Csnk1a1 E98 mutations rewire signaling and metabolism in del(5q) myelodysplastic neoplasms.

Deletion of chromosome 5q [del(5q)] is the most common cytogenetic abnormality in myelodysplastic neoplasms (MDS) and results in haploinsufficiency of multiple genes, including CSNK1A1. Recurrent CSNK1A1 mutations, predominantly affecting the E98 hotspot, occur almost exclusively in del(5q) MDS and are associated with adverse outcomes, yet their impact on CK1ɑ function remains unclear. Using integrated transcriptomic, (phospho)proteomic, and kinome activity profiling in hematopoietic stem and progenitor cells (HSPCs), combined with in vivo serial transplantation assays, we show that Csnk1a1 E98V represents a change-of-function rather than a loss-of-function mutation. Unlike Csnk1a1 haploinsufficiency, Csnk1a1 E98V preserves long-term hematopoietic reconstitution and does not enhance clonal expansion in vivo. Instead, the mutation induces suppression of kinase signaling networks, leading to coordinated repression of ribosomal gene expression, protein translation, and cell cycle programs. This signaling rewiring is accompanied by metabolic reprogramming characterized by reduced mitochondrial respiration, increased glycolytic flux, and an inability to adapt to metabolic challenges, creating a stress-tolerant but inflexible cellular state. Notably, Csnk1a1 E98V cells exhibit impaired megakaryopoiesis and increased vulnerability to iron overload, as well as RSL-3-mediated ferroptosis. Analysis of del(5q) MDS patients confirmed that CSNK1A1 mutations are associated with distinct clinical features, including thrombocytopenia, elevated myeloblasts, and reduced bone marrow iron levels. Together, our findings support a two-step model in which del(5q)-associated CSNK1A1 haploinsufficiency drives clonal expansion, followed by acquisition of CSNK1A1 mutations that promote stress tolerance rather than increased proliferation. This adaptive rewiring exposes metabolic and iron-dependent vulnerabilities that may be therapeutically exploited.