title: Myosin V plays an essential role in the thyroid hormone-dependent endocytosis of type II iodothyronine 5'-deiodinase.
abstract: In astrocytes, thyroxine modulates type II iodothyronine 5'-deiodinase levels by initiating the binding of the endosomes containing the enzyme to microfilaments, followed by actin-based endocytosis. Myosin V is a molecular motor thought to participate in vesicle trafficking in the brain. In this report, we developed an in vitro actin-binding assay to characterize the thyroid hormone-dependent binding of endocytotic vesicles to microfilaments. Thyroxine and reverse triiodothyronine (EC(50) levels approximately 1 nm) were >100-fold more potent than 3,5,3'-triiodothyronine in initiating vesicle binding to actin fibers in vitro. Thyroxine-dependent vesicle binding was calcium-, magnesium-, and ATP-dependent, suggesting the participation of one or more myosin motors, presumably myosin V. Addition of the myosin V globular tail, lacking the actin-binding head, specifically blocked thyroid hormone-dependent vesicle binding, and direct binding of the myosin V tail to enzyme-containing endosomes was thyroxine-dependent. Progressive NH(2)-terminal deletion of the myosin V tail and domain-specific antibody inhibition studies revealed that the thyroxine-dependent vesicle-tethering domain was localized to the last 21 amino acids of the COOH terminus. These data show that myosin V is responsible for thyroid hormone-dependent binding of primary endosomes to the microfilaments and suggest that this motor mediates the actin-based endocytosis of the type II iodothyronine deiodinase.
authors.affiliation: Department of Cellular and Molecular Physiology and the Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA.
authors.forename: S J
authors.initials: SJ
authors.lastname: Stachelek
authors.forename: T F
authors.initials: TF
authors.lastname: Kowalik
authors.forename: A P
authors.initials: AP
authors.lastname: Farwell
authors.forename: J L
authors.initials: JL
authors.lastname: Leonard
mesh_terms: D008841:Actin Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D000199:Actins / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000345:Affinity Labels; D000595:Amino Acid Sequence; D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D002148:Calmodulin-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004705:Endocytosis / Q000187:drug effects*; D011992:Endosomes / Q000187:drug effects / Q000378:metabolism; D007150:Immunohistochemistry; D007453:Iodide Peroxidase / Q000145:classification / Q000276:immunology / Q000378:metabolism*; D020409:Molecular Motor Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D024701:Myosin Type V; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013963:Thyroid Hormones / Q000494:pharmacology*; D013974:Thyroxine / Q000494:pharmacology; D014284:Triiodothyronine / Q000494:pharmacology; D014285:Triiodothyronine, Reverse / Q000494:pharmacology
chemical_list: D000199:Actins; D000345:Affinity Labels; D002148:Calmodulin-Binding Proteins; D020409:Molecular Motor Proteins; D009419:Nerve Tissue Proteins; D011993:Recombinant Fusion Proteins; D013963:Thyroid Hormones; C078829:chicken brain myosin-V p190; D014284:Triiodothyronine; D014285:Triiodothyronine, Reverse; D000255:Adenosine Triphosphate; D007453:Iodide Peroxidase; D024701:Myosin Type V; D013974:Thyroxine