NUSAP1 Drives Endometrial Carcinoma via IP3R Phosphorylation, Calcium Dyshomeostasis, and ER-Stress-Mediated Apoptosis

Nucleolar and spindle-associated protein 1 (NUSAP1), a mitotic regulator critical for cancer cell cycle progression, remains poorly characterized in endometrial carcinoma (EC). Here, we integrated bioinformatics analysis with functional assays, including flow cytometry, Transwell invasion, ER stress imaging (ER fluorescence probe), intracellular Ca²⁺ measurement (Fluo-4 AM), and Western blotting, to dissect the role of NUSAP1 role in EC. NUSAP1 was significantly overexpressed in EC tissues compared to normal controls. Strikingly, we identified a functional interaction between NUSAP1 and the inositol 1,4,5-trisphosphate receptor (IP3R), a key ER calcium release channel. Knocking down NUSAP1 suppressed EC cell proliferation and invasion while inducing mitophagy and apoptosis. These effects were accompanied by elevated cytosolic Ca²⁺ levels, exacerbated ER stress, and increased phosphorylated IP3R (p-IP3R). Conversely, NUSAP1 overexpression reciprocally attenuated these phenotypes. IP3R silencing alone reduced intracellular Ca²⁺ and ER stress without altering NUSAP1 expression, whereas NUSAP1 overexpression combined IP3R knockdown synergistically amplified these effects. Mechanistically, NUSAP1 governs IP3R phosphorylation to regulate Ca²⁺ homeostasis, ER stress, and mitophagy, thereby modulating apoptotic signaling in EC. Our study unveils the NUSAP1-IP3R axis as a central driver of EC progression, offering novel therapeutic targets for calcium-dependent oncogenic pathways.