Jun dimerization protein 2 coactivates transactivation by the progesterone receptor N-domain by a novel allosteric mechanism

Progesterone activity is mediated by the intra-cellular progesterone receptor (PR). PR consists of central DNA binding (DBD), C-terminal ligand binding (LBD), and extended N-terminal domains. PR transactivation is mediated by ligand-dependent activation function (AF) 2 in the LBD and constitutive AF-1 in the N-domain. The N-domain plays a key role in determining receptor activity, but little is known about the conformation of the N-domain, its mechanism of transactivation, or factors that mediate its activity. I describe here an unusual role for AP-1 repressor Jun dimerization protein (JDP) 2 as a PR N-domain coactivator. JDP-2 interacts specifically with the PR DBD, colocalizes with PR to a progesterone-responsive promoter in the context of chromatin, and forms a ternary complex with PR on a minimal progesterone response element. JDP-2 selectively enhances ligand-dependent transactivation by PR, either agonist activity of synthetic progesterone or partial agonist activity of RU486 antagonist, but does not affect unliganded PR and has little effect on transactivation by other nuclear receptors. The most potent JDP-2 coactivation is mediated through the PR N-domain, although JDP-2 and the N-domain do not directly interact in vitro. The mechanism by which JDP-2 modulates N-domain activity is a novel allosteric transmission of an activating signal from the DBD to change the overall N-domain conformation. As detected by circular dichroism, JDP-2-DBD interaction induces a two-fold increase in the alpha helical content of the N-domain, and a corresponding decrease in random coil. The originally defined AF-1 is insufficient to mediate the maximal JDP-2 coactivation of the PR N-domain. Additional intervening sequence (IVS) lying between AF-1 and the upstream inhibitory domain is required. Deletion of the IVS cripples transactivation by PR or just the N-domain, but does not significantly affect JDP-2 coactivation of the N-domain's constitutive activity. The IVS is also dispensable for JDP-2 coactivation of PR agonist activity, but is specifically required for JDP-2 coactivation of partial agonist activity of RU486. Thus, RU486 agonist activity maps to the IVS within the PR N-domain. I conclude that JDP-2 represents a novel class of nuclear receptor coactivators, and that JDP-2 expression may influence pharmacology of both progesterone and RU486.