Abstract 192: Orchestrating CDC42 turnover to regulate membrane protrusion and tumor metastasis

Abstract F-actin cytoskeleton remodeling is essential for cell migration, organ development, and immune responses. CDC42, a factor orchestrating F-actin remodeling for membrane dynamics, switches between its inactive GDP- and active GTP-bound forms. However, the biological and clinical significance of the mechanisms regulating CDC42 protein turnover remains unclear. Here we show that KLHL23-mediated CDC42·GTP polyubiquitylation for degradation and RhoGDI-mediated CDC42·GDP sequestration away from the plasma membrane co-inactivate CDC42 in a spatiotemporal context, influencing membrane dynamics and homeostasis during migration. Via a functional genomic screen, we identified KLHL23 as a suppressor of tumor invasion. Decreased KLHL23 level was associated with tumor metastasis and poor clinical outcomes in patients with liver and pancreas cancers. KLHL23 functions as the E3 ligase responsible for CDC42 polyubiquitylation and degradation. KLHL23 shares with RhoGDI the switch II region of CDC42 for binding, enhancing selective targeting of CDC42·GTP and CDC42·GDP, respectively. KLHL23 depletion in cells leads to F-actin and membrane over-protrusion, as well as epithelial-mesenchymal transition and tumor metastasis. Fluorescence resonance energy transfer assays reveal that the KLHL23—CDC42·GTP interaction plays a primary role in quenching CDC42 activity during membrane protrusion-retraction, while the RhoGDI—CDC42·GDP interaction occurs lately. Our results demonstrate the spatiotemporal interplay between RhoGDI and KLHL23 in regulating CDC42 turnover for membrane dynamics. As KLHL23/RhoGDI—CDC42 axis dysregulation causes tumor metastasis, our findings open avenues for exploring novel therapeutics. Citation Format: Sen-Yung Hsieh. Orchestrating CDC42 turnover to regulate membrane protrusion and tumor metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 192.