ELEVATED CONCENTRATIONS OF GAMMA-ENOLASE IN RENAL-CELL TUMORS IN RATS- SIMILARITY TO RENAL-CELL CARCINOMA IN MAN

Concentrations of enolase isozymes in normal kidney and renal cell tum ors in rats were determined using a highly sensitive enzyme immunoassa y, and the isozymes were immunohistochemically localized in tissue sec tions. Levels of alpha-enolase in renal cell tumors were significantly lower than in normal kidney, whereas those of gamma-enolase were sign ificantly elevated (mean +/- SD: 211 +/- 129 ng/mg protein, n = 15, as compared to 27.1 +/- 2.9 ng/mg protein, n = 7). The proportion of gam ma-enolase in the total enolases in the tumor tissues (1.6 +/- 0.5%) w as signifrcantly higher than in normal kidney (0.15 +/- 0.05%). Immuno histochemistry revealed epithelial cells of all nephron segments to be positive for the alpha-isozyme, whereas gamma-enolase staining was st rongly positive only in the loops of Henle, being faint in the distal tubules and absent in the proximal tubules. Both alpha- and gamma-enol ases demonstrated positive immunostaining in all of the seven renal ce ll tumors studied. These findings indicate that an isozyme switch from alpha- to gamma-enolase occurs during rat kidney carcinogenesis, taki ng into account the derivation from proximal tubules, consistent with the findings for renal cell carcinomas in man.