Liver X receptor-α/β expression ratio is increased in ACTH-secreting pituitary adenomas.

The liver X receptors (LXR-α and -β) are nuclear oxysterol receptors that play pivotal roles in regulating the expression of genes involved in cholesterol transport and metabolism. Recently, several groups have reported that the LXRs also regulate adrenal steroidogenesis. In the previous report, we demonstrated that LXR-α is dominantly expressed in the pituitary and that LXR-α positively regulates the proopiomelanocortin (POMC) gene promoter at the transcriptional level. In this report, we evaluated the expression levels of LXR-α and -β gene in the human pituitary tumor. Even though LXR-α mRNA levels are not significantly increased in ACTH-secreting adenomas, LXR-α/β expression ratio is significantly higher than other pituitary tumors including normal pituitaries. Furthermore, in At-T20 cells, which express POMC gene, overexpression of LXR-β decreased POMC gene promoter activities. Thus, we concluded that LXR-α/β gene expression ratio is a critical factor to activate POMC gene expression in ACTH-secreting pituitary adenomas.