title: Phosphorylation of transglutaminase 2 (TG2) at serine-216 has a role in TG2 mediated activation of nuclear factor-kappa B and in the downregulation of PTEN.
abstract: BACKGROUND
  Transglutaminase 2 (TG2) and its phosphorylation have been consistently found to be upregulated in a number of cancer cell types. At the molecular level, TG2 has been associated with the activation of nuclear factor-kappa B (NF-κB), protein kinase B (PKB/Akt) and in the downregulation of phosphatase and tensin homologue deleted on chromosome 10 (PTEN). However, the underlying mechanism involved is not known. We have reported that protein kinase A (PKA) induced phosphorylation of TG2 at serine-216 (Ser(216)) regulates TG2 function and facilitates protein-protein interaction. However, the role of TG2 phosphorylation in the modulation of NF-κB, Akt and PTEN is not explored.
  
  
  METHODS
  In this study we have investigated the effect of TG2 phosphorylation on NF-κB, Akt and PTEN using embryonic fibroblasts derived from TG2 null mice (MEF(tg2-/-)) overexpressing native TG2 or mutant-TG2 (m-TG2) lacking Ser(216) phosphorylation site with and without dibutyryl cyclic-AMP (db-cAMP) stimulation. Functional consequences on cell cycle and cell motility were determined by fluorescence activated cell sorting (FACS) analysis and cell migration assay respectively.
  
  
  RESULTS
  PKA activation in TG2 overexpressing MEF(tg2-/-) cells resulted in an increased activation of NF-κB and Akt phosphorylation in comparison to empty vector transfected control cells as determined by the reporter-gene assay and immunoblot analysis respectively. These effects were not observed in MEF(tg2-/-) cells overexpressing m-TG2. Similarly, a significant downregulation of PTEN at both, the mRNA and protein levels were found in cells overexpressing TG2 in comparison to empty vector control and m-TG2 transfected cells. Furthermore, Akt activation correlated with the simultaneous activation of NF-κB and a decrease in PTEN suggesting that the facilitatory effect of TG2 on Akt activation occurs in a PTEN-dependent manner. Similar results were found with MCF-7 and T-47D breast cancer cells overexpressing TG2 and m-TG2 further supporting the role of TG2 phosphorylation in NF-κB activation and in the downregulation of PTEN.
  
  
  CONCLUSIONS
  Collectively, these data suggest that phosphorylation of TG2 at Ser(216) plays a role in TG2 mediated activation of NF-κB, Akt and in the downregulation of PTEN. Blocking TG2 phosphorylation may provide a novel strategy to attenuate NF-κB activation and downregulation of PTEN in TG2 overexpressing cancers.
authors: Department of Internal Medicine, University of Manitoba, 843 JBRC/715 McDermot Avenue, Winnipeg, MB R3E 3P4, Canada.
authors: Yi
authors: Y
authors: Wang
authors: Sudharsana R
authors: SR
authors: Ande
authors: Suresh
authors: S
authors: Mishra
mesh_terms: D000818:Animals; D002453:Cell Cycle / Q000502:physiology; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D015536:Down-Regulation; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism*; D051059:PTEN Phosphohydrolase / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012694:Serine / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D011503:Transglutaminases / Q000235:genetics / Q000378:metabolism*
chemical_list: D016328:NF-kappa B; D012333:RNA, Messenger; D012694:Serine; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D051057:Proto-Oncogene Proteins c-akt; D017868:Cyclic AMP-Dependent Protein Kinases; D051059:PTEN Phosphohydrolase; C487757:Pten protein, mouse; D019204:GTP-Binding Proteins