c-FLIP expression in bladder urothelial carcinomas: its role in resistance to Fas-mediated apoptosis and clinicopathologic correlations.

OBJECTIVES

To investigate the incidence of Fas (exon 9) mutations and the expression of Fas, Fas-Fas ligand (FasL) system, and cellular FLICE-like inhibitory protein (c-FLIP) in relation to standard clinicopathologic parameters and patient outcome in bladder carcinoma. Disruption of apoptotic cell death has been implicated in tumor aggressiveness in bladder urothelial carcinomas. The FasL system is involved in the execution of apoptosis induced by the immune system. c-FLIP protein constitutes an important endogenous inhibitor of Fas and other death receptor-mediated apoptosis.

METHODS

The expression of Fas, FasL, and c-FLIP was quantified immunohistochemically in paraffin-embedded tissues from 53 patients for whom clinical information was available. DNA extracted from the same samples was screened for mutations in Fas exon 9 by single-strand conformation polymorphism and sequencing. The effect of Fas, FasL, and c-FLIP on clinical outcome was assessed by univariate and multivariate analyses.

RESULTS

Positive immunostaining was detected for Fas, FasL, and c-FLIP in 72%, 66%, and 81% of cases, respectively. Concurrent expression of Fas and FasL was seen in 27 samples (51%), of which 22 (81.5%) also displayed c-FLIP positivity. FasL and c-FLIP expression increased with advancing stage but was absent from normal urothelium. None of the 53 urothelial carcinoma samples analyzed showed evidence of mutations by polymerase chain reaction single-strand conformation polymorphism and direct sequencing. Survival analysis demonstrated that although both FasL and c-FLIP expression adversely affected survival, only c-FLIP remained statistically significant on multivariate analysis.

CONCLUSIONS

The frequent expression and coexpression of Fas, FasL, and c-FLIP in urothelial carcinomas implicates c-FLIP as an inhibitor of the Fas-FasL-induced death pathway in these tumors. Moreover, c-FLIP conveys independent prognostic information in the presence of classical prognosticators.