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dc.contributor.authorFarwell, Alan P.
dc.contributor.authorLeonard, Jack L.
dc.date2022-08-11T08:10:02.000
dc.date.accessioned2022-08-23T16:53:00Z
dc.date.available2022-08-23T16:53:00Z
dc.date.issued1992-08-01
dc.date.submitted2008-07-09
dc.identifier.citation<p>Endocrinology. 1992 Aug;131(2):721-8.</p>
dc.identifier.issn0013-7227 (Print)
dc.identifier.pmid1322280
dc.identifier.urihttp://hdl.handle.net/20.500.14038/42174
dc.description.abstractT4 dynamically regulates the levels of type II iodothyronine 5'-deiodinase in the brain. Using an astrocyte cell culture model, we have shown that thyroxine increases inactivation of this enzyme through a mechanism using the actin cytoskeleton. In the absence of T4, the filamentous actin (F-actin) stress fibers are absent, and deiodinase inactivation is relatively slow. T4 increases inactivation of type II 5'-deiodinase by 1) restoring the F-actin stress fibers, 2) promoting the binding of the enzyme to F-actin, and 3) stimulating enzyme internalization. To determine whether inactivation of the deiodinase is due solely to the restoration of stress fibers by T4 or also involves direct thyroxine-mediated enzyme-F-actin interactions, we examined the effects of retinoids on both actin polymerization and type II 5'-deiodinase activity in cultured astrocytes, as these hormones have been shown to alter cytoskeletal organization in other tissues. In thyroid hormone-deficient astrocytes, retinoic acid increased F-actin levels, with no change in total cell actin. The F-actin content increased approximately 40% within 30 min after the addition of retinoic acid. After a plateau of 6-8 h, the F-actin content increased further to approximately 90% of the total cell actin and was associated with the reappearance of stress fibers. Only this latter retinoid-stimulated increase in F-actin content was blocked by actinomycin-D. Restoration of the F-actin stress fibers by retinoids did not increase the turnover of the type II 5'-deiodinase (t1/2, 1.99 h-1) or promote binding of the enzyme to F-actin in the absence of T4. Similarly, retinoids did not affect the rapid T4-mediated turnover (t1/2, 0.18 h-1) of type II 5'-deiodinase. These data show that an intact F-actin cytoskeleton in the absence of T4 is inadequate to alter the inactivation of type II 5'-deiodinase and that specific T4-enzyme-F-actin interactions are necessary to initiate the rapid inactivation/internalization of this enzyme.
dc.language.isoen_US
dc.relation<p><a href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&list_uids=1322280&dopt=Abstract">Link to Article in PubMed</a></p>
dc.relation.urlhttps://doi.org/10.1210/en.131.2.721
dc.subjectActins
dc.subjectAnimals
dc.subjectAnimals, Newborn
dc.subjectAstrocytes
dc.subjectBucladesine
dc.subjectCells, Cultured
dc.subjectCycloheximide
dc.subjectDactinomycin
dc.subjectEnzyme Activation
dc.subjectFluorescent Dyes
dc.subjectIodide Peroxidase
dc.subjectKinetics
dc.subjectMicroscopy, Fluorescence
dc.subjectRats
dc.subjectThyroxine
dc.subjectTretinoin
dc.subjectLife Sciences
dc.subjectMedicine and Health Sciences
dc.titleDissociation of actin polymerization and enzyme inactivation in the hormonal regulation of type II iodothyronine 5'-deiodinase activity in astrocytes
dc.typeArticle
dc.source.journaltitleEndocrinology
dc.source.volume131
dc.source.issue2
dc.identifier.legacycoverpagehttps://escholarship.umassmed.edu/oapubs/545
dc.identifier.contextkey545027
html.description.abstract<p>T4 dynamically regulates the levels of type II iodothyronine 5'-deiodinase in the brain. Using an astrocyte cell culture model, we have shown that thyroxine increases inactivation of this enzyme through a mechanism using the actin cytoskeleton. In the absence of T4, the filamentous actin (F-actin) stress fibers are absent, and deiodinase inactivation is relatively slow. T4 increases inactivation of type II 5'-deiodinase by 1) restoring the F-actin stress fibers, 2) promoting the binding of the enzyme to F-actin, and 3) stimulating enzyme internalization. To determine whether inactivation of the deiodinase is due solely to the restoration of stress fibers by T4 or also involves direct thyroxine-mediated enzyme-F-actin interactions, we examined the effects of retinoids on both actin polymerization and type II 5'-deiodinase activity in cultured astrocytes, as these hormones have been shown to alter cytoskeletal organization in other tissues. In thyroid hormone-deficient astrocytes, retinoic acid increased F-actin levels, with no change in total cell actin. The F-actin content increased approximately 40% within 30 min after the addition of retinoic acid. After a plateau of 6-8 h, the F-actin content increased further to approximately 90% of the total cell actin and was associated with the reappearance of stress fibers. Only this latter retinoid-stimulated increase in F-actin content was blocked by actinomycin-D. Restoration of the F-actin stress fibers by retinoids did not increase the turnover of the type II 5'-deiodinase (t1/2, 1.99 h-1) or promote binding of the enzyme to F-actin in the absence of T4. Similarly, retinoids did not affect the rapid T4-mediated turnover (t1/2, 0.18 h-1) of type II 5'-deiodinase. These data show that an intact F-actin cytoskeleton in the absence of T4 is inadequate to alter the inactivation of type II 5'-deiodinase and that specific T4-enzyme-F-actin interactions are necessary to initiate the rapid inactivation/internalization of this enzyme.</p>
dc.identifier.submissionpathoapubs/545
dc.contributor.departmentDepartment of Medicine, Division of Endocrinology & Metabolism
dc.contributor.departmentMolecular Endocrinology Laboratory
dc.source.pages721-8


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