ZBTB7B modulates the androgen receptor as an upstream regulator via colocalization and direct binding in LNCaP prostate cancer cells.

[BACKGROUND] Though ZBTB7B is overexpressed in breast and prostate cancers and dysregulates CD8 T cell response, there is no report on the close relationship between ZBTB7B and androgen receptor (AR) yet. This study aimed to investigate the molecular interaction between ZBTB7B and AR and to determine its role in prostate cancer progression.

[METHODS] Prostate cancer cell lines (AR-dependent LNCaP and AR-independent DU145) were subjected to 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, clonogenic assay, and cell cycle analysis. Protein-protein interaction was examined using immunoprecipitation and immunofluorescence. Protein stability was assessed by cycloheximide chase and ubiquitination assays. RNA interference was employed to deplete ZBTB7B or AR, and tissue expression patterns were analyzed by The Cancer Genome Atlas (TCGA) and human tissue microarray.

[RESULTS] ZBTB7B was overexpressed in prostate cancer cells and tissues with poor prognosis by human tissue microarray and TCGA analysis. However, ZBTB7B depletion suppressed viability, the number of colonies and increased G1 arrest in AR dependent LNCaP cells, but not in AR independent DU145 cells. Interestingly, ZBTB7B depletion suppressed the expression of AR and prostate specific antigen (PSA) in LNCaP cells, while AR depletion did not affect ZBTB7B. Furthermore, AR inhibitor finasteride and AR activator dihydrotestosterone (DHT) did not affect ZBTB7B. However, ZBTB7B was colocalized with AR by immunofluorescence and was bound to AR by immunoprecipitation. Consistently, ZBTB7B depletion attenuated the nuclear translocation and stability of AR through its degradation and also promoted AR degradation by ubiquitination assay. Notably, N-terminal domain (NTD) of AR is requisite for binding with ZBTB7B in HEK293 cells, not AR-DNA-binding domain (DBD) or AR-ligand-binding domain (LBD) in HEK293 cells.

[CONCLUSIONS] Overall, these findings provide a novel insight that ZBTB7B promotes prostate cancer progression as a potent oncogene via colocalization and binding with AR.