Restriction of neuroblastoma to the prostate gland in transgenic mice

Current mouse and cell models in prostate cancer research

Mouse models of prostate cancer (PCa) are critical for understanding the biology of PCa initiation, progression, and treatment modalities. Here, we summarize recent advances in PCa mouse models that led to new insights into specific gene functions in PCa. For example, the study of transgenic mice with TMPRSS2/ERG, an androgen-regulated fusion protein, revealed its role in developing PCa precursor lesions, prostate intraepithelial neoplasia; however, it is not sufficient for PCa development. Double deficiency of Pten and Smad4 leads to a high incidence of metastatic PCa. Targeted deletion of Pten in castration-resistant Nkx3-1-expressing cells results in rapid carcinoma formation after androgen-mediated regeneration, indicating that progenitor cells with luminal characteristics can play a role in initiation of PCa. Transgenic mice with activated oncogenes, growth factors, and steroid hormone receptors or inactivated tumor suppressors continue to provide insights into disease progression from initiation to metastasis. Further development of new PCa models with spatial and temporal regulation of candidate gene expression will probably enhance our understanding of the complex events that lead to PCa initiation and progression, thereby invoking novel strategies to combat this common disease in men.

Advances in mouse models of prostate cancer

Advances in science and technology have allowed us to manipulate the mouse genome and analyse the effect of specific genetic alterations on the development of prostate cancer in vivo. We can now analyse the molecular basis of initiation, invasion and progression to metastatic disease. The current mouse models utilise knockout, knock-in or conditional regulation of expression using Cre-loxP technology. Genes that have been targeted include homeobox genes, tumour suppressors and oncogenes, growth factors (and their receptors), steroid hormones and cell-cycle regulators, as well as pro- and anti-apoptotic proteins. Bigenic models indicate that that two 'hits' are required for progression from intra-epithelial neoplasia (PIN) to invasion carcinoma, and two to five hits are needed for metastasis. Here, we discuss the numerous models that mimic various aspects of the disease process, such as PIN, locally invasive adenocarcinoma and metastatic disease. Currently the PB-Cre4 x PTEN(loxP/loxP) mouse is the only model that spans the entire continuum from initiation to local invasion and metastasis. Such mouse models increase our understanding of the disease process and provide targets for novel therapeutic approaches. Hopefully, the transgenic models will become inducible and ultimately allow both temporal and spatial gene inactivation. Compound mutational models will also develop further, with double and triple knock-in or knockout systems adding to our knowledge of the interaction between different signalling cascades.

Survey of genetically engineered mouse models for prostate cancer: analyzing the molecular basis of prostate cancer development, progression, and metastasis

Genetically engineered mouse models have been generated to study the molecular basis of prostate cancer (PCa) development, progression, and metastasis. Selection of a prostate-specific promoter, such as the probasin (PB) and prostate specific antigen (PSA) promoters, is critical for generating sufficient levels of transgene expression to elicit a phenotypic response. To date, target genes have included growth factors, cell cycle regulators, pro- and anti-apoptotic proteins, steroid hormone and growth factor receptors, oncogenes, tumor suppressors, and homeobox genes. The experimental approaches used to generate these mouse models include overexpression of the transgene, knock-out/knock-in of transgene expression and conditional regulation of expression using Cre/lox technology. This review summarizes the promoters, which have been utilized to create genetically engineered mouse models for PCa. Furthermore, the effects of gene disruption on promoting low- and high-grade intraepithelial neoplasia (LGPIN and HGPIN, respectively), locally invasive carcinoma and metastatic lesions will be discussed. To date, the PB-Cre4 x PTENloxp/loxp model appears to be the only model that represents the entire continuum of prostate adenocarcinoma development, tumor progression, and metastasis, although models that develop prostatic neuroendocrine (NE) cancer can be generated by disrupting one genetic event. Indeed, analysis of bigenic mouse models indicates that two genetic events are generally required for progression from HGPIN to locally invasive adenocarcinoma and that two to five genetic events can promote metastasis to distant sites. Studying the effects of genetic perturbation on PCa biology will increase our understanding of the disease process and potentially provide targets for developing novel therapeutic approaches.

Genetically modified mice and their use in developing therapeutic strategies for prostate cancer

PURPOSE

At the National Cancer Institute a comprehensive program has been developed for accelerating prostate cancer research, especially in the area of mouse models for human cancers. This review focuses on transgenic mouse models for elucidating the molecular and cellular processes that lead to prostate cancer initiation, progression and metastasis, and on their suitability for therapeutic and chemopreventive trials.

MATERIALS AND METHODS

Published data from MEDLINE, http://emice.nci.nih.gov/, our laboratory and other investigators are reviewed.

RESULTS

Currently no 1 mouse model displays the entire continuum of human prostate cancer initiation, development and metastasis. The loss or over expression of a single gene results primarily in epithelial hyperplasia, prostatic intraepithelial neoplasia or more aggressive localized adenocarcinoma. To date the only models that develop lung, liver and occasionally bone metastasis are those that express SV40 large T antigen. A number of models have been used to investigate the efficacy of androgen deprivation, lovastatin, vitamin D, the anti-inflammatory drug E-7869, genistein and (-)-epigallocatechin-3-gallate as therapeutic or chemopreventive agents. Noninvasive optical imaging technologies facilitate the detection of metastatic lesions and the effects of therapeutic agents on tumor regression.

CONCLUSIONS

Integrating mouse studies with human clinical trials would ensure that mechanisms that promote prostate cancer are identified and potential therapeutic targets are validated.

Molecular characterization of prostatic small-cell neuroendocrine carcinoma

OBJECTIVES

A subset of prostate carcinomas is composed predominantly, even exclusively, of neuroendocrine (NE) cells. In this report, we sought to characterize the gene expression profile of a prostate small cell NE carcinoma by assessing the diversity and abundance of transcripts in the LuCaP 49 prostate small cell carcinoma xenograft.

METHODS

We constructed a cDNA library (PRCA3) from the LuCap 49 prostate small cell xenograft. Single pass DNA sequencing of randomly selected cDNA clones followed by sequence assembly and annotation produced a library of Expressed Sequence Tags (ESTs) representing the LuCaP 49 transcriptome. Comparative sequence analysis with ESTs derived from prostate adenocarcinoma libraries was performed using statistical algorithms designed to identify differentially expressed sequences. Putative NE cell-specific genes were further examined by Northern analysis.

RESULTS

Sequence assembly and analysis identified 1,447 distinct genes expressed in the LuCaP 49 cDNA library. These include cDNAs encoding the NE markers secretogranin (SCG2), CD24, and ENO2. Northern analysis revealed that three additional genes, ASCL1, INA, and SV2B are expressed in LuCaP 49 but not in various prostate cancer cell lines or xenografts. Fifteen genes were identified with a statistical probability (P > 0.9) of being up-regulated in LuCaP 49 small cell carcinoma relative to prostate adenocarcinoma (two primary prostate adenocarcinomas and the LNCaP prostate adenocarcinoma cell line).

CONCLUSIONS

Prostate small cell carcinoma expresses a diverse repertoire of genes that reflect characteristics of their NE cell of origin. ASCL1, INA, and SV2B are potential molecular markers for small cell NE tumors and NE cells of the prostate. This small cell NE carcinoma gene expression profile may yield insights into the development, progression, and treatment of subtypes of prostate cancer.

F-MuLV acceleration of myelomonocytic tumorigenesis in SV40 large T antigen transgenic mice is accompanied by retroviral insertion at Fli1 and a novel locus, Fim4

We describe here the development of a murine system for the identification of genes involved in myelomonocytic neoplasms. Transgenic C57BL/6J mice expressing SV40 early region under a myelomonocytic promoter develop histiocytic sarcomas with a latency of 167 days. We used retroviral proviral tagging to accelerate tumorigenesis and to uncover genetic changes that contribute to tumor development. Infection of transgenic mice with Friend murine leukemia virus (F-MuLV) shortened the latency of morbidity to 103 days (P< 0.001); this was associated with clonal proviral integrations in tumor DNA. As expected for F-MuLV, proviral insertions occurred at Fli1 in both transgenic and nontransgenic tumors. Four insertions were found at a novel locus, termed Fim4, on chromosome 6. This region is syntenic to human 7q32, a region that is commonly deleted in human myelodysplastic syndrome and acute myeloid leukemia. A murine BAC containing Fim4 was sequenced and analyzed, and while there was significant human-mouse homology in the area of the insertions, no candidate gene has been identified. Thus we have established a system to identify genes involved in myelomonocytic tumors, and have used it to identify Fim4, a new common site of proviral insertion. Study of this locus may provide insight into genes involved in AML-associated 7q32 deletions in humans.

Mouse models of prostate carcinogenesis

In recent years, numerous mouse models have been generated that recapitulate salient features of prostate carcinogenesis in humans. Here we review progress in the generation and validation of mouse models for prostate cancer, discuss current limitations of these models, and highlight directions of future research.

Transcriptional mechanisms regulating myeloid-specific genes

Myeloid blood cells comprise an important component of the immune system. Proper control of both lineage- and stage-specific gene expression is required for normal myeloid cell development and function. In recent years, a relatively small number of critical transcriptional regulators have been identified that serve important roles both in myeloid cell development and regulation of lineage-restricted gene expression in mature myeloid cells. This review summarizes our current understanding of the regulation of lineage- and stage-restricted transcription during myeloid cell differentiation, how critical transcriptional regulators control myeloid cell development, and how perturbations in transcription factor function results in the development of leukemia.

Mouse models of prostate cancer

The pathogenetic basis of prostate cancer remains highly elusive; its clarification could be facilitated greatly by laboratory and clinical models of the disease. Although the genetically manipulated mouse has been invaluable for the modeling of other human cancer types, it has fared less well with respect to prostate cancer. Nevertheless, several highly valuable transgenic models exist and are highlighted in this review. Emerging reagents and strategies may allow us to use the mouse more effectively to define the molecular, cellular and physiological events that lead to prostate cancer initiation and progression.

The 5′ Flanking Region of the Human Granzyme H Gene Directs Expression to T/Natural Killer Cell Progenitors and Lymphokine-Activated Killer Cells in Transgenic Mice

Human granzyme H is a neutral serine protease that is expressed predominantly in the lymphokine-activated killer (LAK)/natural killer (NK) compartment of the immune system. The gene that encodes this granzyme is located between the granzyme B and cathepsin G genes on human chromosome 14q11.2. Although the murine orthologue of human granzyme H has not yet been identified, murine granzymes C, D, E, F, and G also lie between the murine granzyme B and cathepsin G genes on murine chromosome 14; murine granzymes C, D, and F are also highly expressed in LAK cells, but minimally in cytotoxic T lymphocytes (CTL). We therefore tested whether the 5′ flanking region of human granzyme H contains the cis-acting DNA sequences necessary to target a reporter gene to the LAK/NK compartment of transgenic mice. A 1.2-kb fragment of 5′ flanking human granzyme H sequence was linked to an SV40 large T-antigen (TAg) reporter gene and used to create six transgenic founder lines. SV40 TAg was specifically expressed in the LAK cells of these mice, but not in resting T or NK cells, in CTL, or in any other tissues. Most mice eventually developed a fatal illness characterized by massive hepatosplenomegaly and disseminated organ infiltration by large malignant lymphocytes. Cell lines derived from splenic tumors were TAg+ and NK1.1+ large granular lymphocytes and displayed variable expression of CD3, CD8, and CD16. Although these cell lines contained perforin and expressed granzymes A, B, C, D, and F, they did not exhibit direct cytotoxicity. Collectively, these results suggest that the 5′ flanking sequences of the human granzyme H gene target expression to an NK/T progenitor compartment and to activated NK (LAK) cells. Mice and humans may therefore share a regulatory “program” for the transcription of NK/LAK specific granzyme genes.

The 5′ Flanking Region of the Human Granzyme H Gene Directs Expression to T/Natural Killer Cell Progenitors and Lymphokine-Activated Killer Cells in Transgenic Mice

Human granzyme H is a neutral serine protease that is expressed predominantly in the lymphokine-activated killer (LAK)/natural killer (NK) compartment of the immune system. The gene that encodes this granzyme is located between the granzyme B and cathepsin G genes on human chromosome 14q11.2. Although the murine orthologue of human granzyme H has not yet been identified, murine granzymes C, D, E, F, and G also lie between the murine granzyme B and cathepsin G genes on murine chromosome 14; murine granzymes C, D, and F are also highly expressed in LAK cells, but minimally in cytotoxic T lymphocytes (CTL). We therefore tested whether the 5′ flanking region of human granzyme H contains the cis-acting DNA sequences necessary to target a reporter gene to the LAK/NK compartment of transgenic mice. A 1.2-kb fragment of 5′ flanking human granzyme H sequence was linked to an SV40 large T-antigen (TAg) reporter gene and used to create six transgenic founder lines. SV40 TAg was specifically expressed in the LAK cells of these mice, but not in resting T or NK cells, in CTL, or in any other tissues. Most mice eventually developed a fatal illness characterized by massive hepatosplenomegaly and disseminated organ infiltration by large malignant lymphocytes. Cell lines derived from splenic tumors were TAg+ and NK1.1+ large granular lymphocytes and displayed variable expression of CD3, CD8, and CD16. Although these cell lines contained perforin and expressed granzymes A, B, C, D, and F, they did not exhibit direct cytotoxicity. Collectively, these results suggest that the 5′ flanking sequences of the human granzyme H gene target expression to an NK/T progenitor compartment and to activated NK (LAK) cells. Mice and humans may therefore share a regulatory “program” for the transcription of NK/LAK specific granzyme genes.

Transgenic and gene disruption techniques in the study of neurocarcinogenesis

Transgenic technologies have come of age, and the field of carcinogenesis has profited extensively from the availability of these methods. Both the inappropriate expression of dominant oncogenes in specific tissues and the ability to "knock out" tumor suppressor genes in mammalian organisms have enabled substantial advancements of our understanding of development and progression of the neoplastic phenotype. In the first part of this article, we review the most popular techniques for modification of the mammalian genome in vivo, i.e. microinjection of fertilized eggs, retrovirus-mediated gene transfer, and targeted gene deletion through homologous recombination. Subsequently, we attempt a critical evaluation of the available models of neurocarcinogenesis, and discuss their impact and future potential for the study of cancer in the nervous system.

Relationship between expression of epidermal growth factor and simian virus 40 T antigen in a line of transgenic mice

The pattern of expression of the simian virus 40 (SV40) T antigen gene and resultant dysplasia were re-examined in a line of transgenic mice in which the T antigen gene was under the control of the SV40 early promoter. We found that T antigen expression in the kidney, and resulting dysplastic lesions, occurred exclusively in the distal convoluted tubules and the ascending limbs of Henle. Epidermal growth factor (EGF) expression in the kidney of normal mice was similarly immunolocalized. The correlation between high EGF immunoreactivity in normal mouse tissues and T antigen expression in the transgenic counterpart was also seen in the choroid plexus epithelium and in the submandibular glands of male mice. T antigen was not found in the submandibular gland of transgenic females. Similarly, EGF was only rarely detected in the normal female submandibular gland. In contrast to the correlation between T antigen expression in the transgenic mice and EGF expression in the corresponding tissues of the normal mice, within the dysplastic lesions of the transgenic mice EGF expression was severely diminished. Adenocarcinomas of the male submandibular gland from another line of transgenic mice that expresses the Int-1 transgene, showed similarly reduced levels of immunostaining for EGF. Thus, reduced expression of EGF might be a general feature of dysplasia and tumorigenesis in those tissues that normally express EGF.

Heritable formation of neuroectodermal tumor in transgenic mice carrying the combined E1 region gene of adenovirus type 12 with the deregulated human renin promoter

Adenovirus early 1 (E1) region gene products, including E1A and E1B, are required for transcriptional regulation of viral and cellular promoters in infected and transfected culture cells and for transformation of primary rodent cells. Here, we established a line of transgenic mice carrying the E1 region gene of human adenovirus type 12 under the control of the human renin promoter, in which a neuroectodermal tumor derived from retroperitoneal, olfactory, and/or pelvic regions was heritably developed with varying degrees of incidence and the phenotype was successfully passed through six generations. The transgenes were located in the region E2-E3 bands of chromosome 7 with which no genetic linkage to neuroectodermal tumors was previously demonstrated, and expressed only in the tumors but not in another tissue examined. Notably, in addition to the expression of a neural marker gene N-CAM, the three nuclear oncogenes, c-, L-, and N-myc, were coexpressed in the tumors. These results suggest that E1A and E1B are cooperatively involved in the heritable formation of neuroectodermal tumors associated with co-expression of the three sets of myc family genes.

Activation of the nuclear oncogenes N-myc and c-jun in carcinoid [correction of cartinoid] tumors of transgenic mice carrying the human adenovirus type 12 E1 region gene

The adenovirus (Ad) E1 region genes, E1A and E1B, are well known cooperatively to transform primary rodent cells and activate a number of cellular promoters, including nuclear oncogenes such as N-myc and c-jun, in transfected cell lines. However, there is still less information available on the in vivo mechanism(s) by which the E1 region gene, when chromosomally integrated in the living animals, exerts its effect on nuclear oncogene activation coupled with transformation. To investigate such in vivo activity of E1A we have used a series of microinjection experiments into fertilized eggs to generate three transgenic mice carrying the Ad12-type E1A/E1B genes under the control of the human renin gene. This transgene caused an early onset of bowel cartinoid tumors that express neural cell adhesion molecules, but do not metastasize to any region. Northern blot analysis revealed that the transgenes were considerably expressed in the tumors, but not in other tissues at detectable levels. Interestingly, the levels of N-myc and c-jun mRNAs in the cartinoid tumors were elevated 19- and 8-fold, respectively, as compared with those found in the control intestine. In contrast, the major histocompatibility complex (MHC) class I mRNA level was not altered between the tumor and control intestines, suggesting that this unchanged expression may reflect the loss of tumor metastasis. These findings provide the first in vivo evidence that the expression of the Ad12 E1 region gene induces cartinoid tumors associated with the activation of the nuclear oncogenes N-myc and c-jun.

Rodent models for targeted oncogenesis of the prostate gland

Currently, prostate cancer ranks as the most frequent non-skin malignancy detected in males. Yet, of the major human cancers, it remains one of the least understood in terms of its molecular and genetic basis. Research on prostate cancer has been limited by the paucity of tissues available for study. Much of the tissue obtained through surgery for localized prostate cancer will be required for pathological staging and grading. The more aggressive forms of prostate cancer are usually detected subsequent to metastatic involvement at which point there is little reason to surgically remove the prostate tumor(s). A final complication is the propensity of prostate cancer to metastasize to the bone, a site extremely difficult to obtain suitable biopsies for study. Further hindering research efforts on prostate cancer is the lack of suitable animal models for study. In contrast to its frequent occurrence in humans, prostate cancer is a rare event in most other mammalian species, particularly laboratory rodents. Therefore, in order to make this disease more amenable for study, there is a growing effort to identify or develop a means to target oncogenesis to the prostate gland of rodents. As will be reviewed here, this goal is being approached with the use of 3 different methods; one that takes advantage of the unique androgenic hormone requirement for prostate growth to exaggerate the effects of carcinogens at that site and two methods (recombinant retrovirus transduction prior to organ reconstitution and transgenic targeting) that allow direct genetic manipulation of cells in the prostate gland leading to the development of prostatic malignancy.

Transgenic models for the study of prostate cancer

Transgenic model systems provide tools for obtaining information that clarifies important relationships between genetic alterations and carcinogenesis. One such relationship is the induction of specific growth factor activities by dominantly acting oncogenes. Using a "transgenic organ" model referred to as mouse prostate reconstitution (MPR) under conditions where the ras and myc oncogenes were introduced using a recombinant retrovirus into both the mesenchymal and epithelial compartments of the urogenital sinus, poorly differentiated prostate cancer (PC) was produced with high frequency (> 90%) in inbred C57BL/6 mice. Time-course studies using northern blotting and immunohistochemical analysis showed that the transition from benign to malignant status invariably was associated with the induction of elevated transforming growth factor-beta 1 (TGF-beta 1) expression. Additional immunohistochemical analysis of TGF-beta 1 in human PC and benign prostatic hyperplasia (BPH) showed that positive extracellular staining was significantly more extensive in PC compared with BPH. This differential staining pattern was evident in focal areas of PC adjacent to BPH. These findings in both the MPR model system and human PC suggest that elevated TGF-beta 1 expression is involved in the progression to malignancy and that its pattern of expression may become a useful marker of PC. Additional studies using transgenic animal models will continue to provide important clinically useful information about PC in man.