The pro-apoptotic protein death-associated protein 3 (DAP3) interacts withthe glucocorticoid receptor and affects the receptor function

The yeast two-hybrid system was used to isolate cDNAs encoding proteins tha t interact with the glucocorticoid receptor (GR) ligand-binding domain in a ligand-dependent manner. One isolated cDNA encoded a fragment of death-ass ociated protein 3 (DAP3), which has been implicated as a positive mediator of apoptosis. In vitro experiments showed that the full-length DAP3 also in teracted with GR. The main interaction domain was mapped to the N-terminal region of DAP3 that had previously been shown to function in a dominant-neg ative fashion, protecting cells from apoptosis. Co-transfection experiments in COS-7 cells showed that DAPS had a stimulatory effect on the ligand-ind uced transcriptional activation by GR and also increased the steroid-sensit ivity. Furthermore, DAP3 formed a complex with several other nuclear recept ors and some basic helix-loophelix/Per-Arnt-Sim proteins, as well as with h eat-shock protein 90 (hsp90) (Arnt is the aryl-hydrocarbon-receptor nuclear translocator, and Per and Sim are the Drosophila proteins Period and Singl e-minded). The results suggest that DAP3 could have an important role in GR action, possibly by modulating the cytoplasmic GR-hsp90 complex. Since glu cocorticoids can induce apoptosis, the pro-apoptotic DAP3 protein may be in volved in this function of GR.