Understanding the molecular etiology of prostate cancer (CaP) progression is paramount for broadening current diagnostic and therapeutic modalities. Current interest in the role of wnt pathway signaling in prostate tumorigenesis was generated with the ®nding of b-catenin mutation and corresponding nuclear localization in primary lesions. The recent ®nding of b-catenin-induced enhancement of androgen receptor (AR) function potentially ties b-catenin to key regulatory steps of prostate cell growth, di erentiation, and transformation. By immunohistological analysis of metastatic tumors, we detected nuclear bcatenin in 20% of lethal CaP cases, suggesting a more common role for b-catenin in advanced disease than would be predicted by its mutation rate. Interestingly, bcatenin nuclear localization was found to occur concomitantly with androgen-induced regrowth of normal rat prostate. These in vivo observations likely implicate b-catenin involvement in both normal and neoplastic prostate physiology, thus prompting our interest in further characterizing modes of b-catenin signaling in prostate cells. Extending our previous ®ndings, we demonstrate that transient b-catenin over-expression stimulates T cell factor (TCF) signaling in most CaP cell lines. Further, this activity is not subject to crossregulation by phosphoinositide-3-kinase (PI3-K)/Akt signaling, a stimulatory pathway often upregulated in CaP upon PTEN inactivation. Consistent with a previous report, we observed that transient b-catenin overexpression enhances AR-mediated transcription o two natural target gene promoters. However, we were unable to recapitulate b-catenin-induced stimulation of ectopically expressed AR in AR-negative cells, suggesting that other AR-associated factors are required for this activity. Although LNCaP cells are capable of this mode of AR co-stimulation, stable expression of mutant b-catenin did not alter their proliferative response to androgen. In total, our characterization of b-catenin signaling in CaP reveals the complex nature of its activity in prostate tissue, indicating that b-catenin potentially contributes to multiple stimulatory inputs required for disease progression.

Beta-catenin signaling may contribute to prostate cancer (CaP) progression. Although beta-catenin is known to upregulate T cell factor (TCF) target gene expression in CaP cells, recent evidence demonstrates its capacity to enhance ligand-dependent androgen receptor (AR) function. Thus, we wished to further understand the interaction between these two pathways. We find in both CaP cells (CWR22-Rv1, LAPC-4, DU145) and non-CaP cells (HEK-293, TSU, SW480, HCT-116) that beta-catenin/TCF-related transcription (CRT), as measured by activation of a synthetic promoter and that of cyclin D1, is inhibited by androgen treatment. This inhibition is AR-dependent, as it only occurs in cells expressing AR endogenously or transiently, and is abrogated by AR antagonists. Additional analyses convey that the ligand-dependent nature of CRT suppression depends on transactivation-competent AR in the nucleus, but not on indirect effects stemming from AR target gene expression. Given the recent work identifying an AR/beta-catenin interaction, and from our finding that liganded AR does not prompt gross changes in the constitutive nuclear localization of TCF4 or mutant beta-catenin, we hypothesized that transcription factor (i.e. AR and TCF) competition for beta-catenin recruitment may explain, in part, androgen-induced suppression of CRT. To address this idea, we expressed an AR mutant lacking its DNA-binding domain (DBD). This receptor could not orchestrate ligand-dependent CRT repression, thereby providing support for those recent data implicating the AR DBD/LBD as necessary for beta-catenin interaction. Further supporting this hypothesis, TCF/LEF over-expression counteracts androgen-induced suppression of CRT, and requires beta-catenin binding activity to do so. Interestingly, TCF4 over-expression potently antagonizes AR function; however, this inhibition may occur independently of beta-catenin/TCF4 interaction. These results from TCF4 over-expression analyses, taken together, provide further evidence that AR-mediated suppression of CRT is a consequence of limiting amounts of beta-catenin, and not AR target gene expression. Our analyses point to a reciprocal balance between AR and CRT function that may shape critical processes during normal prostate development and tumor progression.

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Further understanding of the molecular mechanisms responsible for prostate cancer (CaP) development and progression is paramount for overcoming the current diagnostic and therapeutic hurdles presented by this urologic disease. The β-catenin nuclear signaling molecule has been widely implicated as an oncogene in human cancer, including CaP. Pooling together knowledge gathered on the contributions of β-catenin and other factors to human neoplasia may assist in the development of better strategies for management and treatment of prostate tumors of all stages (early, advanced/ androgen-dependent, advanced/androgen-independent). Although there is considerable lack of comprehension regarding the function of β-catenin transcriptional activity in prostate tumors in vivo, recent evidence indicates the probability that β-catenin contributes to multiple signaling pathways for which a causative role in CaP is already known. In this review, we will approach such pathway interactions, perhaps the most notable being androgen receptor (AR) signaling, in order to highlight those avenues through which β-catenin may exert its cancer-related function. To the same end, we will draw attention to normal β-catenin signaling in the prostate; however, as only very limited knowledge exists on this topic, much of the discussion will be correlative. Our final topic will concentrate on how, given realistic scenarios of androgen stimulation or absence in both normal and neoplastic prostate cells, nuclear β-catenin may ultimately potentiate wnt cell-cell signaling and AR activities. Heightening our comprehension of β-catenin signaling mechanisms and its phenotypic consequences in CaP -and in normal prostate -may contribute to that body of knowledge which will eventually prove useful for devising more effective therapies.

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