Cancer may arise from a cancer stem/progenitor cell that shares characteristics with its normal counterpart. We report the reconstitution of the original human prostate cancer specimen from epithelial cell lines (termed HPET for human prostate epithelial/hTERT) derived from this sample. These tumors can be described in terms of Gleason score, a classification not applied to any of the transgenic mouse models currently developed to mimic human disease. Immunohistochemical and Western blot analyses indicate that they do not express androgen receptor or p63, similar to that reported for prostate stem cells. These cell lines also express embryonic stem markers (Oct4, Nanog, and Sox2) as well as early progenitor cell markers (CD44 and Nestin) in vitro. Clonally derived HPET cells reconstitute the original human tumor in vivo and differentiate into the three prostate epithelial cell lineages, indicating that they arise from a common stem/progenitor cell. Serial transplantation experiments reconstitute the tumors, suggesting that a fraction of parental or clonally derived HPET cells have self-renewal potential. Thus, this model may enhance our understanding of human tumor development and provide a mechanism for studying cancer stem/progenitor cells in differentiation, tumorigenesis, preclinical testing, and the development of drug resistance. [Cancer Res 2007;67(10):4807-15]

The oncogenic PIM1 kinase has been implicated as a cofactor for c-MYC in prostate carcinogenesis. Here we show that in human prostate tumors, coexpression of c-MYC and PIM1 is associated with higher Gleason grades. Using a tissue recombination model coupled with lentiviral-mediated gene transfer we find that Pim1 is weakly oncogenic in naïve adult mouse prostatic epithelium. However, it cooperates dramatically with c-MYC to induce prostate cancer within 6-weeks. Importantly, c-MYC/Pim1 synergy is critically dependent on Pim1 kinase activity. c-MYC/Pim1 tumors showed increased levels of the active serine-62 (S62) phosphorylated form of c-MYC. Grafts expressing a phosphomimetic c-MYCS62D mutant had higher rates of proliferation than grafts expressing wild type c-MYC but did not form tumors like c-MYC/Pim1 grafts, indicating that Pim1 cooperativity with c-MYC in vivo involves additional mechanisms other than enhancement of c-MYC activity by S62 phosphorylation. c-MYC/Pim1-induced prostate carcinomas demonstrate evidence of neuroendocrine (NE) differentiation. Additional studies, including the identification of tumor cells coexpressing androgen receptor and NE cell markers synaptophysin and Ascl1 suggested that NE tumors arose from adenocarcinoma cells through transdifferentiation. These results directly demonstrate functional cooperativity between c-MYC and PIM1 in prostate tumorigenesis in vivo and support efforts for targeting PIM1 in prostate cancer.

Our previous studies have found that activation of Wnt/β-Catenin signaling resulted in mouse prostatic intraepithelial neoplasia (mPIN). In the large probasin promoter directed SV40-Large T-antigen (LPB-Tag) expressing mouse prostate, mPIN forms with rare areas of adenocarcinoma. Combining expression of both Wnt-signaling and Tag expression in the mouse prostate, we have studied the role of Wnt/β-Catenin signaling in the progression from mPIN to adenocarcinoma. Our results show that the prostates of mice expressing Tag alone or nuclear β-Catenin alone developed mPIN while the activation of both Tag and the Wnt/β-Catenin pathway resulted in invasive prostate adenocarcinoma. Also, Foxa2, a forkhead transcription factor, was induced by active Wnt/β-Catenin signaling; and the expression of Foxa2 was associated with the invasive phenotype in the primary prostate cancer. In the LPB-Tag/dominant active (D.A.) β-Catenin prostates, MMP7, a Wnt/β-Catenin target gene, was up-regulated. Furthermore, we also assessed AR and AR signaling pathway in these LPB-Tag/D.A. β-Catenin mice. Although β-Catenin is a well known AR co-activator in vitro, our study provides strong in vivo evidences indicating that both AR protein and the AR pathway were down-regulated in the prostate of LPB-Tag/D.A. β-Catenin mice. Histological analysis shows that prostate sections derived from the LPB-Tag/D.A. β-Catenin mice display neuroendocrine differentiation (NED) but NE cancer does not develop. Together, our findings indicate that Wnt/β-Catenin signaling plays an important role in the progression of mPIN to prostate adenocarcinoma.

BACKGROUND The role of Wnt/β-Catenin signaling in embryogenesis and carcinogenesis has been extensively studied in organs such as colon, lung and pancreas, but little is known about Wnt/β-Catenin signaling in the prostate. Although stabilizing mutations in APC and β-Catenin are rare in primary prostate tumors, recent studies suggest that cytoplasmic/nuclear β-Catenin is associated with advanced, metastatic, hormone-refractory prostate carcinoma. METHODS To better understand the role of β-Catenin in prostatic development and carcinogenesis, we studied Wnt expression during prostate development and activated Wnt/β-Catenin signaling in the developing and adult prostate. RESULTS Our results demonstrated that during prostate development Wnt ligands display a dynamic expression pattern. Activation of β-Catenin during prostate development caused epithelial hyperplasia followed by prostatic intraepithelial neoplasia (PIN) in prostate. In the adult prostate, activation of β-Catenin resulted in high grade PIN (HGPIN) and continuous prostatic growth after castration. As a result of activation of β-Catenin, AR was first up-regulated with the emergence of epithelial hyperplasia, but was later down-regulated when HGPIN developed. Furthermore, activation of β-Catenin induced Foxa2 re-expression in adult prostate which normally is only expressed in the embryonic budding stage during prostate development. CONCLUSIONS The results from this study strongly suggest that Wnt/β-Catenin signaling is involved in the regulation of prostate development and confirm that constitutive activation of this pathway enables the mouse prostate to grow after castration.

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