THYROID-HORMONE AFFECTS THE GENE-EXPRESSION OF RETINOID X-RECEPTORS IN THE ADULT-RAT

Gene expression of three nuclear retinoid X receptors (RXRα, β and γ) was examined by Northern blot analysis in various rat tissues. The RXRα mRNA (5.5 kb) was detected in most tissues and particularly expressed at a high level in the liver. The RXRβ transcripts (2.4 and 3.0 kb) were expressed ubiquitously, and particularly at high levels in the brain and testis. In the liver, heart, kidney and lung, the RXRγ mRNA (2.0 kb) was specifically detected. Furthermore, we examined the effect of retinoid, vitamin D and thyroid hormone status on the gene expression of RXRα, β and γ. Though retinoid and vitamin D did not affect the mRNA levels of three RXRs, the mRNA levels of two genes were controlled by thyroid hormone. Namely, positive (RXRβ) and negative (RXRγ) regulations by thyroid hormone were observed with no effect on the gene expression of RXRα. These results suggest that thyroid hormone might affect the signal transduction of retinoid, vitamin D and thyroid hormone by changing RXR levels. © 1993 Academic Press.