexpression of CCNE1 or a vector control. Using a series of in vitro assays, we show that inappropriate Cyclin E1 expression imparts malignant characteristics to immortal fallopian tube secretory epithelial cells, including accelerated proliferation, loss of contact inhibition, and clonal growth ability. In addition, we use a combination of DNA damage assays and PCR array profiling to demonstrate that Cyclin E1 induces DNA double-strand and single-strand breaks, accompanied by up-regulation of DNA damage response genes involved in managing DNA replication stress. In sum, our results suggest that constitutive Cyclin E1 expression drives over-proliferation of untransformed but p53-compromised fallopian tube secretory epithelial cells, accompanied by an accumulation of DNA damage and altered expression of DNA damage response genes. Our data supports the hypothesis that Cyclin E1 promotes fallopian tube transformation by inducing replication stress-associated DNA damage, thus leading to chromosomal instability, and that CCNE1 amplification is a major driver of Cyclin E1 overexpression in high-grade serous carcinoma. This abstract is also presented as Poster A1. Citation Format: Alison M. Karst, Paul M. Jones, Natalie Vena, Azra H. Ligon, Joyce F. Liu, Michelle S. Hirsch, Dariush Etemadmoghadam, David D. Bowtell, Ronny Drapkin. Cyclin E1 deregulation occurs early during fallopian tube tumorigenesis and promotes secretory cell transformation. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: From Concept to Clinic; Sep 18-21, 2013; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2013;19(19 Suppl):Abstract nr PR02.