Abstract 2551: CASC4 drives anoikis resistance in high grade serous ovarian cancer through recycling of EGFR

Abstract Introduction: Ovarian cancer is the deadliest gynecological malignancy, and accounts for over 150,000 deaths per year worldwide. The high grade serous ovarian cancer (HGSOC) subtype accounts for almost 60% of ovarian cancers and is the deadliest. HGSOC originates in the fimbria of the fallopian tube and disseminates through the peritoneal cavity. Survival of tumor cells in the peritoneal fluid requires cells to resist anoikis (anchorage-independent apoptosis). CRISPR/Cas9 and transcriptomic screens identified the Golgi protein CASC4 (GOLM2, H63) as a “driver” of anoikis resistance. As CASC4 is highly uncharacterized in literature, we sought to determine how CASC4 confers anoikis resistance to HGSOC cells. Methods: Mining of publicly available ovarian cancer datasets (TCGA) showed that CASC4 is associated with worse clinical outcomes, such as worse overall survival and increased resistance to platinum-based chemotherapies. For experiments, we used HGSOC cell lines PEO1, CaOV3, and OVCAR3 with shRNA-mediated CASC4 knockdowns (CASC4 KD), cultured in forced suspension. Results: Culturing cells in suspension, to recapitulate the peritoneal fluid environment in vitro, showed that CASC4 KD hampers cell proliferation and colony formation ability, and increases apoptosis. Additionally, a Reverse Phase Protein Assay (RPPA) showed that CASC4 KD results in significant changes in proteins known to be localized to the cell surface or secreted, including decreased protein levels of the receptor tyrosine kinase (RTK) Epidermal Growth Factor Receptor (EGFR), an initiator of several oncogenic signaling pathways. A paralog of CASC4, GOLM1, is known to drive hepatocellular carcinoma through various mechanisms, such as the recycling of internalized RTKs, including EGFR. Indeed, our experiments showed that CASC4 KD in ovarian cancer cells leads to decreased EGFR levels and decreased EGFR recycling. Conclusion: Knocking down CASC4 results in decreased survivability in suspension, decreased EGFR levels at the plasma membrane, and decreased recycling of EGFR. Further elucidating mechanisms of CASC4-dependent anoikis resistance could lead to the development of novel therapeutic approaches, such as inhibitory peptides, and may assist in developing newer biomarkers for predicting ovarian cancer malignancy. Citation Format: Jaidev Bapat, Lindsay W. Brubaker, Zachary L. Watson, Tomomi M. Yamamoto, Benjamin G. Bitler. CASC4 drives anoikis resistance in high grade serous ovarian cancer through recycling of EGFR [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2551.