Abstract B57: Distinct interactions of Ras superfamily members with common protein targets

Abstract

Abstract Ras superfamily members act as molecular switches to many key signaling pathways, including proliferation cytoskeletal integrity, differentiation and cellular cargo transport. The Ras subfamily, consisting of KRas, NRas and HRas are the most widely studied Ras-family members due to the high instance of Ras activating mutation in human cancers. Rab subfamily members are important regulators of endocytosis, consisting of Rab5 (early endosome), Rab7 (recycling endosome) and Rab11 (late endosome). We have discovered that common binding partners exist between these Ras subfamilies, resulting in distinct interactions and regulatory effects. Two such commonalities are scaffold protein ITSN1 and lipid kinase PI3KC2β. There is evidence that the learning disabilities associated with Down syndrome may be somewhat attributed to deregulated vesicular transport in the brain. DS patients also have a 10-20 fold increased risk of developing acute myeloid leukemia (AML). ITSN1, a regulator of endocytosis and activator of the oncogenic AKT pathway (1), is overexpressed in Down syndrome patients. PI3KC2β is a member of the PI3K family of lipid kinases, which phosphorylate phosphatidylinositol leading to AKT activation. Treatment of neuroblastoma and AML cell lines with PI3KC2β-specific inhibitors greatly decreases proliferation (2) and silencing PI3KC2β in neuroblastoma cell lines results in a 50% reduction in tumor volume in xenograft models. Our previous work demonstrated that nucleotide-free HRas preferentially binds to PI3KC2β, inhibiting its activity (see poster by JP O'Bryan; 3). The addition of ITSN1 disrupts this interaction, presumably restoring the active state of both proteins. In contrast, constitutively activated Rab5 and KRas preferentially interact with PI3KC2β. Interestingly KRas sequesters PI3KC2β to the plasma membrane. The current dogma states that Ras proteins must be GTP-loaded and associated with the plasma membrane to activate their classic effectors suggesting that KRas would be active in this capacity and may therefore positively regulate PI3KC2β activity. Here we present evidence of three Ras superfamily members interacting in distinct ways with the same target protein and provide support for their related yet contrasting roles in disease states. Citation Format: Russell Spencer Smith, Katy A. Wong, Angela Russo, John P. O'Bryan. Distinct interactions of Ras superfamily members with common protein targets. [abstract]. In: Proceedings of the AACR Special Conference on RAS Oncogenes: From Biology to Therapy; Feb 24-27, 2014; Lake Buena Vista, FL. Philadelphia (PA): AACR; Mol Cancer Res 2014;12(12 Suppl):Abstract nr B57. doi: 10.1158/1557-3125.RASONC14-B57