The Experts below are selected from a list of 114 Experts worldwide ranked by ideXlab platform
Vassilios Papadopoulos - One of the best experts on this subject based on the ideXlab platform.
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Transcriptional Regulation of Translocator Protein (Tspo) via a SINE B2-Mediated Natural Antisense Transcript in MA-10 Leydig Cells
Biology of reproduction, 2012Co-Authors: Jinjiang Fan, Vassilios PapadopoulosAbstract:Translocator Protein (18 kDa; TSPO) is a mitochondrial cholesterol- and Drug-Binding Protein involved in cholesterol import into mitochondria, the rate-limiting step in steroidogenesis. TSPO is expressed at high levels in Leydig cells of the testis, and its expression levels dictate the ability of the cells to form androgen. In search of mechanisms that regulate Tspo expression, a number of transcription factors acting on its promoter region have been identified. We report herein the presence of a mechanism of regulation of Tspo expression via complementation with a natural antisense transcript (NAT). At the Tspo locus, a short interspersed repetitive element (SINE) of the SINE B2 family has the potential for high transcriptional activity. The extension of the SINE B2 element-mediated transcript overlapped with exon 3 of the Tspo gene and formed a NAT specific for Tspo (Tspo-NAT) in MA-10 mouse tumor Leydig cells. The identified Tspo-NAT was also found in testis and kidney tissues. Overexpression of the Tspo-NAT regulated Tspo gene expression and its function in steroid formation in MA-10 cells. Time-course studies have indicated that Tspo-NAT expression is regulated by cAMP and could regulate TSPO levels to maintain optimal steroid production by MA-10 Leydig cells. Taken together, these results suggest a new micro-transcriptional mechanism that regulates Tspo expression and thus steroidogenesis via an intron-based SINE B2-driven NAT specific for the Tspo gene.
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Regulation of translocator Protein 18 kDa (TSPO) expression in health and disease states.
Molecular and cellular endocrinology, 2010Co-Authors: Amani Batarseh, Vassilios PapadopoulosAbstract:Translocator Protein (TSPO) is an 18 kDa high affinity cholesterol- and Drug-Binding Protein found primarily in the outer mitochondrial membrane. Although TSPO is found in many tissue types, it is expressed at the highest levels under normal conditions in tissues that synthesize steroids. TSPO has been associated with cholesterol import into mitochondria, a key function in steroidogenesis, and directly or indirectly with multiple other cellular functions including apoptosis, cell proliferation, differentiation, anion transport, porphyrin transport, heme synthesis, and regulation of mitochondrial function. Aberrant expression of TSPO has been linked to multiple diseases, including cancer, brain injury, neurodegeneration, and ischemia-reperfusion injury. There has been an effort during the last decade to understand the mechanisms regulating tissue- and disease-specific TSPO expression and to identify pharmacological means to control its expression. This review focuses on the current knowledge regarding the chemicals, hormones, and molecular mechanisms regulating Tspo gene expression under physiological conditions in a tissue- and disease-specific manner. The results described here provide evidence that the PKCepsilon-ERK1/2-AP-1/STAT3 signal transduction pathway is the primary regulator of Tspo gene expression in normal and pathological tissues expressing high levels of TSPO.
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Translocator Protein 2 Is Involved in Cholesterol Redistribution during Erythropoiesis
The Journal of biological chemistry, 2009Co-Authors: Jinjiang Fan, Malena B. Rone, Vassilios PapadopoulosAbstract:Translocator Protein (TSPO) is an 18-kDa cholesterol- and Drug-Binding Protein conserved from bacteria to humans. While surveying for Tspo-like genes, we identified its paralogous gene, Tspo2, encoding an evolutionarily conserved family of Proteins that arose by gene duplications before the divergence of avians and mammals. Comparative analysis of Tspo1 and Tspo2 functions suggested that Tspo2 has become subfunctionalized, typical of duplicated genes, characterized by the loss of diagnostic Drug ligand-Binding but retention of cholesterol-Binding properties, hematopoietic tissue- and erythroid cell-specific distribution, and subcellular endoplasmic reticulum and nuclear membrane localization. Expression of Tspo2 in erythroblasts is strongly correlated with the down-regulation of the enzymes involved in cholesterol biosynthesis. Overexpression of TSPO2 in erythroid cells resulted in the redistribution of intracellular free cholesterol, an essential step in nucleus expulsion during erythrocyte maturation. Taken together, these data identify the TSPO2 family of Proteins as mediators of cholesterol redistribution-dependent erythroblast maturation during mammalian erythropoiesis.
David H. Sherman - One of the best experts on this subject based on the ideXlab platform.
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Characterization of a quinone reductase activity for the mitomycin C Binding Protein (MRD): Functional switching from a Drug-activating enzyme to a Drug-Binding Protein
Proceedings of the National Academy of Sciences of the United States of America, 2001Co-Authors: Paul J. Sheldon, David H. ShermanAbstract:Abstract Self-protection in the mitomycin C (MC)-producing microorganism Streptomyces lavendulae includes MRD, a Protein that binds MC in the presence of NADH and functions as a component of a unique Drug Binding-export system. Characterization of MRD revealed that it reductively transforms MC into 1,2-cis-1-hydroxy-2,7-diaminomitosene, a compound that is produced in the reductive MC activation cascade. However, the reductive reaction catalyzed by native MRD is slow, and both MC and the reduced product are bound to MRD for a relatively prolonged period. Gene shuffling experiments generated a mutant Protein (MRDE55G) that conferred a 2-fold increase in MC resistance when expressed in Escherichia coli. Purified MRDE55G reduces MC twice as fast as native MRD, generating three compounds that are identical to those produced in the reductive activation of MC. Detailed amino acid sequence analysis revealed that the region around E55 in MRD strongly resembles the second active site of prokaryotic catalase-peroxidases. However, native MRD has an aspartic acid (D52) and a glutamic acid (E55) residue at the positions corresponding to the catalytic histidine and a nearby glycine residue in the catalase-peroxidases. Mutational analysis demonstrated that MRDD52H and MRDD52H/E55G conferred only marginal resistance to MC in E. coli. These findings suggest that MRD has descended from a previously unidentified quinone reductase, and mutations at the active site of MRD have greatly attenuated its catalytic activity while preserving substrate-Binding capability. This presumed evolutionary process might have switched MRD from a potential Drug-activating enzyme into the Drug-Binding component of the MC export system.
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Mitomycin Resistance in Streptomyces lavendulae Includes a Novel Drug-Binding-Protein-Dependent Export System
Journal of bacteriology, 1999Co-Authors: Paul J. Sheldon, Yingqing Mao, David H. ShermanAbstract:Sequence analysis of Streptomyces lavendulae NRRL 2564 chromosomal DNA adjacent to the mitomycin resistance locus mrd (encoding a previously described mitomycin-Binding Protein [P. Sheldon, D. A. Johnson, P. R. August, H.-W. Liu, and D. H. Sherman, J. Bacteriol. 179:1796-1804, 1997]) revealed a putative mitomycin C (MC) transport gene (mct) encoding a hydrophobic polypeptide that has significant amino acid sequence similarity with several actinomycete antibiotic export Proteins. Disruption of mct by insertional inactivation resulted in an S. lavendulae mutant strain that was considerably more sensitive to MC. Expression of mct in Escherichia coli conferred a fivefold increase in cellular resistance to MC, led to the synthesis of a membrane-associated Protein, and correlated with reduced intracellular accumulation of the Drug. Coexpression of mct and mrd in E. coli resulted in a 150-fold increase in resistance, as well as reduced intracellular accumulation of MC. Taken together, these data provide evidence that MRD and Mct function as components of a novel Drug export system specific to the mitomycins.
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Characterization of a mitomycin-Binding Drug resistance mechanism from the producing organism, Streptomyces lavendulae.
Journal of bacteriology, 1997Co-Authors: Paul J. Sheldon, David A. Johnson, Paul R. August, Hung-wen Liu, David H. ShermanAbstract:In an effort to characterize the diversity of mechanisms involved in cellular self-protection against the antitumor antibiotic mitomycin C (MC), DNA fragments from the producing organism (Streptomyces lavendulae) were introduced into Streptomyces lividans and transformants were selected for resistance to the Drug. Subcloning of a 4.0-kb BclI fragment revealed the presence of an MC resistance determinant, mrd. Nucleotide sequence analysis identified an open reading frame consisting of 130 amino acids with a predicted molecular weight of 14,364. Transcriptional analysis revealed that mrd is expressed constitutively, with increased transcription in the presence of MC. Expression of mrd in Escherichia coli resulted in the synthesis of a soluble Protein with an Mr of 14,400 that conferred high-level cellular resistance to MC and a series of structurally related natural products. Purified MRD was shown to function as a Drug-Binding Protein that provides protection against cross-linking of DNA by preventing reductive activation of MC.
Paul J. Sheldon - One of the best experts on this subject based on the ideXlab platform.
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Characterization of a quinone reductase activity for the mitomycin C Binding Protein (MRD): Functional switching from a Drug-activating enzyme to a Drug-Binding Protein
Proceedings of the National Academy of Sciences of the United States of America, 2001Co-Authors: Paul J. Sheldon, David H. ShermanAbstract:Abstract Self-protection in the mitomycin C (MC)-producing microorganism Streptomyces lavendulae includes MRD, a Protein that binds MC in the presence of NADH and functions as a component of a unique Drug Binding-export system. Characterization of MRD revealed that it reductively transforms MC into 1,2-cis-1-hydroxy-2,7-diaminomitosene, a compound that is produced in the reductive MC activation cascade. However, the reductive reaction catalyzed by native MRD is slow, and both MC and the reduced product are bound to MRD for a relatively prolonged period. Gene shuffling experiments generated a mutant Protein (MRDE55G) that conferred a 2-fold increase in MC resistance when expressed in Escherichia coli. Purified MRDE55G reduces MC twice as fast as native MRD, generating three compounds that are identical to those produced in the reductive activation of MC. Detailed amino acid sequence analysis revealed that the region around E55 in MRD strongly resembles the second active site of prokaryotic catalase-peroxidases. However, native MRD has an aspartic acid (D52) and a glutamic acid (E55) residue at the positions corresponding to the catalytic histidine and a nearby glycine residue in the catalase-peroxidases. Mutational analysis demonstrated that MRDD52H and MRDD52H/E55G conferred only marginal resistance to MC in E. coli. These findings suggest that MRD has descended from a previously unidentified quinone reductase, and mutations at the active site of MRD have greatly attenuated its catalytic activity while preserving substrate-Binding capability. This presumed evolutionary process might have switched MRD from a potential Drug-activating enzyme into the Drug-Binding component of the MC export system.
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Mitomycin Resistance in Streptomyces lavendulae Includes a Novel Drug-Binding-Protein-Dependent Export System
Journal of bacteriology, 1999Co-Authors: Paul J. Sheldon, Yingqing Mao, David H. ShermanAbstract:Sequence analysis of Streptomyces lavendulae NRRL 2564 chromosomal DNA adjacent to the mitomycin resistance locus mrd (encoding a previously described mitomycin-Binding Protein [P. Sheldon, D. A. Johnson, P. R. August, H.-W. Liu, and D. H. Sherman, J. Bacteriol. 179:1796-1804, 1997]) revealed a putative mitomycin C (MC) transport gene (mct) encoding a hydrophobic polypeptide that has significant amino acid sequence similarity with several actinomycete antibiotic export Proteins. Disruption of mct by insertional inactivation resulted in an S. lavendulae mutant strain that was considerably more sensitive to MC. Expression of mct in Escherichia coli conferred a fivefold increase in cellular resistance to MC, led to the synthesis of a membrane-associated Protein, and correlated with reduced intracellular accumulation of the Drug. Coexpression of mct and mrd in E. coli resulted in a 150-fold increase in resistance, as well as reduced intracellular accumulation of MC. Taken together, these data provide evidence that MRD and Mct function as components of a novel Drug export system specific to the mitomycins.
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Characterization of a mitomycin-Binding Drug resistance mechanism from the producing organism, Streptomyces lavendulae.
Journal of bacteriology, 1997Co-Authors: Paul J. Sheldon, David A. Johnson, Paul R. August, Hung-wen Liu, David H. ShermanAbstract:In an effort to characterize the diversity of mechanisms involved in cellular self-protection against the antitumor antibiotic mitomycin C (MC), DNA fragments from the producing organism (Streptomyces lavendulae) were introduced into Streptomyces lividans and transformants were selected for resistance to the Drug. Subcloning of a 4.0-kb BclI fragment revealed the presence of an MC resistance determinant, mrd. Nucleotide sequence analysis identified an open reading frame consisting of 130 amino acids with a predicted molecular weight of 14,364. Transcriptional analysis revealed that mrd is expressed constitutively, with increased transcription in the presence of MC. Expression of mrd in Escherichia coli resulted in the synthesis of a soluble Protein with an Mr of 14,400 that conferred high-level cellular resistance to MC and a series of structurally related natural products. Purified MRD was shown to function as a Drug-Binding Protein that provides protection against cross-linking of DNA by preventing reductive activation of MC.
Martine Culty - One of the best experts on this subject based on the ideXlab platform.
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Regulation of Translocator Protein 18 kDa (TSPO) Expression in Rat and Human Male Germ Cells.
International journal of molecular sciences, 2016Co-Authors: Gurpreet Manku, Martine CultyAbstract:Translocator Protein 18 kDa (TSPO) is a high affinity cholesterol- and Drug-Binding Protein highly expressed in steroidogenic cells, such as Leydig cells, where it plays a role in cholesterol mitochondrial transport. We have previously shown that TSPO is expressed in postnatal day 3 rat gonocytes, precursors of spermatogonial stem cells. Gonocytes undergo regulated phases of proliferation and migration, followed by retinoic acid (RA)-induced differentiation. Understanding these processes is important since their disruption may lead to the formation of carcinoma in situ, a precursor of testicular germ cell tumors (TGCTs). Previously, we showed that TSPO ligands do not regulate gonocyte proliferation. In the present study, we found that TSPO expression is downregulated in differentiating gonocytes. Similarly, in F9 embryonal carcinoma cells, a mouse TGCT cell line with embryonic stem cell properties, there is a significant decrease in TSPO expression during RA-induced differentiation. Silencing TSPO expression in gonocytes increased the stimulatory effect of RA on the expression of the differentiation marker Stra8, suggesting that TSPO exerts a repressive role on differentiation. Furthermore, in normal human testes, TSPO was located not only in Leydig cells, but also in discrete spermatogenic phases such as the forming acrosome of round spermatids. By contrast, seminomas, the most common type of TGCT, presented high levels of TSPO mRNA. TSPO Protein was expressed in the cytoplasmic compartment of seminoma cells, identified by their nuclear expression of the transcription factors OCT4 and AP2G. Thus, TSPO appears to be tightly regulated during germ cell differentiation, and to be deregulated in seminomas, suggesting a role in germ cell development and pathology.
Jean-paul Tillement - One of the best experts on this subject based on the ideXlab platform.
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Drug Binding in Plasma
Clinical Pharmacokinetics, 1994Co-Authors: Françoise Hervé, Saïk Urien, Edith Albengres, Jean-claude Duché, Jean-paul TillementAbstract:The ligands are generally bound in plasma to a significant extent by several transport Proteins (both high and low affinity), irrespective of their endogenous or exogenous origin. The Protein Binding of endogenous compounds (such as hormones) exhibits higher affinity and specificity than those of exogenous compounds (such as Drugs). For plasma Proteins that bind the same ligand(s), structural similarities or a common genetic origin may be found, although this is not a general rule. Alterations in ligand Binding may be due to modifications of either the structure or the level of the Binding Protein. These modifications may result from genetic make up, physiology or pathology. In some situations, plasma Binding may impair the distribution of Drugs to tissues, with Drug distribution then mainly restricted to the distribution compartment of the Drug-Binding Protein. In other instances, the plasma Drug-Binding is permissive, and does not limit Drug distribution to tissues. A given Drug-transport Protein system may have either a permissive or a restrictive effect on the Drug distribution, depending on the tissue. The physiological significance of the high-affinity transport Proteins is not completely understood. These Proteins may increase the plasma concentration of poorly hydrosoluble ligands, ensure a more uniform tissue distribution and increase the life of the ligands. The life of the Protein may also be increased by ligand Binding. High-affinity transport Proteins are also involved in some specific carrier mediated transfer mechanisms. It is possible to demonstrate structure-Binding relationships or Binding selectivity for the plasma transport Proteins, but these are quite independent of relationships observed at the receptor level.
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Drug Binding in plasma. A summary of recent trends in the study of Drug and hormone Binding.
Clinical pharmacokinetics, 1994Co-Authors: Françoise Hervé, Saïk Urien, Edith Albengres, Jean-claude Duché, Jean-paul TillementAbstract:The ligands are generally bound in plasma to a significant extent by several transport Proteins (both high and low affinity), irrespective of their endogenous or exogenous origin. The Protein Binding of endogenous compounds (such as hormones) exhibits higher affinity and specificity than those of exogenous compounds (such as Drugs). For plasma Proteins that bind the same ligand(s), structural similarities or a common genetic origin may be found, although this is not a general rule. Alterations in ligand Binding may be due to modifications of either the structure or the level of the Binding Protein. These modifications may result from genetic make up, physiology or pathology. In some situations, plasma Binding may impair the distribution of Drugs to tissues, with Drug distribution then mainly restricted to the distribution compartment of the Drug-Binding Protein. In other instances, the plasma Drug-Binding is permissive, and does not limit Drug distribution to tissues. A given Drug-transport Protein system may have either a permissive or a restrictive effect on the Drug distribution, depending on the tissue. The physiological significance of the high-affinity transport Proteins is not completely understood. These Proteins may increase the plasma concentration of poorly hydrosoluble ligands, ensure a more uniform tissue distribution and increase the life of the ligands. The life of the Protein may also be increased by ligand Binding. High-affinity transport Proteins are also involved in some specific carrier mediated transfer mechanisms. It is possible to demonstrate structure-Binding relationships or Binding selectivity for the plasma transport Proteins, but these are quite independent of relationships observed at the receptor level.
