Decreased Proliferation of Myeloid Leukemia Cells through Down-Regulating LYL1 Expression with Small Interference RNA.

Ectopic expression of the basic helix-loop-helix transcription factor LYL1 has been implicated in T-cell acute lymphoblastic leukemia (T-ALL). It has also been found to be over-expressed in cells of acute myeloid leukemia (AML). Myeloid leukemia cells over-expressing LYL1 cDNA had accelerated growth rates, increased plating efficiency and a blockade of differentiation. To further investigate its role in the pathogenesis of leukemia, we used small interference RNA (siRNA) to silence the expression of LYL1 in human leukemia cell line K562, which expresses a moderate level of endogenous LYL1 protein. Three LYL1-specific RNA oligos, the Stealth Select RNAi HSS142834, HSS142835, and HSS142836, purchased from Invitrogen, were introduced into K562 cells by using Invitrogen transfection reagent Lipofectamine RNAiMAX. Two successive transfections at day 1 and day 2 were made according to manufacturer’s manual. Expression levels of LYL1 in LYL1 siRNA transfected cells and control cells (transfected with the Stealth RNAi Negative Controls) were determined with fluorescence real-time quantitative polymerase chain reaction assay. Our result showed that the application of any single RNAi oligo achieved observable inhibition of LYL1 expression levels (30–40%) while a combination of the three RNAi oligos remarkable inhibition (70.4%). The growth rates of K562 cells were not affected by any single RNAi oligo. However, a combination of three RNAi oligos did induce noticeable growth inhibition of cells. Plating efficiency assay showed that the clonogenic recovery rate of K562 cells treated with a combination of thee RNAi oligos was inhibited by 32.5% (P