Wiskott-Aldrich Syndrome Protein Regulates Nuclear Organization, Alternative Splicing and Cell Proliferation

Wiskott-Aldrich syndrome (WAS), caused by mutations in the WASP protein, displaysimmunological dysfunctions and predisposition to cancer. Despite studies in cell linesand mouse models the molecular mechanisms of WAS remain obscure. We generatedinduced pluripotent stem cells (iPSCs) from patients with WAS (WAS-iPSCs) andisogenic gene-corrected iPSCs by genome editing. Immune cells derived from WASiPSCs,genetically engineered B lymphoblastoid cell lines, and patient primarylymphocytes were subjected to imaging, proteomic and transcriptomic analyses. TheWAS-iPSC model not only recapitulated known disease phenotypes but also revealed,for the first time, roles of WASP in the organization of the nucleolus and nuclearspeckles and PML nuclear bodies. WASP interacts with components of the nucleolusand nuclear speckles, including chromatin modifiers and splicing factors. Innate andadaptive immune cells from WAS patients display global dysregulation of cell cycleregulation and alternative splicing. WASP mutation is sufficient to drive an acceleratedcell cycle and tumor-promoting splicing changes. Our data show that WASP acts as atumor suppressor and specific WASP mutants behave as oncogenes and cause cellintrinsicalterations that predispose patients to cancer.