Suppression of MLL-AF4 by Small Interfering RNAs Inhibits Proliferation and Induces Apoptosis in T(4;11)-Positive SEM Cells.

The reciprocal chromosomal translocation t(4;11)(q21;q23) creates the fusion genes MLL-AF4 and AF4-MLL located on derivative chromosome 11 or derivative chromosome 4, respectively. We used small interfering RNAs to suppress the MLL-AF4 fusion gene in the t(4;11)-positive leukaemic cell line SEM. Electroporation of SEM cells with MLL-AF4 siRNAs caused a more than two fold transient decrease in MLL-AF4 mRNA levels, which lasted for three days. The reduction in MLL-AF4 fusion transcript levels were associated with a severely diminished clonogenicity, inhibition of proliferation and of G1-S cell cycle transition and induction of apoptosis. Therefore, MLL-AF4 siRNAs are not only useful to study the functions of MLL-AF4 in leukaemogenesis, but may be also promising agents for novel treatment concepts for t(4;11)-associated leukaemias.