Elevated cyclin E level in human clear cell renal cell carcinoma: possible causes and consequences.

The expression of cyclin E gene (CCNE) in relation to the expression of its major regulatory protein, E2F1, was examined in clear cell renal cell carcinomas (ccRCC). We show that the overexpression of E2F1 is accompanied by the significant increase of the mean amounts of cyclin E mRNA, as well as of total cyclin E protein and its low molecular weight forms in cancer tissues as compared to peritumoral controls. A significant increase of the mean amount of total cyclin E was found in peritumoral tissues compared to cancer-free kidneys, suggesting that cancer cells might secrete factors having a profound influence on the metabolism of neighbouring tissues. A significant, positive correlations between E2F1 protein and total cyclin E mRNA, as well as between E2F1 protein and full length cyclin E protein were found in cancer-free kidneys and in peritumoral tissues, but not in ccRCCs. The overexpression of cyclin E positively correlated with the decreasing degree of tumor differentiation, implicating a role for cyclin E in the promotion of tumorigenesis.