Androgenic induction of prostate-specific antigen gene is repressed by protein-protein interaction between the androgen receptor and AP-1/c-Jun in the human prostate cancer cell line LNCaP.
In exploring the possible mechanisms of androgen independence of prostate-specific antigen (PSA) gene expression, we investigated the effect of elevating AP-1 by both 12-O-tetradecanoylphorbol 13-acetate (TPA) treatment and transfection of the c-Jun expression vector in LNCaP cells.  Transcription of PSA is initiated when ligand-activated androgen receptor (AR) binds to a region in the PSA promoter that contains an androgen-responsive element (ARE).  It was found that TPA inhibited androgen-induced PSA gene expression by a mechanism that did not alter nuclear levels of AR protein.  Overexpression of AP-1 (jun and fos proteins) also inhibited androgen-induced PSA promoter activity.  These observations were apparently related to the disruption of AR.ARE complexes as demonstrated by the results of electrophoretic mobility shift assays.  Specifically, c-Jun inhibited the formation of AR.ARE complexes and conversely that AR-glutathione S-transferase proteins inhibited the formation of c-Jun.TPA-responsive element (TRE) complexes.  Consistent with the inhibitory effect of both proteins, anti-c-Jun antibody blocked the inhibition of AR.ARE complex formation by c-Jun. A similar, but less marked, effect was obtained when anti-AR antibody was used to prevent AR inhibition of c-Jun.TRE complex formation.  These findings together with results obtained from co-immunoprecipitation experiments strongly suggest that mutual repression of DNA binding activity is due to direct interaction between the two proteins and that the degree of repression may be determined by the ratio of AR to c-Jun. The mechanism of repression studied in mutant analysis experiments yielded evidence of an interaction between the DNA- and ligand-binding domains of AR and the leucine zipper region of c-Jun. Thus, the AR is similar to other nuclear receptors in its ability to interact with AP-1.  This association provides a link between AP-1 and AR signal transduction pathways and may play a role in the regulation of the androgen-responsive PSA gene.