TY - JOUR A1 - Singh, Jasbir A1 - Dani, Harinder M. A1 - Sharma, Reeta A1 - Steinberg, Pablo T1 - Inhibition of the biosynthesis of SRP polypeptides and secretory proteins by aflatoxin B-1 can disrupt protein targeting JF - Cell biochemistry and function N2 - Cell culture and western blotting studies revealed that aflatoxin B-1 (AFB(1)) inhibits the biosynthesis of two of the constituent polypeptides of signal recognition particle (SRP) (SRP54 and 72). SRP escorts polyribosomes carrying signal peptides from free form in the cytosol to the bound form on endoplasmic reticulum (ER) membrane during protein targeting. These effects of AFB(1) on SRP biosynthesis may inhibit the formation of functional SRP Our experiments have further shown that AFB(1) also inhibits the biosynthesis/translocation of a secretory protein, preprolactin, which fails to appear in the lumen of ER consequent to the treatment with this hepatocarcinogen. The results of the experiments presented in this article therefore enable us to infer for the first time that aflatoxin B-1 may inhibit the functioning of SRP as an escort and deplete the ER of polyribosomes for secretory protein synthesis. As these secretory proteins are important components of the plasma membrane, gap junctions and intercellular matrix, their absence from these locations could disturb cell to cell communication leading to tumorigenesis. KW - aflatoxin B-1 KW - SRP KW - protein targeting KW - protein translocation KW - western blotting Y1 - 2005 U6 - https://doi.org/10.1027/cbf.1285 SN - 0263-6484 VL - 24 SP - 507 EP - 510 PB - Wiley CY - Chichester ER - TY - JOUR A1 - Schulz, Tim Julius A1 - Thierbach, Renè A1 - Voigt, Anja A1 - Drewes, Gunnar A1 - Mietzner, Brun A1 - Steinberg, Pablo A1 - Pfeiffer, Andreas F. H. A1 - Ristow, Michael T1 - Induction of oxidative metabolism by mitochondrial frataxin inhibits cancer growth : Otto Warburg revisited N2 - More than 80 years ago Otto Warburg suggested that cancer might be caused by a decrease in mitochondrial energy metabolism paralleled by an increase in glycolytic flux. In later years, it was shown that cancer cells exhibit multiple alterations in mitochondrial content, structure, function, and activity. We have stably overexpressed the Friedreich ataxia-associated protein frataxin in several colon cancer cell lines. These cells have increased oxidative metabolism, as shown by concurrent increases in aconitase activity, mitochondrial membrane potential, cellular respiration, and ATP content. Consistent with Warburg's hypothesis, we found that frataxin-overexpressing cells also have decreased growth rates and increased population doubling times, show inhibited colony formation capacity in soft agar assays, and exhibit a reduced capacity for tumor formation when injected into nude mice. Furthermore, overexpression of frataxin leads to an increased phosphorylation of the tumor suppressor p38 mitogen-activated protein kinase, as well as decreased phosphorylation of extracellular signal-regulated kinase. Taken together, these results support the view that an increase in oxidative metabolism induced by mitochondrial frataxin may inhibit cancer growth in mammals Y1 - 2006 UR - http://www.jbc.org/content/281/2/977.full.pdf+html U6 - https://doi.org/10.1074/jbc.M511064200 ER - TY - JOUR A1 - Herbst, Uta A1 - Fuchs, Iris Judith A1 - Teubner, Wera A1 - Steinberg, Pablo T1 - Malignant transformation of human colon epithelial cells by benzo[c]phenanthrene dihydrodiolepoxides as well as 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine N2 - Polycyclic aromatic hydrocarbons (PAHs) and heterocyclic aromatic amines (HCAs) ingested with food have repeatedly been suggested to be involved in the malignant transformation of colon epithelial cells. In order to test this hypothesis, HCEC cells (SV40 large T antigen-immortalized human colon epithelial cells) were incubated with a racemic mixture of benzo[c]phenanthrene dihydrodiol epoxides (B[c]PhDE), extremely potent carcinogenic PAH metabolites in vivo, or with 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine (N-OH-PhIP), the N-hydroxylated metabolite of the most abundant HCA in cooked meat. First, it was shown that HCEC cells express sulfotransferase 1A1, which is needed to metabolize N-OH-PhIP to the corresponding N-sulfonyloxy derivative, the direct precursor molecule of genotoxic nitrenium ions. Thereafter, exponentially growing HCEC cells were exposed five times to 0.1 mu g (0.37 nmol) B[c]PhDE/ml for 30 min or 0.72 mu g (3 mnol) N-OH-PhTP/ml for 24 h. Chemically treated HCEC cells showed an enhanced saturation density and grew faster than the corresponding solvent-treated cell cultures. After five treatment cycles, HCECB[c]PhDE as well as HCECN-OH-PhIP cells lost cell-cell contact inhibition and started piling up and forming foci in the culture flasks. Furthermore, HCECB[c]phDE and HCECN-OH-PhIP cells were injected i.m. into SCID mice. Within 6 weeks after injection, eight animals out of eight injected with HCECB[c]phDE or HCECN-OH-PhIP cells developed tumors at the site of injection, thus demonstrating the high tumorigenic potential of the HCECB[c]PhDE and HCECN-OH-PhIP cell cultures. Taken together, we show for the first time that the abovementioned active PAH metabolites as well as N-OH-PhIP are indeed able to malignantly transform human colon epithelial cells in vitro. Y1 - 2006 UR - http://www.sciencedirect.com/science/journal/0041008X U6 - https://doi.org/10.1016/j.taap.2005.07.016 SN - 0041-008X ER - TY - JOUR A1 - Singh, Jasbir A1 - Singh, S. A1 - Dani, H. M. A1 - Sharma, Reeta A1 - Steinberg, Pablo T1 - Interactions of aflatoxin B-1 with SRP components can disrupt protein targeting N2 - Spectrofluorimetric studies have revealed that aflatoxin B-1 (AFB(1)) interacts with signal recognition particle (SRP), which acts as an escort for polyribosomes with signal peptides to be transported and bound to the cytoplasmic face of the endoplasmic reticulum (ER). We further report that the binding of AFB(1) to SRP is selective as it only binds to two (SRP9 and 14) out of its three constituent polypeptides studied. Binding of AFB(1) to proteins is known to alter their conformations. Interactions of AFB(1) with SRP polypeptides may generate structural and functional alterations in this particle and hinder secretory protein synthesis. Copyright (C) 2004 John Wiley Sons, Ltd Y1 - 2005 SN - 0263-6484 ER - TY - JOUR A1 - Thierbach, Renè A1 - Schulz, Tim Julius A1 - Isken, Frank A1 - Voigt, Aanja A1 - Mietzner, Brun A1 - Drewes, Gunnar A1 - von Kleist-Retzow, Jürgen-Christoph A1 - Wiesner, Rudolf J. A1 - Magnuson, Mark A. A1 - Puccio, Helene A1 - Pfeiffer, Andreas F. H. A1 - Steinberg, Pablo A1 - Ristow, Michael T1 - Targeted disruption of hepatic frataxin expression causes impaired mitochondrial function, decreased life span and tumor growth in mice N2 - We have disrupted expression of the mitochondrial Friedreich ataxia protein frataxin specifically in murine hepatocytes to generate mice with impaired mitochondrial function and decreased oxidative phosphorylation. These animals have a reduced life span and develop multiple hepatic tumors. Livers also show increased oxidative stress, impaired respiration and reduced ATP levels paralleled by reduced activity of iron-sulfur cluster (Fe/S) containing proteins (ISP), which all leads to increased hepatocyte turnover by promoting both apoptosis and proliferation. Accordingly, phosphorylation of the stress-inducible p38 MAP kinase was found to be specifically impaired following disruption of frataxin. Taken together, these findings indicate that frataxin may act as a mitochondrial tumor suppressor protein in mammals Y1 - 2005 ER - TY - JOUR A1 - Fuchs, J. A1 - Teubner, Wera A1 - Steinberg, Pablo T1 - The resistance of intestinal epithelial cells towards the transforming activity of 2-hydroxyamino-1-methyl-6- phenylimidazo[4,5-B]pyridine is accompanied by glutathione S-transferase induction Y1 - 2004 SN - 0028-1298 ER - TY - JOUR A1 - Teubner, Wera A1 - Langheinrich, C. A1 - Seidel, Albrecht A1 - Steinberg, Pablo T1 - Inhibition of p53 transactivation activity does not promote mutagen-induced transformation of IEC-18 Y1 - 2004 SN - 0028-1298 ER - TY - JOUR A1 - Kühnel, Dana A1 - Steinberg, Pablo A1 - Scholtka, Bettina T1 - A human-relevant dose of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PHIP) can induce precancerous lesions in rat intestine after 6 months of exposure Y1 - 2004 SN - 0028-1298 ER - TY - JOUR A1 - Thierbach, Rene A1 - Schulz, Tim Julius A1 - Voigt, Aanja A1 - Drewes, Gunnar A1 - Isken, F. A1 - Pfeiffer, Andreas F. H. A1 - Ristow, Michael A1 - Steinberg, Pablo T1 - Targeted disruption of frataxin in hepatocytes causes spontaneous neoplasia accompanied by increased ROS formation Y1 - 2004 SN - 0028-1298 ER - TY - JOUR A1 - Herbst, Uta A1 - Fuchs, Iris Judith A1 - Teubner, Wera A1 - Seidel, Albrecht A1 - Frank, Heinz A1 - Steinberg, Pablo T1 - Malignant transformation of human colon epithelial cells by polycyclic aromatic hydrocarbons and heterocyclic aromatic amines Y1 - 2004 SN - 0028-1298 ER - TY - JOUR A1 - Stark, Avishay abraham A1 - Porat, Noga A1 - Volohonsky, Gloria A1 - Konlosh, A. A1 - Bluvshtein, Evgenia A1 - Tubi, C. A1 - Steinberg, Pablo T1 - The role of gamma-glutamyl transpeptidase in the biosynthesis of glutathione Y1 - 2003 ER - TY - JOUR A1 - Okano, J. A1 - Shiota, G. A1 - Matsumoto, K. A1 - Yasui, S. A1 - Kurimasa, A. A1 - Hisatome, I. A1 - Steinberg, Pablo A1 - Murawaki, Y. T1 - Hepatocyte growth factor exerts a proliferative effect on oval cells through the PI3K/AKT signaling pathway Y1 - 2003 ER - TY - JOUR A1 - Bartsch, Ingrid A1 - Zschaler, Ingrid A1 - Haseloff, Monika A1 - Steinberg, Pablo T1 - Establishment of a long-term culture system for rat colon epithelial cells N2 - The aim of this study was to establish a long-term culture. system for rat colon epithelia isolaled by incubating a 4-cm-long rat colon segment cut longitudinally with all ethylenediaminetetraacetic acid [disodium salt]- containing buffer, taken up in conditioned medium from the normal rat kidney fibroblast cell line NRK (i.e., the supernatant Of pure NRK cultures), directly plated on mitomycin C-treated NRK cells and subcultured with conditioned medium from NRK cells. Cells started to migrate out of the crypts shortly after plating them on NRK feeder layers. Some of the crypts fell apart during the isolation procedure. whereas the vast majority of them did it within I to 2 Ill after plating. The cells proliferated extremely slowly but continuously over a period of 4 mo and were epithelial because they expressed cytokeratin 19 and were stained by crystal violet at pH 2.8. In conclusion, the experimental system described ill this study allows to maintain rat colon epithelial cells for up to 4 mo in culture and can be used to Study the effects of a variety of tumor-modulating factors on growth and gene expression of normal colon epithelial cells in vitro Y1 - 2003 UR - http://www.springerlink.com/content/120498/ U6 - https://doi.org/10.1290/0404035.1 SN - 1071-2690 ER - TY - JOUR A1 - Barlow, S. M. A1 - Greig, J. B. A1 - Bridges, J. W. A1 - Carere, A. A1 - Carpy, A. J. A1 - Galli, Corrado L. A1 - Kleiner, J. A1 - Knudsen, I. A1 - Koeter, H. B. A1 - Levy, L. S. A1 - Madsen, C. A1 - Mayer, S. A1 - Narbonne, J. F. A1 - Pfannkuch, F. A1 - Prodanchuk, M. G. A1 - Smith, Mason R. A1 - Steinberg, Pablo T1 - Hazard identification by methods of animal-based toxicology Y1 - 2002 ER - TY - JOUR A1 - Dybing, E. A1 - Doe, J. A1 - Groten, J. A1 - Kleiner, J. A1 - O'Brien, J. A1 - Renwick, A. G. A1 - Schlatter, J. A1 - Steinberg, Pablo A1 - Tritschler, A. A1 - Walker, R. A1 - Younes, M. T1 - Hazard characterisation of chemicals in food and diet : dose response, mechanisms and extrapolation issues Y1 - 2002 ER - TY - JOUR A1 - Volohonsky, Gloria A1 - Tuby, Chen N. Y. H. A1 - Porat, Noga A1 - Wellman-Rousseau, Maria A1 - Visvikis, Athanase A1 - Leroy, Pierre A1 - Rashi, Sharon A1 - Steinberg, Pablo A1 - Stark, Avishay Abraham T1 - A spectrophotometric assay of gamma-glutamylcysteine synthetase and glutathione synthetase in crude extracts from tissues and cultured mammalian cells Y1 - 2002 ER - TY - JOUR A1 - Steinberg, Pablo A1 - Zschaler, Ingrid A1 - Thom, Elke A1 - Kuna, Manuela A1 - Wüst, Günter A1 - Schäfer-Schwebel, Angelika A1 - Müller, Rolf A1 - Kramer, Peter-Jürgen A1 - Weiße, Günter T1 - The polycyclic musk 7-acetyl-1,1,3,4,4,6-hexamethyl-1,2,3,4-tetrahydronaphthaline lacks liver tumor initiating and promoting activity in rats exposed to human-relevant doses Y1 - 2001 UR - http://www.springerlink.com/content/100462 U6 - https://doi.org/10.1007/s002040100274 SN - 0340-5761 ER - TY - JOUR A1 - Komlosh, A. A1 - Volohonsky, Gloria A1 - Porat, Noga A1 - Tuby, chen n. y. h. A1 - Bluvshtein, Evgenia A1 - Steinberg, Pablo A1 - Oesch, Franz A1 - Stark, Avishay Abraham T1 - Gamma-glutamyl transpeptidase and glutathione biosynthesis in non-tumorigenic and tumorigenic rat liver oval cell lines Y1 - 2001 ER - TY - JOUR A1 - Hengstler, Jan Georg A1 - Utesch, D. A1 - Steinberg, Pablo T1 - Cryopreserved primary hepatocytes as a constantly available in vitro model for the evaluation of human and animal drug metabolism and enzyme induction Y1 - 2000 ER - TY - JOUR A1 - Schleger, C. A1 - Heck, R. A1 - Steinberg, Pablo T1 - The role of wild-type and mutated N-ras in the malignant transformation of liver cells Y1 - 2000 ER -