THE LEUKEMIC PROTEIN CORE-BINDING-FACTOR-BETA (CBF-BETA)-SMOOTH-MUSCLE MYOSIN HEAVY-CHAIN SEQUESTERS CBF-ALPHA-2 INTO CYTOSKELETAL FILAMENTS AND AGGREGATES
N. Adya et al., THE LEUKEMIC PROTEIN CORE-BINDING-FACTOR-BETA (CBF-BETA)-SMOOTH-MUSCLE MYOSIN HEAVY-CHAIN SEQUESTERS CBF-ALPHA-2 INTO CYTOSKELETAL FILAMENTS AND AGGREGATES, Molecular and cellular biology (Print), 18(12), 1998, pp. 7432-7443
The fusion gene CBFB-MYH11 is generated by the chromosome 16 inversion
associated with acute myeloid leukemias. This gene encodes a chimeric
protein involving the core binding factor beta (CBF beta) and the smo
oth-muscle myosin heavy chain (SMMHC). Mouse model studies suggest tha
t this chimeric protein CBF beta-SMMHC dominantly suppresses the funct
ion of CBF, a heterodimeric transcription factor composed of DNA bindi
ng subunits (CBF alpha 1 to 3) and a non-DNA binding subunit (CBF beta
). This dominant suppression results in the blockage of hematopoiesis
in mice and presumably contributes to leukemogenesis, We used transien
t-transfection assays, in combination with immunofluorescence and gree
n fluorescent protein-tagged proteins, to monitor subcellular localiza
tion of CBF beta-SMMHC, CBF beta, and CBF alpha 2 (also known as AML1
or PEBP2 alpha B). When expressed individually, CBF alpha 2 was locate
d in the nuclei of transfected cells, whereas CBF beta was distributed
throughout the cell. On the other hand, CBF beta-SMMHC formed filamen
t-like structures that colocalized with actin filaments, Upon cotransf
ection, CBF alpha 2 was able to drive localization of CBF beta into th
e nucleus in a dose-dependent manner. In contrast, CBF alpha 2 colocal
ized with CBF beta-SMMHC along the filaments instead of localizing to
the nucleus. Deletion of the CBF alpha-interacting domain within CBF b
eta-SMMHC abolished this CBF alpha 2 sequestration, whereas truncation
of the C-terminal-end SMMHC domain led to nuclear localization of CBF
beta-SMMHC when coexpressed with CBF alpha 2. CBF alpha 2 sequestrati
on by CBF beta-SMMHC was further confirmed in vivo in a knock-in mouse
model. These observations suggest that CBF beta-SHMMC plays a dominan
t negative role by sequestering CBFa2 into cytoskeletal filaments and
aggregates, thereby disrupting CBF alpha 2-mediated regulation of gene
expression.