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 differentiation of pituitary adenomas, we have investigated the expression of RXRγ mRNA in various types of pituitary adenomas usingin situ reverse transcriptase-polymerase chain reaction (RT-PCR). The synergistic function on promoters of specific hormones between these nuclear receptors and pituitary specific transcription factor, Pit-1, has been noticed in in vitro experiments. The colocalization between RXRγ mRNA and Pit-1 protein was examined by combinedin situ RT-PCR and immunohistochemistry. RXRγ mRNA was detected in normal pituitary gland as well as all five growth hormone-(GH)-secreting adenomas and five thyroid stimulating hormone (TSH) secreting adenomas, two of four prolactin- (PRL) secreting adenomas, one of two adrenocorticotropin-(ACTH) secreting adenomas, one of four nonfunctioning adenomas. Byin situ hybridization andin situ RT-PCR followed by immunohistochemistry, the colocalization of Pit-1 mRNA with RXRγ as well as RXRγ mRNA with Pit-1 was observed in adenoma cells of GH-secreting adenomas and TSH-secreting adenomas. We suggest that RXRγ may play a role in cell differentiation and hormonal transcription synergistically with Pit-1 in normal and neoplastic human pituitaries.