CBF-BETA-SMMHC, EXPRESSED IN M4EO AML, REDUCED CBF DNA-BINDING AND INHIBITED THE G1 TO S-CELL-CYCLE TRANSITION AT THE RESTRICTION POINT IN MYELOID AND LYMPHOID-CELLS
Ws. Cao et al., CBF-BETA-SMMHC, EXPRESSED IN M4EO AML, REDUCED CBF DNA-BINDING AND INHIBITED THE G1 TO S-CELL-CYCLE TRANSITION AT THE RESTRICTION POINT IN MYELOID AND LYMPHOID-CELLS, Oncogene, 15(11), 1997, pp. 1315-1327
CBF beta-SMMHC is expressed from the inv(16) chromosome in M4Eo AML. M
ice lacking CBF subunits or expressing the CBF beta-SMMHC or AML1-ETO
onco-proteins failed to develop definitive hematopoiesis. To investiga
te these effects on hematopoiesis, we expressed CBF beta-SMMHC from th
e metallothionein promoter, in both 32D c13 myeloid cells and Ba/F3 B-
lymphoid cells. Addition of zinc increased CBF beta-SMMHC levels more
than tenfold, with higher levels evident in Ba/F3 lines. Levels obtain
ed in 32D c13 cells were similar to those of endogenous CBF beta. Indi
rect immunofluorescence revealed zinc-inducible speckled, nuclear stai
ning in Ba/F3 cells and diffuse nuclear staining in 32D c13 cells. CBF
beta-SMMHC reduced endogenous CBF DNA-binding fivefold in both cell t
ypes, increased cell generation time 1.9-fold, on average, in 32D c13
cells and 1.5-fold in Ba/ F3 cells and decreased tritiated thymidine i
ncorporation into DNA correspondingly. CBFP beta-SMMHC increased the p
roportion of cells in G1 1.7-fold, on average, in 32D c13 and Ba/F3 ce
lls, and decreased the proportion of cells in S phase by a similar deg
ree. CBF beta-SMMHC induced a marked increase in hypophosphorylated Rb
, but did not alter IL-3 Receptor alpha or beta subunit levels. Neithe
r apoptosis nor 32D differentiation was induced by zinc in IL-3 in the
se lines. Induction of CBF beta-SMMHC WC in 32D c13 cells did not inhi
bit their differentiation to neutrophils or their expression of myelop
eroxidase mRNA in GCSF, and did not produce an eosinophilic phenotype.
Additional, proliferative genetic changes in M4eo AMLs might potentia
te inhibition of differentiation by CBF beta-SMMHC by allowing its inc
reased expression.