Differential expression of thyroid hormone receptor isoforms dictates the dominant negative activity of mutant Beta receptor.
Mutations in the thyroid hormone receptor beta gene (TRbeta) cause resistance to thyroid hormone (RTH). Genetic analyses indicate that phenotypic manifestation of RTH is due to the dominant negative action of mutant TRbeta. However, the molecular mechanisms underlying the dominant negative action of mutants and how the same mutation results in marked variability of resistance in different tissues in vivo are not clear. Here we used a knock-in mouse (TRbetaPV mouse) that faithfully reproduces human RTH to address these questions. We demonstrated directly that TRbeta1 protein was approximately 3-fold higher than TRalpha1 in the liver of TRbeta(+/+) mice but was not detectable in the heart of wild-type and TRbetaPV mice. The abundance of PV in the liver of TRbeta(PV/PV) was more than TRbeta(PV/+) mice but not detectable in the heart. TRalpha1 in the liver was approximately 6-fold higher than that in the heart of wild-type and TRbetaPV mice. Using TR isoforms and PV-specific antibodies in gel shift assays, we found that in vivo, PV competed not only with TR isoforms for binding to thyroid hormone response elements (TRE) but also competed with TR for the retinoid X receptors in binding to TRE. These competitions led to the inhibition of the thyroid hormone (T(3))-positive regulated genes in the liver. In the heart, however, PV was significantly lower and thus could not effectively compete with TRalpha1 for binding to TRE, resulting in activation of the T(3)-target genes by higher levels of circulating thyroid hormones. These results indicate that in vivo, differential expression of TR isoforms in tissues dictates the dominant negative activity of mutant beta receptor, thereby resulting in variable phenotypic expression in RTH.
Gene Regulation Section, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA.
Xiao-Yong
XY
Zhang
Masahiro
M
Kaneshige
Yuji
Y
Kamiya
Kumiko
K
Kaneshige
Peter
P
McPhie
Sheue-Yann
SY
Cheng
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001667:Binding, Competitive; D002467:Cell Nucleus / Q000378:metabolism; D024202:Electrophoretic Mobility Shift Assay; D005786:Gene Expression Regulation; D006801:Humans; D008099:Liver / Q000166:cytology / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics*; D009206:Myocardium / Q000166:cytology / Q000378:metabolism; D009928:Organ Specificity; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D037021:Thyroid Hormone Receptors alpha / Q000235:genetics* / Q000378:metabolism*; D037042:Thyroid Hormone Receptors beta / Q000235:genetics* / Q000378:metabolism*; D014162:Transfection; D014284:Triiodothyronine / Q000378:metabolism
D020033:Protein Isoforms; D012333:RNA, Messenger; D037021:Thyroid Hormone Receptors alpha; D037042:Thyroid Hormone Receptors beta; D014284:Triiodothyronine