Session: 603. Oncogenes and Tumor Suppressors: Poster I
Hematology Disease Topics & Pathways:
Diseases, AML, Myeloid Malignancies
To definitively address this question, we generated mice with both Cre-based conditional Runx1 knockout and Cbfb-MYH11 knockin (Runx1f/f, Mx1-Cre, Cbfb+/56M), which express Cbfb-MYH11 but no Runx1 after pIpC (poly I:C) treatment to induce Cre expression. Runx1f/f, Mx1-Cre, Cbfb+/56M mice had higher numbers of Lin-/Sca1-/c-Kit+ (LK) and Lin-/Sca1+/c-Kit+ cells in the bone marrow when comapred with Mx1-Cre, Cbfb+/56M mice at 3 weeks after pIpC. However, none of the Runx1f/f, Mx1-Cre, Cbfb+/56M mice developed leukemia up to one year after pIpC treatment. As reported previously, all Mx1-Cre, Cbfb+/56M mice developed leukemia with an median survival time of 4 months. Moreoever, none of the recipients transplanted with bone marrow cells from Runx1f/f, Mx1-Cre, Cbfb+/56M mice and then treated with pIpC developed leukemia, while all of the recipients of the Mx1-Cre, Cbfb+/56M bone marrow cells did, suggesting that the loss of leukemogenesis is cell autonomous. All together, these results indicate that Runx1 is indispensable for Cbfb-MYH11 induced leukemogenesis.
Even though at 3 weeks after pIpC the Runx1f/f, Mx1-Cre, Cbfb+/56M mice had more c-Kit+ cells, and more significantly the abnormal myeloid progenitors (AMPs) (LK/CD34-/FcRII/III+) from which the leukemia cells arise, these cells started to decrease and disappear 4 weeks after pIpC, suggesting that this is a critical stage for the failure of leukemogenesis in the Runx1f/f, Mx1-Cre, Cbfb+/56M mice. We therefore performed RNA-seq on the AMP population isolated from Mx1-Cre, Cbfb+/56M and Runx1f/f, Mx1-Cre, Cbfb+/56M mice three weeks after pIpC treatment, to explore the global gene expression changes between them. Our preliminary data analysis showed that many genes (1635) were differential expressed (DEGs; Padj ≤0.05, absolute fold change ≥ 2) between Runx1f/f, Mx1-Cre, Cbfb+/56M and Mx1-Cre, Cbfb+/56M mice. Many of these DEGs (37.6%) are RUNX1 target genes (Mandoli et al., Leukemia. 28:770, 2014). Among the significantly enriched gene sets by gene set enrichment analysis of the DEGs, the “GAL_LEUKEMIC_STEM_CELL_DN” gene set, which contains genes down-regulated in leukemic stem cells, is positively correlated with DEGs upregulated in Runx1f/f, Mx1-Cre, Cbfb+/56M cells, suggesting that the AMP population from Runx1f/f, Mx1-Cre, Cbfb+/56M mice lost the leukemia initiating ability. We are preforming ChIP-seq on the AMP population to determine how loss of RUNX1 disrupts binding of CBFβ-SMMHC to target genes. The above results suggest that RUNX1 is required for the regulation of critical genes for leukemogenesis by CBFβ-SMMHC.
Disclosures: No relevant conflicts of interest to declare.