title: Protein phosphatase 1 (PP1) and Casein Kinase II (CK2) regulate Ikaros-mediated repression of TdT in thymocytes and T-cell leukemia.
abstract: BACKGROUND
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: School of Pharmacology, Wenzhou Medical University, Wenzhou, China; Pennsylvania State University College of Medicine, Hershey, Pennsylvania; College of Animal Sciences, Jilin University, Changchun, China.
authors.forename: Haijun
authors.initials: H
authors.lastname: Wang
authors.forename: Chunhua
authors.initials: C
authors.lastname: Song
authors.forename: Zafer
authors.initials: Z
authors.lastname: Gurel
authors.forename: Na
authors.initials: N
authors.lastname: Song
authors.forename: Jisheng
authors.initials: J
authors.lastname: Ma
authors.forename: Hongsheng
authors.initials: H
authors.lastname: Ouyang
authors.forename: Liangxue
authors.initials: L
authors.lastname: Lai
authors.forename: Kimberly J
authors.initials: KJ
authors.lastname: Payne
authors.forename: Sinisa
authors.initials: S
authors.lastname: Dovat
mesh_terms: D000818:Animals; D047390:Casein Kinase II / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation; D002478:Cells, Cultured; D004253:DNA Nucleotidylexotransferase / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D051740:Ikaros Transcription Factor / Q000235:genetics / Q000378:metabolism*; D015458:Leukemia, T-Cell / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D051379:Mice; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D054645:Protein Phosphatase 1 / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D050436:Regulatory Elements, Transcriptional; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D060168:Thymocytes / Q000166:cytology / Q000378:metabolism*
chemical_list: D012333:RNA, Messenger; D051740:Ikaros Transcription Factor; D047390:Casein Kinase II; D004253:DNA Nucleotidylexotransferase; D054645:Protein Phosphatase 1
keywords: CK2; IKZF1; Ikaros; PP1; TdT; leukemia