Abstract 2097: ARHI (DiRAS3): A novel component in the formation of the autophagy initiation complex

The maternally imprinted Ras-related tumor suppressor gene Aplasia Ras homolog member I (ARHI; also known as DiRAS3) is downregulated in more than 60% of ovarian cancers. We reported that re-expression of ARHI in vitro at physiologic levels induces autophagy by blocking PI(3)K-Akt signaling and inhibiting mTOR activity, and participates directly in the autophagic vesicles, co-localizing with MAP-LC3-II in the vesicle membrane. Nucleation of autophagic vesicles is controlled by the activity and formation of multi-protein complexes that include Beclin-1 and several other positive and negative regulators. While binding of Beclin-1 to Vps34 and ATG14 forms proautophagic complexes to promote autophagy, binding of Bcl-2 to Beclin-1, however, disrupts the Beclin-1:Vps34 interaction and inhibits autophagy. The mechanisms that regulate the switch between different binding partners to Beclin-1, and therefore controls the level of autophagy is not clear. Here we report that ARHI physically interacts with endogenous Beclin-1 and Vps34 in ovarian cancer cells. Interaction with ARHI decreases the association between Beclin-1 and its negative regulator Bcl-2, by disrupting Beclin-1 homodimerization. An N-terminal deletion of ARHI that cannot induce autophagy fails to block Beclin-1 homodimerization and cannot disrupt Beclin-1:Bcl-2 interaction. Consistent with its role in promoting the formation of autophagy initiation complex, cells with knockdown of ARHI fail to respond to starvation-mediated dissociation of Beclin-1:Bcl-2 interaction and are unable to induce Beclin-1:Vps34 complex formation. Finally, ARHI knockdown decreases PI(3)KC3 activity and reduces starvation-mediated autophagy. Taken together, our results suggest that ARHI is a positive and necessary regulator of Beclin-1:Vps34 complex and that ARHI regulates starvation-mediated autophagy by promoting the formation of the autophagy initiation complexes. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2097. doi:10.1158/1538-7445.AM2011-2097