CBFbeta-SMMHC, expressed in M4eo acute myeloid leukemia, reduces p53 induction and slows apoptosis in hematopoietic cells exposed to DNA-damaging agents.
CBFbeta-SMMHC is expressed in M4Eo acute myeloid leukemia (AML) as a result of inv(16), but how it contributes to leukemogenesis is unknown. p53 mutations are rare in de novo AML, but they are common in many malignancies. Expression of CBFbeta-SMMHC in Ba/F3 cells reduced p53 induction in response to ionizing radiation or etoposide 3- to 4-fold. However, p53 induction was normal in Ba/F3 cells expressing a CBFbeta-SMMHC variant that does not interfere with DNA binding by CBF, indicating that a CBF genetic target regulates p53 induction. The p53 gene may be regulated by CBF, because p53 mRNA levels were reduced by CBFbeta-SMMHC. Reduced p53 induction was not caused by slowed cell proliferation, a consequence of CBFbeta-SMMHC expression, because p53 was induced similarly in control cultures and in cultures propagated in 10-fold less interleukin-3 (IL-3). CBFbeta-SMMHC did not slow apoptosis resulting from IL-3 withdrawal, where p53 induction is minimal, but slowed apoptosis in Ba/F3 cells exposed to 10 Gy of ionizing radiation or 3 to 8 microgram/mL etoposide, providing 2-fold protection at 6 or 18 hours. Inhibition of apoptosis was temporary, because all the cells exposed to these doses ultimately died, and clonal survival assays performed using 0. 04 microgram/mL etoposide did not show protection by CBFbeta-SMMHC. p21 levels were increased in cells subjected to DNA damage, regardless of CBFbeta-SMMHC expression and attenuated p53 induction. Bcl-2, bcl-xL, bcl-xS, and bax levels were unaffected by CBFbeta-SMMHC. Attenuated p53 induction may contribute to leukemogenesis by CBFbeta-SMMHC by slowing apoptosis via a p21-independent mechanism.
Britos-Bray
M
M
The Johns Hopkins Oncology Center, Division of Pediatric Oncology, Baltimore, MD, USA.
Ramirez
M
M
Cao
W
W
Wang
X
X
Liu
P P
PP
Civin
C I
CI
Friedman
A D
AD
D000208:Acute Disease; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects; D004249:DNA Damage / Q000187:drug effects / Q000528:radiation effects; D005047:Etoposide / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D007951:Leukemia, Myeloid / Q000235:genetics* / Q000473:pathology*; D015514:Oncogene Proteins, Fusion / Q000235:genetics*; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000235:genetics*
D000972:Antineoplastic Agents, Phytogenic; C095514:CBFbeta-MYH11 fusion protein; D015514:Oncogene Proteins, Fusion; D016159:Tumor Suppressor Protein p53; D005047:Etoposide