Abstract A46: Heterozygous mutations in DDX41 cause erythroid progenitor cell defects and cooperate with p53 mutations to cause hematologic malignancy
Authors: Chlon Timothy M , Stepanchick Emily , Sulentic Analise , Wilson Andrew , Starczynowski Daniel T 
Published: May 2023

Abstract
Germline mutations in the RNA Helicase gene DDX41 are the most common cause of inherited susceptibility to adult MDS and AML. These mutations are always heterozygous and are typically frameshifts, causing loss of functional protein. We recently reported that at least one functional copy of DDX41 is essential for hematopoiesis, and that DDX41 is required for ribosome biogenesis (Chlon et al., Cell Stem Cell 2021). While biallelic DDX41 mutations cause dramatic defects in hematopoiesis, the role of heterozygous mutations in MDS pathogenesis is not yet understood. DDX41 mutation carriers frequently experience idiopathic cytopenias of unknown significance (ICUS) prior to MDS onset, suggesting that underlying hematopoietic defects contribute to MDS/AML (Choi et al., Haemotologica 2021). The majority of DDX41-mutant MDS patients have refractory anemia, indicating that the erythroid lineage is particularly affected in these patients (Sebert et al., Blood 2019). Since ribosome defects are a common cause of inherited anemias and also contribute to MDS pathogenesis, we characterized the effect of heterozygous DDX41 mutations on erythropoiesis in murine and human models. Mice that were transplanted with Ddx41+/− bone marrow develop anemia at 12-15 months post-transplant. At younger ages, these mice have normal hematopoietic indices, but when stress erythropoiesis is induced by Pheylhydrazine-treatment, the Ddx41+/− mice have prolonged anemia. These observations indicate that heterozygous loss of DDX41 causes defects in erythropoiesis during stress and aging. We further characterized the effect of Ddx41-hetrozyogisty on erythroid progenitor function in vitro. In colony assays, we found that Ddx41+/− HSPC form fewer BFU-E but comparable numbers of myeloid colonies. In liquid culture erythroid differentiation cultures, we found that Ddx41+/− HSPC produce fewer CD71+ Ter119+ progenitors than controls. Mechanistically, we found that in vitro-derived erythroid progenitors from both mice and cell line models had decreased protein translation, suggesting that ribosome defects underlie the observed inefficiency in erythropoiesis. In congenital ribosomopathy diseases, ribosome defects lead to p53 activation which contributes to defects in erythropoiesis. Interestingly, TP53 mutations are common in DDX41-mutant MDS/AML (Sebert et al., Blood 2019), suggesting that the ribosome deficiency selects for these mutations. To assess the role of p53 mutations in the development of DDX41-mutant MDS, we generated Ddx41+/−;p53+/− mice and transplanted the bone marrow into lethally-irradiated recipients and followed the mice for 1 year. These mice developed a lethal MDS-like phenotype at 7-12 months post-transplant while control mice lived until the end of the study period. The sick mice had anemia and other cytopenias accompanied by enlarged spleens and dysplastic myeloid cells. Collectively, these results indicate that p53 mutations cooperate with Ddx41-heterozygosity to promote hematologic malignancy.
Citation Format: Timothy M Chlon, Emily Stepanchick, Analise Sulentic, Andrew Wilson, Daniel T Starczynowski. Heterozygous mutations in DDX41 cause erythroid progenitor cell defects and cooperate with p53 mutations to cause hematologic malignancy [abstract]. In: Proceedings of the AACR Special Conference: Acute Myeloid Leukemia and Myelodysplastic Syndrome; 2023 Jan 23-25; Austin, TX. Philadelphia (PA): AACR; Blood Cancer Discov 2023;4(3_Suppl):Abstract nr A46.