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 prost ate-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 cel ls, Transcription of PSA is initiated when ligand-activated androgen r eceptor (AR) binds to a region in the PSA promoter that contains an an drogen-responsive element (ARE), It was found that TPA inhibited andro gen-induced PSA gene expression by a mechanism that did not alter nucl ear levels of AR protein, Overexpression of AP-1 (jun and fos proteins ) also inhibited androgen-induced PSA promoter activity, These observa tions 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 c onversely that AR-glutathione S-transferase proteins inhibited the for mation of c-Jun TPA-responsive element (TRE) complexes, Consistent wit h the inhibitory effect of both proteins, anti-c-Jun antibody blocked the inhibition of AR.ARE complex formation by c-Jun, A similar, but le ss marked, effect was obtained when anti-AR antibody was used to preve nt AR inhibition of c-Jun TRE complex formation, These findings togeth er with results obtained from co-immunoprecipitation experiments stron gly suggest that mutual repression of DNA binding activity is due to d irect interaction between the two proteins and that the degree of repr ession 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 n uclear receptors in its ability to interact with AP-1, This associatio n 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 .