PGE2 upregulates IL-8 via p38 MAPK-dependent dual-activation of CHOP and C/EBP-beta in human astrocytomas

We previously showed that in low- as well as in high-grade astrocytomas IL-8 overexpression is triggered by prostaglandin E2 (PGE2) through the upregulation of the transcription factors CCAAT/enhancer-binding protein-beta (C/EBP-beta) and C/EBP homologous protein (CHOP). Here we investigated the signal transduction pathways and the molecular mechanisms underlying the PGE2-dependent IL-8 gene expression in astrocytomas. Low- and high-grade PGE2-treated astrocytoma cells were transfected with wild-type and mutated IL-8 promoter constructs in the presence of various signal transduction pathway inhibitors, and cotransfected with transcription factor overexpressing plasmids or small-interfering RNAs. p38MAPK, C/EBP-beta, and CHOP phosphorylation was analyzed by Western blotting. Electrophoretic mobility shift assay and chromatin immunoprecipitation evaluated the in vitro and in vivo binding of CHOP and C/EBP-beta to IL-8 promoter. The results obtained allowed us to find out the signaling pathways triggered by PGE2 and responsible for the activation of the transcription factors involved in the overproduction of IL-8 by astrocytoma. Therefore, it can be argued that the inhibition of the PGE2 downstream pathways may represent a novel therapeutic approach for the treatment of patients with astrocytoma.