Mechanism Study Of Bcl-2 And Nuclear Receptor Nur77 Mediated Apoptosis/Mitophagy

Nur77(also called TR3 or NGFI-B),an orphan member of the nuclear receptor superfamily,plays a dual role in mediating apoptosis and survival of cancer cells,representing an important anti-tumor target.Bcl-2,an anti-apoptotic Bcl-2 family member,is also one of the most important drug targets.Our labboratory previously reported that Nur77 could induce apoptosis by translocating to mitochondria where it interacts with Bcl-2 to convert Bcl-2 from an anti-apoptotic to a pro-apoptotic molecule.We recently reported a new Nur77-mediated mitophagy mechanism,in which celastrol promotes mitochondrial localization and TRAF2 interaction,resulting in Lys63-linked Nur77 ubiquitination and its interaction with p62/SQSTM1 and subsequently mitophagy.However,small molecules that can bind directly to Nut77 to trigger its mitochondrial localization and Bcl-2 interaction remain to be identified.Furthermore,how Bcl-2 is involved in the regulation of Nut77-p62 mitophagic pathway remains to be determined.Here we reported our identification and characterization of DIM-C-pPhCF3+MeSO3-(BI1071)as a modulator of the Nur77-Bcl-2 apoptotic pathway.BI1071 binds Nur77 with high affinity,promotes Nur77 milochondrial targeting and interaction with Bcl-2,and effectively induces apoptosis of cancer cells in a Nur77-and Bcl-2-dependent manner.Studies with animal model showed that BI1071 potently inhibits the growth of tumor cells in animals through its induction of apoptosis.Futhermore,we reported that Bcl-2 inhibits the mitophagy induced by Celastrol through its interaction with p62.Conversely,knockdown of endogenous Bcl-2 sensitizes toward the mitophagy induced by Celastrol.Bcl-2 can directly interact with p62,induce p62 cleavage and promote apoptosis.Furthermore,we found that BI1071 induces autophagic cell death through its modulation of the interaction between Nur77,Bcl-2 and p62 at mitochondria.The combination of two ligands of Nur77,Celastrol and BI1071,shows synergistic effect on apoptosis induction.Together,our results identify BI1071 as a novel Nur77-binding modulator of the Nur77-Bcl-2 apoptotic pathway,which may serve as a promising lead for treating cancers with overexpression of Bcl-2 and Nur77.Our results also provide a molecular basis for developing Celastrol,BI1071 and Bcl-2 inhibitors as the clinical combination therapy.