CLDN1 and breast cancer: Earlier ChIP assays by our group identified that the Sp1 binding site on the Cldn1 promoter in SMG-C6 cells is between −284 and −84 bp [19], which aligns with binding sites found in the intestinal epithelium (−133 to −61 bp) [34] and human breast cancer epithelium (−138 to −76 bp) [35].