title: [Mechanisms regulating p21 gene expression by retinoic acid-induced gene G protein].
abstract: OBJECTIVE
  To investigate the mechanisms by which retinoic acid-induced gene G (RIG-G) protein regulates p21 gene expression.
  
  
  METHODS
  Western blot was used to detect the effects of RIG-G protein overexpression on p21 protein expression level in leukemia cell line NB4 cells and the phosphorylation of both c-Jun and JNK in U937 cells. The c-Jun expression plasmid and p21 gene promoter-containing reporter plasmid were co-transfected into 293T cells, to explore the regulatory effect of c-Jun protein on p21 gene expression by luciferase reporter assay.
  
  
  RESULTS
  Western blot showed that the overexpression of RIG-G protein significantly upregulated p21 protein level in the NB4 cells, and the level of p21 protein largely increased along with the induction of endogenous RIG-G protein during the differentiation of NB4 cells treated by all-trans retinoic acid (ATRA). Moreover, the phosphorylation of both c-Jun and JNK decreased in RIG-G-overexpressing U937 cells while total c-Jun and JNK proteins remained unchanged. After using the JNK inhibitor SP600125 to block JNK phosphorylation, the level of c-Jun phosphorylation was still dramatically reduced in the RIG-G-overexpressing U937T-RIG-G cells, compared with the control U937T-pTRE cells. These results indicated that the inhibitory effect of Rig-G protein on c-Jun phosphorylation could not only be through the JNK pathway, but also via some JNK-independent pathways. Luciferase reporter assay showed that when 0.1, 0.5, 1.0 and 2.0 µg c-Jun-expressing plasmids were respectively transfected into 293T cells, compared with the empty vector-transfected group, the relative luciferase activities were (83.0 ± 1.7)%, (73.7 ± 0.7)%, (68.9 ± 0.9)% and (64.1 ± 0.9)%, indicating that the transcriptional activity of p21 gene could be inhibited by c-Jun protein.
  
  
  CONCLUSIONS
  RIG-G protein may suppress the phosphorylation of c-Jun protein through different signal pathways, thereby increasing the expression of p21 gene, arresting the cell cycle and inhibiting the cell growth in U937 cells.
authors.affiliation: Faculty of Medical Laboratory Science, State Key Laboratory of Medical Genomics, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai 200025, China.
authors.forename: Qingping
authors.initials: Q
authors.lastname: Zou
authors.affiliation: Faculty of Medical Laboratory Science, State Key Laboratory of Medical Genomics, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai 200025, China.
authors.forename: Guiping
authors.initials: G
authors.lastname: Xu
authors.affiliation: Faculty of Medical Laboratory Science, State Key Laboratory of Medical Genomics, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai 200025, China.
authors.forename: Likun
authors.initials: L
authors.lastname: Zhuang
authors.affiliation: Faculty of Medical Laboratory Science, State Key Laboratory of Medical Genomics, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai 200025, China.
authors.forename: Zhanglin
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Faculty of Medical Laboratory Science, State Key Laboratory of Medical Genomics, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai 200025, China.
authors.forename: Weiwei
authors.initials: W
authors.lastname: Yan
authors.affiliation: Faculty of Medical Laboratory Science, State Key Laboratory of Medical Genomics, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai 200025, China.
authors.forename: Yingting
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Faculty of Medical Laboratory Science, State Key Laboratory of Medical Genomics, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai 200025, China.
authors.forename: Yejiang
authors.initials: Y
authors.lastname: Lou
authors.affiliation: Faculty of Medical Laboratory Science, State Key Laboratory of Medical Genomics, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai 200025, China. Email: jh_tong@126.com.
authors.forename: Jianhua
authors.initials: J
authors.lastname: Tong
mesh_terms: D002453:Cell Cycle; D002454:Cell Differentiation; D002460:Cell Line; D049109:Cell Proliferation; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics* / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D017930:Genes, Reporter; D010766:Phosphorylation; D015398:Signal Transduction; D014162:Transfection; D014212:Tretinoin / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: D050759:Cyclin-Dependent Kinase Inhibitor p21; D014212:Tretinoin; D019204:GTP-Binding Proteins