Abstract B45: Regulation of CRLF2 oncogene expression by the Ikaros tumor suppressor in B cell acute lymphoblastic leukemia that occurs at high frequency in Hispanic children

Hispanic children are 1.24 times more likely to develop acute lymphoblastic leukemia (ALL) than non-Hispanic whites and when they do their death rate is 39% higher. B-cell precursor ALL caused by overexpression of CRLF2 (CRLF2 B-ALL) occurs 5 times more frequently in Hispanic children than others. In addition, over 80% of CRLF2 B-ALL has deletion or inactivation of one allele of the Ikaros (IKZF1) tumor suppressor, which is associated with a 12-fold increase in relapse rate as compared to standard-risk leukemia. Thus, the high rate of CRLF2 overexpression that occurs in combination with the Ikaros defect is likely a major contributor to the increased death rate in Hispanic children with ALL. Currently, these two genetic evens are thought to arise separately, to affect different signaling pathways and to be largely functionally disconnected. Here, we present evidence that expression of CRLF2 is transcriptionally regulated by Ikaros in B-ALL, thus providing evidence to link the two signaling pathways. Our data from chromatin immunoprecipitation coupled with next generation sequencing (ChIP-seq) show that Ikaros strongly binds to the CRLF2 promoter in vivo. This was confirmed by qChIP in different B-ALL cell lines and in primary B-ALL cells. Using Ikaros gain-of-function and loss-of-function experiments we studied how Ikaros binding at the CRLF2 promoter affects transcription of CRLF2 in B-ALL. Overexpression of Ikaros via lentiviral transduction resulted in reduced transcription of CRLF2 as measured by qRT-PCR. As a different approach, we used the luciferase reporter assay to show that transcription of the luciferase reporter gene under the control of the CRLF2 promoter was reduced after Ikaros transfection as compared to the negative control. Targeting Ikaros transcription with Ikaros-specific shRNA in B-ALL cells resulted in increased transcription of CRLF2. In conclusion, the presented data demonstrate that the Ikaros tumor suppressor directly represses transcription of CRLF2 in B-ALL cells and that reduced expression of Ikaros results in increased CRLF2 transcription. These results suggest that the two primary genetic alterations that characterize the high-risk CRLF2 B-ALL that occurs at increased frequency in Hispanic children are interconnected and that impaired Ikaros function affects the CRLF2 signaling pathway. These data underscore the importance of impaired Ikaros function in the pathogenesis of high-risk CRLF2 B-ALL that disproportionately affects Hispanic children. They also suggest that restoring normal Ikaros function could be a crucial step for achieving a therapeutic effect for this type of leukemia and for reducing the health disparity for Hispanic children with ALL.

Citation Format: Sinisa Dovat, Zheng Ge, Chunhua Song, Kimberly J. Payne. Regulation of CRLF2 oncogene expression by the Ikaros tumor suppressor in B cell acute lymphoblastic leukemia that occurs at high frequency in Hispanic children. [abstract]. In: Proceedings of the Ninth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2016 Sep 25-28; Fort Lauderdale, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2017;26(2 Suppl):Abstract nr B45.