The interaction between <scp>NPMc</scp> + and Orai1 induces abnormal calcium influx to facilitate leukemogenesis

Nucleophosmin 1 (NPM1) is a ubiquitously expressed phosphoprotein, mainly located in the nucleolus. It is overexpressed in solid tumors and considered a key target in cancer therapy. NPM1 mutations are the most common genetic abnormalities in acute myeloid leukemia (AML), where they are found in about 30% of patients. In AML, NPM1 mutations result in the cytoplasmic localization of the mutant protein NPMc+. Although NPM1 mutations are known to drive AML, the underlying mechanisms are not fully understood. In this study, we found that primary leukemia cells from NPM1-mutated AML patients exhibited elevated intracellular calcium levels compared with cells from NPM1 wild-type AML patients. Our investigation revealed that NPMc+ interacts with the calcium channel Orai1, disrupting calcium homeostasis in AML cells. Notably, we identified that the N-terminal region of NPM1 contains a calcium-binding domain that directly interacts with Orai1, facilitating calcium influx. Targeting NPMc+, Orai1, or the NPMc+/Orai1 complex using small-molecule inhibitors significantly reduced calcium influx, inhibited calcium-related signaling pathways, and suppressed the proliferation of NPM1-mutated AML cells. These findings uncover a novel mechanism in which NPMc+ interacts with Orai1, disrupting calcium homeostasis and promoting AML progression. This presents a promising therapeutic strategy targeting the NPMc+/Orai1-mediated calcium imbalance in NPM1-mutated AML.