Downregulation of Mg ²⁺ Efflux Protein CNNM3 Predicts Poor Prognosis but Enhances Ferroptosis Sensitivity in Kidney Renal Clear Cell Carcinoma via NCOA4‐Mediated Ferritinophagy

The kidneys play a pivotal role in the reabsorption of Mg²⁺ within the human body. However, the precise functions of Mg²⁺ and its transporters in the context of kidney renal clear cell carcinoma (KIRC) remain limited. In an effort to address this, we have employed bioinformatics analysis of the TCGA database to devise a novel scoring system, termed the Mg²⁺ score, which we have used to establish a diagnosis and prognostication framework for KIRC. This score is predicated on the expression levels of nine Mg²⁺ transporters. It was established that low expression of Mg²⁺ transporters, including TRPM7, SLC41A1, MRS2, MAGT1, CNNM2, CNNM3, and CNNM4, is linked to a poor prognosis in KIRC. We observed that the expression levels of TRPM7, SLC41A1, MRS2, MAGT1, CNNM2, and CNNM3 were significantly reduced in advanced-stage KIRC patients compared to those in early-stage patients. CNNM3 knockdown promoted the proliferation and migration of KIRC cells in vitro, and interestingly, this effect was accompanied by an increase in both intracellular free Mg²⁺ and Fe²⁺. Exogenous Mg²⁺ supplementation has been shown to further sensitize KIRC cells to ferroptosis, under both basal conditions and in the presence of CNNM3 knockdown, with a significant enhancement of lipid peroxidation and ferroptosis being observed. At the subcellular level, CNNM3 knockdown has been shown to exacerbate RSL3-induced mitochondrial damage and mitochondrial ROS production. The study thus identifies a potential "Mg²⁺-Fe²⁺" homeostatic mechanism in KIRC cells, with CNNM3 serving as a critical regulatory component. The findings of the present study offer a new direction for further research, with the potential to develop novel and effective therapeutic strategies for KIRC patients exhibiting CNNM3 low expression and unfavorable clinical outcomes. The therapeutic targeting of ferroptosis may present a viable treatment approach for patients with KIRC who exhibit low CNNM3 expression and poor clinical outcomes.