Cell migration is a highly dynamic process that requires constant remodeling of the plasma membrane. At its core is the small Rho GTPase CDC42, which drives actin polymerization and membrane protrusion. However, as Hsieh’s group previously reported (Peng et al., Hepatology 2018), unchecked cytoskeletal remodeling can push tumor cells toward epithelial–mesenchymal transition or even cell death. Thus, elucidating how cells both activate and quench CDC42 signaling to maintain membrane homeostasis has been a central question.
In this issue of Nature Chemical Biology, Liao and colleagues describe a dual regulatory mechanism that tightly governs CDC42 activity. They identify KLHL23, a substrate adaptor for the Cul3 E3 ubiquitin ligase, as a critical factor that targets CDC42 for polyubiquitylation and proteasomal degradation. Strikingly, KLHL23 and RhoGDI—a well-known factor that stabilizes GDP-bound CDC42 in an inactive pool—compete for binding to the switch II domain of CDC42. This competitive binding underlies their specificity: KLHL23 selectively targets GTP-bound CDC42 for degradation, while RhoGDI preferentially binds GDP-bound CDC42, sequestering it to prevent premature reactivation.
These complementary mechanisms provide precise spatiotemporal control of CDC42 dynamics. KLHL23 eliminates active CDC42 once its signaling role is complete, whereas RhoGDI safeguards the inactive pool for future use. This cooperation ensures balanced cycles of activation and inactivation, maintaining proper membrane dynamics. The clinical importance is underscored by two examples: loss of KLHL23, which promotes EMT or necrosis in tumor cells, and the CDC42-Y64C mutation, which evades KLHL23-mediated degradation and underlies Takenouchi–Kosaki syndrome, a developmental disorder affecting the brain, bone, and hematopoietic system.
Together, these findings highlight the principle of “rein in or ruin”: just as CDC42 activation is indispensable for migration, its timely inactivation is equally essential to prevent pathological outcomes. By establishing KLHL23 as a novel E3 ligase acting in concert with RhoGDI, this work broadens the regulatory landscape of Rho GTPases and opens new avenues for understanding both cancer progression and developmental disease.
Liao, PC., Chang, HC., Liu, YC. et al. KLHL23 and RhoGDI coordinate CDC42 inactivation ensuring membrane homeostasis. Nat Chem Biol (2025). https://doi.org/10.1038/s41589-025-02010-2
Peng JM, Bera R, Chiou CY, Yu MC, Chen TC, Chen CW, Wang TR, Chiang WL, Chai SP, Wei Y, Wang H, Hung MC, Hsieh SY. Actin cytoskeleton remodeling drives epithelial-mesenchymal transition for hepatoma invasion and metastasis in mice. Hepatology. 2018 Jun;67(6):2226-2243. doi: 10.1002/hep.29678.