Androgens are essential for the growth and differentiation of the prostate. Androgen signalling is mediated by the androgen receptor (AR), a ligand-dependent transcription factor. Androgen ablation is the standard treatment for prostate cancer but nearly all patients relapse with androgen-independent disease. Progression of prostate cancer is often associated with changes in the AR-signalling pathway. The project aimed to investigate molecular mechanisms underlying the regulation of AR gene expression in hormone-relapsed prostate cancer. An inducible and a constitutive gene expression system were used to overexpress AR in human prostate cancer cell lines. The TetOff inducible gene expression system, which offers the advantage of quantitatively regulating AR gene expression in response to varying concentrations of tetracycline, was used. A highly tTA-expressing stable ceil line (DUTetOff) was established in the AR- negative DU145 cell line, and a functional AR expression vector (pTRE-AR) was constructed. Transient assays with pTRE-AR in DUTetOff, DU145, PC-3, DUSF and COS-1 cells indicated that, while AR mRNA was expressed in all cells tested, the AR transcript was not translated in DUTetOff and DU145 cells. To develop a constitutive AR gene expression system, the full-length human AR cDNA was introduced into a DU145-derived serum-free subline (termed DUSF). Stable clones were screened for AR expression by immunocytochemistry, Western analysis and RT-PCR. Up- regulation of AR mRNA and protein was detected in DUSF transfectants following androgen treatment. Endogenous PSA mRNA expression was observed in untransfected DUSF cells, while androgen treatment of the transfectants implied an AR- and androgen-independent mechanism for PSA regulation. The work described in this thesis indicates that overexpression of AR in AR-negative cells permits androgen-mediated AR gene expression, and implies an alternative mechanism for PSA activation. The stable AR-expressing DUSF cells provide a useful model system for investigating androgen-independent regulatory elements involved in PSA gene regulation and, elucidating the mechanisms involved in prostate cancer progression.