Hormone-activated phosphorylation of human beta1 thyroid hormone nuclear receptor.
To understand the role of phosphorylation in the hormone-dependent transcriptional activation of thyroid hormone receptors (TRs), the present study evaluated the effect of the thyroid hormone, 3,3',5-triiodo-L-thyronine (T3) on the phosphorylation of TR, human subtype beta1 (h-TRbeta1). The extent of phosphorylation was compared in cells cultured in T3-depleted (Td) or T3-supplemented medium (Td + T3). T3 was found to activate phosphorylation of h-TRbeta1 approximately threefold. Taking into account the T3-induced fourfold downregulation in the expression of h-TRbeta1 in the same period, the specific T3-activated phosphorylation was increased approximately twelvefold. Phosphoamino acid analysis indicates that the phosphorylation of serine and threonine in a ratio of approximately 10:1 was increased approximately threefold by T3. Comparison of the [32P]-labeled tryptic maps of h-TRbeta1 phosphorylated in cells cultured in Td medium or Td + T3 medium indicates that the latter had fewer fragments and changes of intensities in several common fragments, indicating that the phosphorylation sites activated by T3-treatment differed from those of basal phosphorylation. Partial V8 and chymotrypic proteolysis indicates that h-TRbeta1 phosphorylated in cells cultured in Td + T3 medium was more resistant to proteolysis. These results indicate that T3-activated phosphorylation altered the protease susceptibility of h-TRbeta1 that could reflect structural changes in h-TRbeta1. These results raise the possibility that T3-activated phosphorylation may play an important role in transcriptional activation of h-TRbeta1.
Ting
Y T
YT
Laboratory of Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-4255, USA.
Cheng
S Y
SY
D002460:Cell Line; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D006868:Hydrolysis; D010449:Peptide Mapping; D010761:Phosphorus Radioisotopes; D010766:Phosphorylation; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D011988:Receptors, Thyroid Hormone / Q000378:metabolism*; D013963:Thyroid Hormones / Q000502:physiology*; D014357:Trypsin
D010761:Phosphorus Radioisotopes; D018160:Receptors, Cytoplasmic and Nuclear; D011988:Receptors, Thyroid Hormone; D013963:Thyroid Hormones; D014357:Trypsin