Two RAREs and an overlapping CRE are involved in the hepatic transcriptional regulation of the Q10 MHC class I gene

The Q10 gene is a member of the major histocompatibility complex of the mouse that is expressed in the liver and kidney of the adult. Using transient expression assays, we found that the Q10 promoter was activated by retinoic acid (RA) and exogenous RARs and/or RXRs in a cell type-dependent manner. In addition, the basal activity of the Q10 promoter in HepG2 cells is lowered by expressing a dominant negative form of RARalpha. Incidentally, we have identified two cis-elements which consist of sequences related to retinoic acid response elements (RAREs) and a putative cAMP responsive element (CRE) the sequence of which overlaps one of the RAREs. RAR, RXR, CREB-ATF, and COUP-TF factors bind these elements and/or affect their activity. We also demonstrate that the CRE mediates part of the stimulation induced by activation of the cAMP pathway on the Q10 promoter, the residual activation being mediated by RARs. Our results suggest that Q10 expression in liver depends upon RA and the interaction between nuclear receptors that are expressed in this organ. The overlapping of the CRE with one of the RAREs together with the results of PKA activation also suggest that RA and cAMP signalling pathways are linked.