Mapping of the RXRalpha binding elements involved in retinoic acid induced transcriptional activation of the human SOX3 gene.

Sox3/SOX3 gene is implicated in the control of nervous system development and is considered to be one of the earliest neural markers. Expression of human SOX3 gene is modulated during the RA-induced neuronal differentiation cascade of NT2/D1 cells. Our present results demonstrate that the sequences responsible for RA-induced activation of SOX3 gene are localized within the 0.4 kb of its 5'-flanking region and implicate RXRalpha involvement in this regulation. The active RA/RXRalpha responsive region is pinned down to two regulatory elements. Only in the presence of both elements full RA/RXRalpha inducibility is achieved, suggesting they act synergistically. These elements comprise two unique G-rich boxes, separated by 49 bp, that could be considered as a novel, atypical RA-response element. Here, for the first time, we have demonstrated direct interaction of RXRalpha and SOX3 control elements. Furthermore, the functional in vivo analysis revealed that liganded RXRalpha is a potent activator of endogenous SOX3 protein expression. Since it is proven that Sox3 is critical determinant of neurogenesis our data may help in providing new insight into complex regulatory networks involved in retinoic acid induced neural differentiation of NT2/D1 cells.