SummaryProstate cancer is the most frequently diagnosed nonskin cancer and the third leading cause of cancer mortality in men. In the initial stages, prostate cancer is dependent on androgens for growth, which is the basis for androgen ablation therapy. However, in most cases, prostate cancer progresses to a hormone refractory phenotype for which there is no effective therapy available at present. The androgen receptor (AR) is required for prostate cancer growth in all stages, including the relapsed, ''androgen-independent'' tumors in the presence of very low levels of androgens. This review focuses on AR function and AR-target genes and summarizes the major signaling pathways implicated in prostate cancer progression, their crosstalk with each other and with AR signaling. This complex network of interactions is providing a deeper insight into prostate carcinogenesis and may form the basis for novel diagnostic and therapeutic strategies.
IntroductionProstate adenocarcinoma is the most frequently diagnosed non-cutaneous male malignancy and the third leading cause of cancer-related death in men in most western industrialized countries. (1) It is estimated that around 660,000 men worldwide will be diagnosed with prostate cancer and 250,000 men will die from it in 2010; thus, it will remain a major health problem in the future. (1) It was more than 60 years ago that the important role of male sex hormones (androgens) for the development and growth of prostate cancer was demonstrated. (2) Accordingly, androgen ablation therapy has been the main line of therapy for prostate cancer. Therefore, much of the focus in prostate cancer research to date has naturally been on androgens, how to decrease the androgens in the circulation and how to inhibit the androgen receptor (AR).In addition to AR signaling, it has now become evident that other signaling pathways, as well as non-genomic and genomic alterations, are involved in prostate cancer development and progression. Furthermore, recent studies indicated that signaling through AR has a critical role even after androgen ablation and disease progression (for review see Ref.3). In the following sections, we give an overview of androgen signaling in prostate cancer, with a special focus on recent findings about AR function and AR target genes. We then review the involvement of other central signaling pathways in prostate cancer, with a special focus on their cross-talk with the AR signaling pathway. Clinical implications of these findings and potential directions for future research are also outlined.