Down-regulated claudin-7 immunoexpression in urothelial carcinoma of the urinary bladder

To analyse the gene-expression level of claudin-7 in urothelial carcinoma (UC) of the urinary bladder, and its relationship with clinicopathological variables.

This study included 68 specimens of UC of the bladder, comprising 35 with non-muscle-invasive (NMI), stage Ta-T1, and 33 with muscle-invasive (MI) tumours, T2-T4, and 26 of normal urothelium (NU). Total RNA was extracted and 1 μg was reverse transcribed using a cDNA kit. RT-PCR was conducted using SYBR Green I dye to examine the expression levels of the target gene (claudin-7) and the housekeeping gene glyceraldehyde-3-phosphate dehydrogenase. Using confocal-laser scanning light microscopy, immunohistochemistry (IHC) was used to validate the RT-PCR data. The correlation between claudin-7 and the clinicopathological variables was assessed.

Claudin-7 was down-regulated in UC samples compared to NU samples (P < 0.001). NMI (Ta-T1) tumours had significantly higher claudin-7 expression than MI (⩾pT2) tumours (P = 0.012). There was no significant difference between patients with G1-2 tumours and those with G3 tumours (P = 0.19). There was no significant difference between patients with recurrent NMI UC and those with no recurrence (P = 0.61). IHC showed a lower expression of claudin-7 in the UC samples than NU samples, and in MI UC than in NMI UC.

These results indicate that a reduced expression of claudin-7 correlates with the invasiveness and progression of UC of the urinary bladder. Further studies are needed to validate claudin-7 as a marker for UC.