Nuclear factor I/B increases in prostate cancer to support androgen receptor activation

Most prostate cancers express androgen receptor (AR), and our previous studies have focused on identifying transcription factors that interact with and modify AR function. We have shown that transcription factor nuclear factor I/B (NFIB) regulates androgen receptor (AR) activity and that its expression is decreased in the luminal cells of severe benign prostatic hyperplasia. To assess whether changes in NFIB expression are associated with prostate cancer progression, we immunostained a tissue microarray including normal, hyperplastic, prostatic intraepithelial neoplasia, primary prostatic adenocarcinoma, and castration-resistant prostate cancer tissue samples for NFIB, AR, and synaptophysin, a marker of neuroendocrine differentiation. We observed increased NFIB in the nucleus and cytoplasm of prostate cancer samples independent of Gleason score. We also observed strong NFIB staining in primary small cell prostate cancer. While increased NFIB nuclear and cytoplasmic staining were not predictive of biochemical recurrence, the ratio of cytoplasmic-to-nuclear NFIB staining was predictive of earlier biochemical recurrence once the analysis was adjusted for tumor margin status. We next assessed expression of NFIB in prostate cancer cell lines and detected several isoforms (62 kDa, 57 kDa, 49 kDa, and 39 kDa). Using nuclear and cytoplasmic fractionation, we observed NFIB predominantly in the nuclear fraction of prostate cancer cells with increased cytoplasmic expression seen in castration-resistant prostate cancer cell lines. Through transient transfection of AR and NFIB into the AR and NFIB low JEG-3 cells, followed by co-immunoprecipitation, we also observed a physical interaction between AR and NFIB. In order to understand the consequences of NFIB over-expression in prostate cancer, we generated vector or 3X-FLAG-NFIB-expressing androgen-dependent LNCaP and castration-resistant C4-2B cells (a LNCaP derivative cell line). While over-expression of NFIB did not increase AR expression, it did increase prostate specific antigen (PSA) production and PSA promoter activity. In summary, we have described the expression pattern of NFIB in prostate cancer and propose that one consequence of NFIB over-expression in AR-dependent prostate cancers is increased AR activity as measured by PSA induction.