Patrick Nana-Sinkam

Genetic and Epigenetic Regulation of the Human Prostacyclin Synthase Promoter in Lung Cancer Cell Lines

The importance of the arachidonic acid pathway has been established in colon and lung cancers, as well as in inflammatory diseases. In these diseases, prostacyclin I2 (PGI2) and prostaglandin E2 (PGE2) are thought to have antagonistic activities, with PGI2 exerting anti-inflammatory and antiproliferative activities, whereas PGE2 is proinflammatory and antiapoptotic. In human lung cancer, prostacyclin synthase (PGIS) and PGI2 are down-regulated, whereas PGE2 synthase (PGES) and PGE2 are up-regulated. Murine carcinogenesis models of human lung cancer reciprocate the relationship between PGIS and PGES expression. PGIS-overexpressing transgenic mice are protected from carcinogen- and tobacco smoke–induced lung tumor formation, suggesting that PGI2 may play a role in chemoprevention. We investigated several potential mechanisms for the down-regulation of PGIS in human lung cancer. Using transcription reporter assays, we show that single nucleotide polymorphisms in the PGIS promoter can affect transcriptional activity. In addition, PGIS expression in several human lung cancer cell lines is silenced by CpG methylation, and we have mapped these sites across the variable number of tandem repeats (VNTR) sequence in the promoter, as well as CpGs within exon 1 and the first intron. Finally, using fluorescence in situ hybridization, we show that human lung cancer cell lines and lung cancer tissues do not have a loss of the PGIS genomic region but multiple copies. These results show that an individuals PGIS promoter haplotype can play an important role in the predisposition for lung cancer and CpG methylation provides an epigenetic mechanism for the down-regulated PGIS expression. (Mol Cancer Res 2007;5(3):295–308)

Prostacyclin and Lung Cancer Chemoprevention

Eicosanoids are a family of bioactive lipid metabolites of arachidonic acid (AA). AA is hydrolyzed from membrane phospholipids through the action of phospholipase A2 (PLA2). Free AA can then be metabolized through three major pathways: cyclooxygenase (COX) to produce prostaglandins (PG) and thromboxane, lipoxygenase (LOX) to produce leukotrienes and hydroxy eicosatetraenoic acid (HETES), and cytochrome P-450 to produce epoxyeicosatrienoic acids (EETs). Most studies that have examined eicosanoids and cancer have focused on COX-2 in colon cancer. Elevated COX-2 expression was first demonstrated in colon cancer, in which colon tumors increased COX-2 expression compared to normal colon tissues (1).