Purpose: Claudins are the main constituents of tight junctions. Little is known about their expression and localization in the normal bronchial epithelium and in lung cancer.
Patients and methods: One hundred four lung cancer tissue blocks were studied including 46 adenocarcinomas (ADC), 30 squamous cell carcinomas (SCC), 15 small cell lung cancers (SCLC), 8 typical and 5 atypical carcinoids. All slides contained normal bronchial mucosa as well. Immunohistochemistry using antibodies against claudins-1, -2, -3, -4, and -7 proteins, as well as semi-quantitative estimation were performed. RT-PCR analysis was also carried out in 22 immunohistochemically representative tumor samples.
Results: Normal bronchial epithelial cells expressed all the examined claudin proteins. When compared, SCLCs and carcinoids showed striking differences in regard to claudins-1, -3, and -4 expressions (p<0.0001, p<0.0001, and p<0.0004, respectively), whereas ADCs and SCCs revealed significant differences in claudins-3, -4, and -7 expressions (p<0.0001, p<0.0001, and p<0.0053, respectively). However, comparison of ADCs with SCLCs revealed significant difference only in claudin-2 expression (p<0.0002). The comparison of ADCs and carcinoids resulted in significant differences regarding claudins-1, -3, and -4 expressions (p<0.0006, p<0.0001, and p<0.0001, respectively). SCCs and SCLCs varied in respect to claudin-2, -3, and -4 expressions (p<0.0009, p<0.0001, and p<0.0019, respectively), whereas SCCs and carcinoids showed different claudins-1 and -4 expressions (p<0.0076 and p<0.0045, respectively). RT-PCR analysis revealed parallel changes in the mRNA and protein expression of certain claudins.
Conclusions: The observed distinct claudin expression profile within the non-small cell lung cancer group, further, the marked differences between SCLCs and carcinoids may have differential diagnostic impact, and the overexpression of certain claudins might have therapeutic implications.