TY - JOUR T1 - Biphasic Effects of Ingenol 3, 20-Dibenzoate on the Erythropoietin Receptor: Synergism at Low Doses and Antagonism at High Doses JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.114.097436 SP - mol.114.097436 AU - Jin-Gyo Oh AU - Young-Won Chin AU - Sung-Jo Kim AU - Jong Min Choi AU - Sang Kyum Kim AU - Hee Eun Kang AU - Tae-Hwe Heo Y1 - 2015/01/01 UR - http://molpharm.aspetjournals.org/content/early/2015/06/05/mol.114.097436.abstract N2 - Although ingenol 3,20-dibenzoate (IDB) is known as a selective novel protein kinase C (PKC) agonist, its biological actions and underlying mechanisms remain incompletely understood. In this study, we identified IDB as a proliferative agent for an erythropoietin (EPO) dependent cell line, UT-7/EPO, through the screening of a natural compound library. To clarify the underlying mechanism of IDB's EPO-like activities, we thoroughly analyzed the mutual relation between EPO and IDB in terms of in vitro and in vivo activities, signaling molecules, and a cellular receptor. IDB substantially induced the proliferation of UT-7/EPO cells, but not as much as EPO. IDB also lessened the anemia induced by 5-fluorouracil in an in vivo mouse model. Interestingly, IDB showed a synergistic effect on EPO at low concentration, but an antagonistic effect at higher concentration. Physical interaction and activation of PKCs by IDB and EPO-competitive binding of IDB to EPO receptor (EPOR) explains these synergistic and antagonistic activities, respectively. Importantly, we addressed IDB’s mechanism of action by demonstrating the direct binding of IDB to PKCs, and by identifying EPOR as a novel molecular target of IDB. Based on these dual targeting properties, IDB holds promise as a new small molecule modulator of EPO-related pathologic conditions. ER -