Expression of estrogen receptors-α and -β in bladder cancer cell lines and human bladder tumor tissue

BACKGROUND. Estrogen receptors (ERs) are known to mediate important physiologic responses as well as the growth of some tumors in response to estradiol stimulation. In a previous study the selective ER modulator raloxifene was shown to induce apoptosis in an ER beta-positive bladder cancer cell line. However, the expression of ER beta in human bladder cancer has not been thoroughly investigated. METHODS. ER alpha and ER beta expression in 224 bladder tumor samples was evaluated using tissue microarray and immunohistochemistry. Levels of ER alpha and ER beta protein and mRNA expression were determined in several bladder cancer cell lines using quantitative reverse-transcriptase polymerase chain reaction (RT-PCR) and Western blot analysis. The effect of estradiol and antiestrogen treatments on RT4 bladder cancer cell growth was determined by cell proliferation assays. RESULTS. Analyses revealed that only 2 human bladder cancers weakly expressed ERa. In contrast, the expression of ER beta was detected in 141 tumors (63%). ER beta was expressed in 58% of WHO Grade 1 and 2 tumors, whereas 70% of Grade 3 tumors demonstrated expression (P=.085). Importantly, although only 53% and 55% of Ta and T1 tumors demonstrated ER beta expression, 80% of T2,81% of T3, and 75% of T4 tumors showed ERA expression. The differences in ER beta expression between Ta/T1 and T2/T3/T4 tumors were found to be highly significant (P <.001). Metastatic transitional cell carcinomas had ER beta expression (80%) comparable to that of muscle invasive bladder cancers. Western blot analysis detected ER beta protein expression in each of the 5 bladder cancer cell lines tested, whereas no or very low levels of ERa were found. Quantitative RT-PCR revealed that higher levels of ER beta than ERa mRNA were present in 5637, T-24, TSU-Pr1, and TCC-Sup bladder cancer cells, whereas ER-alpha mRNA levels were greater than ER beta in RT4 cells. Treatment with 17 beta-estradiol modestly increased RT4 cell growth, whereas the antiestrogens, 4-hydroxtamoxifen, raloxifene, or ICI 182,780 inhibited the growth of RT4 cells. CONCLUSIONS. ER beta is the dominant receptor expressed in bladder cancer cell lines and in the majority of human bladder tumors. Moreover, the degree of ERA expression increases with increasing stage and grade of differentiation. Antiestrogens have an inhibitory effect on the growth of bladder cancer cells in vitro.