Heterogeneous expression of the aquaporin 1 (AQP1) water channel in tumors of the prostate, breast, ovary, colon and lung: A study using high density multiple human tumor tissue microarrays

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Aquaporin 1 (AQP1) water channels are membrane proteins that control the permeability of endothelial and epithelial barriers by facilitating water movement across cell membranes. Recent studies suggest that AQP1 may be responsible for the high vascular permeability and interstitial fluid pressure in tumors of the brain, colon, breast and pancreas. AQP1 may also play a role in tumor angiogenesis and may be involved in development of effusions or edema fluid. The aim of the present study was to use immunohistochemistry and semi-quantitative histomorphometric analysis to compare the distribution and relative abundance of AQP1 on NCI TARP human multiple tumor tissue microarrays (TMAs) with normal tissues represented on the CHTN TMAs. Immunohistochemistry and semi-quantitative histomorphometric analysis were used to compare the distribution of AQP1 in tumors of the prostate, colon, lung, breast and ovary represented on TARP TMAs with their normal counterparts on CHTN TMAs. AQP1 was expressed in capillary endothelia of all normal tissues. In most tumors AQP1 was confined to endothelial barriers. AQP1 expression was marginally higher in microvascular structures in prostate and ovarian tumors and was higher in advanced mammary and colorectal carcinomas where AQP1 immunoreactivity was also seen in some neoplastic tumor cells. In conclusion, the AQP1 water channel is an excellent marker of microvasculature but it is heterogeneously expressed in different human tumors and not necessarily expressed in all neoplastic cells. Increased AQP1 expression in some human adenocarcinomas may be a consequence of angiogenesis and important for the formation or clearance of tumor edema.