Axin downregulates TCF-4 transcription via beta-catenin, but not p53, and inhibits the proliferation and invasion of lung cancer cells.
BACKGROUND
We previously reported that overexpression of Axin downregulates T cell factor-4 (TCF-4) transcription. However, the mechanism(s) by which Axin downregulates the transcription and expression of TCF-4 is not clear. It has been reported that beta-catenin promotes and p53 inhibits TCF-4 transcription, respectively. The aim of this study was to investigate whether beta-catenin and/or p53 is required for Axin-mediated downregulation of TCF-4.


RESULTS
Axin mutants that lack p53/HIPK2 and/or beta-catenin binding domains were expressed in lung cancer cells, BE1 (mutant p53) and A549 (wild type p53). Expression of Axin or AxinDeltap53 downregulates beta-catenin and TCF-4, and knock-down of beta-catenin upregulates TCF-4 in BE1 cells. However, expression of AxinDeltabeta-ca into BE1 cells did not downregulate TCF-4 expression. These results indicate that Axin downregulates TCF-4 transcription via beta-catenin. Although overexpression of wild-type p53 also downregulates TCF-4 in BE1 cells, cotransfection of p53 and AxinDeltabeta-ca did not downregulate TCF-4 further. These results suggest that Axin does not promote p53-mediated downregulation of TCF-4. Axin, AxinDeltap53, and AxinDeltabeta-ca all downregulated beta-catenin and TCF-4 in A549 cells. Knock-down of p53 upregulated beta-catenin and TCF-4, but cotransfection of AxinDeltabeta-ca and p53 siRNA resulted in downregulation of beta-catenin and TCF-4. These results indicate that p53 is not required for Axin-mediated downregulation of TCF-4. Knock-down or inhibition of GSK-3beta prevented Axin-mediated downregulation of TCF-4. Furthermore, expression of Axin and AxinDeltap53, prevented the proliferative and invasive ability of BE1 and A549, expression of AxinDeltabeta-ca could only prevented the proliferative and invasive ability effectively.


CONCLUSIONS
Axin downregulates TCF-4 transcription via beta-catenin and independently of p53. Axin may also inhibits the proliferation and invasion of lung cancer cells via beta-catenin and p53.
Yang
Lian-He
LH
Department of Pathology, The First Affiliated Hospital and College of Basic Medical Sciences of China Medical University, Shenyang 110001, China.
Xu
Hong-Tao
HT
Han
Yang
Y
Li
Qing-Chang
QC
Liu
Yang
Y
Zhao
Yue
Y
Yang
Zhi-Qiang
ZQ
Dong
Qian-Ze
QZ
Miao
Yuan
Y
Dai
Shun-Dong
SD
Wang
En-Hua
EH
D000818:Animals; D060466:Axin Protein; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D015536:Down-Regulation / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D018021:Lithium Chloride / Q000494:pharmacology; D008175:Lung Neoplasms / Q000201:enzymology / Q000235:genetics* / Q000473:pathology*; D051379:Mice; D050505:Mutant Proteins / Q000378:metabolism; D009361:Neoplasm Invasiveness; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D051820:TCF Transcription Factors / Q000235:genetics* / Q000378:metabolism; D058118:Transcription Factor 7-Like 2 Protein; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D051176:beta Catenin / Q000378:metabolism*
D060466:Axin Protein; D050505:Mutant Proteins; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D012097:Repressor Proteins; D051820:TCF Transcription Factors; C544894:TCF7L2 protein, human; C544895:Tcf7l2 protein, mouse; D058118:Transcription Factor 7-Like 2 Protein; D016159:Tumor Suppressor Protein p53; D051176:beta Catenin; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D038362:Glycogen Synthase Kinase 3; D018021:Lithium Chloride