title: Extracellular transglutaminase 2 has a role in cell adhesion, whereas intracellular transglutaminase 2 is involved in regulation of endothelial cell proliferation and apoptosis.
abstract: OBJECTIVE
  Transglutaminase 2 (TG2) is a multifunctional protein with an important role in vascular biology, where it is involved in cell-matrix interaction, cell attachment and cell population expansion. In efforts to elucidate the role of TG2 in endothelial cell biology, in this study, we measured several endothelial cell characteristics in cells where TG2 was specifically knocked down by RNAi.
  
  
  METHODS
  The effect of small interfering RNA (siRNA)-TG2 on human umbilical vein endothelial cells was studied. Adhesion and cell viability were assessed by chemical reduction of MTT, and cell proliferation was analysed by flow cytometry. Apoptosis was evaluated by annexin V/PI dual staining and protein expression level was assayed by western blotting.
  
  
  RESULTS
  We found that siRNA-TG2 reduced endothelial cell number, lead to cell adhesion deficiency, cell cycle arrest in G₁ phase and induction of apoptosis. Our results show that exogenously added TG2 could reverse loss of adhesion but did not overcome the defect in cell proliferation, nor could it inhibit siRNA-TG2-induced apoptosis.
  
  
  CONCLUSIONS
  We conclude that TG2 loss in endothelial cells causes reduction in cell number as a result of cell cycle arrest, flaws in adhesion and induction of apoptosis. Our results imply that reduction in cell number and increased apoptosis in response to TG2 silencing is independent of the cell adhesion process. Altogether, our findings underline the significance of TG2 in endothelial cell cycle progression and cell survival, in vitro.
authors.affiliation: Paediatric Research Centre, University of Tampere and Tampere University Hospital, Tampere, Finland.
authors.forename: C
authors.initials: C
authors.lastname: Nadalutti
authors.forename: K M
authors.initials: KM
authors.lastname: Viiri
authors.forename: K
authors.initials: K
authors.lastname: Kaukinen
authors.forename: M
authors.initials: M
authors.lastname: Mäki
authors.forename: K
authors.initials: K
authors.lastname: Lindfors
mesh_terms: D017304:Annexin A5 / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects* / Q000235:genetics; D002448:Cell Adhesion / Q000187:drug effects* / Q000235:genetics; D002453:Cell Cycle / Q000187:drug effects / Q000235:genetics; D049109:Cell Proliferation / Q000187:drug effects*; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D015536:Down-Regulation / Q000187:drug effects; D042783:Endothelial Cells / Q000187:drug effects*; D005434:Flow Cytometry; D016650:Fluorescein-5-isothiocyanate / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000502:physiology*; D055785:Gene Knockdown Techniques; D006801:Humans; D010590:Phalloidine / Q000378:metabolism; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D034622:RNA Interference / Q000187:drug effects; D034741:RNA, Small Interfering / Q000235:genetics / Q000494:pharmacology; D011503:Transglutaminases / Q000502:physiology*; D014471:Umbilical Veins / Q000166:cytology
chemical_list: D017304:Annexin A5; D005456:Fluorescent Dyes; D034741:RNA, Small Interfering; D010590:Phalloidine; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D019204:GTP-Binding Proteins; D016650:Fluorescein-5-isothiocyanate