title: TGM2 inhibition attenuates ID1 expression in CD44-high glioma-initiating cells.
abstract: BACKGROUND
  CD44 is a molecular marker associated with cancer stem cell populations and treatment resistance in glioma. More effective therapies will result from approaches aimed at targeting glioma cells high in CD44.
  
  
  METHODS
  Glioma-initiating cell lines were derived from fresh surgical glioblastoma samples. Expression of tissue transglutaminase 2 (TGM2) was attenuated through lentivirus-mediated short hairpin RNA knockdown. MTT assay [(3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] was used to evaluate the growth inhibition induced by TGM2 inhibitor. Terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling was used to evaluate cell apoptosis following TGM2 inhibition. CD44(+) glioma stem cells were sorted by flow cytometry. A nude mice orthotopic xenograft model was used to evaluate the in vivo effect of TGM2 inhibitor.
  
  
  RESULTS
  TGM2 was highly expressed in CD44-high glioblastoma tissues and tumor-derived glioma-initiating cell lines. TGM2 knockdown impaired cell proliferation and induced apoptosis in CD44-high glioma-initiating cell lines. Further studies indicated that expression of inhibitor of DNA binding 1 protein (ID1) is regulated by TGM2 and might be an important mediator for TGM2-regulated cell proliferation in CD44-high glioma-initiating cell lines. TGM2 inhibitor reduces ID1 expression, suppresses cell proliferation, and induces apoptosis in CD44-high glioma-initiating cell lines. Furthermore, TGM2 is highly expressed in CD44(+) glioma stem cells, while pharmacological inhibition of TGM2 activity preferentially eliminates CD44(+) glioma stem cells. Consistently, TGM2 inhibitor treatment reduced ID1 expression and induced apoptosis in our orthotopic mice xenograft model, which can be translated into prolonged median survival in tumor-bearing mice.
  
  
  CONCLUSIONS
  TGM2 regulates ID1 expression in glioma-initiating cell lines high in CD44. Targeting TGM2 could be an effective strategy to treat gliomas with high CD44 expression.
authors.affiliation: Corresponding Author: Zhong-ping Chen, MD, PhD, Department of Neurosurgery/Neuro-oncology, Cancer Center, Sun Yat-Sen University, Guangzhou 510060, China. chenzp57@mail.sysu.edu.cn.
authors.forename: Jun
authors.initials: J
authors.lastname: Fu
authors.forename: Qun-ying
authors.initials: QY
authors.lastname: Yang
authors.forename: Ke
authors.initials: K
authors.lastname: Sai
authors.forename: Fu-rong
authors.initials: FR
authors.lastname: Chen
authors.forename: Jesse C S
authors.initials: JC
authors.lastname: Pang
authors.forename: Ho-keung
authors.initials: HK
authors.lastname: Ng
authors.forename: Aij-lie
authors.initials: AL
authors.lastname: Kwan
authors.forename: Zhong-ping
authors.initials: ZP
authors.lastname: Chen
mesh_terms: D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D001932:Brain Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D002453:Cell Cycle; D049109:Cell Proliferation; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D005910:Glioma / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D018960:Hyaluronan Receptors / Q000378:metabolism*; D007124:Immunoenzyme Techniques; D051798:Inhibitor of Differentiation Protein 1 / Q000378:metabolism*; D051379:Mice; D008819:Mice, Nude; D014411:Neoplastic Stem Cells / Q000378:metabolism* / Q000473:pathology*; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D034741:RNA, Small Interfering / Q000235:genetics; D011503:Transglutaminases / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: C497483:CD44 protein, human; D018960:Hyaluronan Receptors; C497453:ID1 protein, human; D051798:Inhibitor of Differentiation Protein 1; D034741:RNA, Small Interfering; C000717608:TGM2 protein, human; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D019204:GTP-Binding Proteins
keywords: apoptosis; cell proliferation; glioma; tissue transglutaminase; tumor initiating cells