Oxidoreductase interactions include a role for ERp72 engagement with mutant thyroglobulin from the rdw/rdw rat dwarf.
Newly synthesized thyroglobulin (Tg), the secretory glycoprotein that serves as precursor in thyroid hormone synthesis, normally forms transient covalent protein complexes with oxidoreductases of the endoplasmic reticulum (ER). The Tg-G2320R mutation is responsible for congenital hypothyroidism in rdw/rdw rats, in which a lack of secondary thyroid enlargement (goiter) implicates death of thyrocytes as part of disease pathogenesis. We found that mutant Tg-G2320R was retained within the ER with no detectable synthesis of thyroxine, had persistent exposure of free cysteine thiols, and was associated with activated ER stress response but incomplete ER-associated degradation (ERAD). Tg-G2320R associated with multiple ER resident proteins, most notably ERp72, including covalent Tg-ERp72 interactions. In PC Cl3 thyrocytes, inducible overexpression of ERp72 increased the ability of cells to maintain Tg cysteines in a reduced state. Noncovalent interactions of several ER chaperones with newly synthesized Tg-G2320R diminished over time in parallel with ERAD of the mutant protein, yet a small ERAD-resistant Tg fraction remained engaged in covalent association with ERp72 even 2 days post-synthesis. Such covalent protein aggregates may set the stage for apoptotic thyrocyte cell death, preventing thyroid goiter formation in rdw/rdw rats.
Menon
Shekar
S
Program in Cell and Molecular Biology and Division of Endocrinology, University of Cincinnati, Ohio 45267, USA.
Lee
Jaemin
J
Abplanalp
William A
WA
Yoo
Sung-Eun
SE
Agui
Takashi
T
Furudate
Sen-Ichi
S
Kim
Paul S
PS
Arvan
Peter
P
D000818:Animals; D017209:Apoptosis; D004392:Dwarfism / Q000209:etiology* / Q000378:metabolism; D004721:Endoplasmic Reticulum; D006042:Goiter; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D020125:Mutation, Missense; D010088:Oxidoreductases / Q000378:metabolism*; D011485:Protein Binding; D021381:Protein Transport; D051381:Rats; D011922:Rats, Mutant Strains; D013954:Thyroglobulin / Q000235:genetics* / Q000378:metabolism; D013961:Thyroid Gland / Q000166:cytology
D008562:Membrane Glycoproteins; C062477:endoplasmic reticulum glycoprotein p72; D013954:Thyroglobulin; D010088:Oxidoreductases