Promoter methylation regulates cyclooxygenase expression in breast cancer.
BACKGROUND
Overexpression of cyclooxygenase (COX-2) is commonly observed in human cancers. In a murine model of metastatic breast cancer, we observed that COX-2 expression and enzyme activity were associated with enhanced tumorigenic and metastatic potential. In contrast to the high COX-2 expression in metastatic tumors, transplantation of poorly tumorigenic tumor cell lines to syngeneic mice results in less COX-2 expression and less COX-2 activity in vivo. Aberrant CpG island methylation, and subsequent silencing of the COX-2 promoter, has been observed in human cancer cell lines and in some human tumors of the gastrointestinal tract.


METHODS
Using bisulfite modification and a methylation-specific PCR, we examined the methylation status of the COX-2 promoter in a series of four closely-related murine mammary tumors differing in COX-2 expression and metastatic potential.


RESULTS
We showed that line 410, which does not express COX-2 in vivo, exhibited evidence of promoter methylation. Interestingly, the metastatic counterpart of this cell (line 410.4) displayed only the unmethylated COX-2 promoter, as did two additional cell lines (lines 66.1 and 67). The methylation patterns observed in vitro were maintained when these murine mammary tumor lines were transplanted to syngeneic mice. Treatment with the DNA demethylating agent 5-aza-deoxycytidine increased COX-2 mRNA, increased protein and increased enzyme activity (prostaglandin synthesis).


CONCLUSIONS
These results indicate that COX-2 promoter methylation may be one mechanism by which tumor cells regulate COX-2 expression. Upregulation of COX-2 expression in closely related metastatic lesions versus nonmetastatic lesions may represent a shift towards the unmethylated phenotype.
Ma
Xinrong
X
Department of Pathology, University of Maryland School of Medicine, Baltimore, Maryland, USA. XMa@som.umaryland.edu
Yang
Qingyuan
Q
Wilson
Keith T
KT
Kundu
Namita
N
Meltzer
Stephen J
SJ
Fulton
Amy M
AM
D000818:Animals; D001943:Breast Neoplasms / Q000201:enzymology* / Q000235:genetics* / Q000556:secondary; D045744:Cell Line, Tumor; D051546:Cyclooxygenase 2; D019175:DNA Methylation; D004273:DNA, Neoplasm / Q000378:metabolism; D004195:Disease Models, Animal; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics*; D006801:Humans; D007527:Isoenzymes / Q000235:genetics* / Q000502:physiology; D015674:Mammary Neoplasms, Animal / Q000201:enzymology / Q000235:genetics / Q000556:secondary; D008565:Membrane Proteins; D051379:Mice; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011451:Prostaglandin-Endoperoxide Synthases / Q000235:genetics* / Q000502:physiology
D004273:DNA, Neoplasm; D007527:Isoenzymes; D008565:Membrane Proteins; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D011451:Prostaglandin-Endoperoxide Synthases