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Biomedical subjects

W J Muller

Publications and source records attributed to W J Muller.

At least 73 records · Page 4Linked to original sources
PubMed1995

Telomerase activity in normal and malignant murine tissues.

Telomere shortening may contribute to the limited lifespan of somatic cells and telomerase, the enzyme that elongates telomeric DNA and maintains telomere length, may be essential for unlimited cell proliferation in vivo and in vitro. Telomerase is not expressed in most human somatic cells but is a nearly ubiquitous tumour marker, being activated in malignant cells from many cancers. Inhibition of telomerase may lead to telomere shortening and eventually limit the proliferative capacity of malignant cells and hence be of therapeutic value. With the intent of characterizing an animal model for inhibition studies, we investigated telomerase activity during mammary tumorigenesis in transgenic mice overexpressing the neu gene. We detected activity in primary mammary tumours and lung metastases but also in normal mammary glands and other organs. Activity was elevated in tumors versus normal tissues and was enhanced by short-term culturing of normal cells. Telomerase activity was also present in somatic tissues from the non-transgenic parental strain and the outbred Mus spretus strain. As we recently detected telomerase activity in normal human hemopoietic tissues, mouse models of tumorigenesis may provide useful experimental systems for assessing the outcome of in vivo inhibition of telomerase in both malignant and normal cells.

Animals↗
PubMed1995

Intratumoral injection of an adenovirus expressing interleukin 2 induces regression and immunity in a murine breast cancer model.

Rodent tumor cells engineered to secrete cytokines such as interleukin 2 (IL-2) or IL-4 are rejected by syngeneic recipients due to an enhanced antitumor host immune response. An adenovirus vector (AdCAIL-2) containing the human IL-2 gene has been constructed and shown to direct secretion of high levels of human IL-2 in infected tumor cells. AdCAIL-2 induces regression of tumors in a transgenic mouse model of mammary adenocarcinoma following intratumoral injection. Elimination of existing tumors in this way results in immunity against a second challenge with tumor cells. These findings suggest that adenovirus vectors expressing cytokines may form the basis for highly effective immunotherapies of human cancers.

Adenocarcinoma↗
PubMed1995

Induction of mammary epithelial hyperplasias and mammary tumors in transgenic mice expressing a murine mammary tumor virus/activated c-src fusion gene.

Activation of the c-Src tyrosine kinase has been implicated as an important step in the induction of mammary tumors in both mice and humans. To directly assess the effect of mammary gland-specific expression of activated c-Src, we established transgenic mice that carry a constitutively activated form of c-src under transcriptional control of the murine mammary tumor virus long terminal repeat. Female mice derived from several independent transgenic lines lactate poorly as a consequence of an impairment in normal mammary epithelial development. In addition to this lactation defect, female mice frequently develop mammary epithelial hyperplasias, which occasionally progress to frank neoplasias. Taken together, these observations suggest that expression of activated c-Src in the mammary epithelium of transgenic mice is not sufficient for induction of mammary tumors.

Aging↗
PubMed1995

Direct and specific interaction of c-Src with Neu is involved in signaling by the epidermal growth factor receptor.

Transgenic mice expressing either the activated or wild type neu oncogene heritably develop metastatic mammary tumors. Tumor development in this transgenic mouse model correlates with activation of the Neu tyrosine kinase. Recently, we have shown that these Neu-induced mammary tumors possess elevated c-Src tyrosine kinase activity. Here, we demonstrate that c-Src requires tyrosine phosphorylated Neu for its ability to associate with Neu in vivo and this association is likely the result of a direct physical binding of c-Src SH2 domain to the tyrosine phosphorylated Neu. By contrast, the c-Src SH2 domain did not interact directly with tyrosine phosphorylated EGFR. Moreover, in established cell lines expressing elevated levels of EGFR, EGF stimulation results in transphosphorylation of Neu and formation of complexes between c-Src and tyrosine phosphorylated Neu. Taken together, these observations suggest that activation of c-Src by these two closely related EGFR family members results from a direct and specific interaction of c-Src with tyrosine phosphorylated Neu.

Animals↗
PubMed1995

Histopathology of transgenic mouse mammary tumors (a short atlas).

Mammary hyperplasias, dysplasias and tumors have been described in many strains of transgenic mice. Many of the transgenes produce characteristic disturbances of growth, development and neoplasia. The disturbances can now be classified into groups. A classification of transgenic tumors and an atlas illustrating some characteristic examples of common morphological changes in transgenic mammary tissues is provided.

Animals↗
PubMed1995

Sensory irritation in mice exposed to emissions from indoor products.

Sensory irritation (SI) in mice exposed to chemical emissions from products was investigated using a modification of an ASTM standard protocol. Samples of carpet, ceiling tile, wallcovering, resilient flooring, and veneer were tested as typical indoor products. SI during head-only animal exposure was assessed by monitoring changes in respiratory frequency and waveform when test products were continuously ventilated at either 23 or 70 degrees C (73 or 158 degrees F). Animals were subjected to four 1-hour exposures to product emissions, corresponding to 1, 4, 24, and 27 elapsed hours of product exposure. SI was generally not observed when products were tested at 23 degrees C, but could be induced during at least one exposure period from all products except the carpet sample at 70 degrees C. Although the total volatile organic compound emissions from a given product tested at elevated temperature increased between 5- and 30-fold from the emissions at ambient temperature, gas chromatography/mass spectrometry analysis for the individual chemicals showed differences in the relative chemical compositions of the test atmospheres. Therefore, although increasing the temperature to 70 degrees C may increase the total chemical concentration of product emissions, it may not produce a chemical exposure comparable to that at ambient conditions. Since most human exposure to product emissions occurs at ambient conditions, the significance of irritation at elevated temperatures is therefore questionable.

Air Pollution, Indoor↗
PubMed1995

Pathways for uptake of fluorescently labeled liposomes by alveolar type II cells in culture.

Isolated alveolar type II cells are shown in real time to internalize 1-palmitoyl-2-[12-[(7 nitro-2-1,3-benzoxadiazol-4-yl)amino]dodecanoyl] phosphatidyl choline (C12-NBD-PC)-labeled liposomes in an intact manner with the use of fluorescence microscopy. Cells isolated from rat lungs, cultured on plastic for 24 h, are exposed at 37 degrees C to liposomes on the microscope stage, using a microperfusion system. Liposomes composed of a self-quenching concentration of fluorophore (25 mol% C12-NBD-PC) do not dequench at the level of the plasma membrane; rather, they appear to fuse with intracellular lipids primarily in vesicular structures consistent with lamellar bodies. Temperature and energy dependence of this uptake mechanism is demonstrated by the lack of uptake of maximally fluorescent liposomes (15 mol% C12-NBD-PC) at 4 degrees C or when depleted of ATP. Inhibition of the coated-pit endocytic pathway by hypertonic media reduces fluorescent lipid uptake by 50%, suggesting a separate, clathrin-independent endocytic pathway for intact internalization of liposomes by type II cells. Uptake is inhibited by cytochalasin D by 49%, suggesting a dependence on action, and by 88% with combined cytochalasin D and hypertonicity, or nearly the same level as ATP depletion. The evidence is consistent with the existence of two separate endocytic pathways for lipids in type II cells: one clathrin dependent and the other actin dependent.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1995

Transgenic mice bearing the polyomavirus large T antigen directed by 2.1 kb of the keratin 19 promoter develop bronchiolar papillary tumors with progression to lung adenocarcinomas.

Keratin 19 is an intermediate filament protein produced by cells of simple epithelia and basal cells of stratified epithelia of different organs. These cell types are associated with important human cancers. We have used the keratin 19 promoter to target the expression of the polyomavirus (Py) large T-antigen, an immortalizing oncogene known to bind to the tumor suppressor retinoblastoma gene product, to epithelial cells. Individuals of the transgenic mouse line K19PyLT-6 developed one or two nodules in one of their lungs. By histology, the nodules were papillary tumors that consisted of nonciliated epithelial cells of the terminal bronchioles. In addition, infiltrates emanating from the nodules were consistent with the development of pulmonary adenocarcinomas. In situ hybridization techniques demonstrated large T-antigen expression in the tumors. Primary cultures were established from a lung tumor dissected from a K19PyLT-6 transgenic mouse. These large T-antigen-expressing cell lines produced the keratin proteins reminiscent of the epithelial origin of the lung tumor. However, further molecular studies indicated that these cell lines did not express Clara cells or pneumocytes markers. s.c. injection of the cell lines into nontransgenic syngeneic mice produced tumors in 2 weeks that resembled malignant pulmonary adenocarcinomas. These animals, which display tumor progression in situ, and the cell lines derived thereof provide a useful system for the study of lung tumorigenesis.

Adenocarcinoma↗
PubMed1994

Activation of the c-Src tyrosine kinase is required for the induction of mammary tumors in transgenic mice.

Transgenic mice expressing the polyomavirus (PyV) middle T oncogene in the mammary epithelium develop multifocal mammary tumors that metastasize with high frequency. The potent transforming activity of PyV middle T antigen can, in part, be attributed to its ability to associate with and to activate a number of c-Src family tyrosine kinases (c-Src, c-Yes, and Fyn). As a first step toward assessing the role of individual c-Src family tyrosine kinases in PyV middle T antigen-induced mammary tumorigenesis, we have crossed transgenic mice carrying the mouse mammary tumor virus (MMTV)/PyV middle T antigen fusion gene with mice bearing a disrupted c-src proto-oncogene. In contrast to the rapid tumor progression seen in the original MMTV/PyV middle T antigen strains, mice expressing the transgene in the absence of functional c-Src rarely developed mammary tumors. After long latency, these mice did eventually develop abnormal hyperplastic mammary tissue. This growth disturbance was correlated with elevated expression of the PyV middle T antigen and the activation of the PyV middle T antigen-associated c-Yes tyrosine kinase. However, transgenic mice expressing the PyV middle T antigen in the mammary epithelium of wild-type or Yes-deficient mice developed multifocal mammary tumors with comparable kinetics. Taken together, these findings suggest that c-Src tyrosine kinase activity is required for PyV middle T antigen-induced mammary tumorigenesis and also illustrate an in vivo genetic approach to the dissection of mitogenic signal transduction pathways.

Animals↗
PubMed1994

Mammary tumors expressing the neu proto-oncogene possess elevated c-Src tyrosine kinase activity.

Amplification and overexpression of the neu (c-erbB2) proto-oncogene has been implicated in the pathogenesis of 20 to 30% of human breast cancers. Although the activation of Neu receptor tyrosine kinase appears to be a pivotal step during mammary tumorigenesis, the mechanism by which Neu signals cell proliferation is unclear. Molecules bearing a domain shared by the c-Src proto-oncogene (Src homology 2) are thought to be involved in signal transduction from activated receptor tyrosine kinases such as Neu. To test whether c-Src was implicated in Neu-mediated signal transduction, we measured the activity of the c-Src tyrosine kinase in tissue extracts from either mammary tumors or adjacent mammary epithelium derived from transgenic mice expressing a mouse mammary tumor virus promoter/enhancer/unactivated neu fusion gene. The Neu-induced mammary tumors possessed six- to eightfold-higher c-Src kinase activity than the adjacent epithelium. The increase in c-Src tyrosine kinase activity was not due to an increase in the levels of c-Src but rather was a result of the elevation of its specific activity. Moreover, activation of c-Src was correlated with its ability to complex tyrosine-phosphorylated Neu both in vitro and in vivo. Together, these observations suggest that activation of the c-Src tyrosine kinase during mammary tumorigenesis may occur through a direct interaction with activated Neu.

Animals↗
PubMed1994

Novel activating mutations in the neu proto-oncogene involved in induction of mammary tumors.

Amplification of the Neu/c-erbB-2 receptor tyrosine kinase has been implicated as an important event in the genesis of human breast cancer. Indeed, transgenic mice bearing either an activated form of neu or the wild-type proto-oncogene under the transcriptional control of the mouse mammary tumor virus promoter-enhancer frequently develop mammary carcinomas (L. Bouchard, L. Lamarre, P. J. Tremblay, and P. Jolicoeur, Cell 57:931-936, 1989; C. T. Guy, M. A. Webster, M. Schaller, T. J. Parson, R. D. Cardiff, and W. J. Muller, Proc. Natl. Acad. Sci. USA 89:10578-10582, 1992; W. J. Muller, E. Sinn, R. Wallace, P. K. Pattengale, and P. Leder, Cell 54:105-115, 1988). Induction of mammary tumors in transgenic mice expressing the wild-type Neu receptor is associated with activation of the receptor's intrinsic tyrosine kinase activity (Guy et al., Proc. Natl. Acad. Sci. USA 89:10578-10582, 1992). Here, we demonstrate that activation of Neu in these transgenic mice occurs through somatic mutations located within the transgene itself. Sequence analyses of these mutations revealed that they contain in-frame deletions of 7 to 12 amino acids in the extracellular region proximal to the transmembrane domain. Introduction of these mutations into a wild-type neu cDNA results in an increased transforming ability of the altered Neu tyrosine kinase. These observations suggest that oncogenic activation of Neu in mammary tumorigenesis frequently occurs by somatic mutation.

Amino Acid Sequence↗
PubMed1994

Mammary tumorigenesis and metastasis in transgenic mice.

The transgenic mouse has emerged as an important model system to assess the transforming potential of oncogenes in the mammary epithelium. Mammary gland-specific expression of oncogenes in transgenic mice has resulted in the induction of a variety of phenotypes ranging from benign epithelial hyperplasias to metastatic mammary tumors. The induction of tumors in most of these transgenic models is a multi-step process where transgene expression, although required, is not sufficient for conversion of the primary mammary epithelial cell to the transformed phenotype. While the identity of many of these collaborating genetic events is obscure, several approaches have been applied with might shed light on their nature. In a few exceptional transgenic strains, tumor progression can occur very rapidly suggesting that, if additional genetic events are required, they occur very frequently. Recent genetic and biochemical characterization of these strains offers insight into the molecular mechanisms that may underlie the complex phenotypic features exhibited by these transgenic strains.

Animals↗
PubMed1993

Production and secretion of progesterone in vitro and presence of platelet activating factor (PAF) in early pregnancy of the marsupial, Macropus eugenii.

The corpus luteum (CL) of the tammar is suppressed by lactation. Removal of the sucking pouch young induces reactivation of the CL which produces a peak in plasma progesterone concentration on Day 5, 6 or 7; reactivation of the embryo after diapause precedes by one day this transient peak of progesterone. This study examines progesterone production and secretion in vitro by the CL and the production of platelet activating factor (PAF) by the endometrium during this stage of pregnancy (Days 0 and 3-8). Blood samples were collected twice daily to determine for each animal (n = 28) at autopsy the relationship of PAF production to the day of the progesterone peak. Significant changes in basal plasma progesterone concentrations were used to define four groups according to the time the animals were killed: Group A, Day 0; Group B, other animals showing no significant change; Group C, peripheral progesterone concentration increasing; Group D, peripheral progesterone concentration decreasing after the peak. At autopsy on successive days, blood samples were taken from the heart, caudal vein and uterine branch of the ovarian vein, and CL and endometria were prepared for explant culture. Progesterone contents of pre- and post-incubation luteal tissues and of medium were determined at 4, 12 and 24 h to estimate production and secretion rates. The values for all progesterone parameters from animals in Group C were significantly higher than in the other groups. It is concluded that the progesterone peak results from a change in rate of production and secretion of progesterone by the CL, one day before the peak in peripheral plasma, and that this change could provide the first signal to the uterus. Endometrium was incubated for 24 h and the medium assayed for PAF. High concentrations of PAF were detected in half the animals in Groups B and C, that is, before or at the time progesterone was increasing. This is the first measurement of PAF in any marsupial and the first demonstration of the release of PAF by the endometrium. The detection of PAF provides a candidate for an endometrial signal that is responsive to the rising progesterone concentration in the utero-ovarian vein draining the CL-bearing ovary and that may stimulate reactivation of the blastocyst.

Animals↗
PubMed1993

PEA3 is overexpressed in mouse metastatic mammary adenocarcinomas.

Transgenic mice bearing the rat neu proto-oncogene under the transcriptional control of the mouse mammary tumor virus (MMTV) promoter develop focal mammary adenocarcinomas after long latency that are metastatic to the lung in a high percentage of the tumor-bearing animals. Because expression of the neu gene in the mammary epithelium precedes the occurrence of tumors, it appears that another genetic event in addition to neu transgene expression is required for tumorigenesis. We have investigated the expression of PEA3, a new member of the ets oncogene family of transcriptional regulatory factors, in neu-induced mammary tumors to learn whether PEA3 plays a role in tumor progression in this organ. We observed high levels of PEA3 RNA in neu-induced tumors, but little, if any, PEA3 RNA in the surrounding mammary epithelium. Moreover, mammary tumors that had metastasized to the lung also overexpressed the PEA3 gene, whereas normal lung tissue did not. Similar results were obtained after analyses of other transgenic mouse lines bearing metastatic mammary tumors induced by polyomavirus middle T antigen. These findings suggest that enhanced expression of PEA3 may be required to facilitate mammary tumor progression and metastasis.

Adenocarcinoma↗
PubMed1992

Expression of the neu protooncogene in the mammary epithelium of transgenic mice induces metastatic disease.

Overexpression and amplification of the neu (c-erbB2, ERBB2) protooncogene have been implicated in the development of aggressive human breast cancer. To directly assess the effect of mammary gland-specific expression of the neu protooncogene, transgenic mice carrying unactivated neu under the transcriptional control of the mouse mammary tumor virus promoter/enhancer were established. By contrast to the rapid tumor progression observed in several transgenic strains carrying the activated neu transgene, expression of unactivated neu in the mammary epithelium resulted in the development of focal mammary tumors after long latency. The majority of the mammary tumors analyzed expressed elevated levels of neu-encoded mRNA and protein. Overexpression of neu in the mammary tumors was also associated with elevated neu intrinsic tyrosine kinase activity and the de novo tyrosine phosphorylation of several cellular proteins. Interestingly, many of the tumor-bearing transgenic mice developed secondary metastatic tumors in the lung. These observations suggest that overexpression of the unactivated neu protein can induce metastatic disease after long latency.

Animals↗
PubMed1992

Transgenes expressing the Wnt-1 and int-2 proto-oncogenes cooperate during mammary carcinogenesis in doubly transgenic mice.

The Wnt-1 and int-2 proto-oncogenes are transcriptionally activated by mouse mammary tumor virus insertion mutations in virus-induced tumors and encode secretory glycoproteins. To determine whether these two genes can cooperate during carcinogenesis, we have crossed two previously characterized lines of transgenic mice to obtain bitransgenic animals carrying both Wnt-1 and int-2 transgenes under the control of the mouse mammary tumor virus long terminal repeat. Mammary carcinomas appear earlier and with higher frequency in the bitransgenic animals, especially the males, than in either parental line. Nearly all bitransgenic males develop mammary neoplasms within 8 months of birth, whereas only 15% of Wnt-1 transgenic males and none of the int-2 transgenic males have tumors. In virgin bitransgenic females, tumors occur approximately 2 months earlier than in their Wnt-1 transgenic siblings; int-2 transgenic females rarely exhibit tumors. Preneoplastic glands from the bitransgenic animals of either sex demonstrate pronounced epithelial hyperplasia similar to that seen in Wnt-1 transgenic virgin females and males, and both transgenes are expressed in the hyperplastic glands and mammary tumors. RNA from the int-2 transgene is more abundant in mammary glands from bitransgenic animals than from int-2 transgenic animals; the increase is associated with high levels of RNA specific for keratin genes 14 and 18, suggesting that Wnt-1-induced epithelial hyperplasia is responsible for the observed increase in expression of the int-2 transgene.

Animals↗