[Regulatory effect of Smad7 gene on MAPK signal pathway in malignant transformation of immortalized human bronchial epithelial BEP2D cells].
OBJECTIVE
Smad7 is an inhibitor of transforming growth factor-beta (TGF-beta) signal pathway. TGF-beta could induce the expression of several genes through activating SMAD and ras/MEK/ERK pathways. This study was to determine whether Smad7 is involved in regulating mitogen-activated protein kinase (MAPK) signal pathway with TGF-beta in malignant transformation of human bronchial epithelial BEP2D cells.


METHODS
Immortalized BEP2D cells and malignant BERP35T2 cells were co-transfected with full-length Smad7 cDNA constructed pCISmad7.neo or Smad7 siRNA, transactivator vector pTet-Elk or pTet-Jun, and reporter vector pTRE-Luc, and stimulated with TGF-beta. The regulatory effect of Smad7 on MAPK signal pathway was investigated by standard luciferase assay.


RESULTS
In BEP2D cells, when treated with TGF-beta1, phosphorylated activities of Elk and Jun were up-regulated (P(Elk)=0.033, P(Jun)=0.016); after co-transfection of Elk or Jun with pCISmad7.neo, phosphorylated activity of Elk was increased, and that of Jun was decreased (P(Elk)=0.017, P(Jun)=0.028); after co-transfection of Elk or Jun with Smad7 siRNA, phosphorylated activity of Elk was decreased, and that of Jun was increased (P(Elk)=0.018, P(Jun)=0.005). In BERP35T2 cells, when treated with TGF-beta1, phosphorylated activity of Elk was up-regulated (P=0.006); after co-transfection of Elk and Smad7 siRNA, phosphorylated activity of Elk was decreased (P=0.000); no activity of Jun was detected in BERP35T2 cells.


CONCLUSIONS
In the process of malignant transformation of BEP2D cells, the intervention of Smad7 in MAPK signal pathway leads to the activity imbalance between extracellular signal-related protein kinase (ERK) and c-Jun NH2-terminal kinase (JNK), which in turn promotes cell proliferation. All these could contribute to further malignant transformation of these cells.
Wang
Li
L
Institute of Radiation Medicine, Academy of Military Medical Science, Beijing, P.R. China.
Huo
Yan-Ying
YY
Zhang
Kai-Tai
KT
Wang
Ying
Y
Xiang
Xiao-Qiong
XQ
Hu
Ying-Chun
YC
Yu
Gang
G
Li
Gang
G
Mi
Can
C
Wu
De-Chang
DC
D001980:Bronchi / Q000166:cytology; D002471:Cell Transformation, Neoplastic; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000166:cytology*; D006801:Humans; D020935:MAP Kinase Signaling System; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010766:Phosphorylation; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D051906:Smad7 Protein / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D050807:ets-Domain Protein Elk-1 / Q000378:metabolism
C494112:ELK1 protein, human; D016755:Proto-Oncogene Proteins c-jun; D034741:RNA, Small Interfering; D051906:Smad7 Protein; D016212:Transforming Growth Factor beta; D050807:ets-Domain Protein Elk-1; D020928:Mitogen-Activated Protein Kinases