Table 1.
Claudin (CLDN) protein functions, clinical significance, and the associated signaling.
| Claudin type | Main functions and clinical significance in PCa | Signaling molecules involved | Citatio-ns |
|---|---|---|---|
| claudin-1 | • normal expression maintains the normal function of cells • decreased expression promotes tumor cell invasion and metastasis |
• ZEB1-regulated overexpression of ZIP4 reduces the expression of ZO-1 and claudin-1, leading to the phosphorylation of FAK and Paxillin, thus promoting PCa invasion and migration • 5-HT1B, 5-HT1D, and eEF2K/MAPK-Erk pathway |
(28–33) |
| claudin-2 | • decreased expression with an increase in tumor histological grade • decreased expression in exocrine adenocarcinoma, cystic myxoma, and acinar cell carcinoma |
• miR-222-3p and YAP | (33–36) |
| claudin-4 | • differentially expressed in PCa • effective inhibitor of the invasive and metastatic phenotype of PCa cells |
• Ras/Raf/Erk pathway • TGF-β and DEC1 siRNA |
(37–39) |
| claudin-5 | • maintains cell polarity and cell barrier • vascular endothelium, lymphatic vessels, and tumor interstitial blood vessel |
• CD99 | (40–42) |
| claudin-6 | • expression in embryonic stem cells • no expression in normal adult tissues • promotes chemotherapy resistance of MCF-7 cells |
• regulates GSTP1 • promotes the chemotherapy resistance of MCF-7 cells via p53 |
(14, 43–46) |
| claudin-7 | • decrease in expression is parallel to the degree of tumor differentiation • expressed in rapidly proliferating and dominant human PCa cell populations • promotes tumorigenicity, accelerates tumor growth, and migration, and enhances drug resistance |
• CIC-TEX • EpCAM-CLDN-7 complex |
(47–49) |
| claudin-11 | • expression is inhibited in the occurrence of nerve invasion • Increased expression inhibits development of GC |
• MALAT • inhibition of miR-135b with lncRNA PCAT18, promotes the expression of claudin-11 |
(26, 50, 51) |
| claudin-12 | • poor prognostic factor | • SRSF1, LINC00857, and ZNF460 | (52, 53) |
| claudin-18 | • no specific staining detected in the normal pancreatic tissue, which was abnormally activated during the malignant transformation of pancreatic cells | • PKCd, PKCe, and PKCa • TPA and T/EBP/NKX2.1 • therapeutic target of Claudiximab (Zolbetuximab) |
(54–57) |
| claudin-23 | • induced isolation of weakly invasive and migratory PCa cells (PC-1) | • addition of a dissociation factor conditioned medium significantly reduced the expression of claudin-23 mRNA and protein in PC-1 cells | (7, 58) |
ZEB1, zinc finger E-box binding homeobox 1.