Background: We sought to identify and characterize potential alterations in E2F-1, a transcription factor that binds to the retinoblastoma protein (pRB), in bladder neoplasms and to elucidate a possible role for E2F-1 as an oncogene or a tumor suppressor gene.
Methods: Tumor samples from 133 evaluable patients with bladder cancer were analyzed for E2F-1 gene mutations by use of polymerase chain reaction-single-strand conformational polymorphism (PCR-SSCP) analysis and DNA sequencing. In addition, tumors were studied for E2F-1 and pRB protein expression by use of immunohistochemistry. Results from the above analyses were correlated with clinicopathologic parameters and outcome. All P values are two-sided.
Results: A polymorphism, consisting of a nucleotide change at amino acid codon 393 in exon 7 (GGC-->AGC [Gly-->Ser]), was identified in seven of 133 case patients, being present in both tumor and corresponding normal tissues. No bandshifts were identified in the nuclear-localization or DNA-binding domains on PCR-SSCP analysis. On immunohistochemical analysis, E2F-1 nuclear reactivity was observed in less than 5% of the cells from 53 tumors and in 5%-75% of the cells from the remaining 80 tumors. The pattern of E2F-1 protein expression was not altered in relation to the identified polymorphism. pRB nuclear reactivity greater than 20% (of tumor cells stained) was present in 66% of the samples. E2F-1 nuclear reactivity correlated inversely with the percentage of cells showing pRB reactivity (Kendall tau(b) = -0.18; P = .019). On multivariate analysis, patients with lower E2F-1 reactivity had statistically significantly increased risks of progression to metastases (P = .001) and death (P = .02).
Conclusions: E2F-1 alterations occur at the phenotypic level, rather than at the genotypic level, in bladder cancer. The adverse outcome for patients whose tumors exhibit low E2F-1 nuclear expression suggests a possible tumor suppressor role for E2F-1 in bladder cancer.