Abstract 1984: The Ikaros tumor suppressor regulates transcription of genes involved in cell signaling in human leukemia.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC The IKZF1 gene encodes Ikaros, a DNA binding zinc finger protein that is essential for normal hematopoietic differentiation. Deletion or mutation of Ikaros has been associated with a both T and B-cell acute lymphoblastic leukemia (ALL), as well as acute and chronic myelogenous leukemias (AML and CML). Deletion of an Ikaros allele has also been identified as a poor prognostic marker in childhood B-ALL. Thus, Ikaros is established as a major tumor suppressor in hematopoietic malignancies. The Ikaros protein can activate or repress target gene expression via chromatin remodeling. The specific mechanisms by which Ikaros exerts its tumor suppressor activities are unknown. We have defined genome-wide occupancy of Ikaros in human leukemia using ChIP-SEQ and identified a large number of potential Ikaros target genes. The quantitative Chromatin Immunoprecipitation assay (qChIP) was used to identify genes whose expression is directly regulated by Ikaros. Using this technique we show that Ikaros binds to the promoter region of a gene that is part of a pro-oncogenic pathway, as well as a tumor suppressor gene. Both genes are essential components of cell signaling pathways. The promoter regions of the two novel target genes were cloned into luciferase reporter constructs and used to transiently transfect HEK 293T cells that were co-transfected with Ikaros or empty vector (as a control). Luciferase reporter assays demonstrate that Ikaros suppresses transcription of the gene that is involved in oncogenic transformation, while it positively regulates transcription of the tumor suppressor gene. In summary, we have identified two novel Ikaros target genes. Our results suggest that Ikaros exerts its tumor suppression function by regulating the expression of target genes involved in pro-oncogenic and tumor suppressor signaling in leukemia cells. These data identify mechanisms of the tumor suppressor activity of Ikaros in leukemia. Citation Format: Jonathon L. Payne, Justin Sloane, Rebekka M. Bamert, Elanora Dovat, Hui Li, Marie Bulathsinghala, Chandrika Gowda, Chunhua Song, Sinisa Dovat. The Ikaros tumor suppressor regulates transcription of genes involved in cell signaling in human leukemia. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1984. doi:10.1158/1538-7445.AM2013-1984