Inhibition of apoptosis by Nur77 through NF-kappaB activity modulation.

The orphan nuclear receptor Nur77 has been described as a mediator of apoptosis and has also been associated with growth promotion and apoptotic resistance. This study aimed at evaluating the contribution of Nur77 to different apoptotic stimuli. Nur77 overexpression in the fibroblastic cell line HEK293 promoted resistance to programmed cell death induced by death receptor engagement, DNA-damaging agents and endoplasmic reticulum stress. Nur77 overexpression led to enhanced NF-kappaB activity, and DNA-binding inhibitors confirmed the contribution of NF-kappaB to Nur77 antiapoptotic activity. Nur77 overexpression leads to NF-kappaB-dependent induction of the antiapoptotic gene cIAP1. Paradoxically, while dominant-negative Nur77 expression sensitised cells to Fas ligand-induced cell death, it protected cells from endoplasmic reticulum stress apoptosis in a manner similar to wild-type Nur77. These results show that nuclear crosstalk between Nur77 and other transcription factors contribute to cell fate in response to different apoptosis-inducing agents.