Abstract IA22: An oncogenic enhancer drives NOTCH1-induced leukemia.

Abstract

Abstract Most genetic abnormalities found in cancer are located in intergenic regions and their role in cancer development remains poorly understood. Here we report the identification of a long range enhancer driving NOTCH1-induced transformation in T-ALL. Using genome wide ChIPseq mapping of NOTCH1 binding and functional epigenetic marks in T-ALL we identified a NOTCH1-occupied enhancer located in a gene desert island in 8q24, +1,427 kb 3' from the MYC locus. This regulatory element named N-Me for NOTCH-bound MYC enhancer activates MYC reporter constructs in T-ALL cells and directly interacts with MYC promoter sequences via long range chromatin loops. Notably, high resolution aCGH analysis revealed recurrent focal duplications at chromosome 8q24 encompassing this enhancer in 8/160 (5%) T-ALL cases. Functional characterization of N-Me in T-cell development and transformation using N-Me knockout and conditional knockout mice revealed a major role for this enhancer during thymocyte development and in T-ALL. Thus N-Me null animals showed a marked and selective reduction in thymus size and cellularity and were completely resistant to NOTCH1-induced transformation. Moreover, secondary deletion of N-Me in established NOTCH1 induced leukemias from tamoxifen-inducible N-Me conditional knockout mice induced profound antileukemic effects with extended survival and almost complete suppression of leukemia initiating cell activity. Altogether, these results identify N-Me as a major downstream effector NOTCH1 critically required for MYC expression in T-cell development and leukemia. Citation Format: Adolfo Ferrando. An oncogenic enhancer drives NOTCH1-induced leukemia. [abstract]. In: Proceedings of the AACR Special Conference on Hematologic Malignancies: Translating Discoveries to Novel Therapies; Sep 20-23, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(17 Suppl):Abstract nr IA22.