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.