Oncogene expression in mammary epithelial cells

Oncogene HER-2 in canine mammary gland carcinomas: an immunohistochemical and chromogenic in situ hybridization study

Immunohistochemical (IHC) HER-2/neu protein overexpression was found in 17.6% of canine mammary gland carcinomas, a percentage similar to that observed in human breast carcinoma, but there was no gene amplification by chromogenic in situ hybridization (CISH). Canine mammary carcinoma would be a suitable natural model of that subset of human breast carcinomas with HER-2 protein overexpression without gene amplification.

Validity of mouse mammary tumour models for human breast cancer: comparative pathology

In March 1999, a panel of distinguished pathologists was convened by the U.S. National Institutes of Health Breast Cancer Think Tank to develop a classification of breast lesions based on their examination of 39 models of Genetically Engineered Mice (GEM) associated mouse mammary cancer (Cardiff et al., 2000). The meeting, in Annapolis, Maryland, resulted in a published summary report from the Pathology Panel (Cardiff et al., 2000). The Annapolis consensus report, developed from the Panel's deliberations, pointed out that the mammary lesions of GEM were different from most (spontaneous) mouse mammary tumors and could be divided into three distinct categories: (1) lesions that resemble those found in spontaneous mouse mammary tumorigenesis, (2) lesions that have a unique "signature" tumor phenotype that was specific for the transgene, and (3) lesions that resemble those found in human breast diseases (Cardiff et al., 2000). This review emphasizes the proposed nomenclature and the differences between the models and human breast cancer with the intention of stimulating discussion and the development of new models.

Targeted inhibition of osteopontin expression in the mammary gland causes abnormal morphogenesis and lactation deficiency

Osteopontin (OPN) is a sialic acid-rich, adhesive, extracellular matrix (ECM) protein with Arg-Gly-Asp cell-binding sequence that interacts with several integrins, including alpha(v)beta(3). Since the ECM is a key regulator of mammary gland morphogenesis, and mammary epithelial cells express OPN at elevated levels, we sought to determine whether this protein plays a role in the postnatal mammary gland development. By generating transgenic mice that express OPN antisense-RNA (AS-OPN mice) in the mammary epithelia we achieved suppression of OPN production in this organ. The pregnant AS-OPN mice displayed a lack of mammary alveolar structures, a drastic reduction in the synthesis of beta-casein, whey acidic milk protein, and lactation deficiency. In agreement with these findings, we uncovered that a mammary cell line, NMuMG, which undergoes both structural and functional differentiation on ECM-coated plates, when transfected with an antisense OPN-cDNA construct, failed to undergo such differentiation. Furthermore, the results of gel-invasion assays demonstrated that these cells manifest elevated matrix metalloproteinase (MMP) activity when OPN expression is significantly reduced. The identity of this proteinase as MMP-2 is confirmed by Western blotting, zymography, and inhibition of its activity by a specific inhibitor, TIMP-2. Taken together, our results demonstrate, for the first time, an essential role of OPN in mammary gland differentiation and that the molecular mechanism(s) of its action, at least in part, involves down-regulation of MMP-2.

Conditional gene expression in secretory tissues and skin of transgenic mice using the MMTV-LTR and the tetracycline responsive system

Molecular mechanisms of development and disease can be studied in transgenic animals. Controlling the spatial and temporal expression patterns of transgenes, however, is a prerequisite for the elucidation of gene function in the whole organism. Previously we reported that mice carrying a tetR/VP16 hybrid gene (tTA), under the control of the human cytomegalovirus immediate early 1 (HCMV-IE1) gene promoter, can be used to temporally activate the expression of transgenes under the control of a promoter containing tetop sequences. We now show that the MMTV-LTR can be used to target expression of tTA to the epithelial cells of secretory organs and skin in transgenic mice. Notably, nearly uniform expression of a tetop-lacZ transgene was found in seminal vesicle, salivary gland, and Leydig cells of mice carrying also the MMTV-tTA transgene. More heterogeneous patterns of gene expression were observed in mammary epithelial cells and basal cells of the epidermis. Different MMTV-tTA lines had comparable tissue expression patterns. Transcriptional activation mediated by tTA was up to several hundredfold, and it was abrogated after the administration of tetracycline. The MMTV-tTA mice established in this work will be useful for experiments examining the roles of biological factors at defined developmental stages in the epithelial cells of salivary gland, seminal vesicle, mammary gland, and skin and the Leydig cells of testes. In addition, in combination with the CRE/lox recombination system, these mice wil be useful to achieve gene deletions at defined time points in these organs.

Temporal control of gene expression in transgenic mice by a tetracycline-responsive promoter

Promoters whose temporal activity can be directly manipulated in transgenic animals provide a tool for the study of gene functions in vivo. We have evaluated a tetracycline-responsive binary system for its ability to temporally control gene expression in transgenic mice. In this system, a tetracycline-controlled trans-activator protein (tTA), composed of the repressor of the tetracycline-resistance operon (tet from Escherichia coli transposon Tn10) and the activating domain of viral protein VP16 of herpes simplex virus, induces transcription from a minimal promoter (PhCMV*-1; see below) fused to seven tet operator sequences in the absence of tetracycline but not in its presence. Transgenic mice were generated that carried either a luciferase or a beta-galactosidase reporter gene under the control of PhCMV*-1 or a transgene containing the tTA coding sequence under the control of the human cytomegalovirus immediate early gene 1 (hCMV IE1) promoter/enhancer. Whereas little luciferase or beta-galactosidase activity was observed in tissues of mice carrying only the reporter genes, the presence of tTA in double-transgenic mice induced expression of the reporter genes up to several thousand-fold. This induction was abrogated to basal levels upon administration of tetracycline. These findings can be used, for example, to design dominant gain-of-function experiments in which temporal control of transgene expression is required.

[Expression of recombinant proteins in the milk of transgenic animals]

The bulky production of recombinant proteins can be achieved by procaryotes or eucaryotes cells. Cells from higher eucaryotes may be required when proteins have to be modified post-transcriptionally (glycosylation phosphorylation, cleavage, folding...). Cells from higher vertebrates in culture are used to prepare proteins like human factor VIII and erythropoietin. The use of transgenic organism has been suggested to reach the same goal. Indeed a whole living organism allows a very potent amplification, the number of cells involved in the biosynthesis of the recombinant proteins being very numerous and in the best metabolic conditions. Biological fluids (blood, milk, insect hemolymph, egg white...) and possibly organs from transgenic animals are a priori the best sources of recombinant proteins. Blood is abundant and it is a by-product of slaughter house. Its composition is relatively complex and the circulating recombinant proteins may heavily alter health of animals. Milk is very abundant, its composition is relatively simple, it is poor in proteolytic enzymes and it can be collected easily. Hemolymph from insects is relatively scarce. Egg white will be a possible source of recombinant proteins, when transgenesis has become more accessible in birds. Organs from transgenic animals should be solicited only when a particular cell type is required for the biosynthesis of the recombinant proteins. Milk appears therefore, presently, as the best source of recombinant proteins from transgenic animals. About 15 public and private laboratories try to use these techniques. They consist in preparing vectors containing regulatory regions of one of the milk proteins genes and the coding part (cDNA or gene) of the corresponding proteins to be produced. The transfer of these gene constructs to mouse, rabbit, sheep, goat, pig, shows that these techniques are indeed very promising. A single protein, human alpha 1-antitrypsin produced in milk of transgenic sheep, has presently reached the preparation at an industrial scale. This method has two theoretical limitations: 1) some of the proteins secreted in milk may be not matured as their native counterparts. Experiments carried out so far (about 20 proteins has been produced at an experimental scale) indicate that the mammary cell is able to achieve glycosylation in a correct way; 2) a significant proportion of the recombinant proteins migrate from the alveolar compartment of the mammary gland to blood circulation and they can alter health of lactating animals.(ABSTRACT TRUNCATED AT 400 WORDS)