Selective proteolysis of human type 2 deiodinase: a novel ubiquitin-proteasomal mediated mechanism for regulation of hormone activation

Mol Endocrinol. 2000 Nov;14(11):1697-708. doi: 10.1210/mend.14.11.0558.

Abstract

We investigated the mechanism by which T4 regulates its activation to T3 by the type 2 iodothyronine deiodinase (D2). D2 is a short- lived (t1/2 50 min), 31-kDa endoplasmic reticulum (ER) integral membrane selenoenzyme that generates intracellular T3. Inhibition of the ubiquitin (Ub) activating enzyme, E1, or MG132, a proteasome blocker, inhibits both the basal and substrate-induced acceleration of D2 degradation. Using a catalytically active transiently expressed FLAG-tagged-NH2-D2, we found rapid synthesis of high molecular mass (100-300 kDa) Ub-D2 conjugates that are catalytically inactive. Ub-D2 increases when cells are exposed to D2 substrate or MG132 and disappears rapidly after E1 inactivation. Fusion of FLAG epitope to the COOH terminus of D2 prolongs its half-life approximately 2.5-fold and increases the levels of active and, especially, Ub-D2. This indicates that COOH-terminal modification interferes with proteasomal uptake of Ub-D2 that can then be deubiquitinated. Interestingly, the type 1 deiodinase, a related selenoenzyme that also converts T4 to T3 but with a half-life of >12 h, is inactivated but not ubiquitinated or degraded after exposure to substrate. Thus, ubiquitination of the ER-resident enzyme D2 constitutes a specific posttranslational mechanism for T4 regulation of its own activation in the central nervous system and pituitary tissues in which D2-catalyzed T4 to T3 conversion is the major source of intracellular T3.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Base Sequence
  • Cell Line
  • Cysteine Endopeptidases / metabolism*
  • Endoplasmic Reticulum / metabolism
  • Epitopes / genetics
  • Hormones / metabolism*
  • Humans
  • Iodide Peroxidase / genetics
  • Iodide Peroxidase / metabolism*
  • Ligases / metabolism
  • Molecular Sequence Data
  • Multienzyme Complexes / metabolism*
  • Oligopeptides
  • Peptides / genetics
  • Peptides / immunology
  • Peptides / metabolism
  • Proteasome Endopeptidase Complex
  • Protein Processing, Post-Translational
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Thyroxine / metabolism
  • Triiodothyronine / metabolism
  • Ubiquitin-Protein Ligases
  • Ubiquitins / metabolism*

Substances

  • Epitopes
  • Hormones
  • Multienzyme Complexes
  • Oligopeptides
  • Peptides
  • Recombinant Proteins
  • Ubiquitins
  • Triiodothyronine
  • FLAG peptide
  • iodothyronine deiodinase type I
  • iodothyronine deiodinase type II
  • Iodide Peroxidase
  • Ubiquitin-Protein Ligases
  • Cysteine Endopeptidases
  • Proteasome Endopeptidase Complex
  • Ligases
  • Thyroxine