A 470 bp WAP-promoter fragment confers lactation independent, progesterone regulated mammary-specific gene expression in transgenic mice

Hormonal regulation of platypus Beta-lactoglobulin and monotreme lactation protein genes

Endocrine regulation of milk protein gene expression in marsupials and eutherians is well studied. However, the evolution of this complex regulation that began with monotremes is unknown. Monotremes represent the oldest lineage of extant mammals and the endocrine regulation of lactation in these mammals has not been investigated. Here we characterised the proximal promoter and hormonal regulation of two platypus milk protein genes, Beta-lactoglobulin (BLG), a whey protein and monotreme lactation protein (MLP), a monotreme specific milk protein, using in vitro reporter assays and a bovine mammary epithelial cell line (BME-UV1). Insulin and dexamethasone alone provided partial induction of MLP, while the combination of insulin, dexamethasone and prolactin was required for maximal induction. Partial induction of BLG was achieved by insulin, dexamethasone and prolactin alone, with maximal induction using all three hormones. Platypus MLP and BLG core promoter regions comprised transcription factor binding sites (e.g. STAT5, NF-1 and C/EBPα) that were conserved in marsupial and eutherian lineages that regulate caseins and whey protein gene expression. Our analysis suggests that insulin, dexamethasone and/or prolactin alone can regulate the platypus MLP and BLG gene expression, unlike those of therian lineage. The induction of platypus milk protein genes by lactogenic hormones suggests they originated before the divergence of marsupial and eutherians.

Overview of Genetically Engineered Mouse Models of Breast Cancer Used in Translational Biology and Drug Development

Breast cancer is a heterogeneous condition with no single standard of treatment and no definitive method for determining whether a tumor will respond to therapy. The development of murine models that faithfully mimic specific human breast cancer subtypes is critical for the development of patient-specific treatments. While the artificial nature of traditional in vivo xenograft models used to characterize novel anticancer treatments has limited clinical predictive value, the development of genetically engineered mouse models (GEMMs) makes it possible to study the therapeutic responses in an intact microenvironment. GEMMs have proven to be an experimentally tractable platform for evaluating the efficacy of novel therapeutic combinations and for defining the mechanisms of acquired resistance. Described in this overview are several of the more popular breast cancer GEMMs, including details on their value in elucidating the molecular mechanisms of this disorder.

Reconstituting retroviral (ReCon) vectors facilitating delivery of cytotoxic genes in cancer gene therapy approaches

BACKGROUND

We have previously described the generation of reconstituting retroviral (ReCon) vectors designed for cancer gene therapy using cytotoxic gene products. The unique vector structure with a promoter physically separated from the transgene allows generation of stable virus producer cells irrespective of the toxic gene. The mechanism of synthesis of DNA from retroviral RNA dictates that infection leads to the reconstitution of functional expression cassettes in the target cell.

METHODS

To improve vector titres, a cytomegalovirus enhancer was inserted upstream of the 5'-long-terminal repeat (LTR); the Woodchuck hepatitis virus post-transcriptional regulatory element and an elongated attachment site upstream of the 3'-LTR were included. In addition, a bacterial origin of replication was deleted and a functional internal polyadenylation signal mutated. Transcriptional targeting was attempted by introducing mammary tissue-specific promoters such as the U3 region of mouse mammary tumour virus or the promoter of the whey acidic protein encoding gene. All modifications were analysed in detail with respect to virus production and infectivity. Finally, the vector was armed with the lambda-holin encoding gene and transduced cells were analysed for cytotoxic effects.

RESULTS

Distinct modifications of the vector resulted in a titre improvement of more than 560-fold. Compatibility of the optimized vector with targeted cellular promoters was demonstrated. When equipped with the cytotoxic gene, stable producer cells could be successfully established and high titre virus infection resulted in rigorous target cell killing.

CONCLUSIONS

The ReCon vector in its optimized form is an attractive tool for cancer gene therapy approaches.

Magnetic resonance imaging and spectroscopy of transgenic models of cancer

The complexity of cancer, where a single genetic alteration can have multiple functional effects, makes it a fascinating but humbling disease to study, and the necessity of investigating it in its entirety is more imperative than ever before. Advances in transgene technology have made it possible to create cancer cells, or mice with specific genetic alterations, and the application of an array of both functional and molecular non-invasive MR methods to these transgenic cancer cells and mice to characterize their phenotypic traits is revolutionizing our understanding of cancer. With the establishment of multi-modality molecular imaging centers within barrier or pathogen-free facilities, multi-parametric and multi-modality imaging of transgenic mouse models of human cancer are becoming increasingly prevalent. In this review, we outline some of the methods currently available for generating transgenic mice and cancer cell lines. We also present examples of the application of MR methods to transgenic models that are providing novel insights into the molecular and functional characteristics of cancer and are leading to an era of "non-invasive phenotyping" of the effects of specific molecular alterations in cancer.

Mouse models of breast cancer metastasis

Metastatic spread of cancer cells is the main cause of death of breast cancer patients, and elucidation of the molecular mechanisms underlying this process is a major focus in cancer research. The identification of appropriate therapeutic targets and proof-of-concept experimentation involves an increasing number of experimental mouse models, including spontaneous and chemically induced carcinogenesis, tumor transplantation, and transgenic and/or knockout mice. Here we give a progress report on how mouse models have contributed to our understanding of the molecular processes underlying breast cancer metastasis and on how such experimentation can open new avenues to the development of innovative cancer therapy.

WPRE-mediated enhancement of gene expression is promoter and cell line specific

The success of gene therapy approaches relies on sufficiently high levels of expression of the therapeutic gene. However, if tissue specific or tumour specific gene expression is desired, a lower level of transgene expression usually has to be accepted due to the weakness of the majority of available tissue or tumour specific promoters. This obstacle can in part be overcome by the insertion of viral cis-acting elements that enhance gene expression in various expression vector contexts regardless of the respective promoter. We designed a series of murine leukaemia virus (MLV)-based retroviral promoter conversion (ProCon) vectors that contain the woodchuck hepatitis post-transcriptional regulatory element (WPRE) and evaluated its use by measuring enhanced green fluorescent protein (EGFP) levels and viral titres. In viral vector packaging cells, when the EGFP encoding gene was transcribed from the MLV promoter, incorporation of the WPRE resulted in a marked improvement of the vectors in terms of EGFP expression and virus titres. However, in infected cells after promoter conversion had taken place, the effect of the WPRE became promoter and cell line dependent. When the EGFP gene was transcribed from the heterologous mouse mammary tumour virus (MMTV) promoter the same beneficial role of the WPRE on transgene expression was observed in all eight cell lines tested. In contrast, when EGFP gene expression was driven by the murine whey acidic protein (WAP) promoter, the positive effect of the WPRE could only be observed in two cell lines whereas expression was actually reduced in the six other cell lines tested. This decrease of EGFP expression was not only demonstrated at the protein level but also manifested on the RNA level.

Hypoxia- and radiation-inducible, breast cell-specific targeting of retroviral vectors

To facilitate a more efficient radiation and chemotherapy of mammary tumours, synthetic enhancer elements responsive to hypoxia and ionizing radiation were coupled to the mammary-specific minimal promoter of the murine whey acidic protein (WAP) encoding gene. The modified WAP promoter was introduced into a retroviral promoter conversion (ProCon) vector. Expression of a transduced reporter gene in response to hypoxia and radiation was analysed in stably infected mammary cancer cell lines and an up to 9-fold increase in gene expression demonstrated in comparison to the respective basic vector. Expression analyses in vitro, moreover, demonstrated a widely preserved mammary cell-specific promoter activity. For in vivo analyses, xenograft tumours consisting of infected human mammary adenocarcinoma cells were established in SCID/beige mice. Immunohistochemical analyses demonstrated a hypoxia-specific, markedly increased WAP promoter-driven expression in these tumours. Thus, this retroviral vector will facilitate a targeted gene therapeutic approach exploiting the unique environmental condition in solid tumours.