Abstract 2445: Orchestrated expression of the atypical Rho-GTPase RHOV mediates multicellular aggregate formation in ovarian cancer
Authors: Elhaw Amal T. , Kim Yeon Soo , Javed Zaineb , Tang Priscilla , Pan Weihua , Hempel Nadine 
Published: June 2022

Abstract
Transcoelomic spread is a major mode of ovarian cancer (OVCA) metastasis, where cells disseminate into the peritoneal ascites fluid, evade anoikis, and form multi-cellular aggregates (MCAs) that mediate anchorage-independent (a-i) survival and invasion of the peritoneal organs. Isolation of MCAs from patient ascites correlates with poor patient survival and resistance to therapy. However, the mechanisms promoting anoikis evasion and OVCA MCA formation in a-i are not fully understood. Our previous data from patient ascites-derived cells, cell lines, and in vivo studies, demonstrate that OVCA cells upregulate the nutrient/stress sensor SIRT3 in response to a-i. We further illustrated that SIRT3 is necessary for the activation of the primary mitochondrial dismutase, SOD2, which in turn promotes the mitochondrial antioxidant defense to maintain optimal survival in a-i. To identify additional key molecular players important for a-i survival downstream of SIRT3, we employed RNA sequencing analysis to compare the transcriptome of SIRT3 knockdown and wildtype cells in both attached and a-i conditions using the serous adenocarcinoma cell line OVCA433. Analysis of early transcriptomic changes, observed within 2 hrs as well as 24 hrs of a-i, revealed that RHOV, a recently identified atypical member of the Rho GTPase family, is the top gene significantly upregulated in a-i. SIRT3 knock-down significantly decreases RHOV expression in 24hr a-i conditions, implicating RHOV as a potential downstream target of SIRT3 signaling in a-i. RHOV was reported to be overexpressed in lung cancer and found to correlate with poor patient outcome and resistance to therapy. RHOV expression also regulates intercellular adhesion dynamics during development. Our data show that genetic silencing of RHOV expression interferes with the ability of OVCA cells to form MCAs in a-i, suggesting that increased expression of RHOV in a-i conditions acts as an adaptive survival advantage mediating cell-cell adhesion and MCA formation. Current work is exploring how RHOV regulates E-cadherin in this context, by focusing on p21-stimulated serine/threonine protein kinase signaling. In addition, the mechanisms of SIRT3 dependent regulation are being explored by determining how changes in mitochondrial protein deacetylation contribute to RHOV transcription. This work highlights an expanding role of SIRT3 in mediating a-i survival of OVCA and explores the novel role of an understudied member of the Rho family of GTPases, RHOV during OVCA metastasis. Finally, given that the formation of MCAs has been correlated with resistance to therapy and increased rates of recurrence, we aim to test how MCA formation and targeting of key players of cell-cell adhesion in a-i, such as a RHOV, can be exploited for novel therapeutic strategies to prolong survival of OVCA patients diagnosed with metastatic disease.
Citation Format: Amal T. Elhaw, Yeon Soo Kim, Zaineb Javed, Priscilla Tang, Weihua Pan, Nadine Hempel. Orchestrated expression of the atypical Rho-GTPase RHOV mediates multicellular aggregate formation in ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2445.