الفهرس 
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Abstract
Acute myeloid leukemia (AML) is a clonal hematopoietic disorder resulting from genetic alteration in normal hematopoietic stem cells. These alterations disrupt normal differentiation and cause excessive proliferation of abnormal immature leukemic cells called blasts. As the disease progresses, the accumulation of these blast cells occur in the bone marrow, organs, and blood., and interfere with the production of normal blood cells.
AML is mostly found in adult. The over expression of antiapoptotic genes also called oncogenes, that promote tumorgenesis and protection against apoptosis, is one of the critical factors for the development of AML.
It was discovered that the microRNAs (miRNAs) were a novel class of gene regulators, and causally linked to cancer, this discovery led to the extensive profiling of miRNA expression in all cancers, including leukemia. Mature miRNAs are small (19-22 nucleotides) single stranded noncoding RNA molecules that are derived from hairpin structured longer precursors, and they are naturally occurring in cells. They regulate gene expression by targeting mRNAs based on the degree of complementarity with their 3˴UTR.
MiRNAs are involved in the modulation of various cellular pathways, such as cell proliferation, apoptosis, and differentiation. They can function as oncogenes or tumor suppressors in AML. Oncogenic miRNAs are thought to be expressed at high levels in AML with suppression of the translation of mRNAs encoding tumor suppressors. These oncomiRs are not only therapeutic targets, but also important biomarkers for cancer detection and management.
MiR-155 gene can act as an oncogene that enhances the development of AML cells. It is therefore a potential target for future therapy of AML. SHIP1 and CEBPB are targets of miR-155. MiR-155 has been demonstrated to bind to 3˴ UTR of SHIP1 as well as CEBPB mRNAs and, therefore, in order to inhibit its translation. Moreover, the endogenous expressions of SHIP1and CEBPB are reduced in hematopoietic cells overexpressing miR-155, which leads to increased activation of AKT and decreased apoptosis leaded to leukmic progression.
This study aimed to evaluate the impact of miR-155 gene silence on oncogenesis in myeloid leukemia cell lines via dysregulation of SHIP1 and CEBPB in order to access the potentiality of anti-miR-155 as an immunotherapeutic target in Acute Myeloid Leukaemia.
The study includedin vitro study conducted on K562 “human acute myeloid leukemia cells”, in which the cells are transfected with miR-155 inhibitor. The cell line (K562) was purchased from Vacsera, Cairo, Egypt; the 3rd cell passage was used for the transfection experiment, followed by assessment of cytotoxic effect and miR-155 gene expression analysis. Total cell counting, cell viability “Trypan blue” assay and Cell proliferation assay “MTT”of K562 cell line were done using Trypan blue assay and MTT assay. Finally, miR_155, SHIP1 and CEBP genes expression were measured in harvested cell lines in transfected and untreated (MOCK) cells by using qPCR.
Our results revealed that untreated K562 cells shows a high cell count compared to miR155 inhibitor transfected cells and showed a marked reduction of cell viability in miR-155 inhibitor transfected cells when compared to MOCK cells. The comparative analysis of percentage of inhibition between miR-155 transfected K562 and untreated cells showed that transfection of K562 cells with miR-155 inhibitor suppresses the cell proliferation and showed marked decline in tumor load. As the percentage of inhibition for miR-155 inhibited cells was 85% compared to untreated cells.
The expression level of miR-155, CEBPB and SHIP1 were measured in cultured cell lines after transfection with miR-155 inhibitor using qPCR; the expression level was normalized to MOCK cells and our results revealed that all cultured K562 cells shows marked reduction in the miR-155gene expression by 0.01 folds compared to untreated cells. And marked increased in the CEBPB and SHIP1 genes expression by 4.4 folds and 16.7 folds respectively compared to untreated cells.
Conclusion
It could be concluded that the current study has been validated the significance of knock-down miR-155 expression in human AML cell lines (K562). In addition, it was also suggested that miR-155 have an oncogenic role and inhibition of miR-155 was verified to have a tumor suppressive role. And that miR-155 might be used as therapeutic target in acute myeloid leukemia patients in the future.