M. Britosbray et Ad. Friedman, CORE BINDING-FACTOR CANNOT SYNERGISTICALLY ACTIVATE THE MYELOPEROXIDASE PROXIMAL ENHANCER IN IMMATURE MYELOID CELLS WITHOUT C-MYB, Molecular and cellular biology, 17(9), 1997, pp. 5127-5135
The myeloperoxidase (MPO) gene is transcribed specifically in immature
myeloid cells and is regulated in part by a 414-bp proximal enhancer,
Mutation of a core binding factor (CBF)-binding site at -288 decrease
d enhancer activity 30-fold in 32D cl3 myeloid cells cultured in granu
locyte colony-stimulating factor (G-CSF), A novel functional analysis,
linking the CBF-binding site to an enhancer deletion series, located
at -147 an evolutionarily conserved c-Myb-binding site which was requi
red for optimal enhancer activity and synergy with CBF in 32D cells, T
hese sites cooperated in isolation and independent of a precise spacin
g, Deletional analysis carried out in the absence of the c-Myb-binding
site at -147 located at -301 a second c-Myb-binding site which also s
ynergized with CBF to activate the enhancer, A GA-rich region at -162
contributed to cooperation with CBF when the adjacent c-Myb-binding si
te was intact, Mutation of both c-Myb-binding sites in the context of
the entire enhancer greatly impaired activation by endogenous CBF in 3
2D cells, Similarly, activation by c-Myb was impaired in constructs la
cking the CBF-binding site, CBF and c-Myb were required for induction
of MPO proximal enhancer activity when 32D cells differentiated in res
ponse to G-CSF, A fusion protein containing the Gal4 DNA-binding domai
n and the AML-IB activation domain, amino acids 216 to 480, activated
transcription alone and cooperatively with c-Myb in nonmyeloid CV-1 ce
lls, Determining how CBF and c-Myb synergize in myeloid cells might co
ntribute to our understanding of leukemogenesis by the AML1-ETO, AML1-
MDS1, CBF beta-SMMHC, and v-Myb oncoproteins.