Abstract B008: Alternative PER2 (Period2) enhancer usage drives epithelial-mesenchymal transition (EMT) in epithelial ovarian cancer (OC)
Authors: Chiu Yi Chia , Pang Qing You , Chen Yu Jie , Tan Tuan Zea , Ravinath Divya Malathy , Hwang-Verslues Wendy , Huang Ruby Yun Ju 
Published: March 2024

Abstract
Ovarian cancer (OC) is the fifth most prevalent cancer in Taiwanese females and is characterized by molecular heterogeneity. Among the identified gene-expression molecular subtypes (GEMS) of OC, the Epi-A subtype exhibits low epithelial-mesenchymal transition (EMT) and better survival, while the Mes subtype displays high EMT and worse survival. However, the mechanisms governing the conversion between these subtypes remain poorly understood. In this study, we investigated whether alternative enhancer usage could be the driving force behind this interconversion. We focused on the circadian gene Period 2 (PER2), which was found to be significantly associated with better disease-free and overall survival in the Epi-A patient subgroup. Analyzing chromatin states using ChIP-seq data of five histone marks, we observed distinct enhancer usage at the PER2 locus in OC cells of the Epi-A and Mes subtypes. Specifically, three enhancer regions were preferentially utilized by Epi-A cells (PEO1 and OVCA429) but not by Mes cells (SKOV3 and HeyA8). To elucidate the role of these enhancer regions, we generated CRISPR/Cas9-mediated deletion clones targeting individual candidate enhancer regions (A, B, C) of PER2 in OVCA429 cells. The OVCA429_PER2_B and OVCA429_PER2_C clones exhibited a spindly mesenchymal morphology, contrasting with the cobblestone epithelial morphology in the parental OVCA429 and OVCA429_PER2_A clones. Additionally, the OVCA429_PER2_B and OVCA429_PER2_C clones displayed altered expression of EMT markers, such as E-cadherin, vimentin, and GRHL2. Importantly, deletion of enhancer regions B and C reduced the basal expression of PER2, indicating that these enhancer regions are primed for PER2 transcription enhancement, and their loss could drive EMT. Further analysis using Hi-C revealed significantly varied DNA looping frequencies at the PER2 locus in OC cells with different GEMS. Notably, Epi-A OC cells (PEO1) exhibited high interaction frequencies surrounding the PER2 gene, particularly at the intronic enhancer regions corresponding to enhancer regions A, B, and C, compared to the Mes subtype cell line HEY-A8. In conclusion, our findings support the notion that alternative enhancer usage can regulate PER2 transcription, leading to EMT and subtype conversion in the Epi-A subtype of OC cells. Understanding these mechanisms may offer new insights into the development of targeted therapeutic strategies for ovarian cancer patients.
Citation Format: Yi Chia Chiu, Qing You Pang, Yu Jie Chen, Tuan Zea Tan, Divya Malathy Ravinath, Wendy Hwang-Verslues, Ruby Yun Ju Huang. Alternative PER2 (Period2) enhancer usage drives epithelial-mesenchymal transition (EMT) in epithelial ovarian cancer (OC) [abstract]. In: Proceedings of the AACR Special Conference on Ovarian Cancer; 2023 Oct 5-7; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(5 Suppl_2):Abstract nr B008.