Expression study of estrogen receptor-related receptors and steroid hormone receptors in human prostatic cells

Estrogen receptor-related receptors (ERRs) are closely related to the estrogen receptors (ERs) in their protein structures and consist of 3 closely related isofomis: ERRalpha ERRbeta and ERRgamma. However, ERRs do not bind to estrogens (Es) or any other known physiological ligands, and thus they are classified as "orphan nuclear receptors". Studies on the expression pattern of ERRs in prostatic cells and prostate is scarce. As the first step towards a better understanding of the significance of ERRs in prostate, we investigated their expression profiles in human prostatic cell lines, two primary prostatic carcinoma xenografts, and prostatic tissues by RT-PCR, immunohistochemistry, and Western blot analysis. The results of RT-PCR showed that ERRalpha transcripts were widely detected in all tested cell lines and xenografts; ERRbeta transcripts were either not detected or weakly expressed in prostatic cell lines and xenografts, while ERRgamma transcripts were moderately expressed in C4-2B and PC-3 cells, and two xenografts. Similar expression patterns were also shown in human hyperplastic and neoplastic prostatic tissues. ERRgamma immunohistochemistry showed that immunosignals were localized to the prostatic epithelial cells. We also compared mRNA expression of ERRs with that of ERs in prostatic cell lines. The results showed that ERRs and ERs were co-expressed in most cell lines and xenografts. Based on these observations, we speculate that the two members of nuclear receptor subfamily, ERRs and ERs, may control overlapping regulatory pathways in the prostatic cells.