E2F1 and nonpapillary renal cell carcinoma: To further confirm the role of E2F1 in ccRCC malignant progression, we employed E2F1 plasmid transfection technology to increase the expression of E2F1 gene in non-metastatic ccRCC cell lines 786-O and A498 with relatively low expression of E2F1 protein and RNAi knockdown of E2F1 in metastatic cell line Caki-1.