Michael Schnekenburger - Academia.edu (original) (raw)

Papers by Michael Schnekenburger

Exposure to toxic polycyclic aromatic hydrocarbons raises a number of toxic and carcinogenic resp... more Exposure to toxic polycyclic aromatic hydrocarbons raises a number of toxic and carcinogenic responses in experimental animals and humans mediated for the most part by the aryl hydrocarbon---or dioxin---receptor (AHR). The AHR is a ligand-activated transcription factor whose central role in the induction of drugmetabolizing enzymes has long been recognized. For quite some time now, it has become clear that the AHR also functions in pathways outside of its role in detoxification and that perturbation of these pathways by xenobiotic ligands may be an important part of the toxicity of these compounds. AHR activation by some of its ligands participates among others in pathways critical to cell cycle regulation, mitogen-activated protein kinase cascades, immediate-early gene induction, cross-talk within the RAS and SRC pathways and mobilizes crucial calcium stores. Ultimately, the effect of a particular AHR ligand may depend as much on the adaptive interactions that it established with pathways and proteins expressed in a specific cell or tissue as on the toxic responses that it raises.

Exposure to toxic polycyclic aromatic hydrocarbons raises a number of toxic and carcinogenic resp... more Exposure to toxic polycyclic aromatic hydrocarbons raises a number of toxic and carcinogenic responses in experimental animals and humans mediated for the most part by the aryl hydrocarbon--or dioxin---receptor (AHR). The AHR is a ligand-activated transcription factor whose central role in the induction of drug-metabolizing enzymes has long been recognized. For quite some time now, it has become clear that the AHR also functions in pathways outside of its role in detoxification and that perturbation of these pathways by xenobiotic ligands may be an important part of the toxicity of these compounds. AHR activation by some of its ligands participates among others in pathways critical to cell cycle regulation, mitogen-activated protein kinase cascades, immediate-early gene induction, cross-talk within the RB/E2F axis and mobilization of crucial calcium stores. Ultimately, the effect of a particular AHR ligand may depend as much on the adaptive interactions that it established with pathways and proteins expressed in a specific cell or tissue as on the toxic responses that it raises.

Journal of experimental therapeutics & oncology, 2011

Genes & Nutrition, 2012

Protein acetylation status results from a balance between histone acetyltransferase and histone d... more Protein acetylation status results from a balance between histone acetyltransferase and histone deacetylase (HDAC) activities. Alteration of this balance leads to a disruption of cellular integrity and participates in the development of numerous diseases, including cancer. Therefore, modulation of these activities appears to be a promising approach for anticancer therapy. Histone deacetylase inhibitors (HDACi) are epigenetically active drugs that induce the hyperacetylation of lysine residues within histone and non-histone proteins, thus affecting gene expression and cellular processes such as proteinprotein interactions, protein stability, DNA binding and protein sub-cellular localization. Therefore, HDACi are promising anti-tumor agents as they may affect the cell cycle, inhibit proliferation, stimulate differentiation and induce apoptotic cell death. Over the last 30 years, numerous synthetic and natural products, including a broad range of dietary compounds, have been identified as HDACi. This review focuses on molecules from natural origins modulating HDAC activities and presenting promising anticancer activities.

Current Nutrition & Food Science, 2010

Acetylation and deacetylation of lysine residues on histones, which are catalyzed by histone acet... more Acetylation and deacetylation of lysine residues on histones, which are catalyzed by histone acetyltransferases (HATs) and histone deacetylases (HDACs), are epigenetic modifications that play a very important role in the regulation of gene transcription. Perturbation of the balance between histone acetylation and deacetylation leads to a myriad of diseases, including cancer, AIDS, malaria, neurodegenerative diseases, and diabetes. HATs and HDACs have recently been recognized as key targets for chemoprevention and drug discovery, and numerous natural and synthetic compounds have been screened in order to identify promising regulators of subtle balance between histone acetylation and deacetylation. Here, we present dietary compounds and other natural products that have emerged as potent HAT or HDAC activity modulators, and we discuss their current and future applications as chemopreventive or therapeutic agents.

Toxicological Sciences, 2014

is key to their toxicity. Following activation and nuclear translocation, AHR heterodimerizes wit... more is key to their toxicity. Following activation and nuclear translocation, AHR heterodimerizes with the AHR nuclear translocator (ARNT) and binds to AHR response elements (AhREs) in the enhancer of target genes, of which Cyp1a1 is the prototype. Previously, we showed that concomitant with AHR binding, histone H3 in the Cyp1a1 enhancer-promoter AhRE cluster became phosphorylated in serine-10 (H3S10), suggesting that the ligand-activated AHR recruited one or more kinases to the enhancer chromatin to phosphorylate this residue. To test this hypothesis, we used mouse hepatoma Hepa-1c1c7 cells and their c35 mutant derivative, lacking a functional AHR, to search for candidate kinases that would phosphorylate H3S10 in an AHR dependent manner. Using chromatin immunoprecipitation with antibodies to a comprehensive set of protein kinases, we identified three kinases, IB kinase ␣ (IKK␣), mitogen and stress activated protein kinase 1 (MSK1), and mitogen and stress activated protein kinase 2 (MSK2), whose binding to the Cyp1a1 enhancer was significantly increased by TCDD in Hepa-1c1c7 cells and absent in control c35 cells. Complexes of AHR, ARNT, and IKK␣ could be coimmunoprecipitated from nuclei of TCDD treated Hepa-1c1c7 cells and shRNA-mediated IKK␣ knockdown inhibited both H3S10 phosphorylation in the Cyp1a1 enhancer and the induction of Cyp1a1, Aldh3a1, and Nqo1 in TCDD-treated cells. We conclude that AHR recruits IKK␣ to the promoter of its target genes and that AHR-mediated H3S10 phosphorylation is a key epigenetic requirement for induction of AHR targets. Given the role of H3S10ph in regulation of chromosome condensation, AHR-IKK␣ cross-talk may be a mediator of chromatin remodeling by environmental agents.

Toxicological Sciences, 2011

Posttranslational histone modifications are a critical regulatory mechanism of gene transcription... more Posttranslational histone modifications are a critical regulatory mechanism of gene transcription. Previous studies from our laboratory have shown that contingent on binding to its cognate promoter motifs in the Cyp1a1 gene, activation of the aryl hydrocarbon receptor (AHR) by benzo[a]pyrene (BaP) treatment induces histone modifications in the Cyp1a1 promoter that are required for activation of gene transcription. Here, we have studied different AHR ligands, including polychlorinated biphenyls (PCBs) of different toxic equivalency factors (TEF), to determine whether changes in histone modifications are linked to different levels of Cyp1a1 expression or dependent on AHR-ligand affinity. We find that all ligands lead to the same pattern of histone modifications in a relationship that parallels the strength of their AHR-ligand affinity. Thus, whereas PCB126 (TEF 0.1), 3-methylcholanthrene, b-naphthoflavone, and 2,3,7,8tetrachlorodibenzo-p-dioxin (TCDD) initiate a pattern of histone marks similar to those induced by BaP, PCB77 (TEF 0.0001) causes a lower level of change in the same marks and requires a longer activation time than PCB126, BaP, or TCDD. In contrast, the non-dioxin-like PCB153 recruits AHR to the Cyp1a1 enhancer causing a displacement of enhancer-associated histone H3 but does not cause the other observed histone mark changes nor does it induce transcription. These results indicate that AHR recruitment to the promoter is not sufficient to induce the histone modifications needed to activate gene expression and show that there is a good correlation between the regulatory chromatin changes associated with ligand-induced AHR target gene transcription and the resultant toxicity of the ligand.

Oncology Reports, 2012

Histone deacetylase enzymes (HDACs) are emerging as a promising biological target for cancer and ... more Histone deacetylase enzymes (HDACs) are emerging as a promising biological target for cancer and inflammation. Using a fluorescence assay, we tested the in vitro HDAC inhibitory activity of twenty-one natural chalcones, a widespread group of natural products with well-known anti-inflammatory and antitumor effects. Since HDACs regulate the expression of the transcription factor NF-κB, we also evaluated the inhibitory potential of the compounds on NF-κB activation. Only four chalcones, isoliquiritigenin (no. 10), butein (no. 12), homobutein (no. 15) and the glycoside marein (no. 21) showed HDAC inhibitory activity with IC 50 values of 60-190 µM, whereas a number of compounds inhibited TNFα-induced NF-κB activation with IC 50 values in the range of 8-41 µM. Interestingly, three chalcones (nos. 10, 12 and 15) inhibited both TNFα-induced NF-κB activity and total HDAC activity of classes I, II and IV. Molecular modeling and docking studies were performed to shed light into dual activity and to draw structure-activity relationships among chalcones (nos. 1-21). To the best of our knowledge this is the first study that provides evidence for HDACs as potential drug targets for natural chalcones. The dual inhibitory potential of the selected chalcones on NF-κB and HDACs was investigated for the first time. This study demonstrates that chalcones can serve as lead compounds in the development of dual inhibitors against both targets in the treatment of inflammation and cancer.

Molecular Carcinogenesis, 2013

In diseases such as cancer, cells need to degrade the extracellular matrix (ECM) and therefore re... more In diseases such as cancer, cells need to degrade the extracellular matrix (ECM) and therefore require high protease levels. Thus, aberrant tissue degradation is associated to matrix metalloproteinases (MMPs) overexpression resulting from different mechanisms including epigenetic events. One of the most characterized epigenetic mechanisms is DNA methylation causing changes in chromatin conformation, thereby decreasing the accessibility to the transcriptional machinery and resulting in a robust gene silencing. Modulation of DNA methylation by DNA hypomethylating agents such as 5-aza-2'-deoxycytidine (5-azadC) is widely used in epigenetic anticancer treatments. Here, we focus on the effects of this drug on the expression level of MMP-1, -2, and -9 in human HT1080 fibrosarcoma cells. We demonstrate that 5-azadC increases MMP expression at both mRNA and protein levels, and promotes invasion potential of HT1080 cells. Using broadspectrum and specific MMP inhibitors, we establish that MMP-1, but not MMP-2 and -9, plays a key role in 5-azadCenhanced cell invasion. We show that 5-azadC induces MMP-1 expression through a transcriptional mechanism without affecting MMP-1 promoter methylation status. Finally, we demonstrate that 5-azadC treatment increases the nuclear levels of Sp1 and Sp3 transcription factors, and modulates their recruitment to the MMP-1 promoter, resulting in chromatin remodeling associated to 5-azadC-induced MMP-1 expression. All together, our data indicate that the hypomethylating agent 5-azadC modulates, mainly via Sp1 recruitment, MMP-1 expression resulting in an increased invasive potential of HT1080 cells.

Cell Proliferation, 2013

Objective: Chromatin texture patterns of tumour cell nuclei can serve as cancer biomarkers, eithe... more Objective: Chromatin texture patterns of tumour cell nuclei can serve as cancer biomarkers, either to define diagnostic classifications or to obtain relevant prognostic information, in a large number of human tumours. Epigenetic mechanisms, mainly DNA methylation and histone post-translational modification, have been shown to influence chromatin packing states, and therefore nuclear texture. The aim of this study was to analyse effects of these two mechanisms on chromatin texture, and also on correlation with gelatinase expression, in human fibrosarcoma tumour cells. Materials and methods: We investigated effects of DNA hypomethylating agent 5-aza-2′-deoxycytidine (5-azadC) and histone deacetylase inhibitor trichostatin A (TSA) on nuclear textural characteristics of human HT1080 fibrosarcoma cells, evaluated by image cytometry, and expression of gelatinases MMP-2 and MMP-9, two metalloproteinases implicated in cancer progression and metastasis. Results: 5-azadC induced significant variation in chromatin higher order organization, particularly chromatin decondensation, associated with reduction in global DNA methylation, concomitantly with increase in MMP-9, and to a lesser extent, MMP-2 expression. TSA alone did not have any effect on HT1080 cells, but exhibited differential activity when added to cells treated with 5-azadC.

Biochimie, 2012

Epigenetic alterations are involved in every step of carcinogenesis. The development of chromatin... more Epigenetic alterations are involved in every step of carcinogenesis. The development of chromatinmodifying agents (CMAs) has provided the ability to fight cancer by reversing these alterations. Currently, four CMAs have been approved for cancer treatment; two DNA demethylating agents and two deacetylase inhibitors. A number of promising CMAs are undergoing clinical trials in several cancer types. Moreover, already approved CMAs are still under clinical investigation to improve their efficacy and to extend their use to a broader panel of cancers. Combinatorial treatments with CMAs are already considered a promising strategy to improve clinical benefits and to limit side effects. The real mechanisms by which these CMAs allow the improvement and remission of patients are still obscure. A deeper analysis of the molecular features expressed by responding patients should be performed to reveal this information. In this review, we focus on clinical trials with CMAs, discussing the success and the pitfalls of this new class of anti-cancer drugs.

Annals of the New York Academy of Sciences, 2003

Biochemical pharmacology, Jan 15, 2014

Valproic acid (VPA) exhibits important pharmacological properties but has been reported to trigge... more Valproic acid (VPA) exhibits important pharmacological properties but has been reported to trigger side effects, notably on the hematological system. We previously reported that VPA affects hematopoietic homeostasis by inhibiting erythroid differentiation and promoting myeloid and megakaryocyte differentiation. Here, we analyzed the effect of VPA on regulatory factors involved in erythro-megakaryocytic differentiation pathways, including transcription factors and microRNAs (miRs). We demonstrate that VPA inhibited erythroid differentiation in erythropoietin (Epo)-stimulated TF1 leukemia cells and CD34(+)/hematopoietic stem cells (HSCs) and in aclacinomycin-(Acla)-treated K562 cells. Mir-144/451 gene expression was decreased in all erythroid and megakaryocyte models in correlation with GATA-1 inhibition. In Epo-stimulated CD34(+)/HSCs, VPA induced the expression of the ETS family transcription factors PU.1, ETS-1, GABP-α, Fli-1 and GATA-2, which are all known to be negative regulator...

Anti-cancer agents in medicinal chemistry, 2015

Despite recent advances in the treatment of chronic myelogenous leukemia (CML), the development o... more Despite recent advances in the treatment of chronic myelogenous leukemia (CML), the development of drug resistance and minimal residual disease remain major challenges for the treatment of CML patients, thus highlighting the need to develop innovative new approaches to improve therapeutic outcome. Myrtucommulone A (MCA) is a nonprenylated acylphloroglucinol isolated from the leaves of myrtle, a plant traditionally used in folk medicine. To date, studies addressing bioactivities of myrtle and its specific components are rare. Here, we investigated the biological effects of MCA, focusing on its anti-leukemic activity. As evidenced by fragmented nuclei after Hoechst/propidium iodide staining and poly (ADP-ribose) polymerase cleavage, MCA induces apoptosis in CML cells through down-regulation of anti-apoptotic proteins. Interestingly, we showed that chronic treatment with MCA at low doses induced senescence in CML cells. Taken together, this study highlights the chemotherapeutical poten...

Leukemia research, 2006

Over-expression of glutathione S-transferase P1 is related to chemotherapeutic drug resistance as... more Over-expression of glutathione S-transferase P1 is related to chemotherapeutic drug resistance as well as to differentiation of human erythroleukemia cells. In opposition to previously described differentiating inducers which enhance the GST-resistance phenotype, time- and concentration-dependent activation of both erythroid and megakaryocytic differentiation pathways by butyric acid progressively diminished GSTP1 mRNA expression. GSTP1 mRNA expression decreased by 25% (p<0.01) and 64% (p<0.01) in 1mM and 2mM butyric acid-differentiated K562 cells, respectively. These results were associated to both a reduction of GATA-1 binding activity to the GSTP1 promoter and to a posttranscriptional destabilization of GSTP1 mRNA in a concentration dependent manner. Indeed, GSTP1 mRNA half-life decreased from 43.8 to 36.2 h and 12.6 h in 1mM- and 2mM-treated cells, respectively.

Neoplasia, 2014

Increased proliferation rates as well as resistance to apoptosis are considered major obstacles f... more Increased proliferation rates as well as resistance to apoptosis are considered major obstacles for the treatment of patients with chronic myelogenous leukemia (CML), thus highlighting the need for novel therapeutic approaches. Since senescence has been recognized as a physiological barrier against tumorigenesis, senescence-based therapy could represent a new strategy against CML. DNA demethylating agent 5-aza-2′-deoxycytidine (DAC) was reported to induce cellular senescence but underlying mechanisms remain to be elucidated. Here, we report that exposure to DAC triggers senescence in chronic leukemia cell lines as evidenced by increased senescenceassociated β-galactosidase activity and lysosomal mass, accompanied by an up-regulation of cell cycle-related genes. We provide evidence that DAC is able to decrease telomere length, to reduce telomerase activity and to decrease human telomerase reverse transcriptase (hTERT) expression through decreased binding of c-myc to the hTERT promoter. Altogether, our results reveal the role of c-myc in telomere-dependent DAC-induced senescence and therefore provide new clues for improving chronic human leukemia treatments.

Frontiers in Pharmacology, 2014

† Michael Schnekenburger, Tommy Karius, and Marc Diederich have contributed equally to this work.

Exposure to toxic polycyclic aromatic hydrocarbons raises a number of toxic and carcinogenic resp... more Exposure to toxic polycyclic aromatic hydrocarbons raises a number of toxic and carcinogenic responses in experimental animals and humans mediated for the most part by the aryl hydrocarbon--or dioxin---receptor (AHR). The AHR is a ligand-activated transcription factor whose central role in the induction of drug-metabolizing enzymes has long been recognized. For quite some time now, it has become clear that the AHR also functions in pathways outside of its role in detoxification and that perturbation of these pathways by xenobiotic ligands may be an important part of the toxicity of these compounds. AHR activation by some of its ligands participates among others in pathways critical to cell cycle regulation, mitogen-activated protein kinase cascades, immediate-early gene induction, cross-talk within the RB/E2F axis and mobilization of crucial calcium stores. Ultimately, the effect of a particular AHR ligand may depend as much on the adaptive interactions that it established with pathways and proteins expressed in a specific cell or tissue as on the toxic responses that it raises.