Regulation of Iron Regulatory Protein 1 during Hypoxia and Hypoxia/Reoxygenation (1998)

Given the important relationship between O2 and iron (Fenton chemistry) a study was undertaken to characterize the effects of hypoxia, as well as subsequent reoxygenation, on the iron-regulatory proteins 1 and 2 (IRP1 and IRP2) in a rat hepatoma cell line. IRP1 and IRP2 are cytosolic RNA-binding proteins that bind RNA stem-loops located in the 5′- or 3′-untranslated regions of specific mRNAs encoding proteins that are involved in iron homeostasis. In cells exposed to hypoxia, IRP1 RNA binding was decreased ∼2.8-fold after a 6-h exposure to 3% O2. Hypoxic inactivation of IRP1 was abolished when cells were pretreated with the iron chelator desferrioxamine, indicating a role for iron in inactivation. IRP1 inactivation was reversible since re-exposure of hypoxically-treated cells to 21% O2 increased RNA binding activity ∼7-fold after 21 h with an increase in activity seen as early as 1-h post-reoxygenation. IRP1 protein levels were unaffected during hypoxia as well as during reoxygenation. Whereas the protein synthesis inhibitor cycloheximide did not block IRP1 inactivation during hypoxia, it completely blocked IRP1 reactivation during subsequent reoxygenation. Reactivation of IRP1 during reoxygenation was also partially blocked by the phosphatase inhibitor okadaic acid. Finally, reactivated IRP1 was found to be resistant to inactivation by exogenous iron known to down-regulate its activity during normoxia. These data demonstrate that IRP1 RNA binding activity is post-translationally regulated during hypoxia and hypoxia/reoxygenation. Regulation of IRP1 by changing oxygen tension may provide a novel mechanism for post-transcriptionally regulating gene expression under these stresses. Given the important relationship between O2 and iron (Fenton chemistry) a study was undertaken to characterize the effects of hypoxia, as well as subsequent reoxygenation, on the iron-regulatory proteins 1 and 2 (IRP1 and IRP2) in a rat hepatoma cell line. IRP1 and IRP2 are cytosolic RNA-binding proteins that bind RNA stem-loops located in the 5′- or 3′-untranslated regions of specific mRNAs encoding proteins that are involved in iron homeostasis. In cells exposed to hypoxia, IRP1 RNA binding was decreased ∼2.8-fold after a 6-h exposure to 3% O2. Hypoxic inactivation of IRP1 was abolished when cells were pretreated with the iron chelator desferrioxamine, indicating a role for iron in inactivation. IRP1 inactivation was reversible since re-exposure of hypoxically-treated cells to 21% O2 increased RNA binding activity ∼7-fold after 21 h with an increase in activity seen as early as 1-h post-reoxygenation. IRP1 protein levels were unaffected during hypoxia as well as during reoxygenation. Whereas the protein synthesis inhibitor cycloheximide did not block IRP1 inactivation during hypoxia, it completely blocked IRP1 reactivation during subsequent reoxygenation. Reactivation of IRP1 during reoxygenation was also partially blocked by the phosphatase inhibitor okadaic acid. Finally, reactivated IRP1 was found to be resistant to inactivation by exogenous iron known to down-regulate its activity during normoxia. These data demonstrate that IRP1 RNA binding activity is post-translationally regulated during hypoxia and hypoxia/reoxygenation. Regulation of IRP1 by changing oxygen tension may provide a novel mechanism for post-transcriptionally regulating gene expression under these stresses. Mammalian cells employ multiple mechanisms that allow them to adapt to changes in oxygen concentration. During hypoxia, a cellular response is mounted aimed at counteracting the effects of limited O2 by the increased expression of specific genes such as erythropoietin, vascular endothelial growth factor, glycolytic enzymes, and inducible nitric oxide synthase (reviewed in Ref. 1Bunn H.F. Poyton R.O. Physiol. Rev. 1996; 76: 839-885Crossref PubMed Scopus (1041) Google Scholar). The transcriptional regulation of these and other hypoxia-induced genes is dependent on the activation of hypoxia-inducible transcription factor-1 (reviewed in Refs. 1Bunn H.F. Poyton R.O. Physiol. Rev. 1996; 76: 839-885Crossref PubMed Scopus (1041) Google Scholar and 2Guillemin K. Krasnow M.A. Cell. 1997; 89: 9-12Abstract Full Text Full Text PDF PubMed Scopus (421) Google Scholar), although post-transcriptional processes have been described (1Bunn H.F. Poyton R.O. Physiol. Rev. 1996; 76: 839-885Crossref PubMed Scopus (1041) Google Scholar). The mechanism by which O2concentration is sensed by cells is not known. One clue comes from studies showing that iron chelation mimics the hypoxic response (3Wang G.L. Semenza G.L. Blood. 1993; 82: 3610-3615Crossref PubMed Google Scholar, 4Melillo G. Taylor L.S. Brooks A. Musso T. Cox G.W. Varesio L. J. Biol. Chem. 1997; 272: 12236-12243Abstract Full Text Full Text PDF PubMed Scopus (185) Google Scholar), suggesting that O2 concentration may be sensed by a hemoprotein (1Bunn H.F. Poyton R.O. Physiol. Rev. 1996; 76: 839-885Crossref PubMed Scopus (1041) Google Scholar, 5Goldberg M.A. Dunning S.P. Bunn H.F. Science. 1988; 242: 1412-1415Crossref PubMed Scopus (872) Google Scholar).When O2 is restored to hypoxic cells, reactive oxygen species (ROS), 1The abbreviations used are: ROS, reactive oxygen species; IRP, iron regulatory protein; IRE, iron responsive element; c-aconitase, cytosolic aconitase; FAC, ferric ammonium citrate; Df, desferrioxamine mesylate. 1The abbreviations used are: ROS, reactive oxygen species; IRP, iron regulatory protein; IRE, iron responsive element; c-aconitase, cytosolic aconitase; FAC, ferric ammonium citrate; Df, desferrioxamine mesylate. including superoxide (O·̄2), hydrogen peroxide (H2O2), and hydroxyl radical (HO·) increase (6McCord J.M. New Engl. J. Med. 1985; 312: 159-163Crossref PubMed Scopus (4951) Google Scholar). The elevated levels of ROS produced during oxidative stress can damage DNA, proteins, and lipids. Iron is central in contributing to ROS-induced cell damage due to its ability to catalyze the formation of the highly reactive HO· via Fenton chemistry. This notion is supported by studies showing that iron chelation can protect cells from H/ReO2 injury (7Aust S.D. White B.C. Adv. Free Rad. Biol. Med. 1985; 1: 1-17Crossref Scopus (87) Google Scholar, 8Patt A. Horesh I.R. Berger E.M. Harken A.H. Repine J.E. J. Pediatr. Surg. 1992; 25: 224-227Abstract Full Text PDF Scopus (94) Google Scholar, 9Palmer C. Roberts R.L. Bero C. Stroke. 1994; 25: 1039-1045Crossref PubMed Scopus (190) Google Scholar, 10Fantini G.A. Yoshioka T. Am. J. Physiol. 1993; 264: 1953-1959PubMed Google Scholar).Although free iron is toxic, it is required by most cells for survival, and consequently, cells have developed mechanisms to regulate iron uptake and sequestration. In eukaryotes, iron levels are post-transcriptionally regulated by the iron regulatory proteins 1 and 2 (IRP1 and IRP2) (reviewed in Refs. 11Hentze M.W. Kühn L.C. A. 1996; PubMed Scopus Google Scholar and 1996; Full Text PDF PubMed Scopus Google Scholar). regulatory by binding to RNA known as iron responsive are located in the 5′- or 3′-untranslated regions of specific mRNAs encoding proteins involved in iron or are found in the regions of the iron protein as well as in the mRNAs for the iron proteins of and are found in the 3′-untranslated regions of mRNAs encoding iron uptake proteins, such as the and the Berger 1997; PubMed Scopus Google Scholar). IRP1 binding to the of IRP1 binding to located in the 3′-untranslated regions of the is to with the that can a Cell. Full Text PDF PubMed Scopus Google and are G.A. A. 1992; 89: PubMed Scopus Google L. G.A. A. 1992; 89: PubMed Scopus Google Scholar). cells are formation IRP1 to the cytosolic G.A. A. 1992; 89: PubMed Scopus Google Scholar, L. G.A. A. 1992; 89: PubMed Scopus Google Scholar). The ability of IRP1 to between a RNA-binding and a for the regulation of the of iron and by cells, iron levels are and iron is to IRP1 and mRNAs C. J. 1992; PubMed Scopus Google Scholar, J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). IRP2 RNA binding activity is by iron J. K. J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar, J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar), is not to a to IRP1 activity J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar, 1996; PubMed Scopus Google Scholar). In cells, IRP2 RNA binding activity is decreased due to by the J. K. J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar, J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar, J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, J. PubMed Scopus Google Scholar, Kühn L.C. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google ROS R.L. PubMed Scopus Google Scholar, K. J. Scopus Google Scholar, K. G. M.W. Biol. 1996; PubMed Scopus Google Scholar, K. A. M.W. J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar), nitric oxide K. G. M.W. Biol. 1996; PubMed Scopus Google Scholar, G. K. G. M.W. J. 1993; PubMed Scopus Google Scholar, J. Kühn L. J. 1993; PubMed Scopus Google Scholar, K. M.W. A. PubMed Scopus Google Scholar, Blood. 1996; Scholar, J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar), and J. Biol. Chem. Full Text PDF PubMed Google Scholar, J. Biol. Chem. 1992; Full Text PDF PubMed Google Scholar, J. Biol. Chem. 1993; Full Text PDF PubMed Google Scholar, A. J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar, White J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google and by the of the In have been in IRP1 regulation in cells K. J. Scopus Google Scholar, K. G. M.W. Biol. 1996; PubMed Scopus Google Scholar, K. A. M.W. J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar). The regulation of IRP1 activity by ROS the regulation of iron with the oxidative of the cellular of ROS is to and since a relationship between iron and the effects of hypoxia and H/ReO2 on IRP1 and IRP2 RNA binding demonstrate that not IRP2 RNA binding decreased during hypoxia, and was reversible subsequent reoxygenation. The regulation of IRP1 during hypoxia and H/ReO2 post-translationally changes in protein IRP1 inactivation during hypoxia required indicating a role for the IRP1 activation was not in the of exogenous the effects of O2 on the regulation of IRP1 and and that IRP1 is post-translationally regulated by hypoxia and During hypoxia, IRP1 RNA binding activity from rat hepatoma cells and Hypoxic inactivation of IRP1 was during subsequent reoxygenation. data that regulation was due in to the of the indicating that the as a for regulating IRP1 during hypoxia and IRP2 RNA binding activity did not under of hypoxia and it not a to IRP1 1996; PubMed Scopus Google chelation the in IRP1 RNA binding activity during hypoxia, indicating a for IRP1 to its of ability to IRP1 from its RNA-binding to its an increase in iron during hypoxia is a for the in IRP1 be that IRP2 activity cellular iron levels increased during was not the IRP2 can to exogenous indicating that hypoxic cells can In the of IRP1 and IRP2 to iron were found to be IRP2 as an of cellular iron that hypoxic inactivation of IRP1 may be due to other increased cellular to hypoxia-induced inactivation of IRP1 activity is in which the of the is in an O2 In IRP1 from cells in a between the and the RNA-binding O2 is the of the to a in IRP1 RNA binding and a increase in activity not The increase in activity in is not since under cells of IRP1 in the RNA-binding and in the IRP1 inactivation in increased synthesis to that in hypoxic G. J. PubMed Scopus Google the be during One is the of ROS, and are by via J. Biol. Chem. Full Text PDF PubMed Google Scholar, J. Biol. Chem. 1992; Full Text PDF PubMed Google Scholar, A. J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar, White J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar), and IRP1 activity was increased in cells with the K. G. M.W. Biol. 1996; PubMed Scopus Google Scholar). on these studies it that a in during hypoxia for IRP1 inactivation by of its H/ReO2 been to ROS in a of cell and since IRP1 is to ROS R.L. PubMed Scopus Google Scholar, K. J. Scopus Google Scholar, K. G. M.W. Biol. 1996; PubMed Scopus Google Scholar, K. A. M.W. J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar), the IRP1 activity was during reoxygenation of hypoxic IRP1 RNA binding activity increased in cells and in an increase in IRP1 protein The increase in IRP1 activity during reoxygenation may from an increase in ROS, to reactivation of RNA binding activity of IRP1 during reoxygenation was to exogenous iron was cells is by the in IRP2 activity in One for the of exogenous iron to IRP1 RNA binding activity is that ROS-induced of the is in the of The increase in IRP1 RNA binding during reoxygenation increase to increased iron In synthesis be contributing to in cellular IRP2 can for IRP1 during reoxygenation to be The iron regulation of IRP1 during reoxygenation to cellular damage seen during to the IRP1 activation during H/ReO2 may by of ROS on the are to be as been described for IRP1 activation K. A. M.W. J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar). for comes from data that cycloheximide completely okadaic partially IRP1 reactivation during reoxygenation. These data the that H/ReO2 the synthesis of a which is in a to IRP1 One may be a of at to be the have been to RNA binding activity 1997; PubMed Scopus Google Scholar, J. Biol. Chem. 1993; Full Text PDF PubMed Google Scholar). is that or other of IRP1 by H/ReO2 formation of the the that cycloheximide have ROS during data a IRP1 activation during H/ReO2 a that IRP1 by in to the of the of the IRP1 to the of the cell as a mechanism for post-transcriptionally regulating gene expression during hypoxia and regulation in other cells to be of and be an important in the role of IRP1 regulation by changing O2 The of O2 regulation of IRP1 may to be in of cellular to hypoxia as well as cellular damage seen during Mammalian cells employ multiple mechanisms that allow them to adapt to changes in oxygen concentration. During hypoxia, a cellular response is mounted aimed at counteracting the effects of limited O2 by the increased expression of specific genes such as erythropoietin, vascular endothelial growth factor, glycolytic enzymes, and inducible nitric oxide synthase (reviewed in Ref. 1Bunn H.F. Poyton R.O. Physiol. Rev. 1996; 76: 839-885Crossref PubMed Scopus (1041) Google Scholar). The transcriptional regulation of these and other hypoxia-induced genes is dependent on the activation of hypoxia-inducible transcription factor-1 (reviewed in Refs. 1Bunn H.F. Poyton R.O. Physiol. Rev. 1996; 76: 839-885Crossref PubMed Scopus (1041) Google Scholar and 2Guillemin K. Krasnow M.A. Cell. 1997; 89: 9-12Abstract Full Text Full Text PDF PubMed Scopus (421) Google Scholar), although post-transcriptional processes have been described (1Bunn H.F. Poyton R.O. Physiol. Rev. 1996; 76: 839-885Crossref PubMed Scopus (1041) Google Scholar). The mechanism by which O2concentration is sensed by cells is not known. One clue comes from studies showing that iron chelation mimics the hypoxic response (3Wang G.L. Semenza G.L. Blood. 1993; 82: 3610-3615Crossref PubMed Google Scholar, 4Melillo G. Taylor L.S. Brooks A. Musso T. Cox G.W. Varesio L. J. Biol. Chem. 1997; 272: 12236-12243Abstract Full Text Full Text PDF PubMed Scopus (185) Google Scholar), suggesting that O2 concentration may be sensed by a hemoprotein (1Bunn H.F. Poyton R.O. Physiol. Rev. 1996; 76: 839-885Crossref PubMed Scopus (1041) Google Scholar, 5Goldberg M.A. Dunning S.P. Bunn H.F. Science. 1988; 242: 1412-1415Crossref PubMed Scopus (872) Google Scholar). O2 is restored to hypoxic cells, reactive oxygen species (ROS), 1The abbreviations used are: ROS, reactive oxygen species; IRP, iron regulatory protein; IRE, iron responsive element; c-aconitase, cytosolic aconitase; FAC, ferric ammonium citrate; Df, desferrioxamine mesylate. 1The abbreviations used are: ROS, reactive oxygen species; IRP, iron regulatory protein; IRE, iron responsive element; c-aconitase, cytosolic aconitase; FAC, ferric ammonium citrate; Df, desferrioxamine mesylate. including superoxide (O·̄2), hydrogen peroxide (H2O2), and hydroxyl radical (HO·) increase (6McCord J.M. New Engl. J. Med. 1985; 312: 159-163Crossref PubMed Scopus (4951) Google Scholar). The elevated levels of ROS produced during oxidative stress can damage DNA, proteins, and lipids. Iron is central in contributing to ROS-induced cell damage due to its ability to catalyze the formation of the highly reactive HO· via Fenton chemistry. This notion is supported by studies showing that iron chelation can protect cells from H/ReO2 injury (7Aust S.D. White B.C. Adv. Free Rad. Biol. Med. 1985; 1: 1-17Crossref Scopus (87) Google Scholar, 8Patt A. Horesh I.R. Berger E.M. Harken A.H. Repine J.E. J. Pediatr. Surg. 1992; 25: 224-227Abstract Full Text PDF Scopus (94) Google Scholar, 9Palmer C. Roberts R.L. Bero C. Stroke. 1994; 25: 1039-1045Crossref PubMed Scopus (190) Google Scholar, 10Fantini G.A. Yoshioka T. Am. J. Physiol. 1993; 264: 1953-1959PubMed Google Scholar). free iron is toxic, it is required by most cells for survival, and consequently, cells have developed mechanisms to regulate iron uptake and sequestration. In eukaryotes, iron levels are post-transcriptionally regulated by the iron regulatory proteins 1 and 2 (IRP1 and IRP2) (reviewed in Refs. 11Hentze M.W. Kühn L.C. A. 1996; PubMed Scopus Google Scholar and 1996; Full Text PDF PubMed Scopus Google Scholar). regulatory by binding to RNA known as iron responsive are located in the 5′- or 3′-untranslated regions of specific mRNAs encoding proteins involved in iron or are found in the regions of the iron protein as well as in the mRNAs for the iron proteins of and are found in the 3′-untranslated regions of mRNAs encoding iron uptake proteins, such as the and the Berger 1997; PubMed Scopus Google Scholar). IRP1 binding to the of IRP1 binding to located in the 3′-untranslated regions of the IRP1 is to with the that can a Cell. Full Text PDF PubMed Scopus Google and are G.A. A. 1992; 89: PubMed Scopus Google L. G.A. A. 1992; 89: PubMed Scopus Google Scholar). cells are formation IRP1 to the cytosolic G.A. A. 1992; 89: PubMed Scopus Google Scholar, L. G.A. A. 1992; 89: PubMed Scopus Google Scholar). The ability of IRP1 to between a RNA-binding and a for the regulation of the of iron and by cells, iron levels are and iron is IRP2 to IRP1 and mRNAs C. J. 1992; PubMed Scopus Google Scholar, J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). IRP2 RNA binding activity is by iron J. K. J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar, J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar), is not to a to IRP1 activity J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar, 1996; PubMed Scopus Google Scholar). In cells, IRP2 RNA binding activity is decreased due to by the J. K. J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar, J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar, J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, J. PubMed Scopus Google Scholar, Kühn L.C. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). The ROS R.L. PubMed Scopus Google Scholar, K. J. Scopus Google Scholar, K. G. M.W. Biol. 1996; PubMed Scopus Google Scholar, K. A. M.W. J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar), nitric oxide K. G. M.W. Biol. 1996; PubMed Scopus Google Scholar, G. K. G. M.W. J. 1993; PubMed Scopus Google Scholar, J. Kühn L. J. 1993; PubMed Scopus Google Scholar, K. M.W. A. PubMed Scopus Google Scholar, Blood. 1996; Scholar, J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar), and J. Biol. Chem. Full Text PDF PubMed Google Scholar, J. Biol. Chem. 1992; Full Text PDF PubMed Google Scholar, J. Biol. Chem. 1993; Full Text PDF PubMed Google Scholar, A. J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar, White J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google and by the of the In have been in IRP1 regulation in cells K. J. Scopus Google Scholar, K. G. M.W. Biol. 1996; PubMed Scopus Google Scholar, K. A. M.W. J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar). The regulation of IRP1 activity by ROS the regulation of iron with the oxidative of the cellular of ROS is to and since a relationship between iron and the effects of hypoxia and H/ReO2 on IRP1 and IRP2 RNA binding demonstrate that not IRP2 RNA binding decreased during hypoxia, and was reversible subsequent reoxygenation. The regulation of IRP1 during hypoxia and H/ReO2 post-translationally changes in protein IRP1 inactivation during hypoxia required indicating a role for the IRP1 activation was not in the of exogenous the effects of O2 on the regulation of IRP1 and and that IRP1 is post-translationally regulated by hypoxia and During hypoxia, IRP1 RNA binding activity from rat hepatoma cells and Hypoxic inactivation of IRP1 was during subsequent reoxygenation. data that regulation was due in to the of the indicating that the as a for regulating IRP1 during hypoxia and IRP2 RNA binding activity did not under of hypoxia and it not a to IRP1 1996; PubMed Scopus Google chelation the in IRP1 RNA binding activity during hypoxia, indicating a for IRP1 to its of ability to IRP1 from its RNA-binding to its an increase in iron during hypoxia is a for the in IRP1 be that IRP2 activity cellular iron levels increased during was not the IRP2 can to exogenous indicating that hypoxic cells can In the of IRP1 and IRP2 to iron were found to be IRP2 as an of cellular iron that hypoxic inactivation of IRP1 may be due to other increased cellular to hypoxia-induced inactivation of IRP1 activity is in which the of the is in an O2 In IRP1 from cells in a between the and the RNA-binding O2 is the of the to a in IRP1 RNA binding and a increase in activity not The increase in activity in is not since under cells of IRP1 in the RNA-binding and in the IRP1 inactivation in increased synthesis to that in hypoxic G. J. PubMed Scopus Google the be during One is the of ROS, and are by via J. Biol. Chem. Full Text PDF PubMed Google Scholar, J. Biol. Chem. 1992; Full Text PDF PubMed Google Scholar, A. J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar, White J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar), and IRP1 activity was increased in cells with the K. G. M.W. Biol. 1996; PubMed Scopus Google Scholar). on these studies it that a in during hypoxia for IRP1 inactivation by of its H/ReO2 been to ROS in a of cell and since IRP1 is to ROS R.L. PubMed Scopus Google Scholar, K. J. Scopus Google Scholar, K. G. M.W. Biol. 1996; PubMed Scopus Google Scholar, K. A. M.W. J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar), the IRP1 activity was during reoxygenation of hypoxic IRP1 RNA binding activity increased in cells and in an increase in IRP1 protein The increase in IRP1 activity during reoxygenation may from an increase in ROS, to reactivation of RNA binding activity of IRP1 during reoxygenation was to exogenous iron was cells is by the in IRP2 activity in One for the of exogenous iron to IRP1 RNA binding activity is that ROS-induced of the is in the of The increase in IRP1 RNA binding during reoxygenation increase to increased iron In synthesis be contributing to in cellular IRP2 can for IRP1 during reoxygenation to be The iron regulation of IRP1 during reoxygenation to cellular damage seen during to the IRP1 activation during H/ReO2 may by of ROS on the are to be as been described for IRP1 activation K. A. M.W. J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar). for comes from data that cycloheximide completely okadaic partially IRP1 reactivation during reoxygenation. These data the that H/ReO2 the synthesis of a which is in a to IRP1 One may be a of at to be the have been to RNA binding activity 1997; PubMed Scopus Google Scholar, J. Biol. Chem. 1993; Full Text PDF PubMed Google Scholar). is that or other of IRP1 by H/ReO2 formation of the the that cycloheximide have ROS during data a IRP1 activation during H/ReO2 a that IRP1 by in to the of the of the IRP1 to the of the cell as a mechanism for post-transcriptionally regulating gene expression during hypoxia and regulation in other cells to be of and be an important in the role of IRP1 regulation by changing O2 The of O2 regulation of IRP1 may to be in of cellular to hypoxia as well as cellular damage seen during the effects of O2 on the regulation of IRP1 and and that IRP1 is post-translationally regulated by hypoxia and During hypoxia, IRP1 RNA binding activity from rat hepatoma cells and Hypoxic inactivation of IRP1 was during subsequent reoxygenation. data that regulation was due in to the of the indicating that the as a for regulating IRP1 during hypoxia and IRP2 RNA binding activity did not under of hypoxia and it not a to IRP1 1996; PubMed Scopus Google Scholar). Iron chelation the in IRP1 RNA binding activity during hypoxia, indicating a for IRP1 to its of ability to IRP1 from its RNA-binding to its an increase in iron during hypoxia is a for the in IRP1 be that IRP2 activity cellular iron levels increased during was not the IRP2 can to exogenous indicating that hypoxic cells can In the of IRP1 and IRP2 to iron were found to be IRP2 as an of cellular iron that hypoxic inactivation of IRP1 may be due to other increased cellular to hypoxia-induced inactivation of IRP1 activity is in which the of the is in an O2 In IRP1 from cells in a between the and the RNA-binding O2 is the of the to a in IRP1 RNA binding and a increase in activity not The increase in activity in is not since under cells of IRP1 in the RNA-binding and in the IRP1 inactivation in increased synthesis to that in hypoxic G. J. PubMed Scopus Google Scholar). the be during One is the of ROS, and are by via J. Biol. Chem. Full Text PDF PubMed Google Scholar, J. Biol. Chem. 1992; Full Text PDF PubMed Google Scholar, A. J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar, White J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar), and IRP1 activity was increased in cells with the K. G. M.W. Biol. 1996; PubMed Scopus Google Scholar). on these studies it that a in during hypoxia for IRP1 inactivation by of its H/ReO2 been to ROS in a of cell and since IRP1 is to ROS R.L. PubMed Scopus Google Scholar, K. J. Scopus Google Scholar, K. G. M.W. Biol. 1996; PubMed Scopus Google Scholar, K. A. M.W. J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar), the IRP1 activity was during reoxygenation of hypoxic IRP1 RNA binding activity increased in cells and in an increase in IRP1 protein The increase in IRP1 activity during reoxygenation may from an increase in ROS, to reactivation of RNA binding activity of IRP1 during reoxygenation was to exogenous iron was cells is by the in IRP2 activity in One for the of exogenous iron to IRP1 RNA binding activity is that ROS-induced of the is in the of The increase in IRP1 RNA binding during reoxygenation increase to increased iron In synthesis be contributing to in cellular IRP2 can for IRP1 during reoxygenation to be The iron regulation of IRP1 during reoxygenation to cellular damage seen during In to the IRP1 activation during H/ReO2 may by of ROS on the are to be as been described for IRP1 activation K. A. M.W. J. Biol. Chem. 1997; 272: Full Text Full Text PDF PubMed Scopus Google Scholar). for comes from data that cycloheximide completely okadaic partially IRP1 reactivation during reoxygenation. These data the that H/ReO2 the synthesis of a which is in a to IRP1 One may be a of at to be the have been to RNA binding activity 1997; PubMed Scopus Google Scholar, J. Biol. Chem. 1993; Full Text PDF PubMed Google Scholar). is that or other of IRP1 by H/ReO2 formation of the the that cycloheximide have ROS during data a IRP1 activation during H/ReO2 a that IRP1 by in to the of the The of the IRP1 to the of the cell as a mechanism for post-transcriptionally regulating gene expression during hypoxia and regulation in other cells to be of and be an important in the role of IRP1 regulation by changing O2 The of O2 regulation of IRP1 may to be in of cellular to hypoxia as well as cellular damage seen during and for during the of and for the