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

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. mRNA from human cord blood-derived CD34+cells expressing wild-type and mutant SAMD9 and SAMD9L