Expression and Functional Study of Estrogen Receptor-Related Receptors in Human Prostatic Cells and Tissues

Abstract

Estrogen receptor-related receptors (ERRs; alpha, beta, gamma) are orphan nuclear receptors and constitutively active without binding to estrogen. Like estrogen receptors (ERs), ERRs bind to estrogen receptor elements and estrogen receptor element-related repeats. Growing evidence suggests that ERRs can cross-talk with ERs in different cell types via competition for DNA sites and coactivators. We hypothesize that ERRs might play regulatory roles in normal and neoplastic prostatic cells by sharing similar ER-mediated pathways or acting independently. In this study, we investigated mRNA and protein expression patterns of three ERR members in normal human prostate epithelial cells, established cell lines, cancer xenografts, and prostatic tissues. Additionally, effects of transient transfection of ERRs on prostatic cell proliferation and ER expression were also examined. RT-PCR showed that ERRalpha and ERRgamma transcripts were detected in most cell lines and xenografts, whereas ERRbeta was detected in normal epithelial cells and few immortalized cell lines but not in most cancer lines. Similar results were demonstrated in clinical prostatic specimens. Western blottings and immunohistochemistry confirmed similar expression patterns that ERR proteins were detected as nuclear proteins in epithelial cells, whereas their expressions became reduced or undetected in neoplastic prostatic cells. Transient transfection confirmed that ERRs were expressed in prostatic cells as nuclear proteins and transcriptionally active in the absence of estradiol. Transfection results showed that overexpression of ERRs inhibited cell proliferation and repressed ERalpha transcription in PC-3 cells. Our study shows that ERRs, which are coexpressed with ERs in prostatic cells, could regulate cell growth and modulate ER-mediated pathways via interference on ERalpha transcription in prostatic cells.

Orphan nuclear receptor estrogen-related receptor-β suppresses in vitro and in vivo growth of prostate cancer cells via p21WAF1/CIP1 induction and as a potential therapeutic target in prostate cancer

“…We demonstrated previously that members of ERRs and ERs are co-expressed in normal prostatic epithelial cells and exhibit differential expression patterns in neoplastic prostatic tissues (Cheung et al, 2005), suggesting that the ligand-independent ERRs and ligand-dependent ERs may co-regulate the growth and functions of prostatic cells. Among ERRs, ERRb and ERRg, which are closely related in their structures, display an apparent downregulation pattern in prostate cancer cells and lesions.…”

“…The cell lines were obtained from ATCC (American Type Culture Collection), ECACC (European Collection of Animal Cell Cultures) and other investigators and cultured in conditions as described previously (Cheung et al, 2005).…”

“…We previously reported that ERRb exhibits a downregulation pattern in many prostate cancer cell lines and prostatic neoplastic lesions (Cheung et al, 2005). In this study, we analysed the expression profile of three splice variants of ERRb, as identified by Zhou et al (2006), in a panel of immortalized non-transformed prostatic epithelial cell and cancer lines.…”

“…Immunohistochemistry of ERRb was performed on archival paraffin blocks of formalin-fixed fetal, pubertal, neoplastic human prostates using an enhanced immunoperoxidase procedure (Chan et al, 1999;Cheung et al, 2005). All human tissues were obtained with informed consent and approval from the Clinical Research Ethics Committee, CUHK.…”

“…Total cellular or nuclear proteins, extracted from 70% confluence cultured cells, were separated by sodium dodecyl sulfate-PAGE and transblotted onto polyvinylidene difluoride membranes (Cheung et al, 2005). Transblotted membranes were probed with primary antibodies followed by a colorimetric method for immunosignal detection.…”