The leukemic core binding factor β-smooth muscle myosin heavy chain (CBFβ-SMMHC) chimeric protein requires both CBFβ and myosin heavy chain domains for transformation of NIH 3T3 cells

摘要

An inversion of chromosome 16 associated with the M4Eo subtype of acute myeloid leukemia produces a chimeric protein fusing the β subunit of the transcription factor core binding factor (CBFβ) to the tail region of smooth muscle myosin heavy chain (SMMHC). We investigated the oncogenic properties of this CBFβ-SMMHC chimeric protein using a 3T3 transformation assay. NIH 3T3 cells expressing CBFβ-SMMHC acquired a transformed phenotype, as indicated by their ability to form foci, grow in soft agarose, and form tumors in nude mice. Cells expressing normal CBFβ or the SMMHC tail domain did not become transformed. Elec-trophoretic mobility-shift assays showed that extracts from cells transformed by CBFβ-SMMHC no longer formed the normal CBF/DNA complex but instead formed a much larger complex that did not migrate into the gel. Analysis of CBFβ-SMMHC deletion mutants demonstrated that the chimeric protein was transforming only if two domains were both present: (ⅰ) CBFβ sequences necessary for association with the CBFα subunit, and (ⅱ) SMMHC sequences important for the formation of multimeric filaments. These results are direct evidence that CBFβ-SMMHC can function as an oncoprotein.