title: Loss of genomic imprinting of insulin-like growth factor 2 is strongly associated with cellular proliferation in normal hematopoietic cells.
abstract: OBJECTIVE
  The human insulin-like growth factor 2 (IGF2) gene was thought to be imprinted and expressed only from the paternal allele in normal tissue.
  
  
  METHODS
  Initially, we analyzed the imprinting status of IGF2 in bone marrow cells from 49 patients with myelodysplastic syndromes (MDS) utilizing the Apa I polymorphism of IGF2. Thirteen bone marrow and 14 peripheral blood samples from normal individuals served as controls. We utilized normal peripheral blood T lymphocytes to examine the relationship between genomic imprinting and cell proliferation. Expression of IGF2 was quantified by real-time PCR and proliferation of T cells was measured by 3H-thymidine incorporation. Furthermore, methylation status of the imprinting controlling region (ICR) was analyzed by subcloning and sequencing of genomic DNA after sodium bisulfite modification.
  
  
  RESULTS
  Among 24 patients who were heterozygous for IGF2, loss of imprinting (LOI) occurred in 22 cases (92%). Surprisingly, LOI of IGF2 occurred in the normal bone marrow cells, but the normal peripheral blood cells showed retention of imprinting (ROI). Unstimulated normal T cells showed ROI. After 24 hours of exposure to PHA, these cells changed their IGF2 imprinting status from ROI to LOI. Concomitantly, their IGF2 RNA levels increased up to sixfold and their proliferation increased 10- to 20-fold. In contrast, normal T cells not stimulated with PHA did not develop LOI of IGF2, had negligible levels of IGF2 RNA, and did not increase their proliferation. In unstimulated T cells, the CpG islands of the ICR were completely methylated on one allele and nearly completely unmethylated on the other allele. After PHA stimulation, the CpG islands at the ICR became completely methylated on both alleles.
  
  
  CONCLUSIONS
  LOI of IGF2 is strongly associated with cell proliferation and is not limited to cancer cells.
authors.affiliation: Division of Hematology/Oncology, Cedars Sinai Research Institute, UCLA School of Medicine, Los Angeles, CA, USA. W.K.Hofmann@em.uni-frankfurt.de
authors.forename: Wolf K
authors.initials: WK
authors.lastname: Hofmann
authors.forename: Seisho
authors.initials: S
authors.lastname: Takeuchi
authors.forename: Malka A
authors.initials: MA
authors.lastname: Frantzen
authors.forename: Dieter
authors.initials: D
authors.lastname: Hoelzer
authors.forename: H Phillip
authors.initials: HP
authors.lastname: Koeffler
mesh_terms: D001854:Bone Marrow Cells / Q000378:metabolism / Q000473:pathology; D016022:Case-Control Studies; D002455:Cell Division; D018899:CpG Islands / Q000235:genetics; D019175:DNA Methylation; D005260:Female; D018392:Genomic Imprinting; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D007335:Insulin-Like Growth Factor II / Q000235:genetics*; D008297:Male; D009190:Myelodysplastic Syndromes / Q000473:pathology; D011110:Polymorphism, Genetic; D012333:RNA, Messenger / Q000096:biosynthesis; D013601:T-Lymphocytes / Q000166:cytology / Q000378:metabolism
chemical_list: D012333:RNA, Messenger; D007335:Insulin-Like Growth Factor II