Defining the genomic and biologic impact of LINE-1 activity in fallopian tube epithelial cells

Massachusetts General Hospital, Boston MA

Investigators

Abstract

High-grade serous ovarian cancer (HGSOC) is the deadliest gynecologic cancer in the United States. Unfortunately, we have a limited understanding of the mechanisms contributing to the genesis of pre-cancerous lesions identified as serous tubal intraepithelial carcinoma (STIC) of the fallopian tube, and their transition to HGSOC. Ovulation occurring over a woman’s reproductive lifespan may contribute to the malignant transformation by exposing the FT fimbria to follicular fluid (FF), which contains factors promoting follicle rupture, inflammation, and tissue remodeling. Long INterspersed Element-1 (LINE-1, L1) is an endogenous mutagen. The only active protein-coding human transposon, L1 mobilizes by a “copy and paste” mechanism that creates a new copy in a new genomic location. L1 is repressed in normal somatic tissue by multiple mechanisms, including DNA methylation and the p53 tumor suppressor. We and others have revealed that L1 expression and new L1 genomic insertions are hallmarks of cancer. Ovarian cancers have some of the highest levels of L1 protein expression, and we now detect L1 ORF1 protein (ORF1p) in plasma from these cancer patients but not healthy females. Insertional mutagenesis by L1 can cause malignancies in humans by disrupting tumor suppressor genes, and our data in in vitro experimental models show L1 causes chromosomal instability (CIN). However, whether L1 contributes to ovarian tubal carcinogenesis is unknown. Supporting a potential causal role, DNA hypomethylation has been implicated as one of the early events in tumorigenesis and promotes L1 activity. ORF1p expression is induced in STIC lesions. STICs are concurrent with the histologic transformation of these cells and their development of CIN. This raises the intriguing possibility that L1 activity represents an important contributor to CIN in the pathogenesis of HGSOC. Based on our recent findings and accumulating evidence, we hypothesize that ovarian FF and promote L1 expression in fallopian tube epithelial cells (FTE), leading to DNA damage and genetic instability. We propose the following aims to test our hypothesis: 1: that FF promotes L1 expression in the FTE ; and 2: expression of L1 in FTE contributes to genetic instability independently or in concert with other known FTE premalignant genetic alterations, promoting a hyperplastic and eventually neoplastic phenotype. Our proposed aims will utilize patient samples to ensure applicability, well-established as well as novel assays and state-of-the-art technologies to test whether by itself or in concert with known genetic alterations L1 promotes sufficient DNA damage and genetic instability to facilitate tumorigenesis in our in vitro and in vivo preclinical models.Understanding the genomic impact of L1 in FTE and its potential contributions to malignant transformation will allow for the development of novel strategies to target or prevent ovarian cancer.