The Experts below are selected from a list of 201 Experts worldwide ranked by ideXlab platform
D M Stocco - One of the best experts on this subject based on the ideXlab platform.
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Effects of disruption of the mitochondrial Electrochemical Gradient on steroidogenesis and the Steroidogenic Acute Regulatory (StAR) protein.
The Journal of steroid biochemistry and molecular biology, 1999Co-Authors: S R King, S Eimerl, J Orly, D M StoccoAbstract:The steroidogenic acute regulatory (StAR) protein, which mediates cholesterol delivery to the inner mitochondrial membrane and the P450scc enzyme, has been shown to require a mitochondrial Electrochemical Gradient for its activity in vitro. To characterize the role of this Gradient in cholesterol transfer, investigations were conducted in whole cells, utilizing the protonophore carbonyl cyanide m-chlorophenylhydrazone (m-CCCP) and the potassium ionophore valinomycin. These reagents, respectively, dissipate the mitochondrial Electrochemical Gradient and inner mitochondrial membrane potential. Both MA-10 Leydig tumor cell steroidogenesis and mitochondrial import of StAR were inhibited by m-CCCP or valinomycin at concentrations which had only minimal effects on P450scc activity. m-CCCP also inhibited import and processing of both StAR and the truncated StAR mutants, N-19 and C-28, in transfected COS-1 cells. Steroidogenesis induced by StAR and N-47, an active N-terminally truncated StAR mutant, was reduced in transfected COS-1 cells when treated with m-CCCP. This study shows that StAR action requires a membrane potential, which may reflect a functional requirement for import of StAR into the mitochondria, or more likely, an unidentified factor which is sensitive to ionophore treatment. Furthermore, the ability of N-47 to stimulate steroidogenesis in nonsteroidogenic HepG2 liver tumor cells, suggests that the mechanism by which StAR acts may be common to many cell types.
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effects of disruption of the mitochondrial Electrochemical Gradient on steroidogenesis and the steroidogenic acute regulatory star proteinproceedings of xth international congress on hormonal steroids quebec canada 17 21 june 1998
The Journal of Steroid Biochemistry and Molecular Biology, 1999Co-Authors: S R King, S Eimerl, J Orly, D M StoccoAbstract:Abstract The steroidogenic acute regulatory (StAR) protein, which mediates cholesterol delivery to the inner mitochondrial membrane and the P450scc enzyme, has been shown to require a mitochondrial Electrochemical Gradient for its activity in vitro . To characterize the role of this Gradient in cholesterol transfer, investigations were conducted in whole cells, utilizing the protonophore carbonyl cyanide m -chlorophenylhydrazone ( m -CCCP) and the potassium ionophore valinomycin. These reagents, respectively, dissipate the mitochondrial Electrochemical Gradient and inner mitochondrial membrane potential. Both MA-10 Leydig tumor cell steroidogenesis and mitochondrial import of StAR were inhibited by m -CCCP or valinomycin at concentrations which had only minimal effects on P450scc activity. m -CCCP also inhibited import and processing of both StAR and the truncated StAR mutants, N-19 and C-28, in transfected COS-1 cells. Steroidogenesis induced by StAR and N-47, an active N-terminally truncated StAR mutant, was reduced in transfected COS-1 cells when treated with m -CCCP. This study shows that StAR action requires a membrane potential, which may reflect a functional requirement for import of StAR into the mitochondria, or more likely, an unidentified factor which is sensitive to ionophore treatment. Furthermore, the ability of N-47 to stimulate steroidogenesis in nonsteroidogenic HepG2 liver tumor cells, suggests that the mechanism by which StAR acts may be common to many cell types.
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atp and a mitochondrial Electrochemical Gradient are required for functional activity of the steroidogenic acute regulatory star protein in isolated mitochondria
Endocrine Research, 1996Co-Authors: S R King, D M StoccoAbstract:The Steroidogenic Acute Regulatory (StAR) protein has been put forth as the rapidly synthesized, cycloheximide-sensitive protein that is required for the transport of cholesterol to the inner mitochondrial membrane and the P450scc enzyme and thereby acutely regulates steroidogenesis in Steroidogenic tissues. In this study, several of the factors that may be required for StAR activity were examined using an in vitro system. Lysates from StAR-transfected COS-1 cells were added to mitochondria isolated from MA-10 Leydig tumor cells. Results obtained demonstrated that StAR-containing cell lysate increased steroidogenesis in isolated mitochondria, but failed to do so in the presence of m-CCCP, apyrase, or AMP-PNP, suggesting that StAR function requires ATP hydrolysis as well as an Electrochemical Gradient for maximal Steroidogenic activity.
Ping H Wang - One of the best experts on this subject based on the ideXlab platform.
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insulin like growth factor 1 prevents loss of Electrochemical Gradient in cardiac muscle mitochondria via activation of pi 3 kinase akt pathway
Molecular and Cellular Endocrinology, 2003Co-Authors: Chihtai Ting, Prem M Sharma, Ping H WangAbstract:Abstract Insulin-like growth factor-1 (IGF 1) suppresses myocardial apoptosis and improves myocardial function in experimental models of cardiomyopathy. Apoptosis is triggered by mitochondria dysfunction and subsequent activation of caspases. We had previously shown that IGF 1 inhibited cardiomyocyte apoptosis via suppression of caspase, however, how IGF 1 and its signaling pathway modulates mitochondria function in cardiac muscle is not yet known. In this study we investigated how IGF 1 signaling modulates mitochondria membrane depolarization in the cardiomyocytes treated with doxorubicin. Doxorubicin rapidly induced loss of mitochondria Electrochemical Gradient and triggered mitochondria depolarization in primary cardiomyocytes, whereas addition of IGF 1 restored mitochondria Electrochemical Gradient. The effects of IGF 1 was blocked by a chemical inhibitor of PI 3 kinase and a dominant negative Akt, suggesting that IGF 1 signaling to mitochondria involves the PI 3 kinase-Akt pathway. Transducing cardiomyocytes with constitutive active PI 3 kinase partially restored the mitochondria Electrochemical Gradient in doxorubicin-treated cells. These findings provide direct evidence that IGF 1 modulation of mitochondria function is mediated through activation of PI 3 kinase and Akt. Additional experiments using agonist and antagonist of mitochondria KATP channel suggest that IGF 1 signaling to mitochondria membrane does not directly involve KATP channel. These findings suggest that cytosolic signaling to mitochondria may play a fundamental role in the cardiotoxic actions of doxorubicin and cardioprotective actions of IGF 1.
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Insulin-like growth factor-1 prevents loss of Electrochemical Gradient in cardiac muscle mitochondria via activation of PI 3 kinase/Akt pathway
Molecular and Cellular Endocrinology, 2003Co-Authors: Chihtai Ting, Prem M Sharma, Ping H WangAbstract:Abstract Insulin-like growth factor-1 (IGF 1) suppresses myocardial apoptosis and improves myocardial function in experimental models of cardiomyopathy. Apoptosis is triggered by mitochondria dysfunction and subsequent activation of caspases. We had previously shown that IGF 1 inhibited cardiomyocyte apoptosis via suppression of caspase, however, how IGF 1 and its signaling pathway modulates mitochondria function in cardiac muscle is not yet known. In this study we investigated how IGF 1 signaling modulates mitochondria membrane depolarization in the cardiomyocytes treated with doxorubicin. Doxorubicin rapidly induced loss of mitochondria Electrochemical Gradient and triggered mitochondria depolarization in primary cardiomyocytes, whereas addition of IGF 1 restored mitochondria Electrochemical Gradient. The effects of IGF 1 was blocked by a chemical inhibitor of PI 3 kinase and a dominant negative Akt, suggesting that IGF 1 signaling to mitochondria involves the PI 3 kinase-Akt pathway. Transducing cardiomyocytes with constitutive active PI 3 kinase partially restored the mitochondria Electrochemical Gradient in doxorubicin-treated cells. These findings provide direct evidence that IGF 1 modulation of mitochondria function is mediated through activation of PI 3 kinase and Akt. Additional experiments using agonist and antagonist of mitochondria KATP channel suggest that IGF 1 signaling to mitochondria membrane does not directly involve KATP channel. These findings suggest that cytosolic signaling to mitochondria may play a fundamental role in the cardiotoxic actions of doxorubicin and cardioprotective actions of IGF 1.
S R King - One of the best experts on this subject based on the ideXlab platform.
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Effects of disruption of the mitochondrial Electrochemical Gradient on steroidogenesis and the Steroidogenic Acute Regulatory (StAR) protein.
The Journal of steroid biochemistry and molecular biology, 1999Co-Authors: S R King, S Eimerl, J Orly, D M StoccoAbstract:The steroidogenic acute regulatory (StAR) protein, which mediates cholesterol delivery to the inner mitochondrial membrane and the P450scc enzyme, has been shown to require a mitochondrial Electrochemical Gradient for its activity in vitro. To characterize the role of this Gradient in cholesterol transfer, investigations were conducted in whole cells, utilizing the protonophore carbonyl cyanide m-chlorophenylhydrazone (m-CCCP) and the potassium ionophore valinomycin. These reagents, respectively, dissipate the mitochondrial Electrochemical Gradient and inner mitochondrial membrane potential. Both MA-10 Leydig tumor cell steroidogenesis and mitochondrial import of StAR were inhibited by m-CCCP or valinomycin at concentrations which had only minimal effects on P450scc activity. m-CCCP also inhibited import and processing of both StAR and the truncated StAR mutants, N-19 and C-28, in transfected COS-1 cells. Steroidogenesis induced by StAR and N-47, an active N-terminally truncated StAR mutant, was reduced in transfected COS-1 cells when treated with m-CCCP. This study shows that StAR action requires a membrane potential, which may reflect a functional requirement for import of StAR into the mitochondria, or more likely, an unidentified factor which is sensitive to ionophore treatment. Furthermore, the ability of N-47 to stimulate steroidogenesis in nonsteroidogenic HepG2 liver tumor cells, suggests that the mechanism by which StAR acts may be common to many cell types.
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effects of disruption of the mitochondrial Electrochemical Gradient on steroidogenesis and the steroidogenic acute regulatory star proteinproceedings of xth international congress on hormonal steroids quebec canada 17 21 june 1998
The Journal of Steroid Biochemistry and Molecular Biology, 1999Co-Authors: S R King, S Eimerl, J Orly, D M StoccoAbstract:Abstract The steroidogenic acute regulatory (StAR) protein, which mediates cholesterol delivery to the inner mitochondrial membrane and the P450scc enzyme, has been shown to require a mitochondrial Electrochemical Gradient for its activity in vitro . To characterize the role of this Gradient in cholesterol transfer, investigations were conducted in whole cells, utilizing the protonophore carbonyl cyanide m -chlorophenylhydrazone ( m -CCCP) and the potassium ionophore valinomycin. These reagents, respectively, dissipate the mitochondrial Electrochemical Gradient and inner mitochondrial membrane potential. Both MA-10 Leydig tumor cell steroidogenesis and mitochondrial import of StAR were inhibited by m -CCCP or valinomycin at concentrations which had only minimal effects on P450scc activity. m -CCCP also inhibited import and processing of both StAR and the truncated StAR mutants, N-19 and C-28, in transfected COS-1 cells. Steroidogenesis induced by StAR and N-47, an active N-terminally truncated StAR mutant, was reduced in transfected COS-1 cells when treated with m -CCCP. This study shows that StAR action requires a membrane potential, which may reflect a functional requirement for import of StAR into the mitochondria, or more likely, an unidentified factor which is sensitive to ionophore treatment. Furthermore, the ability of N-47 to stimulate steroidogenesis in nonsteroidogenic HepG2 liver tumor cells, suggests that the mechanism by which StAR acts may be common to many cell types.
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atp and a mitochondrial Electrochemical Gradient are required for functional activity of the steroidogenic acute regulatory star protein in isolated mitochondria
Endocrine Research, 1996Co-Authors: S R King, D M StoccoAbstract:The Steroidogenic Acute Regulatory (StAR) protein has been put forth as the rapidly synthesized, cycloheximide-sensitive protein that is required for the transport of cholesterol to the inner mitochondrial membrane and the P450scc enzyme and thereby acutely regulates steroidogenesis in Steroidogenic tissues. In this study, several of the factors that may be required for StAR activity were examined using an in vitro system. Lysates from StAR-transfected COS-1 cells were added to mitochondria isolated from MA-10 Leydig tumor cells. Results obtained demonstrated that StAR-containing cell lysate increased steroidogenesis in isolated mitochondria, but failed to do so in the presence of m-CCCP, apyrase, or AMP-PNP, suggesting that StAR function requires ATP hydrolysis as well as an Electrochemical Gradient for maximal Steroidogenic activity.
Donald P Briskin - One of the best experts on this subject based on the ideXlab platform.
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reversal of the red beet tonoplast h atpase by a pyrophosphate generated proton Electrochemical Gradient
Archives of Biochemistry and Biophysics, 1993Co-Authors: Arthur L Schmidt, Donald P BriskinAbstract:Abstract The reversal of the tonoplast H + -ATPase to mediate ATP synthesis was investigated in tonoplast vesicles isolated from red beet ( Beta vulgaris L.) storage tissue. Our approach involved use of the H + - PP i ase to establish a proton Electrochemical Gradient (ΔμH + ) across the tonoplast vesicle membrane to drive the H + -ATPase in reverse. However, an initial problem with this approach was the presence of an adenylate kinase activity in the tonoplast fraction that interfered with measurement of ATP synthesis as a coupling between the H + -ATPase and H + PP i ase. Inclusion of the adenylate kinase inhibitor plp5-di(adenosine)pentaphosphate (Ap5A) in assays at 50 μM led to a complete inhibition of this activity and allowed measurement of ATP synthesis coupled to PP i hydrolysis. When measured in the presence of Ap5A, PP i -dependent ATP synthesis was blocked by Triton X-100 and inhibited by gramicidin D, imidodiphosphate, nitrate, and bafilomycin A. These results are consistent with PP i -dependent ATP synthesis occurring as a coupled process involving a ΔμH + established across the membrane. Furthermore, the observation that ATP synthesis is inhibited by inhibitors of the tonoplast H + -ATPase (nitrate and bafilomycin A) would suggest that this enzyme is involved in the synthetic reaction and can operate in reverse to synthesize ATP from ADP and P i . A thermodynamic analysis of coupling between the H + - PP i ase and H + -ATPase suggests that PP i -driven ATP synthesis could only occur under these reaction conditions if the H + /substrate stoichiometries for the H + - PP i ase and H + -ATPase were 1 and 2, respectively. These values are consistent with transport stoichiometries previously determined for these enzymes in red beet tonoplast vesicles using kinetic methods.
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Reversal of the red beet tonoplast H(+)-ATPase by a pyrophosphate-generated proton Electrochemical Gradient.
Archives of Biochemistry and Biophysics, 1993Co-Authors: Arthur L Schmidt, Donald P BriskinAbstract:Abstract The reversal of the tonoplast H + -ATPase to mediate ATP synthesis was investigated in tonoplast vesicles isolated from red beet ( Beta vulgaris L.) storage tissue. Our approach involved use of the H + - PP i ase to establish a proton Electrochemical Gradient (ΔμH + ) across the tonoplast vesicle membrane to drive the H + -ATPase in reverse. However, an initial problem with this approach was the presence of an adenylate kinase activity in the tonoplast fraction that interfered with measurement of ATP synthesis as a coupling between the H + -ATPase and H + PP i ase. Inclusion of the adenylate kinase inhibitor plp5-di(adenosine)pentaphosphate (Ap5A) in assays at 50 μM led to a complete inhibition of this activity and allowed measurement of ATP synthesis coupled to PP i hydrolysis. When measured in the presence of Ap5A, PP i -dependent ATP synthesis was blocked by Triton X-100 and inhibited by gramicidin D, imidodiphosphate, nitrate, and bafilomycin A. These results are consistent with PP i -dependent ATP synthesis occurring as a coupled process involving a ΔμH + established across the membrane. Furthermore, the observation that ATP synthesis is inhibited by inhibitors of the tonoplast H + -ATPase (nitrate and bafilomycin A) would suggest that this enzyme is involved in the synthetic reaction and can operate in reverse to synthesize ATP from ADP and P i . A thermodynamic analysis of coupling between the H + - PP i ase and H + -ATPase suggests that PP i -driven ATP synthesis could only occur under these reaction conditions if the H + /substrate stoichiometries for the H + - PP i ase and H + -ATPase were 1 and 2, respectively. These values are consistent with transport stoichiometries previously determined for these enzymes in red beet tonoplast vesicles using kinetic methods.
Chihtai Ting - One of the best experts on this subject based on the ideXlab platform.
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insulin like growth factor 1 prevents loss of Electrochemical Gradient in cardiac muscle mitochondria via activation of pi 3 kinase akt pathway
Molecular and Cellular Endocrinology, 2003Co-Authors: Chihtai Ting, Prem M Sharma, Ping H WangAbstract:Abstract Insulin-like growth factor-1 (IGF 1) suppresses myocardial apoptosis and improves myocardial function in experimental models of cardiomyopathy. Apoptosis is triggered by mitochondria dysfunction and subsequent activation of caspases. We had previously shown that IGF 1 inhibited cardiomyocyte apoptosis via suppression of caspase, however, how IGF 1 and its signaling pathway modulates mitochondria function in cardiac muscle is not yet known. In this study we investigated how IGF 1 signaling modulates mitochondria membrane depolarization in the cardiomyocytes treated with doxorubicin. Doxorubicin rapidly induced loss of mitochondria Electrochemical Gradient and triggered mitochondria depolarization in primary cardiomyocytes, whereas addition of IGF 1 restored mitochondria Electrochemical Gradient. The effects of IGF 1 was blocked by a chemical inhibitor of PI 3 kinase and a dominant negative Akt, suggesting that IGF 1 signaling to mitochondria involves the PI 3 kinase-Akt pathway. Transducing cardiomyocytes with constitutive active PI 3 kinase partially restored the mitochondria Electrochemical Gradient in doxorubicin-treated cells. These findings provide direct evidence that IGF 1 modulation of mitochondria function is mediated through activation of PI 3 kinase and Akt. Additional experiments using agonist and antagonist of mitochondria KATP channel suggest that IGF 1 signaling to mitochondria membrane does not directly involve KATP channel. These findings suggest that cytosolic signaling to mitochondria may play a fundamental role in the cardiotoxic actions of doxorubicin and cardioprotective actions of IGF 1.
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Insulin-like growth factor-1 prevents loss of Electrochemical Gradient in cardiac muscle mitochondria via activation of PI 3 kinase/Akt pathway
Molecular and Cellular Endocrinology, 2003Co-Authors: Chihtai Ting, Prem M Sharma, Ping H WangAbstract:Abstract Insulin-like growth factor-1 (IGF 1) suppresses myocardial apoptosis and improves myocardial function in experimental models of cardiomyopathy. Apoptosis is triggered by mitochondria dysfunction and subsequent activation of caspases. We had previously shown that IGF 1 inhibited cardiomyocyte apoptosis via suppression of caspase, however, how IGF 1 and its signaling pathway modulates mitochondria function in cardiac muscle is not yet known. In this study we investigated how IGF 1 signaling modulates mitochondria membrane depolarization in the cardiomyocytes treated with doxorubicin. Doxorubicin rapidly induced loss of mitochondria Electrochemical Gradient and triggered mitochondria depolarization in primary cardiomyocytes, whereas addition of IGF 1 restored mitochondria Electrochemical Gradient. The effects of IGF 1 was blocked by a chemical inhibitor of PI 3 kinase and a dominant negative Akt, suggesting that IGF 1 signaling to mitochondria involves the PI 3 kinase-Akt pathway. Transducing cardiomyocytes with constitutive active PI 3 kinase partially restored the mitochondria Electrochemical Gradient in doxorubicin-treated cells. These findings provide direct evidence that IGF 1 modulation of mitochondria function is mediated through activation of PI 3 kinase and Akt. Additional experiments using agonist and antagonist of mitochondria KATP channel suggest that IGF 1 signaling to mitochondria membrane does not directly involve KATP channel. These findings suggest that cytosolic signaling to mitochondria may play a fundamental role in the cardiotoxic actions of doxorubicin and cardioprotective actions of IGF 1.