Foruzan Moradi - Department of Genetics, School of Biological Sciences, Tarbiat Modares University, Tehran, Iran
Sadegh Babashah - Department of Genetics, School of Biological Sciences, Tarbiat Modares University, Tehran, Iran

Leukemia is a group of cancers that usually begins in the bone marrow and results in highnumbers of abnormal white blood cells. Musashi2 (Msi2) is a RNA-binding protein that ishighly expressed in hematopoietic stem cell (HSC) and leukemic stem cells (LSCs). Theelevated level of Msi2 leads to the downregulation of the cell-fate determinant, Numb. Numbis known to reduce the growth of LSCs. With this regard in this study we knocked down Msi2by siRNA strategy and we used HL-60 cell line (a leukemic cell line), to investigate whetherMsi2 knockdown is able to induce apoptosis in the leukemic cell via Musashi-Numb pathway.Lipofectamin RNAiMax, siRNA and other reagents that used for transfection of siRNA werepurchased from Invitrogen. Rate of apoptosis was demonstrated by Annexin-V staining andpropidium iodide (PI) exclusion using the Annexin-V FITC apoptosis detection kit (Sigma)according to the manufacturer’s protocol. With inhibition of Msi2, Numb expressionincreased. To explore whether and how Msi2 downregulation, apoptosis rate in transfected HL-60 cells was determined using Annexin-PI method by flow cytometry. After transfection of cellswith Msi2-siRNA, rate of apoptosis increased in transfected cells. AnnexinV-PI histogramsshowed 19.44%, and 60.48%, of apoptosis (late+early apoptosis) for 24, and 48 hours afterMsi2 Knockdown, respectively. Msi2 has been shown to play an important role inhematopoietic malignancies. Msi2 downregulation inhibited leukemic cell growth andincreased apoptosis. The effect of knocking down/deletion of Msi2 on eradicating LSCs mightbe performed with the aim of cell fate regulatory, Numb. As Msi2 downregulation leads to theincreasing in the expression level of Numb, which consequently causes leukemic stem cellsdepletion. It was proposed that Msi2-Numb pathway should control the proliferation andapoptosis of leukemic cells, this pathway could be a novel target for leukemia treatment.

HL-60, Msi2, Numb, Leukemic cell, Apoptosis