Carcinogenesis Advance Access published online on December 23, 2004
Carcinogenesis, doi:10.1093/carcin/bgi009
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 Department of Medicine, McGill University Health Center, Montreal, Canada
* To whom correspondence should be addressed. Expression of urokinase-type plasminogen activator (uPA), a protease expressed only in highly invasive human breast cancer cells, is inhibited by DNA methylation of its promoter. We tested here the hypothesis that upregulation of DNMT1 will lead to methylation, silencing of uPA and inhibition of the invasiveness of metastatic breast cancer cells. Since RAS was previously shown to up-regulate DNA methylation, we examined the effects of ectopic expression of constitutively active RAS on methylation and expression of uPA. Transfection of Ha-Ras into human breast cancer cells MDA-MB-231 resulted in a significantly shorter cell doubling time compared to the controls. However, the expression and the activity of the metastatic gene uPA and invasive capacity of the cells were significantly reduced by oncogenic RAS. The silencing of uPA by Ras is mediated by a cis-modification of uPA promoter and not through an effect on a trans-acting factor since a transiently transfected unmethylated uPA-luicferase reporter is expressed at a similar level in Ras transfected and control cells. We then examined the levels of DNA methyltransferase 1 (DNMT1) and methylated DNA binding protein 2 (MBD2) expressions in these cells to determine whether this reduction in uPA expression is associated with changes in DNA methylation machinery. Our results showed that ectopic expression of RAS induced DNMT1 expression and activity and inhibited MBD2 expression. Consistent with a methylation-mediated repression, uPA was partially methylated in RAS transfected cells and uPA expression was induced upon treatment of RAS transfectants with the demethylating agent 5'-azacytidine (5-azaC). These results therefore imply that the RAS-DNMT1-DNA methylation pathway, which promotes oncogenic growth in many cancers can express opposite effects on the invasive capacity of the highly invasive MDA-MB-231 cells, thus illustrating the divergence of growth and metastasis promoting pathways in cancer. This has important implications on our therapeutic approaches to metastasizing cancer.
Received October 19, 2004
Revised December 7, 2004
Accepted December 15, 2004
CANCER BIOLOGY
Methylation and inhibition of uPA expression by RAS oncogene: divergence of growth control and invasion in breast cancer cells
2 Department of Pharmacology, McGill University Health Center, Montreal, Canada
Shafaat A. Rabbani, E-mail: shafaat.rabbani{at}mcgill.ca
Abstract 
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  M. Szyf The Dynamic Epigenome and its Implications in Toxicology Toxicol. Sci., November 1, 2007; 100(1): 7 - 23. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. M. Wuerzberger-Davis, P.-Y. Chang, C. Berchtold, and S. Miyamoto Enhanced G2-M Arrest by Nuclear Factor-{kappa}B-Dependent p21waf1/cip1 Induction Mol. Cancer Res., June 1, 2005; 3(6): 345 - 353. [Abstract] [Full Text] [PDF]
|
|