THYROID-HORMONE AND ESTROGEN-RECEPTOR EXPRESSION IN NORMAL PITUITARY AND NONFUNCTIONING TUMORS OF THE ANTERIOR-PITUITARY

Nonfunctioning tumors (NFTs) of the anterior pituitary often express e levated levels of the glycoprotein hormone alpha-subunit, which, under normal physiological conditions, is under negative feedback control b y thyroid and gonadal steroid hormones. We postulate that inappropriat ely elevated levels of expression of alpha-subunit in the face of norm al levels of these target organ hormones may reflect an abnormality of thyroid hormone receptors (TRs) and/or gonadal steroid receptors in N FTs. Using immunocytochemistry and Western blotting we have examined T R and estrogen receptor (ER) protein expression in normal human anteri or pituitary glands and NFTs. Pretranslational expression of these rec eptors was examined using semiquantitative reverse transcriptase-PCR. Expression of all TR variant and ER proteins was reduced in pituitary tumors compared with that in normal pituitaries. The expression of mes senger ribonucleic acids encoding the TR beta(1) and TR beta(2) isofor ms and ER was also significantly reduced in tumors compared with norma l tissues, although there was no difference between tumors and normals in the level of expression of TR alpha(1) and alpha(2) messenger ribo nucleic acids. We suggest that reduced expression of TRs and ER may ac count for inappropriate expression of the glycoprotein hormone alpha-s ubunit gene in some NFTs and may contribute to uncontrolled tumor grow th.