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.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA100225-04
Application #
7289310
Study Section
Hematopoiesis Study Section (HP)
Program Officer
Howcroft, Thomas K
Project Start
2004-09-20
Project End
2009-07-31
Budget Start
2007-08-01
Budget End
2008-07-31
Support Year
4
Fiscal Year
2007
Total Cost
$282,663
Indirect Cost
Name
Stanford University
Department
Anatomy/Cell Biology
Type
Schools of Medicine
DUNS #
009214214
City
Stanford
State
CA
Country
United States
Zip Code
94305
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