title: Promoter methylation regulates cyclooxygenase expression in breast cancer.
abstract: 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.
authors.affiliation: Department of Pathology, University of Maryland School of Medicine, Baltimore, Maryland, USA. XMa@som.umaryland.edu
authors.forename: Xinrong
authors.initials: X
authors.lastname: Ma
authors.forename: Qingyuan
authors.initials: Q
authors.lastname: Yang
authors.forename: Keith T
authors.initials: KT
authors.lastname: Wilson
authors.forename: Namita
authors.initials: N
authors.lastname: Kundu
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Meltzer
authors.forename: Amy M
authors.initials: AM
authors.lastname: Fulton
mesh_terms: 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
chemical_list: D004273:DNA, Neoplasm; D007527:Isoenzymes; D008565:Membrane Proteins; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D011451:Prostaglandin-Endoperoxide Synthases