title: Induction of DNA synthesis by ligation of the CD53 tetraspanin antigen in primary cultures of mesangial cells.
abstract: BACKGROUND
  The interaction of mesangial cells with the extracellular matrix plays a major role in kidney biology. Tetraspanin proteins modulate cell interaction with the extracellular matrix. Tetraspanins form supramolecular structures on the cell membrane that send signals after engagement by unknown ligands, modulate different signaling processes, and regulate cell adhesion and motility.
  
  
  METHODS
  CD53 was determined by immunohistochemistry, and on the cell surface of cultured rat mesangial cells by flow cytometry. Mesangial cell cultures were stimulated with MRC OX-44 antibody. DNA synthesis was measured by thymidine incorporation. Extracellular signal-regulated kinase (ERK) activation was determined by Western blot.
  
  
  RESULTS
  CD53 was present in mesangial cells in vivo and in culture. Ligation of CD53 antigen with a monoclonal antibody triggered the induction of DNA synthesis, which was not sensitive to inhibitors of signaling pathways that use phosphatidylinositol 3-kinase (PI3K) and protein kinase C, or to calcium channel inhibitors, such as thapsigargin and verapamil. The DNA synthesis was inhibited by PD98059, a specific inhibitor of MEK that prevents ERK1/ERK2 activation. In addition, ERK1 and ERK2 activation by phosphorylation occurred following CD53 antigen ligation. The DNA synthesis was due to de novo synthesis and not to DNA repair as a consequence of the initiation of apoptosis, determined by flow cytometry, and lack of proteolytic activation of PARP by caspase 3. CD53 antigen ligation also induced an increase in mitochondrial activity.
  
  
  CONCLUSIONS
  To our knowledge this is the first identification of a tetraspanin protein in mesangial cells. CD53 antigen delivers a signal that initiates DNA synthesis. This signal is mediated by ERK1/ERK2 activation, but it is not sufficient to complete the cell cycle.
authors.affiliation: Centro de Investigación del Cáncer, Instituto de Biología Molecular y Celular del Cáncer, Consejo Superior deInvestigaciones Científicas, Universidad de Salamanca, Salamanca, Spain.
authors.forename: Mónica
authors.initials: M
authors.lastname: Yunta
authors.forename: Alicia
authors.initials: A
authors.lastname: Rodríguez-Barbero
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Arévalo
authors.forename: José M
authors.initials: JM
authors.lastname: López-Novoa
authors.forename: Pedro A
authors.initials: PA
authors.lastname: Lazo
mesh_terms: D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D015703:Antigens, CD / Q000276:immunology / Q000378:metabolism*; D000945:Antigens, Differentiation, T-Lymphocyte / Q000276:immunology / Q000378:metabolism*; D002453:Cell Cycle / Q000502:physiology; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis*; D005920:Glomerular Mesangium / Q000166:cytology / Q000378:metabolism*; D007150:Immunohistochemistry; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction / Q000502:physiology; D060265:Tetraspanin 25
chemical_list: D000906:Antibodies; D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; C554896:Cd53 protein, rat; D060265:Tetraspanin 25; D004247:DNA; D020928:Mitogen-Activated Protein Kinases