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Blood, 1 May 2008, Vol. 111, No. 9, pp. 4771-4779. Prepublished online as a Blood First Edition Paper on January 28, 2008; DOI 10.1182/blood-2007-08-105072.
Submitted August 3, 2007
Department of Cancer Biology, and Kimmel Cancer Center, Thomas Jefferson University Medical College, Philadelphia, PA, United States * Corresponding author; email: b_calabretta{at}mail.jci.tju.edu.
The c-Myb gene encodes a transcription factor required for proliferation and survival of normal myeloid progenitors and leukemic blast cells. Targeting of c-Myb by antisense oligodeoxynucleotides has suggested that myeloid leukemia blasts (including CML-blast crisis cells) rely on c-Myb expression more than normal progenitors but a genetic approach to assess the requirement of c-Myb by p210BCR/ABL-transformed myeloid progenitors has not been taken. By comparing different progenitor subsets (Lin-, Lin-Sca-1+, Lin-Sca-1+Kit+) of mice with one or two functional c-Myb alleles, we show here that loss of a c-Myb allele had modest effects (20-25% decrease) on colony formation of non-transduced progenitors while the effect on p210BCR/ABL-expressing progenitors was more pronounced (50-80% decrease). Using a model of CML-blast crisis, mice (n=14) injected with p210BCR/ABL-transduced p53-/-c-Mybw/w marrow cells developed leukemia rapidly and had a median survival of 26 days, while only 67% of mice (n=12) injected with p210BCR/ABL-transduced p53-/-c-Mybw/d marrow cells died of leukemia with a median survival of 96 days. On assessing the expression of c-Myb-regulated genes, p210BCR/ABL-transduced c-Mybw/w and c-Mybw/d marrow progenitors expressed similar levels of c-Myc and cyclin B1 while those of Bcl-2 were reduced. However, ectopic Bcl-2 expression did not enhance colony formation of p210BCR/ABL-transduced c-Mybw/d Lin-Sca-1+Kit+ cells. Together, these studies support the requirement of c-Myb for p210BCR/ABL-dependent leukemogenesis.
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