Thyroid hormone down-regulates p55, a thyroid hormone-binding protein that is homologous to protein disulfide isomerase and the beta-subunit of prolyl-4-hydroxylase.
We have previously characterized a cellular thyroid hormone-binding protein (p55) that is found concentrated on the lumenal face of the endoplasmic reticulum and nuclear envelope (Cheng, S.-y., Hasumura, S., Willingham, M.C., and Pastan, I. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 947-951). To understand the role p55 plays in thyroid hormone action, we examined the regulation of p55 by 3,3',5-triiodo-L-thyronine (T3). Rat pituitary tumor GH3 cells cultured in regular medium, thyroid hormone-depleted medium (Td medium), or Td medium supplemented with 50 nM T3 (Td + T3 medium) were metabolically labeled with [35S]methionine and immunoprecipitated with antibodies against p55. Treatment with T3 caused a fall in p55 levels. Poly(A+) RNA from cells cultured in regular, Td, or Td + T3 medium was hybridized to a cDNA from p55. T3 withdrawal or addition had no effect on p55 mRNA levels. Furthermore, the initial rates of synthesis of p55 from cells cultured in regular, Td, and Td + T3 were found to be similar. However, analysis of the decay curves from cells in which p55 was pulse-labeled with [35S]methionine indicated that p55 is 2-fold less stable in T3 containing medium. These results indicated that down-regulation of p55 by T3 occurs at the post-translational level. Since DNA sequence analysis indicates that p55 is identical to protein disulfide isomerase and the beta-subunit of prolyl-4-hydroxylase, T3 may mediate its effects on the synthesis, secretion, and/or transport of proteins via p55.
Obata
T
T
Laboratory of Molecular Biology, National Cancer Institute, Bethesda, Maryland 20892.
Kitagawa
S
S
Gong
Q H
QH
Pastan
I
I
Cheng
S Y
SY
D000818:Animals; D002352:Carrier Proteins / Q000032:analysis* / Q000235:genetics; D006207:Half-Life; D007535:Isomerases / Q000032:analysis*; D008565:Membrane Proteins / Q000032:analysis* / Q000235:genetics; D008715:Methionine / Q000378:metabolism; D010911:Pituitary Neoplasms / Q000378:metabolism*; D011393:Procollagen-Proline Dioxygenase / Q000032:analysis*; D019704:Protein Disulfide-Isomerases; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D013963:Thyroid Hormones; D014284:Triiodothyronine / Q000494:pharmacology*; D014407:Tumor Cells, Cultured / Q000187:drug effects; D000097810:Thyroid Hormone-Binding Proteins
D002352:Carrier Proteins; D007535:Isomerases; D008565:Membrane Proteins; D008715:Methionine; D011393:Procollagen-Proline Dioxygenase; D019704:Protein Disulfide-Isomerases; D012333:RNA, Messenger; D013963:Thyroid Hormones; D014284:Triiodothyronine; D000097810:Thyroid Hormone-Binding Proteins