However, the mRNA levels of occludin (OCLN), tight junction protein 1/zonula occludens-1 (TJP1/ZO-1), connexin 43 (GJA1), connexin 26 (GJB2), and cytokeratin 18 (KRT18) were significantly increased in CF vs control tissue. Here, TJP1 is linked to cystic fibrosis.