Retroviral and transposon-based mutagenesis screens in mice have been useful for identifying candidate cancer genes for some tumor types. However, many of the organs that exhibit the highest cancer rates in humans, including the prostate, have not previously been amenable to these approaches. This study shows for the first time that the Sleeping Beauty transposon system can be used to identify candidate prostate cancer genes in mice. Somatic mobilization of a mutagenic transposon resulted in focal epithelial proliferation and hyperplasia in the prostate. Efficient methods were established to identify transposon insertion sites in these lesions, and analysis of transposon insertions identified candidate prostate cancer genes at common insertion sites, including Pde4d. PDE4D was also overexpressed in human prostate cancer patient samples and cell lines, and changes in PDE4D mRNA isoform expression were observed in human prostate cancers. Furthermore, knockdown of PDE4D reduced the growth and migration of prostate cancer cells in vitro, and knockdown of PDE4D reduced the growth and proliferation rate of prostate cancer xenografts in vivo. These data indicate that PDE4D functions as a proliferation promoting factor in prostate cancer, and the Sleeping Beauty transposon system is a useful tool for identifying candidate prostate cancer genes. [Cancer Res 2009;69(10):4388-97]

Expression of the c-myc gene is frequently dysregulated in malignant tumors and translocations of c-myc into the Ig H chain locus are associated with Burkitt’s-type lymphoma. There is indirect evidence that bcl-x, an anti-apoptotic member of the bcl-2 gene family, may also contribute to a variety of B lymphoid tumors. In this study, we show that mice transgenic for both B cell-restricted c-myc and bcl-xL developed aggressive, acute leukemias expressing early B lineage and stem cell surface markers. Of interest, the tumor cells proliferated and differentiated down the B cell developmental pathway following in vitro treatment with IL-7. Analysis of sorted leukemic cells from spleen indicated constitutive expression of sterile μ and κ transcripts in combination with evidence for D-JH DNA rearrangements. Several B cell-specific genes were either not expressed or were expressed at low levels in primary tumor cells and were induced following culture with IL-7. IL-7 also increased V-Jκ and V-DJH rearrangements. These data demonstrate oncogenic synergy between c-myc and bcl-xL in a new mouse model for acute lymphoblastic leukemia. Tumors in these animals target an early stage in B cell development characterized by the expression of both B lineage and stem cell genes.

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The prostate gland develops from the urogenital sinus in response to circulating androgens. Androgens initiate and stimulate branching morphogenesis in the urogenital sinus via unknown mediators. Heparan sulfate proteoglycans are important extracellular molecules that sequester many growth factors in the extracellular matrix and facilitate signaling by some growth factors as part of ternary complexes that include growth factors, receptors, and heparan sulfate chains. Several enzymes modify the chemical structure of heparan sulfate to further regulate its activity. An examination of these enzymes for sexually dimorphic expression in the urogenital sinus identified Sulfatase 1 (Sulf1) as an enzyme that was down-regulated in the male urogenital sinus coincident with the initiation of prostatic morphogenesis. Down-regulation of Sulf1 was accompanied by an increase in the most highly sulfated forms of heparan sulfate, and a similar increase was observed in female urogenital sinuses treated with testosterone. Inhibiting de novo sulfation of heparan sulfate blocked prostatic morphogenesis, supporting the importance of heparan sulfate modification for prostate development. To functionally test the specific role of Sulf1 during prostate development, Sulf1 was ectopically expressed in the urogenital sinus. It partially inhibited testosterone-stimulated ductal morphogenesis, and it reduced the activation of fibroblast growth factor receptors as well as the ERK1 and ERK2 MAPKs. These data identify sulfatase 1 as an inhibitor of prostatic branching morphogenesis and growth factor signaling that is down-regulated as part of the normal response to androgen action in the male urogenital sinus.