The movement of water across cell membrane is essential to life. Recent investigations have demonstrated that aquaporins (AQPs), a family of water channels, are essential for maintaining the transmembrane water transport. Among at least 11 AQPs identified in mammalian tissues, AQP1, AQP3, AQP4, and AQP5 have been recognized in the lung, however, their expression and functions in the normal and diseased human lungs are poorly understood. In this study, we aimed to investigate the expression of AQPs in the human lung cancer tissue. We examined expression of AQP1, AQP3, and AQP5 by immunohistochemical staining and real-time PCR.
A total 48 fresh frozen lung tissue samples including 45 lung cancer samples (27 adenocarcinomas, 10 squamous cell carcinomas, 4 large cell carcinomas, and 4 small cell carcinomas) and 3 normal lung tissue samples were studied. Expression of AQP1, AQP3, and AQP5 were examined by immunohistochemical staining with polyclonal antibodies against AQP1, AQP3, and AQP5. Their mRNA was extracted following laser-captured microdissection, and real-time PCR was used for quantitative analyses of mRNA expression of AQP1, AQP3, and AQP5.
AQP3 was well expressed in non-mucinous bronchioloalveolar carcinoma (BAC) and well-differentiated adenocarcinoma, however, AQP3 was poorly expressed in mucionus BAC. In contrast, AQP5 was poorly expressed in non-mucinous BACs, however, AQP5 was well expressed in mucious BAC. In mucinous BAC and well-differentiated adenocarcinoma, AQP1 was well expressed in 50% of the cases. The real-time PCR study confirmed the results of immunohistochemical staining.
Our results indicate that AQP1, AQP3, and AQP5 are differentially expressed in the human lung cancer tissue. The results were confirmed by both immunohitochemical staining and real-time PCR. Furthermore, the expression patterns of AQPs are found to be associated with pathohistological characteristics.
We speculate that the distinct expression patterns of AQPs are associated with cancer-related genes. Therefore, expression patterns of AQPs may be used not only for markers of the lung cancer, but also for the therapeutic targets.
Makoto Sugita, None.