Abstract 2515: DIRAS3 suppresses ovarian cancer cell growth through the inhibition of fibronectin-mediated FAK/AKT signaling

Abstract Autophagy is a highly conserved cellular process that maintains homeostasis by degrading and recycling long-lived or misfolded proteins and damaged organelles. In addition, autophagy can protect cells from diverse types of cellular stress produced by amino acid starvation and hypoxia, providing energy to retain the function of organelles and cellular signaling pathways. In cancer, autophagy can play dual roles, inhibiting tumor cell growth and viability or sustaining cancer cells in hypoxic, nutrient poor microenvironments. DIRAS3 (ARHI), a maternally imprinted tumor suppressor gene, encodes a 26-kDa GTPase that has 60% homology to Ras and is downregulated in the majority of ovarian cancers. Re-expression of DIRAS3 inhibits growth of ovarian cancer cells, slows their motility and induces autophagy by inhibiting the PI3K/AKT/mTOR signaling pathway. Previously, we have shown that DIRAS3-induced autophagy inhibits ovarian cancer cell growth and promotes autophagic cell death in culture while inducing tumor dormancy in vivo. We have demonstrated that growth factors and extracellular membrane components including fibronectin (FN) in the tumor microenvironment can rescue ovarian cancer cells from DIRAS3-induced autophagic death in cell culture and the use of antibodies against those growth factors or their receptors can eliminate dormant autophagic ovarian cancer cells in ovarian cancer xenografts. In the current study, we explored whether FN, a ubiquitous extracellular matrix (ECM) glycoprotein also plays an important role in DIRAS3-induced tumor dormancy. We hypothesized that FN blocks DIRAS3-induced growth inhibition in ovarian cancer. We investigated the effect of FN on cultured ovarian cancer cells in the presence and absence of DIRAS3. We found that DIRAS3-induced autophagy was inhibited by FN in ovarian cancer cells, judged by decreased conversion of LC3I to LC3II on Western blots and reduced LC3 puncta detected by fluorescence staining. We also found that FN partially rescues ovarian cancer cells from DIRAS3-induced cell death in culture. Mechanistically, FN weakened the inhibitory effect of DIRAS3 on p-FAK and p-AKT, whereas addition of neutralizing antibody against integrin β1 decreased p-FAK and p-AKT. In addition, FN and FN-mediated FAK/AKT signaling is elevated in tumor xenograft tissue when compared to cancer cells in culture. Pharmacologic inhibition of FAK using defactinib, enhanced DIRAS3-induced autophagy, inducing cell death in ovarian cancer cells in the presence of FN. Together, our data demonstrate that factors such as FN, block DIRAS3-induced autophagic cell death, contributing to the survival of ovarian cancer cells. Citation Format: Janice M. Santiago-OFarrill, Jing Guo, Hailing Yang, Maggie Mao, Zhen Lu, Robert Bast. DIRAS3 suppresses ovarian cancer cell growth through the inhibition of fibronectin-mediated FAK/AKT signaling [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 2515.