Self-Renewal of Normal and Leukemic Stem Cells

Stanford University, Stanford CA

Investigators

Linked publications & trials

Abstract

DESCRIPTION (provided by applicant): A central issue in normal and leukemic hematopoietic stem cell (HSC) biology is to understand the mechanisms that regulate self-renewal, which is required for hematopoiesis to persist for the lifetime of the animal. Stem cell self-renewal is under genetic constraints. Leukemia is a disease in which mutations allow either normal HSCs to escape the genetic constraints on self renewal or allow progenitor cells to acquire the ability to self-renew. To begin to understand the molecular mechanisms that regulate self-renewal, a cDNA library was constructed from pure populations of HSCs with self-renewal capacity and used to analyze genes that were differentially expressed by this population and pluripotent hematopoietic progenitor cells without self-renewal capacity. We found that the HSCs expressed the bmi1 oncogene, which is a Polycomb-group gene that represses expression of Hox genes during development and regulates cell proliferation and senescence by down-regulating the ink4a locus. The ink4a locus expresses two genes by alternative splicing: p16 is a G1 cyclin inhibitor and p19 ARF stabilizes expression of p53 by binding to Mdm2. We thus examined the HSC compartment in bmi1-deficient ("knockout" or "KO") mice and found that such mice had normal numbers of fetal liver HSCs. However, these mice displayed a reduction in adult HSCs and adult neuronal stem cells. Mutation of p16 Ink4a partially restores the stem cell defect in bmi-1 -/- mice. We then examined human HSCs and human AML stem cells and found that they both expressed bmi-1. This suggests that this gene may play a role in human hematopoiesis and leukemogenesis. The aims of this grant are to extend these findings and to gain further insights into the regulation of stem cell functions, particularly self-renewal, via the following aims. Specific Aim #1: To determine whether alteration of the expression of putative bmi-1 downstream targets restores the ability of bmi-1 deficient bone marrow cells to give rise to leukemia. Specific Aim #2: To identify the target cell for transformation in AML induced by certain leukemia genes.