A toxic palmitoylation on Cdc42 drives a severe autoinflammatory syndrome

BackgroundAutoinflammatory diseases (AID) result from dysregulation of the first lines of innate immune responses. Recently, development of high throughput genome sequencing technology led to the rapid emergence of important knowledge in the genetic field. About 20 genes have been identified so far in monogenic forms of distinct AID. However, 70-90 % of patients with AID remain without genetic diagnosis.ObjectiveWe report the identification and characterization of a mutation in the C-terminal region of the Rho GTPase Cdc42 in a patient presenting a severe autoinflammatory phenotype.MethodsWe have analyzed the consequences of the mutation on the subcellular localization of the Cdc42 protein using imaging techniques. Molecular studies were performed using proteomic and biochemical experiments to provide mechanistic bases of the observed defects. Functional assays were also conducted using flow cytometry and cytokine production measurements.ResultsWe show that mutant Cdc42 is trapped in the Golgi apparatus due to the aberrant addition of a palmitate that both enhances the interaction of mutant Cdc42 with Golgi membranes and inhibit its extraction by GDP dissociation inhibitor (GDI), thus impairing its cytosol/membrane shuttling. At the functional level, mutant Cdc42 fails to sustain actin filaments polymerization and induces an exacerbated profile of pro-inflammatory cytokine production due to increased NF-κB activation.ConclusionsOur study now provides a molecular explanation for mutations that have been identified recently in our AID patient and others in the C-terminal part of Cdc42. Mutations located in this region of Cdc42 impair the intracellular localization of Cdc42, preventing its interaction with the plasma membrane. Thus, our results definitively link mutations in the CDC42 gene to a complex immune-hemato-autoinflammatory phenotype in humans.