Project description:Most cases of adult myeloid neoplasms are routinely assumed to be sporadic. Here, we describe an adult familial acute myeloid leukemia (AML) syndrome caused by germline mutations in the DEAD/H-Box helicase gene DDX41. DDX41 was also found to be affected by somatic mutations in sporadic cases of myeloid neoplasms as well as in a biallelic fashion in 50% of patients with germline DDX41 mutations. Moreover, corresponding deletions on 5q35.3 present in 6% of cases lead to haploinsufficient DDX41 expression. DDX41 lesions caused altered pre-mRNA splicing and RNA processing. DDX41 is exemplary of other RNA helicase genes also affected by somatic mutations, suggesting that they constitute a family of tumor suppressor genes. Affymetrix SNP arrays were performed according to the manufacturer's directions on DNA extracted from cryopreserved diagnostic bone marrow or peripheral blood samples.
Project description:Most cases of adult myeloid neoplasms are routinely assumed to be sporadic. Here, we describe an adult familial acute myeloid leukemia (AML) syndrome caused by germline mutations in the DEAD/H-Box helicase gene DDX41. DDX41 was also found to be affected by somatic mutations in sporadic cases of myeloid neoplasms as well as in a biallelic fashion in 50% of patients with germline DDX41 mutations. Moreover, corresponding deletions on 5q35.3 present in 6% of cases lead to haploinsufficient DDX41 expression. DDX41 lesions caused altered pre-mRNA splicing and RNA processing. DDX41 is exemplary of other RNA helicase genes also affected by somatic mutations, suggesting that they constitute a family of tumor suppressor genes.
Project description:Germline mutations in the RNA Helicase gene DDX41 cause inherited predisposition to Myelodysplastic Syndrome and other myeloid blood malignancies. We characterized the effect of loss of one or both copies of the Ddx41 gene on the gene expression profile of immortalized hematopoietic progenitor cells.
Project description:Genetic expression profiling (GEP) has previously proven useful in B-ALL for identifying signatures of oncogenes, with the recognition of novel subgroups, as well as with outcome. Therefore, we adopted GEP of bonemarrow samples of B-ALL with t(9;22) to uncover the contribution of DDX41 to leukemogenesis. The germline mutations of DDX41, also known as DEAD box RNA helicase 41, have been found in about 1.5% of myeloid neoplasms (MNs). Development of MDS/AML is relatively common in germline DDX41 mutations. However, a variety of hematological malignancies (HMs) have been reported. We report a novel case of bi-alleleic DDX41 mutations in B-cell lymphoblastic leukemia (B-ALL), with unusual location of DDX41 mutations. The gene expression profile (GEP) of Ph+ B-ALL with bi-alleleic DDX41 mutations showed heterogeneously transitional GEP and altered gene expression levels of genes involved in the process essential for red blood cells and myeloid cell differentiation were noted. We report that DDX41 mutations are unusual but can be an underlying event in Ph+B-ALL and screening DDX41 mutations can be also informative for patients awaiting for haploidentical stem cell transplantation and choosing the therapy.
Project description:Although DEAD-box helicase 41 (DDX41) is implicated in oncogenic and innate immune mechanisms, there are many unanswered questions about how the ever-increasing spectrum of genetic variants impacts DDX41 activity. Here, we describe a facile genetic rescue assay that discriminates activities of DDX41 from those of human myeloid malignancy-linked germline and somatic DDX41 mutants. Our analyses revealed that the variants were impaired in their intrinsic RNA-regulatory activities and to induce monocytic differentiation markers. It will be instructive to extend these analyses to more broadly conduct structure/function assessments for clinical genetic curation and leverage the quantitative assay to elucidate mechanisms and interventions that promote and/or oppose DDX41 function, thereby influencing DDX41-linked pathogenicity.
Project description:Kynureninase is a member of a large family of catalytically diverse but structurally homologous pyridoxal 5'-phosphate (PLP) dependent enzymes known as the aspartate aminotransferase superfamily or alpha-family. The Homo sapiens and other eukaryotic constitutive kynureninases preferentially catalyze the hydrolytic cleavage of 3-hydroxy-l-kynurenine to produce 3-hydroxyanthranilate and l-alanine, while l-kynurenine is the substrate of many prokaryotic inducible kynureninases. The human enzyme was cloned with an N-terminal hexahistidine tag, expressed, and purified from a bacterial expression system using Ni metal ion affinity chromatography. Kinetic characterization of the recombinant enzyme reveals classic Michaelis-Menten behavior, with a Km of 28.3 +/- 1.9 microM and a specific activity of 1.75 micromol min-1 mg-1 for 3-hydroxy-dl-kynurenine. Crystals of recombinant kynureninase that diffracted to 2.0 A were obtained, and the atomic structure of the PLP-bound holoenzyme was determined by molecular replacement using the Pseudomonas fluorescens kynureninase structure (PDB entry 1qz9) as the phasing model. A structural superposition with the P. fluorescens kynureninase revealed that these two structures resemble the "open" and "closed" conformations of aspartate aminotransferase. The comparison illustrates the dynamic nature of these proteins' small domains and reveals a role for Arg-434 similar to its role in other AAT alpha-family members. Docking of 3-hydroxy-l-kynurenine into the human kynureninase active site suggests that Asn-333 and His-102 are involved in substrate binding and molecular discrimination between inducible and constitutive kynureninase substrates.
Project description:Germline heterozygous mutations in DDX41 predispose individuals to hematologic malignancies in adulthood. Most of these DDX41 mutations result in a truncated protein, leading to loss of protein function. To investigate the impact of these mutations on hematopoiesis, we generated mice with hematopoietic-specific knockout of one Ddx41 allele. Under normal steady-state conditions, there was minimal effect on lifelong hematopoiesis, resulting in a mild yet persistent reduction in red blood cell counts. However, stress induced by transplantation of the Ddx41+/- BM resulted in hematopoietic stem/progenitor cell (HSPC) defects and onset of hematopoietic failure upon aging. Transcriptomic analysis of HSPC subsets from the transplanted BM revealed activation of cellular stress responses, including upregulation of p53 target genes in erythroid progenitors. To understand how the loss of p53 affects the phenotype of Ddx41+/- HSPCs, we generated mice with combined Ddx41 and Trp53 heterozygous deletions. The reduction in p53 expression rescued the fitness defects in HSPC caused by Ddx41 heterozygosity. However, the combined Ddx41 and Trp53 mutant mice were prone to developing hematologic malignancies that resemble human myelodysplastic syndrome and acute myeloid leukemia. In conclusion, DDX41 heterozygosity causes dysregulation of the response to hematopoietic stress, which increases the risk of transformation with a p53 mutation.
Project description:Germline heterozygous mutations in DDX41 predispose individuals to hematologic malignancies in adulthood. Most of these DDX41 mutations result in a truncated protein, leading to loss of protein function. To investigate the impact of these mutations on hematopoiesis, we generated mice with hematopoietic-specific knockout of one Ddx41 allele. Under normal steady-state conditions, there was minimal effect on lifelong hematopoiesis, resulting in a mild yet persistent reduction in red blood cell counts. However, stress induced by transplantation of the Ddx41+/- BM resulted in hematopoietic stem/progenitor cell (HSPC) defects and onset of hematopoietic failure upon aging. Transcriptomic analysis of HSPC subsets from the transplanted BM revealed activation of cellular stress responses, including upregulation of p53 target genes in erythroid progenitors. To understand how the loss of p53 affects the phenotype of Ddx41+/- HSPCs, we generated mice with combined Ddx41 and Trp53 heterozygous deletions. The reduction in p53 expression rescued the fitness defects in HSPC caused by Ddx41 heterozygosity. However, the combined Ddx41 and Trp53 mutant mice were prone to developing hematologic malignancies that resemble human myelodysplastic syndrome and acute myeloid leukemia. In conclusion, DDX41 heterozygosity causes dysregulation of the response to hematopoietic stress, which increases the risk of transformation with a p53 mutation.