ERK phosphorylation is RAF independent in naïve and activated B cells but RAF dependent in plasma cell differentiation.

Members of the RAF family of serine-threonine kinases are intermediates in the mitogen-activated protein kinase and extracellular signal-regulated kinase (MAPK-ERK) signaling pathway, which controls key differentiation processes in B cells. By analyzing mice with B cell-specific deletion of , , or both, we showed that Raf-1 and B-Raf acted together in mediating the positive selection of pre-B and transitional B cells as well as in initiating plasma cell differentiation. However, genetic or chemical inactivation of RAFs led to increased ERK phosphorylation in mature B cells.

Chemotherapeutic drugs inhibit ribosome biogenesis at various levels.

Drugs for cancer therapy belong to different categories of chemical substances. The cellular targets for the therapeutic efficacy are often not unambiguously identified. Here, we describe the process of ribosome biogenesis as a target of a large variety of chemotherapeutic drugs.

Egr-1 regulates expression of the glial scar component phosphacan in astrocytes after experimental stroke.

Ischemic brain injury causes tissue damage and neuronal death. The deficits can often be permanent because adult neurons fail to regenerate. One barrier to neuronal regeneration is the formation of the glial scar, a repair mechanism that is otherwise necessary to seal off necrotic areas.

Activated Notch1 alters differentiation of embryonic stem cells into mesodermal cell lineages at multiple stages of development.

Signals of Notch transmembrane receptors function to regulate a wide variety of developmental cell fates. Here we investigate the role of Notch signaling in the development of mesodermal cell types by expressing a tamoxifen-inducible, activated form of Notch1 in embryonic stem cells (ESC). For differentiation of ESC into first mesodermal progenitor cells and then endothelial, mural, cardiac muscle and hematopoietic cells, the OP9 stroma co-culture system was used.

Embryonic endothelial progenitor cells expressing a broad range of proangiogenic and remodeling factors enhance vascularization and tissue recovery in acute and chronic ischemia.

Clonal embryonic endothelial progenitor cells (eEPCs) isolated from embryonic day 7.5 mice home specifically to hypoxic areas in mouse tumor metastases but spare normal organs and do not form carcinomas. Based on these results, we assessed the potential of eEPCs to enhance vascularization and limit organ dysfunction after ischemia in syngenic and xenotypic organisms.

Epstein-Barr virus latent membrane protein 2A mimics B-cell receptor-dependent virus reactivation.

Latent membrane protein 2A (LMP2A) of Epstein-Barr virus (EBV) shares protein motifs with the B-cell receptor that play a role in B-cell receptor signalling and has been shown to mimic an activated B-cell receptor by providing a survival signal for mature B cells in transgenic mice. Conversely, LMP2A has been reported not to support but to inhibit B-cell receptor signalling with respect to virus reactivation and to block lytic virus induction after anti-Ig treatment of EBV-infected B cells. To solve this apparent paradox, the role of LMP2A in lytic-cycle induction was re-examined in B cells conditionally immortalized by EBV.

Participation of bone marrow-derived cells in long-term repair processes after experimental stroke.

Bone marrow-derived cells participate in remodeling processes of many ischemia-associated diseases, which has raised hopes for the use of bone marrow as a source for cell-based therapeutic approaches. To study the participation of bone marrow-derived cells in a stroke model, bone marrow from C57BL/6-TgN(ACTbEGFP)1Osb mice that express green fluorescent protein (GFP) in all cells was transplanted into C57BL/6J mice. The recipient mice underwent permanent occlusion of the middle cerebral artery, and bone marrow-derived cells were tracked by fluorescence.

Control of Epstein-Barr virus reactivation by activated CD40 and viral latent membrane protein 1.

In humans, Epstein-Barr virus (EBV) establishes a persistent latent infection in peripheral resting B lymphocytes. Virus reactivation is highly restricted. Whereas in healthy humans the infection usually is benign, immunocompromised patients show an increased risk for EBV-associated malignancies, accompanied by an increase in virus replication and in the number of virus-infected cells.

Myc/Max/Mad regulate the frequency but not the duration of productive cell cycles.

Upregulation of the proto-oncoprotein Myc, a basic, helix-loop-helix, leucin zipper domain transcription factor has profound consequences on cell proliferation, cell growth and apoptosis. Cell cultures of somatic c-myc-/- rat fibroblasts show extremely prolonged doubling times of 52 h. Using time-lapse microscopy, we show here that individual c-myc-/- cells proceeded within approximately 24 h through the cell cycle as fast as c-myc+/+ cells.

Cloning and developmental expression of zebrafish GTP cyclohydrolase I.

GTP cyclohydrolase I (GCH) catalyses the conversion of GTP to dihydroneopterin triphosphate, initiating the pteridine pathway. The final product tetrahydrobiopterin (H4biopterin) is the cofactor for neurotransmitter synthesis and for tyrosine supply during melanogenesis. Sepiapterin accumulates as a pigment.

TRAF6 is a critical mediator of signal transduction by the viral oncogene latent membrane protein 1.

The oncogenic latent membrane protein 1 (LMP1) of the Epstein-Barr virus recruits tumor necrosis factor-receptor (TNFR)-associated factors (TRAFs), the TNFR-associated death domain protein (TRADD) and JAK3 to induce intracellular signaling pathways. LMP1 serves as the prototype of a TRADD-binding receptor that transforms cells but does not induce apoptosis. Here we show that TRAF6 critically mediates LMP1 signaling to p38 mitogen-activated protein kinase (MAPK) via a MAPK kinase 6-dependent pathway.

Activated Notch1 can transiently substitute for EBNA2 in the maintenance of proliferation of LMP1-expressing immortalized B cells.

Epstein-Barr virus (EBV) nuclear antigen 2 (EBNA2) and latent membrane protein 1 (LMP1) are essential for immortalization of human B cells by EBV. EBNA2 and activated Notch transactivate genes by interacting with the cellular transcription factor RBP-Jkappa/CBF1. Therefore, EBNA2 can be regarded as a functional homologue of activated Notch.

Cell cycle activation by c-myc in a burkitt lymphoma model cell line.

The product of the proto-oncogene c-myc (myc) is a potent activator of cell proliferation. In Burkitt lymphoma (BL), a human B-cell tumor, myc is consistently found to be transcriptionally activated by chromosomal translocation. The mechanisms by which myc promotes cell cycle progression in B-cells is not known.

Conditional expression of RNA polymerase II in mammalian cells. Deletion of the carboxyl-terminal domain of the large subunit affects early steps in transcription.

The carboxyl-terminal domain (CTD) of the large subunit of mammalian RNA polymerase II contains 52 repeats of a heptapeptide that is the target of a variety of kinases. The hyperphosphorylated CTD recruits important factors for mRNA capping, splicing, and 3'-processing. The role of the CTD for the transcription process in vivo, however, is not yet clear.

Activated Notch1 modulates gene expression in B cells similarly to Epstein-Barr viral nuclear antigen 2.

Both Epstein-Barr viral nuclear antigen 2 (EBNA2) and activated Notch transactivate genes by interacting with the transcription factor RBP-Jkappa. The viral protein EBNA2 may hence be regarded as a functional equivalent of an activated Notch receptor. Until now, nothing has been known about the physiological role of Notch signaling in B cells.

Regulation of c-myc and immunoglobulin kappa gene transcription by promoter-proximal pausing of RNA polymerase II.

In normal cells, the proto-oncogene c-myc is regulated by promoter-proximal pausing of RNA polymerase II (pol II). In Burkitt lymphoma cells, c-myc is chromosomally translocated to one of the three immunoglobulin (Ig) gene loci and its transcription is driven constitutively by Ig enhancers. Promoter-proximal pausing of pol II is abolished on the translocated c-myc allele.

LMP1 signal transduction differs substantially from TNF receptor 1 signaling in the molecular functions of TRADD and TRAF2.

The Epstein-Barr virus latent membrane protein 1 (LMP1) binds tumor necrosis factor receptor (TNFR)-associated factors (TRAFs) and the TNFR-associated death domain protein (TRADD). Moreover, it induces NF-kappaB and the c-Jun N-terminal kinase 1 (JNK1) pathway. Thus, LMP1 appears to mimick the molecular functions of TNFR1.

Requirement of the carboxy-terminal domain of RNA polymerase II for the transcriptional activation of chromosomal c-fos and hsp70A genes.

The carboxy-terminal domain of the large subunit of mouse and human RNA polymerase II contains 52 repeats of a heptapeptide which are the targets for a variety of kinases. We have used an alpha-amanitin resistant form of the large subunit of pol II to study the role of the carboxy-terminal domain in the expression of chromosomal genes. The large subunit of RNA polymerase II and deletion mutants thereof, which contain only 31 (LSdelta31) and 5 (LSdeltaS) repeats, were expressed in 293 cells.

Improving stable transfection efficiency: antioxidants dramatically improve the outgrowth of clones under dominant marker selection.

Many cell lines are sensitive to growth at low cell density and undergo apoptosis induced by oxidative stress if the cell density is decreased below a critical threshold. In stable transfection experiments this cell density-dependent growth may be the limiting factor, since during drug selection the cell density falls below the critical threshold, precluding outgrowth of transfected clones. We describe here a simple protocol for the establishment of stably transfected human B cell lines making use of the protective action of antioxidants.

Epstein-Barr virus latent membrane protein-1 triggers AP-1 activity via the c-Jun N-terminal kinase cascade.

The Epstein-Barr virus latent membrane protein-1 (LMP-1) is an integral membrane protein which transforms fibroblasts and is essential for EBV-mediated B-cell immortalization. LMP-1 has been shown to trigger cellular NF-kappa B activity which, however, cannot fully explain the oncogenic potential of LMP-1. Here we show that LMP-1 induces the activity of the AP-1 transcription factor, a dimer of Jun/Jun or Jun/Fos proteins.