STRUCTURE OF THE THYROTROPIN-RELEASING-HORMONE RECEPTOR IN HUMAN PITUITARY-ADENOMAS

BACKGROUND AND OBJECTIVE TRH acts on specific G-protein coupled recept ors sited in cells of the anterior pituitary gland. Pituitary tumours expressing either TSH, PRL or ON may respond to TRH by enhanced, blunt ed or paradoxical hormone release. Non-functioning pituitary tumours m ay also show abnormal responses to TRH. Little is understood of the me chanisms regulating inappropriate hormone release in these tumours. Ac tivating or inactivating mutations found in G-protein coupled receptor s have been implicated in human pathological conditions. Mutations in the G-protein coupled TRH receptor might be involved in the aetiology of pituitary adenomas resulting in aberrant hormone secretion. We ther efore screened samples of pituitary adenomas for the presence of somat ic mutations in the TRH receptor gene. PATIENTS Pituitary adenoma tiss ue samples were obtained at surgery from 50 patients with pituitary ad enoma (17 acromegaly, 15 prolactinoma, 11 TSH-secreting and 7 non-func tioning adenoma) along with blood samples to provide lymphocyte DNA as control sequence. METHODS Genomic DNA was extracted from adenoma and lymphocyte samples and the entire coding region of the TRH receptor wa s amplified using 5 overlapping pairs of PCR primers. The PCR products were analysed for mutations by non-denaturing polyacrylamide gel elec trophoresis which reveals single-strand conformational polymorphisms ( SSCP) as a mobility shift in product migration. Wild-type and mutant T RH receptor cDNA were similarly analysed to confirm the sensitivity of the method. Additionally, PCR products were ligated into a POR clonin g vector and DNA sequencing carried out to confirm the findings of SSC P analysis. RESULTS The human TRH receptor retained normal wildtype se quence in the large group of TSH secreting, PRL secreting, on secretin g and non-functioning pituitary adenomas investigated in this study. C ONCLUSION Our observations suggest that the TRH receptor structure is normal in TSH secreting, PRL secreting, GH secreting and non-functioni ng pituitary adenomas. It is therefore unlikely that the TRH receptor is involved in the pathology associated with the types of pituitary ad enomas investigated in this study. It is possible that some other comp onent of the pathway controlling TRH-signalling events may be implicat ed in pituitary tumorigenesis.