Biomedical subjects

Richard Jäger

Publications and source records attributed to Richard Jäger.

9 recordsLinked to original sources

PubMed2005

The AP-2 family of transcription factors.

The AP-2 family of transcription factors consists of five different proteins in humans and mice: AP-2alpha, AP-2beta, AP-2gamma, AP-2delta and AP-2epsilon. Frogs and fish have known orthologs of some but not all of these proteins, and homologs of the family are also found in protochordates, insects and nematodes. The proteins have a characteristic helix-span-helix motif at the carboxyl terminus, which, together with a central basic region, mediates dimerization and DNA binding. The amino terminus contains the transactivation domain. AP-2 proteins are first expressed in primitive ectoderm of invertebrates and vertebrates; in vertebrates, they are also expressed in the emerging neural-crest cells, and AP-2alpha-/- animals have impairments in neural-crest-derived facial structures. AP-2beta is indispensable for kidney development and AP-2gamma is necessary for the formation of trophectoderm cells shortly after implantation; AP-2alpha and AP-2gamma levels are elevated in human mammary carcinoma and seminoma. The general functions of the family appear to be the cell-type-specific stimulation of proliferation and the suppression of terminal differentiation during embryonic development.

Animals↗

PubMed2005

Cell-specific deletion of glucosylceramide synthase in brain leads to severe neural defects after birth.

Sialic acid-containing glycosphingolipids, i.e., gangliosides, constitute a major component of neuronal cells and are thought to be essential for brain function. UDP-glucose:ceramide glucosyltransferase (Ugcg) catalyzes the initial step of glycosphingolipid (GSL) biosynthesis. To gain insight into the role of GSLs in brain development and function, a cell-specific disruption of Ugcg was performed as indicated by the absence of virtually all glucosylceramide-based GSLs. Shortly after birth, mice showed dysfunction of cerebellum and peripheral nerves, associated with structural defects. Axon branching of Purkinje cells was significantly reduced. In primary cultures of neurons, dendritic complexity was clearly diminished, and pruning occurred early. Myelin sheaths of peripheral nerves were broadened and focally severely disorganized. GSL deficiency also led to a down-regulation of gene expression sets involved in brain development and homeostasis. Mice died approximately 3 weeks after birth. These results imply that GSLs are essential for brain maturation.

Animals↗

PubMed2005

Transcription factor AP-2gamma, a novel marker of gonocytes and seminomatous germ cell tumors.

Most germ cell tumors (GCTs) arise from intratubular germ cell neoplasias (IGCNUs, also referred to as carcinoma in situ), which are thought to originate from a transformed fetal germ cell, the gonocyte. However, the nature of the molecular pathways involved in IGCNU formation remains elusive. Therefore, identification of novel oncofetal markers is an important prerequisite to further our understanding of the etiology of this tumor entity. In the present study, we show that in humans AP-2gamma is expressed in gonocytes at weeks 12-37 of gestation, indicating a role of this transcription factor in fetal germ cell development. AP-2gamma and c-KIT, a known target of AP-2 transcription factors, were coexpressed in gonocytes, making a direct regulation possible. With increasing differentiation of fetal testis, gradual downregulation of AP-2gamma from the 12th to 37th week of gestation was observed. Furthermore, AP-2gamma was expressed abundantly in 25/25 IGCNUs, 52/53 testicular seminomas, 10/10 metastatic seminomas, 9/9 extragonadal seminomas and 5/5 dysgerminomas. In embryonal carcinomas and choriocarcinomas, focal staining only was observed. Spermatocytic seminomas, teratomas and yolk sac tumors as well as normal adult testis and various control tissues were negative for AP-2gamma. The expression pattern of AP-2gamma, like that of other oncofetal markers, supports the model of a gonocytal origin of IGCNUs and germ cell tumors. Finally, our results provide the basis for applying AP-2gamma immunohistochemistry to the detection of GCT, a tumor entity with a steadily growing incidence in the male population worldwide.

Biomarkers, Tumor↗

PubMed2005

Dual role of AP-2gamma in ErbB-2-induced mammary tumorigenesis.

A causative role of the membrane-bound tyrosine kinase ErbB-2 in breast tumorigenesis has been well established. MMTV/neu transgenic mice which overexpress ErbB-2 consistently develop mammary carcinomas with a high incidence. In human breast cancer, ErbB-2 is overexpressed in 25-30 of all cases and is representing a clinical marker of a poor prognosis. Besides to gene amplification, ErbB-2 overexpression has been attributed to transcription factors of the AP-2 family which were shown to control the ErbB-2 gene promoter in cell culture studies. Particularly AP-2alpha and gamma are often coexpressed in ErbB-2-positive breast carcinomas. However, LTRgamma transgenic mice which overexpress AP-2gamma in their mammary epithelium display only a very weak upregulation of the erbB-2 gene and do not develop mammary carcinoma. These findings therefore raise the possibility of functional cooperativity between both genes in breast cancer. To experimentally address the impact of AP-2gammaon ErbB-2-induced breast carcinogenesis we crossed MMTV/neu transgenic mice with LTRgamma transgenic mice and monitored tumor development in bitransgenic female progeny. AP-2gamma overexpression negatively influenced tumor incidence, as reflected by a reduced tumor number and a prolonged tumor latency. Histological analysis revealed three major types of tumors corresponding to different stages of tumor progression. Interestingly, an increased proportion of advanced stage carcinomas was observed in bitransgenic mice. Moreover, the AP-2gamma transgene differentially affected proliferation rates between the different progression stages: proliferation was enhanced at early stages but reduced in advanced stages in comparison to control tumors. Therefore, AP-2gamma while reducing the incidence of mammary tumors is promoting tumor progression.

Animals↗

PubMed2005

Distinct spatial expression patterns of AP-2alpha and AP-2gamma in non-neoplastic human breast and breast cancer.

Although transcription factors AP-2alpha and AP-2gamma have been implicated in the control of estrogen receptor (ER) and ErbB-2, their impact for breast cancer is still controversial. To better understand the role of AP-2 proteins in mammary neoplasia, the analysis of their spatial expression pattern in normal breast and breast cancer is required. A total of 51 specimens of female breast cancer patients and a tissue microarray containing 93 additional female breast cancer cases were immunohistochemically stained for AP-2alpha, AP-2gamma, ER and ErbB-2. In 70 cases of the tissue microarray, survival data comprising a period of up to 30 years were present. In non-neoplastic breast tissue, AP-2alpha was expressed in the inner glandular cell layer while AP-2gamma was expressed in the outer myoepithelial cell layer. Ductal carcinoma in situ revealed strongly AP-2alpha-positive tumor cells surrounded by a layer of AP-2gamma-positive myoepithelial cells. In invasive carcinoma, expression of AP-2alpha and AP-2gamma was variable. High expression of ER and AP-2alpha showed better survival rates than low expression of these markers. AP-2gamma expression had no effect on survival. These results for the first time reveal a distinct spatial expression pattern of AP-2alpha and AP-2gamma in normal breast and in ductal carcinoma in situ with specific AP-2gamma expression in myoepithelium. High ER and AP-2alpha expression in invasive breast cancer showed favorable survival rates. Therefore, AP-2alpha expression seems to be associated with better prognosis of breast cancer. AP-2gamma expression has no influence on survival reflecting that myoepithelial cells are not involved in the neoplastic process.

Actins↗

PubMed2004

Cell type-specific conditional regulation of the c-myc proto-oncogene by combining Cre/loxP recombination and tamoxifen-mediated activation.

Development of inducible genetic switches for in vivo use with transgenic mice has revolutionized many areas in modern molecular biology. Combining two techniques, Cre/loxP-based genetic recombination and ligand-dependent activation of a chimeric protein, we generated transgenic mice which allow for the spatiotemporal control of expression and of activity of the proto-oncogene c-myc. To these ends, the gene encoding the tamoxifen-inducible c-mycER(T) fusion protein (mycER(T)) was inserted in the ubiquitously active ROSA 26 gene locus by gene targeting. In the resulting ROSAMER allele, generalized transcription of the mycER(T) gene is prevented by a preceding transcriptional stop sequence which is flanked by loxP sites. Crosses of ROSAMER transgenic mice with Mox2 cre transgenic mice revealed tight control of mycER(T) transcription in various tissues unless the transcriptional stop sequence was removed by cre-mediated excision. Furthermore, we were able to demonstrate tamoxifen-dependent activation of the MycER(T) protein in embryonic fibroblasts derived from such mice. As a proof of principle, we demonstrate that primary neural crest cultures established from ROSAMER mice maintain their proliferative capacity in a 4-OHT-dependent manner. Furthermore, we demonstrate that such neural crest cells retain their differentiation potential as shown by expression of NF 160, a marker of neuronal differentiation upon 4-OHT withdrawal. The transgenic mice produced may thus be valuable tools for studying the cell type-specific effects of c-myc activity in development and disease.

Animals↗

PubMed2003

Transcription factor AP-2gamma stimulates proliferation and apoptosis and impairs differentiation in a transgenic model.

AP-2 transcription factors play pivotal roles in orchestrating embryonic development by influencing the differentiation, proliferation, and survival of cells. Furthermore, AP-2 transcription factors have been implicated in carcinogenesis, a process where the normal growth and differentiation program of cells is disturbed. To experimentally address the potential involvement of AP-2 in mammary gland tumorigenesis, we generated mice overexpressing AP-2gamma by transgenesis using the mouse mammary tumor virus-long terminal repeat as the transgene-driving promoter unit. In the mammary gland, transgene expression elicited a hyperproliferation that, however, was counterbalanced by the enhanced apoptosis of epithelial cells leading to a hypoplasia of the alveolar epithelium during late pregnancy. In addition, secretory differentiation was impaired, resulting in a lactation failure. In male transgenic mice, the seminal vesicles were sites of strong transgene expression. There the effects of AP-2gamma on proliferation and apoptosis were even more pronounced, and differentiation was impaired, too, as revealed by the absence of androgen receptor immunoreactivity. In both tissues, the mammary gland and the seminal vesicles, enhanced steady-state transcript levels of the AP-2 target gene IGFBP-5 were detected, revealing a potential mechanism of AP-2-induced apoptosis. Our results suggest a role of AP-2 transcription factors in the maintenance of a proliferative and undifferentiated state of cells, characteristics not only important during embryonic development but also in tumorigenesis.

Animals↗

PubMed2002

Altered mammary epithelial development, pattern formation and involution in transgenic mice expressing the EphB4 receptor tyrosine kinase.

We have previously documented the cell-type-specific and hormone-dependent expression of the EphB4 receptor in the mouse mammary gland. To investigate its role in the biology of the mammary gland, we have established transgenic mice bearing the EphB4 receptor under the control of the MMTV-LTR promoter, which represents the first transgenic mouse model to investigate the effect(s) of unscheduled expression of EphB4 in adult organisms. Transgene expression in the mammary epithelium was induced at puberty, increased during pregnancy, culminated at early lactation and persisted until day three of post-lactational involution. In contrast, expression of the endogenous EphB4 gene is downregulated during pregnancy, is essentially absent during lactation and is re-induced after day three of post-lactational involution. The unscheduled expression of EphB4 led to a delayed development of the mammary epithelium at puberty and during pregnancy. During pregnancy, less lobules were formed, these however exhibited more numerous but smaller alveolar units. Transgenic mammary glands were characterized by a fragile, irregular morphology at lactation; however, sufficient functionality was maintained to nourish the young. Transgenic mammary glands exhibited untimely epithelial apoptotic cell death during pregnancy and abnormal epithelial DNA synthesis at early post-lactational involution, indicating a disturbed response to proliferative/apoptotic signals. Mammary tumours were not observed in the EphB4 transgenic animals; however, in double transgenic animals expressing both EphB4 and the neuT genes, tumour appearance was significantly accelerated and, in contrast to neuT-only animals, metastases were observed in the lung. These results implicate EphB4 in the regulation of tissue architecture, cellular growth response and establishment of the invasive phenotype in the adult mammary gland.

Animals↗

PubMedDate not supplied

Mice transgenic for NPM-ALK develop non-Hodgkin lymphomas.

BACKGROUND: The t(2;5)(p23;q35) translocation is associated with a high percentage of anaplastic large-cell lymphomas (ALCL) of T- or null-cell phenotype. The translocation produces an 80 kDa hyperphosphorylated chimeric protein (p80) derived from the fusion of the anaplastic lymphoma kinase (ALK) with nucleophosmin (NPM). The NPM-ALK chimeric protein is an activated tyrosine kinase that has been shown to be a potent oncogene and presumably plays a causative role in lymphomagenesis. MATERIALS AND METHODS: A transgenic mouse line was generated, where the human NPM-ALK cDNA is driven by the lck promoter conferring transgene expression to early T-cells. RESULTS: Mice rapidly developed large cell lymphoblastic lymphomas with a median latency of 8 weeks, primarily involving the thymus, with lymph node as well as histologically evident extranodal organ infiltration by large tumor cells. CONCLUSION: The transgenic approach described provides direct evidence for the strong transforming potential of NPM-ALK in T-cells and furthermore represents a system for the analysis of the oncogenic events mediated by NPM-ALK in vivo, which might be instrumental in the development of tyrosine kinase inhibitor therapies of potential clinical use.

Animals↗