Reduced expression of beta-subunit of Na,K-ATPase in human clear-cell renal cell carcinoma

Purpose: Multiple subtypes of renal cancer have been identified. Clear-cell renal cell carcinoma (RCC) is the most common subtype of RCC and one of th e more aggressive. The goal of this study was to investigate in RCC the lev els of Na,K-ATPase, an abundant enzyme in the kidney which is crucial for v arious kidney functions. Na,K-ATPase is a heterodimer consisting of a catal ytic alpha-subunit and a glycosylated beta-subunit whose function is still not well-defined. Materials and Methods: Fourteen clear-cell RCC specimens were studied. The levels of the Na,K-ATPase alpha and beta-subunits in normal kidney and RCC tissues were determined by immunoblot analysis. The localization of the alp ha and beta-subunits was studied by immunofluorescence and laser scanning c onfocal microscopy. Na,K-ATPase activity was determined using a coupled-enz yme spectrophotometric assay. Results: In normal kidney, the cells demonstrate an epithelial morphology w ith distinct basolateral plasma membrane localization of the alpha and beta -subunits. Conversely, the cells of the clear-cell RCC have lost their epit helial phenotype and the alpha and beta-subunits show a diffuse intracellul ar staining. Clear-cell RCC tumor cell lysates showed a consistent 95.6 +/- 2.8% (mean +/- SD) reduction in protein levels of beta-subunit relative to the levels in normal kidney. The alpha-subunit level in RCC lysates was ge nerally near or above the levels relative to normal kidney. The reduced bet a-subunit expression was accompanied by a significant reduction in the Na,K -ATPase activity in RCC membranes. Conclusions: These results suggest that the beta-subunit may regulate the N a,K-ATPase activity in vivo. Diminished Na,K-ATPase activity in conjunction with the reduced beta-subunit level is associated with the clear-cell RCC phenotype.