“…48 members of NR superfamily can be subdivided into three major categories, namely, the endocrine nuclear receptors, adopted orphan receptors, and orphan receptors such as NR4A for which cognate ligands have not yet been identified. The NR4A orphan receptor subfamily includes NR4A1 (Nur77, NGFI-B,TR3), NR4A2 (Nurr1, NOT), and NR4A3 (Nor-1, MINOR) [17,18,19,20] , and it has been suggested that the failure to identify an endogenous ligand may be due to the lack of a typical NR ligand binding pocket in the LBD domain of Nurr1 or NR4A2 receptors [21] . Instead, Nurr1 are immediate early genes whose expression is induced by various stimuli including cyclic AMP, growth factors, inflammatory signals, and hormones [17] .…”