PGE2 Induces Epigenetic Modifications and Up-Regulation of IL-8 Gene in Astrocytoma

Background: It is now well recognized that chronic inflammation is a risk factor for cancer. Several pro-inflammatory gene products, among which interleukin-8 (IL-8), have been linked to tumorigenesis, promotion, proliferation, invasion, angiogenesis, and metastasis. We previously reported that astrocytomas express high levels of this chemokine in response to an increased synthesis of prostaglandin E2 (PGE2). Here, we investigated whether the PGE2-induced IL-8 activation is mediated by epigenetic modifications. Methods: DNA methylation status of the 6 CpG sites within IL-8 promoter region and histone acetylation levels were analyzed in two astrocytoma cell lines of different malignancy grade and normal astrocytic cells by bisulphite sequencing and chromatin immunoprecipitation, respectively. IL-8 mRNA was quantized by real-time PCR and protein levels were measured by enzyme immunoassay. Results: PGE2 activated IL-8 transcription through specific demethylation of an individual CpG residue (nucleotide -83) located within the C/EBP-beta consensus sequence in the IL-8 promoter and abnormal acetylation of histone H3 in this region of chromatin. These events promoted the recruitment of C/EBP-beta transcription factor which, in turn, formed a docking platform for p300 cofactor, leading ultimately to enhanced transcriptional potential of IL-8. Conclusions: Our findings have elucidated an orchestrated mechanism triggered by PGE2 whereby concurrent association of site-specific demethylation and histone H3 hyperacetylation resulted in derepression of IL-8 gene expression in astrocytomas. These observations imply that anti-inflammatory agents that suppress IL-8 or IL-8- regulated products should have a potential in both the prevention and treatment of this cancer.