casein-kinase-ii and Leukemia--T-Cell

Ikaros is a DNA-binding protein that acts as master-regulator of hematopoiesis and a tumor suppressor. In thymocytes and T-cell leukemia, Ikaros negatively regulates transcription of terminal deoxynucleotide transferase (TdT), a key protein in lymphocyte differentiation. The signaling pathways that regulate Ikaros-mediated repression of TdT are unknown. Our previous work identified Casein Kinase II (CK2) and Protein Phosphatase 1 (PP1) as regulators of Ikaros DNA binding activity. Here, we investigated the role of PP1 and CK2 in regulating Ikaros-mediated control of TdT expression.. Ikaros phosphomimetic and phosphoresistant mutants and specific CK2 and PP1 inhibitors were used in combination with quantitative chromatin immunoprecipitation (qChIP) and quantitative reverse transcriptase-PCR (q RT-PCR) assays to evaluate the role of CK2 and PP1 in regulating the ability of Ikaros to bind the TdT promoter and to regulate TdT expression.. We demonstrate that phosphorylation of Ikaros by pro-oncogenic CK2 decreases Ikaros binding to the promoter of the TdT gene and reduces the ability of Ikaros to repress TdT expression during thymocyte differentiation. CK2 inhibition and PP1 activity restore Ikaros DNA-binding affinity toward the TdT promoter, as well as Ikaros-mediated transcriptional repression of TdT in primary thymocytes and in leukemia.. These data establish that PP1 and CK2 signal transduction pathways regulate Ikaros-mediated repression of TdT in thymocytes and leukemia. These findings reveal that PP1 and CK2 have opposing effects on Ikaros-mediated repression of TdT and establish novel roles for PP1 and CK2 signaling in thymocyte differentiation and leukemia.

Topics: Animals; Casein Kinase II; Cell Differentiation; Cells, Cultured; DNA Nucleotidylexotransferase; Humans; Ikaros Transcription Factor; Leukemia, T-Cell; Mice; Phosphorylation; Promoter Regions, Genetic; Protein Phosphatase 1; Real-Time Polymerase Chain Reaction; Regulatory Elements, Transcriptional; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Signal Transduction; Thymocytes

Aberrant activation of Wnt/β-catenin signaling has been implicated in carcinogenesis. Identification of inhibitors of this pathway may help in cancer therapy. The purpose of this study is to investigate the inhibitory effect of 3-methoxyapigenin (3-MA) with β-catenin/LEF reporter system. The anti-cancer mechanisms in Jurkat leukemic cells were also examined.. HEK 293-TOP/FOP reporter cells were used to determine the inhibitory effect of 3-MA on Wnt/β-catenin pathway. We also used Jurkat-TOP reporter cells to confirm the inhibitory effect and the action mechanisms of 3-MA. Target genes and cell proliferation were analyzed by RT-PCR and (3)H-thymidine uptake assay. The effects of 3-MA on β-catenin phosphorylation was determined by Western blotting and by in vitro kinase assays. β-catenin translocation and its transactivation were verified by cellular fractionation and EMSA.. 3-MA inhibited Wnt-3A-induced luciferase activity in the HEK 293-TOP/FOP reporter system. Western blotting analysis showed that phosphorylation sites in β-catenin by glycogen synthase kinase-3β (GSK-3β) and casein kinase 2 (CK2) were inhibited by 3-MA in Jurkat. In parallel, in vitro kinase assays verified this effect. As a result, total β-catenin turnover remained balanced by this dual inhibitory effect of 3-MA. Although the β-catenin protein level remained unchanged, 3-MA did inhibit β-catenin translocation. Finally, we found that the β-catenin/LEF transcriptional activity, expression of c-myc and cyclin-D3, and cell proliferation were inhibited by 3-MA.. 3-MA modulates the turnover of β-catenin and suppresses the Wnt/β-catenin signaling pathway through inhibition of β-catenin translocation. We suggested that 3-MA has potential as an anti-cancer drug.

Topics: Anthocyanins; Antineoplastic Agents, Phytogenic; Apigenin; beta Catenin; Casein Kinase II; Cell Proliferation; Cyclin D3; Gene Expression Regulation, Leukemic; Genes, myc; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; HEK293 Cells; Humans; Jurkat Cells; Leukemia, T-Cell; Protein Stability; Protein Transport; Wnt Proteins; Wnt Signaling Pathway; Zingiberaceae

The loss of Ikaros is associated with the development of B and T cell leukemia. Data on Ikaros function, including its role as a tumor suppressor and a regulator of cell cycle progression, come almost exclusively from murine studies; little is known of the mechanisms that regulate human Ikaros function. Our studies are the first to examine the function and regulation of human Ikaros isoforms during the cell cycle in human ALL.. Electromobility shift assay (EMSA), confocal microscopy, and phosphopeptide mapping were used to study Ikaros function during different stages of the cell cycle.. The DNA-binding activity of human Ikaros complexes undergoes dynamic changes as the cell cycle progresses. In S phase, Ikaros DNA-binding affinity for regulatory regions of its target genes decreases, while its binding to pericentromeric heterochromatin is preserved and correlates with Ikaros pericentromeric localization. These S phase-specific changes in Ikaros function are controlled by phosphorylation via the CK2 kinase pathway. During cell cycle progression, the subcellular pericentromeric localization of the largest human Ikaros isoforms is different from that in mouse cells, suggesting unique functions for human Ikaros.. Our results demonstrate that the function of Ikaros is cell cycle-specific and controlled by CK2-mediated phosphorylation during S phase of the cell cycle in human T-cell and B-cell ALL. The differences we observe in murine and human Ikaros function highlight the importance of using human cells in studies of ALL. These data identify the CK2 pathway as a target for therapies in ALL.

Topics: Casein Kinase II; Cell Line, Tumor; Gene Expression Regulation, Leukemic; Humans; Ikaros Transcription Factor; Leukemia, B-Cell; Leukemia, T-Cell; Neoplasm Proteins; Phosphorylation; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Protein Isoforms; S Phase

We have isolated a mouse cDNA clone corresponding to a novel isoform of the NBMPR-sensitive equilibrative nucleoside transporter (ENT1). The cDNA contains a 6 bp deletion in the open reading frame that changes the amino acid composition in a consensus casein kinase II (CKII) phosphorylation site at Ser-254. The clone containing Ser-254 is termed mENT1.1 and the clone lacking the serine termed mENT1.2. The deduced amino acid sequence of mENT1.1 corresponds to the previously cloned human and rat ENT1 proteins at Ser-254. Tissue distribution studies show that mRNA for both ENT1 isoforms are ubiquitously co-expressed in mouse. Analysis of genomic DNA corresponding to mouse ENT1 indicates the isoforms can be produced by alternative splicing at the end of exon 7. CEM/C19 cells stably expressing mENT1.1 and mENT1.2 show similar dose response curves for NBMPR and dipyridamole inhibition of [(3)H]adenosine uptake as well as exhibiting comparable selectivity for both purine and pyrimidine nucleosides but not the corresponding nucleobases.

Topics: Amino Acid Sequence; Animals; Carrier Proteins; Casein Kinase II; Cloning, Molecular; Dipyridamole; Equilibrative Nucleoside Transporter 1; Gene Expression Regulation; Humans; Inhibitory Concentration 50; Leukemia, T-Cell; Membrane Proteins; Mice; Molecular Sequence Data; Nucleoside Transport Proteins; Phosphorylation; Protein Isoforms; Protein Serine-Threonine Kinases; Rats; Sequence Homology, Amino Acid; Thioinosine; Tumor Cells, Cultured