Studies On Regulation Of KDM5B Expression By Ikaros And CK2in Human Leukemia

Ikaros is an important regulator in blood cell differentiation and development,which plays a critical transcription factor role in the early development ofhematopoietic cells and progenitor cells differentiated into the three main blood celllines (Erythroid cells, Lymphocytes, Myelocytes). Ikaros protein’s mutation willdirectly lead to the blood system diseases. It has been found that Ikaros gene deletionin the patient with hematologic malignancy (mainly Pre-B ALL leukemia), will resultin the occurrence of leukemia in human.Ikaros protein can bind to KDM5B upstream regulatory sequences along withHDAC1, and then cause chromatin histone modifications and chromatin structureremodeling, finally inhibit oncogene KDM5B’s transcription and expression. Whenuse the HDAC1inhibitor TSA or MS-275treatment, which could alleviate Ikaros’srepression effect on KDM5B gene transcription and expression.In human cells, Ikaros’s bilogical function is regulated by some protein enzymes,including casine kinase2(CK2) and protein phosphatase1(PP1). According toDovat’s research and other studies, Ikaros has several sites which can bephosphorylated by CK2. After the phosphorylation, Ikaros will be degradation in thefurther pathway of ubiquitination/lysosomal. The dephosphorylation of Ikaros isregulated by the protein phosphatase1(PP1). Through RVXF motif is identified byPP1, Ikaros can be dephosphorylated.In this study, We used Ikaros mutants to explore the interaction between Ikarosand KDM5B transcription. mIkaros-VI-A11, which has11sites Ala mutantion, couldbe against the phosphorylation of CK2and then enhance the activity of Ikaros inorder to suppress KDM5B’s transcription and expression. mIkaros-VI-D5, which has5sites Asp mutation, could promote the phosphorylation of CK2, but induce thetranscription and expression of KDM5B regulated by Ikaros.TBB is an inhibitor of CK2. When the leukemia cell lines were treated with TBB,The biological activity of Ikaros was enhanced and the expression of KDM5B wasinhibited. TBB can inhibit the activity of CK2, but not the expression level. The inbition effect of Ikaros on KDM5B could be restored when Nalm6cell lines whichwere transfected with shRNA-Ikaros. And that could increase the transcription andexpression of KDM5B.Meanwhile, when the cells from Pre-B ALL leukemia patient were treated withTBB or without TBB, the changes were accessed through the ChIP and ChIP-qPCR.Pre-B ALL is highly risk malignant pre-B acute lymphoblastic leukemia. In the Pre-BALL cells,an allele Ikaros is deleted, it is a single copy Ikaros, so the Ikaros can notplay the role normally in the cells, and this type patients have a high rate of recurrenceafter curing. Compared this two group, we found that HDAC1, H3K27me3andH3K4me3would increase, but H3K9ac would decreased by ChIP-PCR.Moreover, from Chip-seq results shown, Ikaros-HDAC1complex was binding toKDM5B upstream regulatory sequence, which could result in histone modificationsand chromatin remodeling. These changes included the reduction of histone H3K9acetylation, high expression of H3K27methylation and H3K4methylation.In summary, Ikaros suppress KDM5B gene expression through the regulation ofhistone modifications and chromatin remodeling. These datas will be useful forfurther to explore the mechanism of Irkaros and the treatment with KDM5B forhuman leukemia.