Abstract 5095: Concurrent Dnmt3a haploinsufficiency partially abrogates competitive disadvantage in Smc3 haploinsufficient myeloid cells

Abstract

Abstract SMC3 encodes a subunit of cohesin associated with recurrent heterozygous mutations in acute myeloid leukemia (AML) and other myeloid malignancies. About one-third of these mutations are predicted loss-of-function (nonsense and splice-site mutations) and the rest are missense with unclear function. To understand whether these missense mutations might have dominant-negative effects or phenocopy loss-of-function effects, we compared the consequences of Smc3 deficient and haploinsufficient mouse models. We found that both embryonic and somatic deletion of homozygous Smc3 alleles led to complete hematopoietic failure. Furthermore, in competitive transplantation, following engraftment and subsequent tamoxifen treatment, the Smc3fl/fl/ERT2-Cre+/- BM cells were rapidly outcompeted, with earliest cell loss in the Gr1+ myeloid compartment. Hence, Smc3 is indispensable for hematopoiesis and AML-associated SMC3 missense mutations are unlikely to have dominant-negative effects. We examined the consequences of somatic Smc3 haploinsufficiency using Smc3fl/+/ERT2-Cre+/-. We found that Smc3 haploinsufficiency did not lead to increased number of initial methylcellulose colonies, nor did these cells replate beyond two weeks. In competitive transplantations, we again observed a significant competitive disadvantage in the Smc3fl/+/ERT2-Cre+/- BM cells, most pronounced in the Gr1+ myeloid cells. Competitive disadvantage is counter-intuitive for a leukemia-associated mutation. SMC3 mutations frequently co-occur with DNMT3A mutations. We, therefore, asked whether Smc3 haploinsufficiency might lead to a competitive advantage if it occurred in the background of Dnmt3a haploinsufficiency. With the addition of Dnmt3a haploinsufficiency, the severe myeloid competitive disadvantage was partially ameliorated, but the significant competitive disadvantage in other lineages remained intact. In summary, our data demonstrate that homozygous Smc3 deletion was incompatible with embryonic or adult hematopoiesis, with the greatest defects noted within myeloid compartment, indicating that AML-associated SMC3 mutations are unlikely to have dominant-negative effects. Smc3 haploinsufficiency resulted in a myeloid competitive disadvantage, which was partially abrogated in the presence of concurrent Dnmt3a haploinsufficiency, suggesting lineage-specific interactions between the mutations. Citation Format: Tianjiao Wang, John S. Welch. Concurrent Dnmt3a haploinsufficiency partially abrogates competitive disadvantage in Smc3 haploinsufficient myeloid cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5095.