Mda-7/IL-24 And IL-24 DelE5 Induce Differentiation Of Acute Myeloid Leukemic Cells And Their Expression In Leukemia Patients.

Melanoma differentiation associated gene-7 (mda-7), also known as interleukin-24 (IL-24), has been shown to suppress growth and induce apoptosis in various tumor types. The aim of this study is to investigate the correlation between mda-7/IL-24 and leukemic cells differentiation. We showed that the expression of both mda-7/IL-24 and IL-24 delE5, a mda-7/IL-24 splice variant, was induced in U937 and HL60 cells during 12-O-tetradecanoylphorbol-13-acetate (TPA)-mediated monocytic differentiation, and activation of MAPK/ERK pathway was required for their induction. Knockdown of mda-7/IL-24 and IL-24 delE5 resulted in significant inhibition of the monocytic differentiation induced by TPA. Ectopic overexpression of mda-7/IL-24 and/or IL-24 delE5 significantly induced U937, HL60 cells, and primary leukemic cells from patients with acute myeloid leukemia (AML)-M5 to differentiate, altered the expression of lineage-specific transcription factors, without affecting normal hematopoietic progenitors. Furthermore, the key molecular effector associated with selective differentiation induction by mda-7/IL-24 and IL-24 delE5 was reactive oxygen species (ROS) generated by nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. Taken together, our results reveal the mechanism by which TPA induces monocytic differentiation, and show for the first time the differentiation-inducing effects of mda-7/IL-24 and IL-24 delE5 on human myeloid leukemic cells. Although mda-7/IL-24 has been known as tumor inhibitor gene, and our results have shown mda-7/IL-24 and its splice variant IL-24 delE5 could induce differentiation of leukemia cells, their expression in leukemia patients remains elusive. In this study, we detected the expression of mda-7/IL-24 and its splice variant IL-24 delE5 in various leukemia patients. To analyze the expression of mda-7/IL-24 and IL-24 delE5 in various leukemia patients and its clinical significance, a real-time quantitive RT-PCR method was applied to assay mda-7/IL-24 and IL-24 delE5 expression levels in bone marrow cells of 89 leukemia patients including 59 AML,30 CML,16 ALL,10 anaemia patients and 13 ITP patients were used as normal controls. The relationship between expression levels and the established prognostic factors such as age, tissue infiltration, karyotype, CD34 expression, blast percentage and FAB subtypes was investigated. Either blast percentage, peripheral blood white blood cells (WBC) or age were found to significantly correlate with the expression of mda-7/IL-24 and IL-24 delE5. With respect to FAB cytotypes, expression of mda-7/IL-24 and IL-24 delE5 in ALL was statistically lower than that in normal controls (p<0.05), median mda-7/IL-24 and IL-24 delE5 expression level in CML patients with tissue infiltration was significantly lower than that in CML patients without tissue infiltration (p< 0.05). mda-7/IL-24 and IL-24 delE5 expression level in AML patients with tissue infiltration, karyotype, CD34 expression is lower than that in AML patients without tissue infiltration, karyotype, CD34 expression. These observations suggest that testing the expression of mda-7/IL-24 and IL-24 delE5 may help to evaluate prognosis of leukemia patients.