CLDN15 and colorectal carcinoma: At the mRNA level, CLDN1, CLDN2, CLDN12, and CLDN14 were upregulated whereas CLDN3, CLDN5, CLDN7, CLDN8, CLDN11, CLDN15, and CLDN23 were downregulated (FC > 1.5) in patients with CRC (Figure 1).