Abstract PO5-24-04: Fibronectin, DHPS and SLC3A2 Signaling Cooperate to Control Tumor Spheroid Growth, Subcellular eIF5A1/2 Distribution and CDK4/6 Inhibitor Resistance
Authors: Geller Cameron , Maddela Joanna , Ortiz-Soto Gabriela , Tuplano Ranel , Runa Farhana , Adamian Yvess , Güth Robert , Tomaneng Luke , Cantor Joseph , Kelber Jonathan A. 
Published: May 2024

Abstract
Extracellular matrix (ECM) protein expression/deposition within and stiffening of the breast cancer (BC) microenvironment, facilitates disease progression and correlates with poor patient survival. However, the mechanisms by which ECM components control tumorigenic behaviors and responses to therapeutic intervention remain poorly understood. Fibronectin (FN) is a major ECM protein controlling multiple processes related to cancer metastasis. In this regard, we previously reported that DHPS-dependent hypusination of eIF5A1/2 is necessary for fibronectin-mediated BC metastasis and epithelial to mesenchymal transition (EMT). Here, we explored the clinical significance of an interactome generated using hypusination pathway components and markers of intratumoral heterogeneity. Solute carrier 3A2 (SLC3A2 or CD98hc) stood out as an indicator of poor overall survival among patients with basal-like BCs that express elevated levels of DHPS. We subsequently discovered that blockade or knockdown (KD) of DHPS or SLC3A2 reduced BC spheroid growth. Interestingly, spheroids stimulated with exogenous fibronectin were less sensitive to inhibition of either DHPS or SLC3A2 – an effect that could be abrogated by dual DHPS/SLC3A2 blockade or KD. In this regard, we observed that inhibition of both SLC3A2 and DHPS reduced total and hypusinated eIF5A1/2 levels most effectively. We further discovered that a subset of BC cells responded to fibronectin by increasing cytoplasmic localization of eIF5A1/2. Notably, these fibronectin-induced subcellular localization phenotypes correlated with a G0/G1 cell cycle arrest. Fibronectin-treated BC cells responded to dual DHPS/SLC3A2 blockade by shifting eIF5A1/2 localization back to a nucleus-dominant state, suppressing proliferation and further arresting cells in the G2/M phase of the cell cycle. Finally, we observed that dual DHPS/SLC3A2 inhibition increased the sensitivity of both Rb-negative and -positive BC cells to the CDK4/6 inhibitor palbociclib. Taken together, these data identify an uncharacterized mechanism through which extracellular fibronectin controls cancer cell tumorigenicity by modulating subcellular eIF5A1/2 localization. These findings provide prognostic/therapeutic utility for targeting the cooperative DHPS/SLC3A2 signaling axis to improve BC treatment responses.
Citation Format: Cameron Geller, Joanna Maddela, Gabriela Ortiz-Soto, Ranel Tuplano, Farhana Runa, Yvess Adamian, Robert Güth, Luke Tomaneng, Joseph Cantor, Jonathan A. Kelber. Fibronectin, DHPS and SLC3A2 Signaling Cooperate to Control Tumor Spheroid Growth, Subcellular eIF5A1/2 Distribution and CDK4/6 Inhibitor Resistance [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-24-04.