Water Channel Protein Subtype Suggests the Origin of Renal Cell Carcinoma

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Abstract
Several subtypes of water selective channel protein have been cloned. In normal kidneys, CHIP-28 (channel forming integral protein of 28 kd) is expressed solely in the proximal tubules and descending thin limbs, and aquaporin-CD (AQP-CD) expression is restricted to collecting ducts. We assessed expression of these 2 distinct types of water channels in renal cancer tissues. Expression of CHIP-28 and AQP-CD was examined in 12 samples of primary renal cell carcinoma by Northern blot, reverse transcriptase-polymerase chain reaction and immunohistochemistry. We also evaluated expression of these 2 molecules immunohistochemically in 4 samples of Bellini duct tumor which has been though to arise from renal collecting ducts. Expression of CHIP-28 was detected in all of the samples of primary renal cell carcinoma, whereas none of them expressed AQP-CD. None of 4 samples ofBellini duct tumor expressed CHIP-28, although expression of AQP-CD was recognized in 2. Our current observation confirms the idea of the proximal or descending tubule origin of renal cell carcinoma.