CLDN4 and breast cancer: BC treatment significantly strengthened the epithelial barrier, inducing a marked upregulation of Claudin 1 (CLDN1) (11.3 fold), CLDN4 (2.4 fold), Occludin (OCLN, 1.7 fold), and increasing key proteins including ZO-2 and cingulin while reducing LPS-induced FITC-Dextran permeability to 94.5%.