Abstract 669: Compound heterozygous Sf3b1-K700E mutation and Atm deletion in B cells leads to CLL in mice

Abstract

Abstract Unbiased next-generation sequencing using primary samples has identified SF3B1 as among the most frequently mutated genes in chronic lymphocytic leukemia (CLL). These mutations localize to a restricted gene region, with more than 50% at the K700E site. The presence of mutation is associated with poor clinical outcomes. These lines of evidence together emphasize the high priority for gaining an understanding of role of SF3B1 in CLL. However, the mechanistic basis for how mutated SF3B1 impacts CLL remains unknown. Prior transcriptomic studies using primary CLL samples have led to the appreciation of altered RNA splicing induced by this mutated gene, but studies of the functional impact of mutated SF3B1 in primary human samples have been complicated by its variable mutant allele frequency across samples as well as its common co-occurrence with other diverse gene mutations. We therefore generated a mouse line that conditionally expressed heterozygous Sf3b1-K700E mutation in B lineage cells. We sought to characterize the effects of Sf3b1-K700E on RNA splicing and B cell function in this in vivo model. By RNA-sequencing of splenic B cells from wild-type and mutant mice (n = 3, each), we detected, classified, and quantified 54 differentially spliced transcripts (p10%) using the tool JuncBASE. Consistent with prior findings in human CLL samples, the splice variants in our mouse model were highly enriched with altered selection of 3’ splice sites (49 of 54 events, p<0.001), suggesting that Sf3b1-K700E mutation in the mouse lines cause altered RNA splicing in vivo and functions in a manner faithful to the human leukemia. B cell characterization of the mutant mice revealed that expression of Sf3b1-K700E caused subtle impairments in B cell development and function, and induced a state of cellular senescence based on gene expression and secretome characterization. Mice with heterozygous Sf3b1-K700E did not develop evidence of CLL-associated immunopathologic changes, even with prolonged aging to 24 months. Nevertheless, expression of Sf3b1-K700E with heterozygous deletion of Atm in B cells led to the overcoming of cellular senescence and resulted in the accumulation of clonal B220+CD5+ cells in peripheral blood, marrow, and spleen of elderly mice. We thus dissect the impact of mutated SF3B1 individually and in combination with Atm deletion on paving the path towards B cell leukemogenesis. This novel murine model faithfully recapitulates features of human CLL and has the potential to shed light on mechanisms of cooperation between Atm deletion and SF3B1 mutation in the pathogenesis of CLL. Citation Format: Lili Wang, Rutendo Gambe, Jean Fan, Angela N. Brooks, Jing Sun, Donna Neuberg, Peter Kharchenko, Matthew Meyerson, Mark D. Fleming, Benjamin L. Ebert, Ruben Carrasco, Catherine J. Wu. Compound heterozygous Sf3b1-K700E mutation and Atm deletion in B cells leads to CLL in mice. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 669.