Biomedical subjects

Bettina Hartenstein

Publications and source records attributed to Bettina Hartenstein.

9 recordsLinked to original sources

PubMed2006

JunB is required for endothelial cell morphogenesis by regulating core-binding factor beta.

The molecular mechanism triggering the organization of endothelial cells (ECs) in multicellular tubules is mechanistically still poorly understood. We demonstrate that cell-autonomous endothelial functions of the AP-1 subunit JunB are required for proper endothelial morphogenesis both in vivo in mouse embryos with endothelial-specific ablation of JunB and in in vitro angiogenesis models. By cDNA microarray analysis, we identified core-binding factor beta (CBFbeta), which together with the Runx proteins forms the heterodimeric core-binding transcription complex CBF, as a novel JunB target gene. In line with our findings, expression of the CBF target MMP-13 was impaired in JunB-deficient ECs. Reintroduction of CBFbeta into JunB-deficient ECs rescued the tube formation defect and MMP-13 expression, indicating an important role for CBFbeta in EC morphogenesis.

Animals↗

PubMed2006

The anti-apoptotic livin gene is an important determinant for the apoptotic resistance of non-small cell lung cancer cells.

Cancer cells are typically characterized by increased resistance towards apoptosis. Livin (alternatively called ML-IAP or KIAP) is an anti-apoptotic protein which is expressed in several cancer forms. Using real-time reverse transcription-polymerase chain reaction (RT-PCR), we confirmed livin expression in a significant portion of non-small cell lung cancer (NSCLC) tissue samples and, in addition, detected livin expression in a number of NSCLC cell lines. In order to elucidate whether livin contributes to the apoptotic resistance of lung cancer cells, we silenced endogenous livin expression in a panel of cancer-derived NSCLC cell lines by RNA interference (RNAi). We observed that the targeted inhibition of livin strongly sensitized NSCLC cells to different pro-apoptotic stimuli, such as UV-irradiation or the chemotherapeutic drug etoposide. In addition, long-term silencing of livin blocked the outgrowth of NSCLC cells in colony formation assays. These effects of small interfering (si)RNA were specific for livin-expressing tumor cells. Our results indicate that Livin is an important contributor to the apoptosis resistance of NSCLC cells and may serve as a novel molecular target for therapeutic inhibition in NSCLC.

Adaptor Proteins, Signal Transducing↗

PubMed2006

Cutting edge: the AP-1 subunit JunB determines NK cell-mediated target cell killing by regulation of the NKG2D-ligand RAE-1epsilon.

The activating receptor NKG2D and its ligands RAE-1 play an important role in the NK, gammadelta+, and CD8+ T cell-mediated immune response to tumors. Expression levels of RAE-1 on target cells have to be tightly controlled to allow immune cell activation against tumors but to avoid destruction of healthy tissues. In this study, we report that cell surface expression of RAE-1epsilon is greatly enhanced on cells lacking JunB, a subunit of the transcription complex AP-1. Furthermore, tissue-specific junB knockout mice respond to 12-O-tetradecanoyl-phorbol-13-acetate, a potent AP-1 activator, with markedly increased and sustained epidermal RAE-1epsilon expression. Accordingly, junB-deficient cells are efficiently killed via NKG2D by NK cells and induce IFN-gamma production. Our data indicate that the transcription factor AP-1, which is involved in tumorigenesis and cellular stress responses, regulates RAE-1epsilon. Thus, up-regulated RAE-1epsilon expression due to low levels of JunB could alert immune cells to tumors and stressed cells.

Animals↗

PubMed2006

Epidermal development and wound healing in matrix metalloproteinase 13-deficient mice.

Degradation of the extracellular matrix, which is an indispensable step in tissue remodelling processes such as embryonic development and wound healing of the skin, has been attributed to collagenolytic activity of members of the matrix metalloproteinase family (MMPs). Here, we employed mmp13 knockout mice to elucidate the function of MMP13 in embryonic skin development, skin homeostasis, and cutaneous wound healing. Overall epidermal architecture and dermal composition of non-injured skin were indistinguishable from wild-type mice. Despite robust expression of MMP13 in the early phase of wound healing, wild-type and mmp13 knockout animals did not differ in their efficiency of re-epithelialization, inflammatory response, granulation tissue formation, angiogenesis, and restoration of basement membrane. Yet, among other MMPs also expressed during wound healing, MMP8 was found to be enhanced in wounds of MMP13-deficient mice. In summary, skin homeostasis and also tissue remodelling processes like embryonic skin development and cutaneous wound healing are independent of MMP13 either owing to MMP13 dispensability or owing to functional substitution by other collagenolytic proteinases such as MMP8.

Animals↗

PubMed2006

A novel aspartic proteinase-like gene expressed in stratified epithelia and squamous cell carcinoma of the skin.

Homeostasis of stratified epithelia, such as the epidermis of the skin, is a sophisticated process that represents a tightly controlled balance between proliferation and differentiation. Alterations of this balance are associated with common human diseases including cancer. Here, we report the cloning of a novel cDNA sequence, from mouse back skin, that is induced by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) and codes for a hitherto unknown aspartic proteinase-like protein (Taps). Taps represents a potential AP-1 target gene because TPA-induced expression in epidermal keratinocytes critically depends on c-Fos, and co-treatment with dexamethasone, a potent inhibitor of AP-1-mediated gene regulation, resulted in impaired activation of Taps expression. Taps mRNA and protein are restricted to stratified epithelia in mouse embryos and adult tissues, implicating a crucial role for this aspartic proteinase-like gene in differentiation and homeostasis of multilayered epithelia. During chemically induced carcinogenesis, transient elevation of Taps mRNA and protein levels was detected in benign skin tumors. However, its expression is negatively associated with dedifferentiation and malignant progression in squamous cell carcinomas of the skin. Similar expression was observed in squamous skin tumors of patients, suggesting that detection of Taps levels represents a novel strategy to discriminate the progression state of squamous skin cancers.

Amino Acid Sequence↗

PubMed2004

Altered endochondral bone development in matrix metalloproteinase 13-deficient mice.

The assembly and degradation of extracellular matrix (ECM) molecules are crucial processes during bone development. In this study, we show that ECM remodeling is a critical rate-limiting step in endochondral bone formation. Matrix metalloproteinase (MMP) 13 (collagenase 3) is poised to play a crucial role in bone formation and remodeling because of its expression both in terminal hypertrophic chondrocytes in the growth plate and in osteoblasts. Moreover, a mutation in the human MMP13 gene causes the Missouri variant of spondyloepimetaphyseal dysplasia. Inactivation of Mmp13 in mice through homologous recombination led to abnormal skeletal growth plate development. Chondrocytes differentiated normally but their exit from the growth plate was delayed. The severity of the Mmp13- null growth plate phenotype increased until about 5 weeks and completely resolved by 12 weeks of age. Mmp13-null mice had increased trabecular bone, which persisted for months. Conditional inactivation of Mmp13 in chondrocytes and osteoblasts showed that increases in trabecular bone occur independently of the improper cartilage ECM degradation caused by Mmp13 deficiency in late hypertrophic chondrocytes. Our studies identified the two major components of the cartilage ECM, collagen type II and aggrecan, as in vivo substrates for MMP13. We found that degradation of cartilage collagen and aggrecan is a coordinated process in which MMP13 works synergistically with MMP9. Mice lacking both MMP13 and MMP9 had severely impaired endochondral bone, characterized by diminished ECM remodeling, prolonged chondrocyte survival, delayed vascular recruitment and defective trabecular bone formation (resulting in drastically shortened bones). These data support the hypothesis that proper ECM remodeling is the dominant rate-limiting process for programmed cell death, angiogenesis and osteoblast recruitment during normal skeletal morphogenesis.

Animals↗

PubMed2003

Defective endochondral ossification in mice with strongly compromised expression of JunB.

Functional analysis in mice has established an absolute requirement of JunB, a member of the AP-1 transcription factor family, during early embryonic development. To investigate the role of JunB during mid and late gestation and postnatally Ubi-junB transgenic mice were used to generate two junB-/- Ubi-junB mutant lines, in which embryonic lethality was rescued but strongly reduced JunB expression in several adult tissues was observed. Mutant mice from both rescue lines were growth retarded and shared significantly reduced longitudinal bone growth. Mutant long bones were characterised by reduced numbers of growth plate chondrocytes and a severe osteoporosis. Decreased JunB levels in epiphysal growth plate chondrocytes and bone lining osteoblasts correlated with deregulated expression of Cyclin A, Cyclin D1 and p16INK4a, key regulators of cell cycle control. Furthermore, junB-/- Ubi-junB bone marrow stromal cells were unable to differentiate into bone forming osteoblasts in vitro. Our data demonstrate that JunB plays a crucial role in endochondral ossification by regulating proliferation and function of chondrocytes and osteoblasts.

Animals↗

PubMed2002

Th2 cell-specific cytokine expression and allergen-induced airway inflammation depend on JunB.

Naïve CD4+ T cells differentiate into effector T helper 1 (Th1) or Th2 cells, which are classified by their specific set of cytokines. Here we demonstrate that loss of JunB in in vitro polarized Th2 cells led to a dysregulated expression of the Th2-specific cytokines IL-4 and IL-5. These cells produce IFN-gamma and express T-bet, the key regulator of Th1 cells. In line with the essential role of Th2 cells in the pathogenesis of allergic asthma, mice with JunB-deficient CD4+ T cells exhibited an impaired allergen-induced airway inflammation. This study demonstrates novel functions of JunB in the development of Th2 effector cells, for a normal Th2 cytokine expression pattern and for a complete Th2-dependent immune response in mice.

Allergens↗

PubMed2002

Cell cycle promoting activity of JunB through cyclin A activation.

JunB, a major component of the AP-1 transcription factor, is known to act antagonistically to c-Jun in transcriptional regulation and is proposed to be a negative regulator of cell proliferation. Employing fibroblasts derived from E9.5 junB(-/-) mouse embryos we provide evidence for a novel cell cycle promoting role of JunB. Despite a normal proliferation rate, primary and immortalized junB(-/-) fibroblasts exhibited an altered cell cycle profile, which was characterized by an increase in the population of S-phase cells, while that of cells in G(2)/M-phase was diminished. This delay in G(2)/M-transition is caused by impaired cyclin A-CDK2 and cyclin B-CDC2 kinase activities and counteracts the accelerated S-phase entry. Cells lacking JunB show severely delayed kinetics of cyclin A mRNA expression due to the loss of proper transcriptional activation mediated via binding of JunB to the CRE element in the cyclin A promoter. Upon reintroduction of an inducible JunB-ER(TM) expression vector the cell cycle distribution and the cell cycle-associated cyclin A-CDK2 kinase activity could be restored. Thus, cyclin A is a direct transcriptional target of JunB driving cell proliferation.

3T3 Cells↗