miR-126 Regulates Distinct Self-Renewal Outcomes in Normal and Malignant Hematopoietic Stem Cells

SummaryTo investigate miRNA function in human acute myeloid leukemia (AML) stem cells (LSC), we generated a prognostic LSC-associated miRNA signature derived from functionally validated subpopulations of AML samples. For one signature miRNA, miR-126, high bioactivity aggregated all in vivo patient sample LSC activity into a single sorted population, tightly coupling miR-126 expression to LSC function. Through functional studies, miR-126 was found to restrain cell cycle progression, prevent differentiation, and increase self-renewal of primary LSC in vivo. Compared with prior results showing miR-126 regulation of normal hematopoietic stem cell (HSC) cycling, these functional stem effects are opposite between LSC and HSC. Combined transcriptome and proteome analysis demonstrates that miR-126 targets the PI3K/AKT/MTOR signaling pathway, preserving LSC quiescence and promoting chemotherapy resistance

The unfolded protein response governs integrity of the haematopoietic stem-cell pool during stress.

The blood system is sustained by a pool of haematopoietic stem cells (HSCs) that are long-lived due to their capacity for self-renewal. A consequence of longevity is exposure to stress stimuli including reactive oxygen species (ROS), nutrient fluctuation and DNA damage. Damage that occurs within stressed HSCs must be tightly controlled to prevent either loss of function or the clonal persistence of oncogenic mutations that increase the risk of leukaemogenesis. Despite the importance of maintaining cell integrity throughout life, how the HSC pool achieves this and how individual HSCs respond to stress remain poorly understood. Many sources of stress cause misfolded protein accumulation in the endoplasmic reticulum (ER), and subsequent activation of the unfolded protein response (UPR) enables the cell to either resolve stress or initiate apoptosis. Here we show that human HSCs are predisposed to apoptosis through strong activation of the PERK branch of the UPR after ER stress, whereas closely related progenitors exhibit an adaptive response leading to their survival. Enhanced ER protein folding by overexpression of the co-chaperone ERDJ4 (also called DNAJB9) increases HSC repopulation capacity in xenograft assays, linking the UPR to HSC function. Because the UPR is a focal point where different sources of stress converge, our study provides a framework for understanding how stress signalling is coordinated within tissue hierarchies and integrated with stemness. Broadly, these findings reveal that the HSC pool maintains clonal integrity by clearance of individual HSCs after stress to prevent propagation of damaged stem cells

Investigation of genes involved in osteosarcoma development

grantor: University of TorontoMany genes involved in osteosarcoma development have yet to be described. The chromosomal regions commonly altered in osteosarcoma mark the location of further tumor suppressor genes and oncogenes. The study of these regions may yield further understanding of known cancer genes and the isolation of novel ones. I therefore had two objectives: (i) the investigation of 12q13-15, a region commonly amplified in osteosarcoma and (ii) the isolation of novel genes involved in osteosarcoma pathogenesis. Three genes located at 12q13-15 are most likely to be driving amplification: SAS, CDK4 and MDM2. Analysis of gene amplification and expression indicated that the region is more frequently amplified in the parosteol subtype of osteosarcoma and that SAS may be the most critical gene. In addition, the analysis of gene expression in osteosarcoma tumor samples isolated a number of genes potentially involved in tumor development and progression, including the von Willebrand factor gene.M.Sc