title: The gene expression signature of anagrelide provides an insight into its mechanism of action and uncovers new regulators of megakaryopoiesis.
abstract: BACKGROUND
  Anagrelide is a cytoreductive agent used to lower platelet counts in essential thrombocythemia. Although the drug has been known to selectively inhibit megakaryopoiesis for many years, the molecular mechanism accounting for this activity is still unclear.
  
  
  OBJECTIVE
  To address this issue we have compared the global gene expression profiles of human hematopoietic cells treated ex-vivo with and without anagrelide while growing under megakaryocyte differentiation conditions, using high-density oligonucleotide microarrays. Gene expression data were validated by the quantitative polymerase chain reaction and mined to identify functional subsets and regulatory pathways.
  
  
  RESULTS
  We identified 328 annotated genes differentially regulated by anagrelide, including many genes associated with platelet functions and with the control of gene transcription. Prominent among the latter was TRIB3, whose expression increased in the presence of anagrelide. Pathway analysis revealed that anagrelide up-regulated genes that are under the control of the transcription factor ATF4, a known TRIB3 inducer. Notably, immunoblot analysis demonstrated that anagrelide induced the phosphorylation of eIF2α, which is an upstream regulator of ATF4, and increased ATF4 protein levels. Furthermore, salubrinal, an inhibitor of eIF2α dephosphorylation, increased the expression of ATF4-regulated genes and blocked megakaryocyte growth.
  
  
  CONCLUSIONS
  These findings link signaling through eIF2α/ATF4 to the anti-megakaryopoietic activity of anagrelide and identify new potential modulators of megakaryopoiesis.
authors: School of Health Sciences, Cardiff Metropolitan University, Cardiff, UK.
authors: M
authors: M
authors: Ahluwalia
authors: School of Health Sciences, Cardiff Metropolitan University, Cardiff, UK.
authors: L
authors: L
authors: Butcher
authors: School of Health Sciences, Cardiff Metropolitan University, Cardiff, UK.
authors: H
authors: H
authors: Donovan
authors: School of Health Sciences, Cardiff Metropolitan University, Cardiff, UK.
authors: C
authors: C
authors: Killick-Cole
authors: School of Health Sciences, Cardiff Metropolitan University, Cardiff, UK.
authors: P M
authors: PM
authors: Jones
authors: School of Health Sciences, Cardiff Metropolitan University, Cardiff, UK.
authors: J D
authors: JD
authors: Erusalimsky
mesh_terms: D051701:Activating Transcription Factor 4 / Q000235:genetics / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D049109:Cell Proliferation; D002478:Cells, Cultured; D019295:Computational Biology; D030541:Databases, Genetic; D015852:Eukaryotic Initiation Factor-2 / Q000235:genetics / Q000378:metabolism; D020869:Gene Expression Profiling / Q000379:methods; D005786:Gene Expression Regulation; D053263:Gene Regulatory Networks; D006401:Hematologic Agents / Q000494:pharmacology*; D006801:Humans; D008533:Megakaryocytes / Q000187:drug effects* / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D011799:Quinazolines / Q000494:pharmacology*; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D034061:Thrombopoiesis / Q000187:drug effects* / Q000235:genetics; D013997:Time Factors
chemical_list: C497109:ATF4 protein, human; D018797:Cell Cycle Proteins; D015852:Eukaryotic Initiation Factor-2; D006401:Hematologic Agents; D011799:Quinazolines; D012097:Repressor Proteins; C474831:TRIB3 protein, human; D051701:Activating Transcription Factor 4; D017346:Protein Serine-Threonine Kinases; C021139:anagrelide
keywords: activating transcription factor 4; anagrelide; eukaryotic initiation factor-2, alpha subunit; megakaryocyte; thrombocytosis