LPS-Induced Chromatin and DNA Methylation Changes in HumanIntestinal Epithelial Cells

Background: A possible novel additional strategy used by bacterial pathogens during infection is to interfere with host cellular processes by inducing epigenetic modifications and consequently determining a new specific cell transcriptional profile. These mechanisms may operate at a gene-specific level and include chromatin modifications, orchestrated by chromatin-remodeling complexes and histone-modifying enzymes, and DNA methylation directed by DNA-methyl transferases. The release of LPS by bacteria is mainly responsible for systemic reactions and stimulates both immune and specific epithelial cell types to release inflammatory mediators. It is known that LPS induces the release of IL-8 by intestinal mucosal cells. Because bacteria may induce alteration of epigenetic patterns in host cells, we have investigated whether LPS induced IL-8 activation in human intestinal epithelial cells involves changes of histone modifications and/or DNA methylation at the IL-8 gene regulatory region. Methods: Chromatin-immunoprecipitation (ChIP), DNA methylation analysis by MALDI- TOF. Results: Our data demonstrate an important role of histone modifications, including histone H3 acetylation and H3K4, H3K9 and H3K27 methylation state, in LPS-mediated IL-8 gene activation in intestinal epithelial cells. In particular we demonstrate that H3- acetyl, H3K4me2 and H3K9me2 changes are early, transient and correlate with the modulation of transcriptional activity. Conversely, increase of H3K27me3 levels at IL-8 gene are later and long lasting. Conclusions: Our data raise the intriguing possibility that the observed chromatin modifications could be potentially involved in two important phenomena such as the LPS tolerance, and the hypermethylation of PcG target genes in intestinal cancer.