Deletion of the thyroid hormone beta1 receptor increases basal and triiodothyronine-induced growth hormone messenger ribonucleic acid in GH3 cells.
The conserved diversity, restricted distribution, and differential regulation of the thyroid hormone receptor (TR) isoforms raise the possibility of isoform-specific functions. We have addressed the roles of individual TRs in GH gene expression in GH3 cells by using an isoform-specific antisense RNA to delete TRbeta1. An antisense RNA vector, directed against the isoform-specific coding sequence of the parent TRbeta1 complementary DNA, was constructed. Stable transfected GH3-derived cell lines expressing this construct were established. Appropriate control cell lines were established in parallel. Depletion of TRbeta1 in cells expressing the antisense construct was confirmed at both the messenger RNA and protein levels. Total TR expression was maintained in these cells by a reciprocal increase in TRbeta2 levels. This perturbation of the TR population was associated with a 10.5-fold increase in basal and a 5.0-fold increase in T3-stimulated GH gene expression, but no increase in total T3 binding of nuclear extracts. In transient cotransfection experiments, there were no differences between control cells and those expressing the antisense construct in either basal or T3-stimulated expression of reporters containing a variety of thyroid hormone response elements. Depletion of TRbeta1 in GH3 cells results in a reciprocal increase in TRbeta2. These changes are associated with increased basal and T3-stimulated GH gene expression, which are not due to a nonspecific enhancement of basal or hormone-stimulated transcription. We demonstrate that TRbeta1 is not required for T3 induction of the GH gene in GH3 cells and that TRbeta1 and TRbeta2 are not equivalent in their effects on basal repression of the GH promoter. The data illustrate the potential for isoform- and promoter-specific dissociation of the repression and activation properties of the TRs.
Ball
S G
SG
Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA. nsgb%ALBA@newcastle.ac.uk
Ikeda
M
M
Chin
W W
WW
D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D002460:Cell Line; D017931:DNA Primers / Q000032:analysis / Q000737:chemistry / Q000235:genetics; D017353:Gene Deletion; D005786:Gene Expression Regulation; D013006:Growth Hormone / Q000235:genetics*; D007457:Iodine Radioisotopes; D007536:Isomerism; D010903:Pituitary Gland, Anterior / Q000737:chemistry / Q000166:cytology / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D011988:Receptors, Thyroid Hormone / Q000032:analysis / Q000235:genetics* / Q000502:physiology; D014162:Transfection; D014284:Triiodothyronine / Q000494:pharmacology*
D017931:DNA Primers; D007457:Iodine Radioisotopes; D012333:RNA, Messenger; D011988:Receptors, Thyroid Hormone; D014284:Triiodothyronine; D013006:Growth Hormone