GTP-Binding Proteins ; Receptors, Thyrotropin-Releasing Hormone ; Thyrotropin-Releasing Hormone*

The syndrome of resistance to thyroid hormone (RTH) is characterized by reduced tissue sensitivity to thyroid hormone (TH). In the majority of subjects, RTH is caused by mutations in the thyroid hormone receptor beta (TRbeta) gene, located on the chromosome locus 3p24.3. RTH is inherited in an autosomal dominant manner. The clinical presentation of RTH is variable, but common features include elevated serum levels of thyroid hormone (TH), a normal or slightly increased thyrotropin (thyroid stimulating hormone, TSH) level that responds to thyrotropin releasing hormone (TRH), and goiter. We report a 4 year-old girl, who was clinically euthyroid in spite of high total and free T4, and T3 concentrations, while TSH was slightly increased. Sequence analysis of the thyroid hormone receptor beta gene (THRB) confirmed a heterozygous C to T change at nucleotide number 1303, resulting in a substitution of histidine by tyrosine at codon 435 (H435Y). Further analysis of her parents revealed that the H435Y variation was a de novo mutation since neither parents had the variation. Her parents' TH and TSH levels were within normal range.
Child, Preschool ; Codon ; Female ; Genes, erbA* ; Goiter ; Histidine ; Humans ; Parents ; Reference Values ; Sequence Analysis ; Thyroid Gland* ; Thyroid Hormone Receptors beta ; Thyrotropin ; Thyrotropin-Releasing Hormone ; Tyrosine

We investigated the effect of alpha-subunit of the stimulatory GTP-binding protein (Galphas) gene mutation on the expression of the thyrotropin-releasing hormone (TRH) receptor (TRH-R) gene in GH3 cells and in growth hormone (GH)-secreting adenomas of acromegalic patients. In the presence of cycloheximide, forskolin and isobutylmethylxanthine, cholera toxin, and GH-releasing hormone (GBRH) decreased rat TRH-R (rTRH-R) gene expression by about 39%, 43.7%, and 46.7%, respectively. Transient expression of a vector expressing mutant-type Galphas decreased the rTRH-R gene expression by about 50% at 24 h of transfection, whereas a wild-type Galphas expression vector did not. The transcript of human TRH-R (hTRH-R) gene was detected in 6 of 8 (75%) tumors. Three of them (50%) showed the paradoxical GH response to TRH and the other three patients did not show the response. The relative expression of hTRH-R mRNA in the tumors from patients with the paradoxical response of GH to TRH did not differ from that in the tumors from patients without the paradoxical response. Direct PCR sequencing of GALPHAs gene disclosed a mutant allele and a normal allele only at codon 201 in 4 of 8 tumors. The paradoxical response to TRH was observed in 2 of 4 patients without the mutation, and 2 of 4 patients with the mutation. The hTRH-R gene expression of pituitary adenomas did not differ between the tumors without the mutation and those with mutation. The present study suggests that the expression of TRH-R gene is not likely to be a main determinant for the paradoxical response of GH to TRH, and that Galphas mutation may suppress the gene expression of TRH-R in GH-secreting adenoma. However, a certain predisposing factor(s) may play an important role in determining the expression of TRH-R.
Acromegaly ; Adenoma ; Alleles ; Animals ; Cholera Toxin ; Codon ; Colforsin ; Cycloheximide ; Gene Expression ; Growth Hormone ; GTP-Binding Proteins ; Humans ; Pituitary Neoplasms ; Polymerase Chain Reaction ; Rats ; Receptors, Thyrotropin-Releasing Hormone* ; RNA, Messenger* ; Thyrotropin-Releasing Hormone ; Transfection

OBJECTIVETo investigate the expression regulation of thyrotrophin-releasing hormone (TRH) and TRH receptor (TRH-R), and their role in the development of rat testis.

METHODSOligonucleotide primers were designed from the sequences of rat hypothalamus prepro TRH (ppTRH) and pituitary TRH-R cDNA for reverse transcription polymerase chain reaction (RT-PCR). Specific fragments of ppTRH and TRH-R cDNA were cloned and sequenced. Expression plasmids containing ppTRH and TRH-R genes were then constructed, and expression was found in E. coli DH5-alpha. ppTRH and TRH-R mRNA in the testis was quantitated in RNA samples prepared from rats at different developmental stages by real time quantitative RT-PCR.

RESULTSThe quantitative analyses demonstrated that no ppTRH and TRH mRNA could be detected at the earliest stage (day 8). ppTRH and TRH mRNA signals were detected on day 15 and increased progressively on days 20, 35, 60 and 90.

CONCLUSIONOur results suggest that rat testis could specifically express TRH and TRH-R, and the transcriptions of ppTRH and TRH-R genes in the rat testis were development-dependent. The acquirement of expressed products for ppTRH and TRH-R can be used for further research on the physiological significance of TRH and TRH-R expression in rat testis.

Age Factors ; Animals ; Male ; Protein Precursors ; genetics ; RNA, Messenger ; analysis ; Rats ; Rats, Sprague-Dawley ; Receptors, Thyrotropin-Releasing Hormone ; genetics ; Reverse Transcriptase Polymerase Chain Reaction ; Testis ; growth & development ; metabolism ; Thyrotropin-Releasing Hormone ; genetics

Background: To test the hypothesis that Galphas gene mutation may suppress the expression of TRH-R gene, we investigated whether hTRH-R gene expression is lower in human GH-secreting pituitary adenomas with Galphas mutation than in tumors without the mutation. Method: TRH-induced paradoxical response of GH was observed in 8 acromegalic patients. The mutation of gene was identified by direct sequencing of the genomic DNA prepared from GH-secreting pituitary adenomas. The expression of hTRHT mRNA was quantitated by RT-PCR. Results: The transcript of hTRH-R gene was detected in 6 of 8(75%) tumors. Three of these(50%) showed the paradoxical GH response to TRH and the other three patients did not show the response. The relative expression of hTRH-R mRNA in the tumors from patients with the paradoxical response of GH to TRH did not differ from that in the tumors from patients without the paradoxical response. Direct PCR sequencing of Galphas disclosed a mutant allele and a normal allele only at codon 201 in 4 of 8 tumors. The paradoxical response to TRH was observed in 2 of 4 patients without the mutation, and 2 of 4 patients with the mutation. The hTRH-R gene expression of pituitary adenomas did not differ between the tumors without the mutation and those with mutation. Conclusion: This study suggests that the expression of TRH-R gene is not likely to be a main determinant for the paradoxical response of GH to TRH, and that Galphas mutation does not seem to suppress the gene expression of TRH-R in GH secreting adenoma.
Acromegaly ; Adenoma* ; Alleles ; Codon ; DNA ; Gene Expression ; Growth Hormone-Secreting Pituitary Adenoma ; GTP-Binding Proteins ; Humans ; Pituitary Neoplasms ; Polymerase Chain Reaction ; Receptors, Thyrotropin-Releasing Hormone* ; RNA, Messenger

BACKGROUND: Gs alpha gene mutation, that constitutively increases intracellular cAMP, is found in some acromegalic patients. It was demonstrated that increased intracellular cAMP levels suppress the expression of rat TRH receptor (TRH-R) mRNA. We previously demonstrated that transient expression of a mutant Gs alpha gene suppress the rat TRH-R gene expression in the cultured rat growth hormone-secreting tumor cell line (GH3), whereas TRH-R gene expression in adenomas with Gs alpha gene mutation (gsp oncogene) did not differ from that in tumors without the mutation. The discrepancy suggests the possibilities that the effect of permanent expression of mutant Gs alpha gene on TRH-R gene expression is different from that of transient expression of the mutant gene and hypothalamic hormones including TRH regulate the gene expression. METHODS: We investigated whether permanent expression of the mutant-type Gs alpha does not suppress the TRH receptor gene expression in GH3 cells, and whether TRH suppresses the gene expression by using reverse transcription-polymerase chain reaction (RT-PCR) and in vitro transcription. RESULTS: Permanent expression of a mutant-type Gs alpha increased basal cAMP levels up to 1.7-fold relative to the controls, whereas the wild-type cell line did not show increased cAMP levels. Permanent expression of a mutant-type Gs alpha increased TRH receptor mRNA level up to 2.8 fold compared with the controls. Treatment of the permanently transfected GH3 cells with TRH suppressed TRH-R gene expression more prominently compared to the wild type GH3 cells. CONCLUSION: These results suggest that permanent expression of mutant Gs alpha enhances the expression of TRH-R in GH-secreting pituitary tumors with gsp oncogene, but the gene expression may also be regulated by other factors including TRH.
Acromegaly ; Adenoma ; Animals ; Cell Line ; Cell Line, Tumor ; Gene Expression* ; GTP-Binding Proteins ; Humans ; Hypothalamic Hormones ; Oncogenes ; Pituitary Neoplasms ; Rats ; Receptors, Thyrotropin-Releasing Hormone ; RNA, Messenger