tRNA Fragments: Expression and Function in Ovarian Cancer

Abstract

Deep sequencing studies of noncoding RNA in liquid biopsies are revealing a vast repertoire of potential biomarkers. Ovarian cancer is a difficult-to-diagnose disease, urgently requiring novel and readily accessible biomarkers. We hypothesized that urine, one source of liquid biopsy samples, may contain novel noncoding RNAs (ncRNAs) that could serve as biomarkers for ovarian cancer. We proceeded to deep sequence RNA extracted from urine collected from ovarian cancer patients to better understand the repertoire of small RNAs in this type of liquid biopsy sample. The ncRNAs identified in these urine samples were predominantly microRNAs (miRNAs), ribosomal RNA (rRNA) fragments and tRNA fragments (tRFs). tRFs are a group of ncRNAs, which have been found across the biological kingdom and are increasingly being studied for their role in cancer biology. Several tRFs have been studied in cancer, although not previously in ovarian cancer. We have studied the expression of one specific tRF, 5’ fragment of tRNA-Glu-CTC (tRF5-Glu), in five different ovarian cancer cell lines. Several variants of tRF5-Glu were identified and we have now confirmed the expression of tRF5-Glu in ovarian cancer cells by quantitative real-time PCR (qRT-PCR), Northern analysis and ligation PCR. Additionally, we determined that angiogenin (ANG) plays a role in the biogenesis of tRF5-Glu. Furthermore, we have shown that tRF5-Glu targets the mRNA of the Breast Cancer Anti-estrogen Resistance 3 (BCAR3). While BCAR3 is known to regulate cancer cell migration and contributes to anti-estrogen resistance in breast cancer cells, it has not previously been studied in ovarian cancer or shown to be targeted by a tRF. Using synthetic mimics of tRF5-Glu and siRNAs targeting BCAR3, we were able to show that tRF5-Glu expression and the knock down of BCAR3 expression inhibits proliferation in ovarian cancer cells. These studies demonstrate that tRF5-Glu contributes to the regulation of BCAR3 and provides a novel mechanism of the regulation of proliferation in ovarian cancer cell lines.