Following up on our observation that the recombinant LBDs of TLX and RXRα dimerized (Figure ) and that this interaction was responsive to 30 (Figure ), we further probed whether TLX and RXR would also interact in cellular setting. For this, we co-transfected HEK293T cells with Gal4-responsive firefly luciferase, constitutive renilla luciferase, and a VP16-RXRα-LBD fusion construct with or without Gal4-TLX (Figure ). In absence of Gal4-TLX, VP16-RXRα failed to induce reporter transcription but upon addition Gal4-TLX, reporter activity increased with increasing Gal4-TLX doses demonstrating that the interaction between the TLX and RXRα LBDs is relevant in cells as well. When we studied the effect of istradefylline (30) on this interaction (Figure ), we detected an increase in the TLX-RXRα interaction as observed in elevated reporter activity. These findings support our observation of a TLX repressor activity on various nuclear receptors and further suggest that direct LBD interactions are involved in these effects.