Regulation of EP receptors in non-small cell lung cancer by epigenetic modifications.

BACKGROUND: Cyclooxygenase (COX)-2 is frequently overexpressed in non-small cell lung cancer (NSCLC) and results in increased levels of prostaglandin E2 (PGE(2)), an important signalling molecule implicated in tumourigenesis. PGE(2) exerts its effects through the E prostanoid (EP) receptors (EPs1-4).

METHODS: The expression and epigenetic regulation of the EPs were evaluated in a series of resected fresh frozen NSCLC tumours and cell lines.

RESULTS: EP expression was dysregulated in NSCLC being up and downregulated compared to matched control samples. For EPs1, 3 and 4 no discernible pattern emerged. EP2 mRNA however was frequently downregulated, with low levels being observed in 13/20 samples as compared to upregulation in 5/20 samples examined. In NSCLC cell lines DNA CpG methylation was found to be important for the regulation of EP3 expression, the demethylating agent decitabine upregulating expression. Histone acetylation was also found to be a critical regulator of EP expression, with the histone deacteylase inhibitors trichostatin A, phenylbutyrate and suberoylanilide hydroxamic acid inducing increased expression of EPs2-4. Direct chromatin remodelling was demonstrated at the promoters for EPs2-4.

CONCLUSIONS: These results indicate that EP expression is variably altered from tumour to tumour in NSCLC. EP2 expression appears to be predominantly downregulated and may have an important role in the pathogenesis of the disease. Epigenetic regulation of the EPs may be central to the precise role COX-2 may play in the evolution of individual tumours.