FDX1 and nonpapillary renal cell carcinoma: Importantly, FDX1 knockdown in OSRC-2 cells led to Cu2+ accumulation, whereas OSRC-2 cells exposed to the miR-21-5p inhibitor had a lower Cu2+ level than the control cells (Figure 6J), suggesting that the miR-21-5p-mediated ccRCC phenotype at least partially depends on FDX1-mediated cuproptosis.