ARID4B and breast cancer: Since BCKDK is known for its role in regulating the catabolic flux of BCAA that localized in mitochondria, we confirmed the nuclear localization of BCKDK by performing immunofluorescence (IF) staining, and observed that the majority of the BCKDK signal co‐localized with the nuclear counterstain DAPI in various breast cancer cell lines and patient‐derived organoids (Figure 1d; Figure S1a, Supporting Information).