Publications by authors named "Stephan Bergmann"

15 Publications

  • Page 1 of 1

Smart microgels investigated by super-resolution fluorescence microscopy: influence of the monomer structure on the particle morphology.

Soft Matter 2020 Sep 13;16(34):8078-8084. Epub 2020 Aug 13.

Biomolecular Photonics, Department of Physics, Bielefeld University, Universitätsstraße 25, 33615 Bielefeld, Germany.

In a recent publication [Bergmann et al. Phys. Chem. Chem. Phys., 2018, 20, 5074-5083] we presented a method which enables to investigate the morphology of microgels by superresolution fluorescence microscopy. Here, this method is applied to three microgel species, based on N-isopropylmethacrylamide (NIPMAM), N-n-propylacrylamide (NNPAM) and N-n-propylmethacrylamide (NNPMAM)) with 5, 7.5 and 10 mol% cross-linker, respectively. Super-resolution microscopy reveals differences of the network morphology of the synthesized particles showing the importance of the monomer structure.
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http://dx.doi.org/10.1039/d0sm00597eDOI Listing
September 2020

Super-resolution optical microscopy resolves network morphology of smart colloidal microgels.

Phys Chem Chem Phys 2018 Feb;20(7):5074-5083

Biomolecular Photonics, Department of Physics, Bielefeld University, Bielefeld, Germany.

We present a new method to resolve the network morphology of colloidal particles in an aqueous environment via super-resolution microscopy. By localization of freely diffusing fluorophores inside the particle network we can resolve the three dimensional structure of one species of colloidal particles (thermoresponsive microgels) without altering their chemical composition through copolymerization with fluorescent monomers. Our approach utilizes the interaction of the fluorescent dye rhodamine 6G with the polymer network to achieve an indirect labeling. We calculate the 3D structure from the 2D images and compare the structure to previously published models for the microgel morphology, e.g. the fuzzy sphere model. To describe the differences in the data an extension of this model is suggested. Our method enables the tailor-made fabrication of colloidal particles which are used in various applications, such as paints or cosmetics, and are promising candidates for drug delivery, smart surface coatings, and nanocatalysis. With the precise knowledge of the particle morphology an understanding of the underlying structure-property relationships for various colloidal systems is possible.
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http://dx.doi.org/10.1039/c7cp07648gDOI Listing
February 2018

Comment on "Magnetic-field-enabled resolution enhancement in super-resolution imaging" by M. Zhang et al., Phys. Chem. Chem. Phys., 2015, 17, 6722-6727.

Phys Chem Chem Phys 2017 Feb;19(6):4887-4890

Biomolecular Photonics Group, Department of Physics, University of Bielefeld, 33615 Bielefeld, Germany.

Certain fluorophores, in particular those that can undergo photoinduced radical pair reactions are known to exhibit a magnetic field dependent fluorescence summarized in the term magnetic field effect (MFE). We tried to reproduce experiments that reported magnetic field enhanced fluorescence for commonly used organic dyes with a high quantum yield suitable for single molecule localization microscopy. We find that the enhanced fluorescence is due to fluorescence reflected by the magnet's surface rather than MFE.
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http://dx.doi.org/10.1039/c6cp05108aDOI Listing
February 2017

Quantitative Super-Resolution Microscopy of Nanopipette-Deposited Fluorescent Patterns.

ACS Nano 2015 Aug 21;9(8):8122-30. Epub 2015 Jul 21.

Department of Biotechnology & Biophysics, Biozentrum, Julius Maximilians University Würzburg , Am Hubland, 97075 Würzburg, Germany.

We describe a method for the deposition of minute amounts of fluorophore-labeled oligonucleotides with high local precision in conductive and transparent solid layers of poly(vinyl alcohol) (PVA) doped with glycerin and cysteamine (PVA-G-C layers). Deposition of negatively charged fluorescent molecules was accomplished with a setup based on a scanning ion conductance microscope (SICM) using nanopipettes with tip diameters of ∼100 nm by using the ion flux flowing between two electrodes through the nanopipette. To investigate the precision of the local deposition process, we performed in situ super-resolution microscopy by direct stochastic optical reconstruction microscopy (dSTORM). Exploiting the single-molecule sensitivity and reliability of dSTORM, we determine the number of fluorescent molecules deposited in single spots. The correlation of applied charge and number of deposited molecules enables the quantification of delivered molecules by measuring the charge during the delivery process. We demonstrate the reproducible deposition of 3-168 fluorescent molecules in single spots and the creation of fluorescent structures. The fluorescent structures are highly stable and can be reused several times.
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http://dx.doi.org/10.1021/acsnano.5b02220DOI Listing
August 2015

Giving blood: a new role for CD40 in tumorigenesis.

J Exp Med 2006 Oct 16;203(11):2409-12. Epub 2006 Oct 16.

Cancer Biology and Genetics Program, Department of Pathology, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.

CD40 was initially identified as a receptor expressed by B cells that is crucial for inducing an effective adaptive immune response. CD40 was subsequently shown to be expressed by endothelial cells and to promote angiogenesis. New data now show that in tumor-prone transgenic mice, CD40-mediated neovascularization is essential for early stage tumorigenicity. This suggests, at least in this mouse model, that CD40 has an important role in the angiogenic process that is coupled to carcinogenesis, a finding that could lead to novel therapeutic opportunities.
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http://dx.doi.org/10.1084/jem.20061754DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2118122PMC
October 2006

Deregulated TGF-beta signaling in leukemogenesis.

Oncogene 2005 Aug;24(37):5693-700

Department of Pathology, Memorial Sloan-Kettering Cancer Center, Sloan-Kettering Institute, 1275 York Avenue, New York, NY 10021, USA.

Cellular homeostasis is tightly controlled by the various pathways that regulate cell proliferation and cell death. Breaking this balance is often associated with cancer development. The transforming growth factor-beta (TGF-beta) pathway plays an important role in cellular homeostasis by regulating cell growth inhibition, cellular senescence, differentiation and apoptosis. Deregulated TGF-beta signaling is known to be involved in a variety of human cancers, including those of the colon, pancreas, breast and prostate. While TGF-beta is a potent negative regulator of hematopoiesis, the role of aberrant TGF-beta signaling in leukemogenesis remains largely unknown. Recently, evidence demonstrating deregulated TGF-beta signaling in leukemogenesis, particularly in acute promyelocytic leukemia (APL), has started to emerge. In this review, we summarize the current progress towards the understanding of the molecular mechanisms by which aberrant TGF-beta signaling may participate in leukemogenesis.
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http://dx.doi.org/10.1038/sj.onc.1208923DOI Listing
August 2005

YB-1 provokes breast cancer through the induction of chromosomal instability that emerges from mitotic failure and centrosome amplification.

Cancer Res 2005 May;65(10):4078-87

Max-Delbrück Center for Molecular Medicine, Charité, Humboldt, University, Berlin, Germany.

YB-1 protein levels are elevated in most human breast cancers, and high YB-1 levels have been correlated with drug resistance and poor clinical outcome. YB-1 is a stress-responsive, cell cycle-regulated transcription factor with additional functions in RNA metabolism and translation. In this study, we show in a novel transgenic mouse model that human hemagglutinin-tagged YB-1 provokes remarkably diverse breast carcinomas through the induction of genetic instability that emerges from mitotic failure and centrosome amplification. The increase of centrosome numbers proceeds during breast cancer development and explanted tumor cell cultures show the phenotype of ongoing numerical chromosomal instability. These data illustrate a mechanism that might contribute to human breast cancer development.
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http://dx.doi.org/10.1158/0008-5472.CAN-04-4056DOI Listing
May 2005

YB-1 facilitates basal and 5-fluorouracil-inducible expression of the human major vault protein (MVP) gene.

Oncogene 2005 May;24(22):3606-18

Max-Delbrück-Center for Molecular Medicine, Robert-Rössle-Strasse 10, 13092 Berlin, Germany.

Vaults have been suggested to play a direct role in multidrug resistance (MDR) to anticancer drugs. The human major vault protein (MVP) also known as lung resistance-related protein (LRP) represents the predominant component of vaults that may be involved in the defense against xenobiotics. Here, we demonstrate that besides MDR-related cytostatics, also the non-MDR-related drug 5-fluorouracil (5-FU) was able to induce MVP mRNA and protein expression. Treatment with 5-FU amplified the binding activity and interaction of the transcription factor Y-box binding protein-1 (YB-1) with the Y-box of the human MVP gene promoter in a time-dependent manner. 5-FU also induced reporter expressions driven by a panel of newly generated MVP promoter deletion mutants. Interestingly, stably YB-1 overexpressing cell clones showed enhanced binding of YB-1 to the Y-box motif, associated with enhanced basal as well as 5-FU-inducible MVP promoter-driven reporter expressions. Moreover, transduction of YB-1 cDNA led to increased expression of endogenous MVP protein. Under physiological conditions, we observed a strong coexpression of MVP and YB-1 in human colon carcinoma specimen. In summary, our data demonstrate a direct involvement of YB-1 in controlling basal and 5-FU-induced MVP promoter activity. Therefore, YB-1 is directly linked to MVP-mediated drug resistance.
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http://dx.doi.org/10.1038/sj.onc.1208386DOI Listing
May 2005

The promyelocytic leukemia protein PML regulates c-Jun function in response to DNA damage.

Blood 2005 May 30;105(9):3686-90. Epub 2004 Dec 30.

Memorial Sloan-Kettering Cancer Center, 1275 York Ave, New York, NY, USA.

The promyelocytic leukemia (PML) gene, a tumor suppressor inactivated in acute promyelocytic leukemia (APL), regulates apoptosis induced by DNA damage. However, the molecular mechanisms by which PML modulates apoptosis following genotoxic stress are only partially elucidated. PML is essential for p53-dependent induction of programmed cell death upon gamma-irradiation through PML-nuclear body (NB)-mediated control of p53 acetylation. Here, we show that PML selectively regulates proapoptotic transcription factors upon different types of DNA damage. We find that Pml inactivation protects fibroblasts from UV-induced apoptosis in a p53-independent manner. We demonstrate that c-Jun is required for UV-induced apoptosis and that PML is essential for both c-Jun transcriptional activation and DNA binding upon UV radiation. We find that PML physically interacts with c-Jun and that upon UV radiation the PML-NBs reorganize into novel nuclear microspeckled structures (UV-NBs), where PML and c-Jun dynamically accumulate. These data identify a novel PML-dependent pathway for c-Jun transcriptional activation and induction of apoptosis in response to DNA damage and shed new light on the role of PML in tumor suppression.
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http://dx.doi.org/10.1182/blood-2004-09-3782DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1895009PMC
May 2005

Cytoplasmic PML function in TGF-beta signalling.

Nature 2004 Sep;431(7005):205-11

Cancer Biology and Genetics Program, Department of Pathology, Memorial Sloan-Kettering Cancer Center, Sloan-Kettering Institute, 1275 York Avenue, New York, New York, 10021, USA.

Transforming growth factor beta (TGF-beta) is a pluripotent cytokine that controls key tumour suppressive functions, but cancer cells are often unresponsive to it. The promyelocytic leukaemia (PML) tumour suppressor of acute promyelocytic leukaemia (APL) accumulates in the PML nuclear body, but cytoplasmic PML isoforms of unknown function have also been described. Here we show that cytoplasmic Pml is an essential modulator of TGF-beta signalling. Pml-null primary cells are resistant to TGF-beta-dependent growth arrest, induction of cellular senescence and apoptosis. These cells also have impaired phosphorylation and nuclear translocation of the TGF-beta signalling proteins Smad2 and Smad3, as well as impaired induction of TGF-beta target genes. Expression of cytoplasmic Pml is induced by TGF-beta. Furthermore, cytoplasmic PML physically interacts with Smad2/3 and SARA (Smad anchor for receptor activation) and is required for association of Smad2/3 with SARA and for the accumulation of SARA and TGF-beta receptor in the early endosome. The PML-RARalpha oncoprotein of APL can antagonize cytoplasmic PML function and APL cells have defects in TGF-beta signalling similar to those observed in Pml-null cells. Our findings identify cytoplasmic PML as a critical TGF-beta regulator, and further implicate deregulated TGF-beta signalling in cancer pathogenesis.
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http://dx.doi.org/10.1038/nature02783DOI Listing
September 2004

YB-1 and CTCF differentially regulate the 5-HTT polymorphic intron 2 enhancer which predisposes to a variety of neurological disorders.

J Neurosci 2004 Jun;24(26):5966-73

Department of Biological Sciences, University of Essex, Essex CO4 3SQ, United Kingdom.

The serotonin transporter (5-HTT) gene contains a variable number tandem repeat (VNTR) domain within intron 2 that is often associated with a number of neurological conditions, including affective disorders. The implications of this polymorphism are not yet understood, however, we have previously demonstrated that the 5-HTT VNTR is a transcriptional regulatory domain, and the allelic variation supports differential reporter gene expression in vivo and in vitro. The aim of this study was to identify transcription factors responsible for the regulation of this VNTR. Using a yeast one-hybrid screen, we found the transcription factor Y box binding protein 1 (YB-1) interacts with the 5-HTT VNTR. Consistent with this, we demonstrate in a reporter gene assay that the polymorphic VNTR domains differentially respond to exogenous YB-1 and that YB-1 will bind to the VNTR in vitro in a sequence-specific manner. Interestingly, the transcription factor CCTC-binding factor (CTCF), previously shown to interact with YB-1, interferes with the ability of the VNTR to support YB-1-directed reporter gene expression. In addition, CTCF blocks the binding of YB-1 to its DNA recognition sequences in vitro, thus providing a possible mechanism of regulation of YB-1 activation of the VNTR by CTCF. Therefore, we have identified YB-1 and CTCF as transcription factors responsible, at least in part, for modulation of VNTR function as a transcriptional regulatory domain. Our data suggest a novel mechanism that explains, in part, the ability of the distinct VNTR copy numbers to support differential reporter gene expression based on YB-1 binding sites.
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http://dx.doi.org/10.1523/JNEUROSCI.1150-04.2004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6729234PMC
June 2004

PML regulates p53 stability by sequestering Mdm2 to the nucleolus.

Nat Cell Biol 2004 Jul 13;6(7):665-72. Epub 2004 Jun 13.

Cancer Biology and Genetics Program, Department of Pathology and Medicine, Sloan-Kettering Institute, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.

The promyelocytic leukaemia (PML) tumour-suppressor protein potentiates p53 function by regulating post-translational modifications, such as CBP-dependent acetylation and Chk2-dependent phosphorylation, in the PML-Nuclear Body (NB). PML was recently shown to interact with the p53 ubiquitin-ligase Mdm2 (refs 4-6); however, the mechanism by which PML regulates Mdm2 remains unclear. Here, we show that PML enhances p53 stability by sequestering Mdm2 to the nucleolus. We found that after DNA damage, PML and Mdm2 accumulate in the nucleolus in an Arf-independent manner. In addition, we found that the nucleolar localization of PML is dependent on ATR activation and phosphorylation of PML by ATR. Notably, in Pml(-/-) cells, sequestration of Mdm2 to the nucleolus was impaired, as well as p53 stabilization and the induction of apoptosis. Furthermore, we demonstrate that PML physically associates with the nucleolar protein L11, and that L11 knockdown impairs the ability of PML to localize to nucleoli after DNA damage. These findings demonstrate an unexpected role of PML in the nucleolar network for tumour suppression.
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http://dx.doi.org/10.1038/ncb1147DOI Listing
July 2004

Multidrug-resistant cancer cells facilitate E1-independent adenoviral replication: impact for cancer gene therapy.

Cancer Res 2004 Jan;64(1):322-8

Institut für Experimentelle Onkologie und Therapieforschung, Technische Universität München, Klinikum Rechts der Isar, München, Germany.

Resistance to chemotherapy is responsible for a failure of current treatment regimens in cancer patients. We have reported previously that the Y-box protein YB-1 regulates expression of the P-glycoprotein gene mdr1, which plays a major role in the development of a multidrug resistant-tumor phenotype. YB-1 predicts drug resistance and patient outcome in breast cancer. Thus, YB-1 is a promising target for new therapeutic approaches to defeat multidrug resistance. In drug-resistant cancer cells and in adenovirus-infected cells YB-1 is found in the nucleus. Nuclear accumulation of YB-1 in adenovirus-infected cells is a function of the E1 region, and we have shown that YB-1 facilitates adenovirus replication. Here we report that E1A-deleted or mutant adenovirus vectors, such as Ad312 and Ad520, replicate efficiently in multidrug-resistant (MDR) cancer cells and induce an adenovirus cytopathic effect resulting in host cell lysis. Thus, replication-defective adenoviruses are a previously unrecognized vector system for a selective elimination of MDR cancer cells. Our work forms the basis for the development of novel oncolytic adenovirus vectors for the treatment of MDR malignant diseases in the clinical setting.
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http://dx.doi.org/10.1158/0008-5472.can-0482-2DOI Listing
January 2004

YB-1 as a cell cycle-regulated transcription factor facilitating cyclin A and cyclin B1 gene expression.

J Biol Chem 2003 Jul 14;278(30):27988-96. Epub 2003 Apr 14.

Max-Delbrück-Centrum für Molekulare Medizin, Robert-Rössle-Strasse 10, 13092 Berlin, Germany.

Expression of the Y-box protein YB-1 is increased in proliferating normal and cancer cells, but its role in cell proliferation and cell cycle progression is unclear. We have identified a cell cycle-dependent relocalization of YB-1 from the cytoplasm to the nucleus at the G1/S phase transition and demonstrate that both the charged zipper and the cold shock domain are involved in regulating this process. Using cell lines that constitutively overexpress YB-1, we show that nuclear accumulation of YB-1 is associated with increased cyclin A and cyclin B1 mRNA and protein expression. We provide evidence that deregulated YB-1 expression is linked to adhesion-independent cell proliferation through the induction of cyclin A. Thus, we have identified YB-1 as a cell cycle stage-specific transcription factor important for cell proliferation.
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http://dx.doi.org/10.1074/jbc.M212966200DOI Listing
July 2003

YB-1 relocates to the nucleus in adenovirus-infected cells and facilitates viral replication by inducing E2 gene expression through the E2 late promoter.

J Biol Chem 2002 Mar 11;277(12):10427-34. Epub 2002 Jan 11.

Institut für Experimentelle Onkologie und Therapieforschung, Technische Universität München, Klinikum Rechts der Isar, München 81675, Germany.

The adenovirus early proteins E1A and E1B-55kDa are key regulators of viral DNA replication, and it was thought that targeting of p53 by E1B-55kDa is essential for this process. Here we have identified a previously unrecognized function of E1B for adenovirus replication. We found that E1B-55kDa is involved in targeting the transcription factor YB-1 to the nuclei of adenovirus type 5-infected cells where it is associated with viral inclusion bodies believed to be sites of viral transcription and replication. We show that YB-1 facilitates E2 gene expression through the E2 late promoter thus controlling E2 gene activity at later stages of infection. The role of YB-1 for adenovirus replication was demonstrated with an E1-minus adenovirus vector containing a YB-1 transgene. In infected cells, AdYB-1 efficiently replicated and produced infectious progeny particles. Thus, adenovirus E1B-55kDa protein and the host cell factor YB-1 act jointly to facilitate adenovirus replication in the late phase of infection.
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http://dx.doi.org/10.1074/jbc.M106955200DOI Listing
March 2002