Retinoid X receptors (RXRs) mRNA expression in human pituitary adenomas

Retinoid-X receptors (RXRs) are transcriptional factors that belong to the steroid/thyroid hormone receptor (TR) superfamily. It has been demonstrated that those nuclear receptors act as ligand-activated transcription factors in pituitary cells. To determine whether RXRs play roles in the cell diffe rentiation of pituitary adenomas, we have investigated the expression of RX R gamma mRNA in various types of pituitary adenomas using in situ reverse t ranscriptase-polymerase chain reaction (RT-PCR). The synergistic function o n promoters of specific hormones between these nuclear receptors and pituit ary specific transcription factor, Pit-1, has been noticed in in vitro expe riments. The colocalization between RXR gamma mRNA and Pit-1 protein was ex amined by combined in situ RT-PCR and immunohistochemistry. RXR gamma mRNA was detected in normal pituitary gland as well as all five growth hormone- (GH)-secreting adenomas and five thyroid stimulating hormone (TSH) secretin g adenomas, two of four prolactin- (PRL) secreting adenomas, one of two adr enocorticotropin- (ACTH) secreting adenomas one of four nonfunctioning aden omas. By in situ hybridization and in situ RT-PCR followed by immunohistoch emistry, the colocalization of Pit-1 mRNA with RXR gamma as well as RXR gam ma mRNA with Pit-1 was observed in adenoma cells of GH-secretinig adenomas and TSH-secreting adenomas. We suggest that RXR gamma may play a role in ce ll differentiation and hormonal transcription synergistically with Pit-1 in normal and neoplastic human pituitaries.