A NOVEL TRANSCRIPT FOR THE THYROTROPIN-RELEASING-HORMONE RECEPTOR IN HUMAN PITUITARY AND PITUITARY-TUMORS

We measured the amounts of TRH receptor (TRHR) messenger ribonucleic a cid (mRNA) in human normal pituitary and pituitary tumors and found a novel transcript of the TRHR gene. Competitive PCR revealed expression of the TRHR mRNA in all pituitary adenomas examined, and its level wa s variable and similar to that in the normal pituitary. When the C-ter minal region was amplified by PCR, an additional short product was obs erved. Cloning and sequence analysis of this short fragment revealed t hat the deleted sequence corresponded exactly to the 5'-sequence of ex on 3, indicating alternative splicing of the TRHR mRNA. This alternati ve splicing resulted in a frame shift, yielding a C-terminal truncated protein (HTRHR2) on translation. Expression analysis of HTRHR2 in Chi nese hamster ovary cells showed no significant binding to [H-3]MeTRH o r response of intracellular calcium to TRH administration. However, th e mRNA ratio of HTRHR2 vs. the wild type (HTRHR1) was significantly di fferent among pituitary tumors. The highest ratio was observed in prol actinomas (30%), and almost no detectable expression was found in GH-p roducing tumors. These findings indicate that this novel transcript of the human TRH receptor gene is produced in a tumor-specific manner an d may be a useful parameter for evaluation of individual pituitary tum ors.