Myosin V plays an essential role in the thyroid hormone-dependent endocytosis of type II iodothyronine 5'-deiodinase
Graduate School of Biomedical Sciences; Department of Cellular and Molecular Physiology; Department of Molecular Genetics and Microbiology; Department of Physiology
Medical Subject Headings
Actins; Adenosine Triphosphate; Affinity Labels; Amino Acid Sequence; Animals; Animals, Newborn; Astrocytes; Calmodulin-Binding Proteins; Endocytosis; Endosomes; Immunohistochemistry; Iodide Peroxidase; Microfilaments; Molecular Motor Proteins; Molecular Sequence Data; Mutation; *Myosin Type V; Nerve Tissue Proteins; Protein Binding; Rats; Recombinant Fusion Proteins; Thyroid Hormones; Thyroxine; Triiodothyronine; Triiodothyronine, Reverse
Life Sciences | Medicine and Health Sciences
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.
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Citation: J Biol Chem. 2000 Oct 13;275(41):31701-7. Link to article on publisher's site