Identification of Different Classes of Luminal Progenitor Cells within Prostate Tumors

Primary prostate cancer almost always has a luminal phenotype. However, little is known about the stem/progenitor properties of transformed cells within tumors. Using the aggressive Pten/Tp53-null mouse model of prostate cancer, we show that two classes of luminal progenitors exist within a tumor. Not only did tumors contain previously described multipotent progenitors, but also a major population of committed luminal progenitors. Luminal cells, sorted directly from tumors or grown as organoids, initiated tumors of adenocarcinoma or multilineage histological phenotypes, which is consistent with luminal and multipotent differentiation potentials, respectively. Moreover, using organoids we show that the ability of luminal-committed progenitors to self-renew is a tumor-specific property, absent in benign luminal cells. Finally, a significant fraction of luminal progenitors survived in vivo castration. In all, these data reveal two luminal tumor populations with different stem/progenitor cell capacities, providing insight into prostate cancer cells that initiate tumors and can influence treatment response.

TMPRSS2- driven ERG expression in vivo increases self-renewal and maintains expression in a castration resistant subpopulation

Genomic rearrangements commonly occur in many types of cancers and often initiate or alter the progression of disease. Here we describe an in vivo mouse model that recapitulates the most frequent rearrangement in prostate cancer, the fusion of the promoter region of TMPRSS2 with the coding region of the transcription factor, ERG. A recombinant bacterial artificial chromosome including an extended TMPRSS2 promoter driving genomic ERG was constructed and used for transgenesis in mice. TMPRSS2-ERG expression was evaluated in tissue sections and FACS-fractionated prostate cell populations. In addition to the anticipated expression in luminal cells, TMPRSS2-ERG was similarly expressed in the Sca-1^hi/EpCAM⁺ basal/progenitor fraction, where expanded numbers of clonogenic self-renewing progenitors were found, as assayed by in vitro sphere formation. These clonogenic cells increased intrinsic self renewal in subsequent generations. In addition, ERG dependent self-renewal and invasion in vitro was demonstrated in prostate cell lines derived from the model. Clinical studies have suggested that the TMPRSS2-ERG translocation occurs early in prostate cancer development. In the model described here, the presence of the TMPRSS2-ERG fusion alone was not transforming but synergized with heterozygous Pten deletion to promote PIN. Taken together, these data suggest that one function of TMPRSS2-ERG is the expansion of self-renewing cells, which may serve as targets for subsequent mutations. Primary prostate epithelial cells demonstrated increased post transcriptional turnover of ERG compared to the TMPRSS2-ERG positive VCaP cell line, originally isolated from a prostate cancer metastasis. Finally, we determined that TMPRSS2-ERG expression occurred in both castration-sensitive and resistant prostate epithelial subpopulations, suggesting the existence of androgen-independent mechanisms of TMPRSS2 expression in prostate epithelium.

MiR-1 and miR-200 inhibit EMT via Slug-dependent and tumorigenesis via Slug-independent mechanisms

Epithelial-mesenchymal transition (EMT) is a developmental program of signaling pathways that determine commitment to epithelial and mesenchymal phenotypes. In the prostate, EMT processes have been implicated in benign prostatic hyperplasia and prostate cancer progression. In a model of Pten- and TP53-null prostate adenocarcinoma that progresses via transforming growth factor β-induced EMT, mesenchymal transformation is characterized by plasticity, leading to various mesenchymal lineages and the production of bone. Here we show that SLUG is a major regulator of mesenchymal differentiation. As microRNAs (miRs) are pleiotropic regulators of differentiation and tumorigenesis, we evaluated miR expression associated with tumorigenesis and EMT. Mir-1 and miR-200 were reduced with progression of prostate adenocarcinoma, and we identify Slug as one of the phylogenetically conserved targets of these miRs. We demonstrate that SLUG is a direct repressor of miR-1 and miR-200 transcription. Thus, SLUG and miR-1/miR-200 act in a self-reinforcing regulatory loop, leading to amplification of EMT. Depletion of Slug inhibited EMT during tumorigenesis, whereas forced expression of miR-1 or miR-200 inhibited both EMT and tumorigenesis in human and mouse model systems. Various miR targets were analyzed, and our findings suggest that miR-1 has roles in regulating EMT and mesenchymal differentiation through Slug and functions in tumor-suppressive programs by regulating additional targets.

Abstract B28: TMPRSS2- driven ERG in primary prostate epithelium demonstrates castration-resistant expression and expands a unique population of progenitor cells

It has become increasingly appreciated that recurrent genomic rearrangements contribute to the genesis of solid tumors. The genomic rearrangement of the Ets transcription factor, Ets related gene (ERG), with the promoter of the highly expressed Transmembrane protease serine 2 (TMPRSS2) gene, has been demonstrated in 20-65% of prostate adenocarcinoma precursor lesions, implying that ERG may contribute a function selected early in cancer formation. However, the functional role of ERG in developing prostate cancer is unclear. This study utilized bacterial artificial chromosome transgenesis, to produce a mouse model that recapitulates the genetic regulatory features of the genomic TMPRSS2-ERG translocation, where exon 1 and 2 of TMPRSS2 is fused to the region downstream of ERG exon 8. This model allows mechanistic investigations into the function and regulation of expression for TMPRSS2 promoter-driven ERG in the earliest initiating phase of tumorigenesis.

Using QRT-PCR, TMPRSS2-ERG was expressed in the progenitor containing, Sca-1hi fraction of FACS-separated primary prostate cells. In addition, the fusion gene functioned to expand a unique subpopulation of prostate epithelial progenitors when compared to wild type, as demonstrated by serially passaged in vitro sphere forming assays. Androgen regulation of TMPRSS2 has been shown in a limited number of androgen receptor positive luminal prostate cancer cell lines. In this study, TMPRSS2-ERG expression demonstrated a significant castration-resistant component, suggesting mechanisms of AR-independent transcriptional regulation for the TMPRSS2 promoter in the setting of primary prostate epithelial cells. Introduction of the TMPRSS2-ERG fusion alone did not result in histological change, where prostate sections from mice up to 15 months of age were examined. However, the functionality of the model was shown as TMPRSS2-ERG synergized with heterozygous Pten loss to promote PIN. No apparent genetic interaction was observed between TMPRSS2-ERG and Nkx3.1 loss.

These studies demonstrate the potential for androgen independent TMPRSS2-ERG expression in primary prostate epithelium and show that TMPRSS2-ERG expression promotes increased self-renewal of prostate progenitors. These data support a model whereby TMPRSS2-ERG regulates progenitor cell de-differentiation or survival, including within a population of castration-resistant progenitors.

Citation Format: Orla M. Casey, Paul G. Hynes, Lei Fang, Wassim G. Abou-Kheir, Philip L. Martin, Heather S. Tillman, Hibah O. Awwad, Luhua Zhang, Kathleen Kelly. TMPRSS2- driven ERG in primary prostate epithelium demonstrates castration-resistant expression and expands a unique population of progenitor cells [abstract]. In: Proceedings of the AACR Special Conference on Advances in Prostate Cancer Research; 2012 Feb 6-9; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(4 Suppl):Abstract nr B28.

Abstract 3240: A transgenic mouse model of a common genetic aberration in prostate cancer: Chromosomal rearrangement of TMPRSS2:ERG

The most prevalent gene fusion identified in prostate cancer (PC) to date is the recurrent fusion of the 5’ region of Transmembrane Serine Protease 2 (TMPRSS2) to the transcription factor Ets related gene (ERG). The fusion occurs in ∼50% of PC and has been identified in malignant cells preceding the development of prostate adenocarcinoma. This has led to the hypothesis that the rearrangement is an early and critical event in PC. The purpose of this study is to generate a novel mouse model to investigate the role of the transgene in development of PC, and to examine the biological and molecular properties of prostate epithelial cells carrying a translocation of the ERG oncogene.

The fusion is a result of deletion in the genomic region between TMPRSS2 and ERG, which are both located on chromosome 21. Several fusion variants have been described and the focus of this study is the TMPRSS2 exon 2 and ERG exon 4 variant which has been associated with aggressive disease. Importantly, expression of the fusion gene initiates from the TMPRSS2 promoter which is primarily expressed in the prostate and regulated by androgen receptor (AR), which is central to PC development. The objectives of this study included the generation of a novel model that maintains regulation and processing of the translocation. This was achieved by using the complete promoter region, including androgen regulatory regions, and the human genomic sequence thus maintaining the intron/exon arrangement and facilitating alternative splicing. Transgenic mice in the FVB and C57/BL6 background were produced using a 230 Kb construct generated by recombineering technology, where ∼25Kb of the TMPRSS2 promoter region and its first two exons were fused to the entire genomic ERG locus following exon 4.

Two splice variants of the transgene have been identified in mouse prostates corresponding to the presence and absence of a 72bp exon, replicating the pattern in human PC, where this has been associated with aggressive disease. No distinct histological phenotypic change has been observed in the murine prostate of transgenic animals at six to twelve months. Towards the aim of determining the role of this fusion in PC - further in vitro and in vivo assays are currently in progress with the objectives of 1) determining the role of AR in regulation of the promoter and 2) investigating alterations in gene expression profiles in distinct cell populations of the prostate harboring the transgene. Additional crosses with other mice carrying mutations significant to prostate cancer, e.g. Nkx 3.1 and PTEN mice are being performed thus allowing the investigation of the phenotypic effect of this fusion when combined with other common genetic events.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3240.

Analysis of gene expression in non-regressed and regressed bovine corpus luteum tissue using a customized ovarian cDNA array

The lifespan of the bovine corpus luteum (CL) is an important factor in the control of normal ovarian cyclicity and the establishment and maintenance of pregnancy. There is increasing evidence that CL lifespan is regulated by alternative expression of genes that promote or inhibit luteolysis. To gain further insights into these events a 434 character ovarian cDNA array comprising genes attributed to key aspects of CL function including more than 100 anonymous expressed sequence tags (ESTs) was constructed and screened with alpha(33)P dATP labeled RNA isolated from non-regressed (n=6) and regressed (n=6) CL tissue. Significance analysis of microarrays (SAM) identified 15 genes that changed expression 1.7-fold or more with a false discovery rate of <5%. The differentially expressed genes encoded enzymes involved in steroid biosynthesis and oxygen radical metabolism and proteins involved in extracellular matrix remodeling, apoptosis and cell structure. Results for five of the differentially expressed genes including matrix gla protein and collagen alpha1(I) (extracellular matrix), glutathione-S-transferase alpha I (oxygen metabolism), clusterin (apoptosis) and scavenger receptor BI (steroid biosynthesis) were confirmed by Northern blot analysis and found to be significantly different (P<0.01) between non-regressed and regressed CL tissue. Collectively this study identified genes with recognized roles in CL regression, genes with potential roles in this process and genes whose function have yet to be defined in this event.

Analysis of gene expression in the bovine corpus luteum through generation and characterisation of 960 ESTs

To gain new insights into gene identity and gene expression in the bovine corpus luteum (CL) a directionally cloned CL cDNA library was constructed, screened with a total CL cDNA probe and clones representing abundant and rare mRNA transcripts isolated. The 5'-terminal DNA sequence of 960 cDNA clones, composed of 192 abundant and 768 rare mRNA transcripts was determined and clustered into 351 non-redundant expressed sequence tag (EST) groups. Bioinformatic analysis revealed that 309 (88%) of the ESTs showed significant homology to existing sequences in the protein and nucleotide public databases. Several previously unidentified bovine genes encoding proteins associated with key aspects of CL function including extracellular matrix remodelling, lipid metabolism/steroid biosynthesis and apoptosis, were identified. Forty-two (12%) of the ESTs showed homology with human or with other uncharacterised ESTs, some of these were abundantly expressed and may therefore play an important role in primary CL function. Tissue-specificity and temporal CL gene expression of selected clones previously unidentified in bovine CL tissue was also examined. The most interesting finds indicated that mRNA encoding squalene epoxidase was constitutively expressed in CL tissue throughout the oestrous cycle and 7-fold down-regulated (P < 0.05) in late luteal tissue, concomitant with the disappearance of systemic progesterone, suggesting that de novo cholesterol biosynthesis plays an important role in steroidogenesis. The mRNA encoding the growth factor, insulin-like growth factor-binding protein-related protein 1 (IGFBP-rP1), remained constant during the oestrous cycle and was 1.8-fold up-regulated (P < 0.05) in late luteal tissue implying a role in CL regression.

Postmortem stability of RNA isolated from bovine reproductive tissues

Molecular biology is being increasingly used to address the complex problem of bovine infertility. One common concern shared by many of these studies is the postmortem delay in obtaining reproductive tissues and the effect this may have on RNA dependent studies. To address this concern, bovine ovarian, oviduct and uterine tissue samples, collected over intervals ranging from 0 to 96 h postmortem to freeze storage, were analysed to determine the potential effects on RNA quantity and quality. The analysis showed that total RNA yields were not changed significantly by postmortem interval up to 96 h while 28S ribosomal RNA remained intact up to 24 h postmortem. Specific messenger RNA transcripts encoding beta-actin, GAPDH and transforming growth factor-beta were detected in all tissues up to 96 h postmortem using reverse transcriptase-polymerase chain reaction and Northern analysis indicated no detectable mRNA degradation up to 24 h postmortem. Finally, using poly(A)(+) mRNA isolated from ovarian tissues frozen 2 h postmortem, we constructed corpus luteum and ovarian cortex cDNA libraries containing 7.65x10(4) and 1.9x10(6) primary transformants with average cDNA lengths of 2.3 and 1.6 kb respectively. Taken together, these data show that a postmortem delay of up to 24 h does not significantly affect the yield or quality of RNA prepared from bovine reproductive tissues.

Osteomalacia and osteoporosis: evaluation of a diagnostic index

Data from a retrospective study in 41 patients is used to suggest an index of bone disease. This is designed as a means of collating available results, clarifying the significance of each in diagnosing either osteomalacia or osteoporosis, and reducing the significance of a single abnormal finding--for example, a raised alkaline phosphatase activity or low serum 25 hydroxy vitamin D, when the overall index score is low. Index scores above 35% would be diagnostic of osteomalacia; scores below 15% if associated with collapsed vertebrae suggest osteoporosis. Scores between 15% and 35% would indicate the need for a bone biopsy to discriminate between osteoporosis and osteomalacia.