Novel dimeric Nur77 signaling mechanism in endocrine and lymphoid cells

Within the nuclear receptor family Nur77 (also known as NGFI-B) distinguishes itself by its ability to bind a target sequence (the NBRE) as a monomer and by its role in T-cell receptor (TCR)-induced apoptosis in T cells, We now report on a novel mechanism of Nur77 action that is mediated by homodimers. These dimers bind a Nur77 response element (NurRE), which has been identified as a target of CRH-induced Nur77 in the pro-opiomelanocortin (POMC) gene promoter, Both halves of the palindromic NurRE are required for responsiveness to physiological signals, like CRH in pituitary-derived AT-2O cells. Similarly, in T-cell hybridomas, TCR activation induced NurRE but not NBRE reporters. The in vivo signaling function of Nur77 thus appears to be mediated by dimers acting on a palindromic response element of unusual spacing between its half-sites, This mechanism mag represent the biologically relevant paradigm of action for this subfamily of orphan nuclear receptors.