UBIQUITOUS RECEPTOR - A RECEPTOR THAT MODULATES GENE ACTIVATION BY RETINOIC ACID AND THYROID-HORMONE RECEPTORS

The cDNA for a member of the nuclear receptor family was cloned and named ubiquitous receptor (UR), since UR protein and mRNA are detected in many cell types. Rat UR/human retinoid X receptor alpha (hRXR alpha) heterodimers bound preferentially to double-stranded oligonucleotide direct repeats having the consensus half-site sequence AGGTCA and 4-nt spacing (DR-4). Coexpression of UR in COS-1 cells inhibited the stimulation of chloramphenicol acetyltransferase (CAT) reporter gene expression by hRXR alpha and human retinoic acid receptor alpha in the presence of all-trans-retinoic acid when DR-4 (but not DR-5) was present upstream of the promoter of a CAT reporter gene (DR-4-CAT). UR expression also inhibited the activation of a DR-4-CAT reporter gene by hRXR alpha and 9-cis-retinoic acid or by thyroid hormone receptor beta in the presence df thyroid hormone. However, in the absence of 9-cis-retinoic acid, UR in combination with hRXR alpha stimulated DR-4-CAT expression. Coexpression of thyroid hormone receptor markedly reduced this stimulation in the absence of thyroid hormone. UR may play Bd important role in normal growth and differentiation by modulating gene activation in retinoic acid and thyroid hormone signaling pathways.