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Pediatric MDS-Associated Germline Mutations in SAMD9 and SAMD9L Impair Multiple Pathways in Primary Hematopoietic Cells

ABSTRACT: Here, we used a lentiviral over-expression approach to assess the functional impact and underlying cellular processes of wild-type and mutant SAMD9 or SAMD9L in primary mouse or human hematopoietic stem and progenitor cells (HSPC). Using a combination of protein interactome analyses, transcriptional profiling and functional validation, we found that SAMD9 and SAMD9L are multifunctional proteins that cause profound alterations in cell cycle, protein translation, and proliferation of HSPCs. Importantly, our molecular and functional studies also demonstrated that expression of these genes and their mutations leads to a toxic cellular environment that promotes DNA-damage repair defects and ultimately lead to apoptosis in hematopoietic cells. This study provides novel functional insights into SAMD9 and SAMD9L and how their mutations can potentially alter hematopoietic function and lead to bone marrow hypocellularity, a hallmark of pediatric MDS.

ORGANISM(S): Homo sapiens

PROVIDER: GSE152420 | GEO | 2020/11/30

REPOSITORIES: GEO

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Project description:Myelodysplastic syndromes (MDS) are clonal disorders of hematopoietic progenitors characterized by ineffective hematopoiesis and high propensity to leukemias. Although a number of gene targets have been identified, in many MDS cases, particular genetic targets are unknown. In this study, we performed genome-wide profiling of copy number (CN) abnormalities and allelic imbalances in MDS genomes in order to clarify the distribution of LOH (loss of heterozygosity) and identify their target genes. We analyzed a total of 171MDS and MDS/MPD specimens, including 7 RA/RARS, 23 RCMD/RCMD-RS, 6 5q-syndrome, 30 RAEB-1, 40 RAEB-2, 4 therapy related-MDS/AML, 5 MDSu, 17 CMML-1, 16 CMML-2, 24 overt AML, using high-density SNP arrays. The data were analyzed by CNAG/AsCNAR software we specifically developed for allele-specific CN analysis and sensitive LOH detection. MDS showed characteristic CN profiles in SNP array analysis. Of particular interest is the finding of high frequency of CN-neutral LOH (Uniparental disomy,UPD), which were observed in 51 of 171 (30%) MDS cases. They preferentially involved 1p, 1q, 4q, 7q, 11q, 17p and other chromosomal segments, which were associated with homozygous mutations of both loss-of-function mutations and gain-of function mutations of tumor suppressor genes and cellular oncogenes, including TP53 (17p UPD), AML1/RUNX1 (21q UPD), Nras and cMPL (1p UPD), JAK-2 (9p UPD), and FLT3 (13q UPD). Next we tried to identify a new gene target in 11q UPD, which was most common UPD region in this study and many of these cases were CMML with a normal karyotype. The minimum 11q UPD segment is about 2Mb which existed in 11q23. We sequenced coding exons of c-cbl and detected homozygous mutations in 8 of 9 MDS cases with 11q UPD (CMML= 5, RAEB= 3, overt leukemia= 1), but very rare in cases without 11q UPD (1/162), demonstrating that the mutation is tightly linked to 11q UPD. These mutations were 8 point mutations and 1 micro-deletion, they were accumulated in the linker or RING domain. These c-cbl mutants can transform NIH3T3 in a dominant manner and these mutants are phosphorylated and activate PI3K-Akt pathway. To investigate the functions of these mutants in hematopoietic cells, we introduced these mutants into c-kit(+)Sca1(+)Lin(-) murine bone marrow cells, it prolonged replating capacity of these hematopoietic progenitors. Keywords: SNP-chip To identify oncogenic lesions in MDS, we performed a genome-wide analysis of primary MDS samples using high-density SNP arrays (Affymetrix GeneChip).

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Pediatric MDS-Associated Germline Mutations in SAMD9 and SAMD9L Impair Multiple Pathways in Primary Hematopoietic Cells

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