fMLP Induces Hsp27 Expression, Attenuates NF-κB Activation, and Confers Intestinal Epithelial Cell Protection

Sustained expression of cytoprotective intestinal epithelial heat shock proteins (Hsps), particularly Hsp27, depends on stimuli derived from bacterial flora. In this study, we examined the role of the bacterial chemotactic peptide, fMLP, in stimulating colonic epithelial Hsp expression at concentrations encountered in a physiological milieu. Treatment of the polarized human intestinal epithelial cell line Caco2bbe with physiological concentrations of fMLP (10-100nM) induced expression of Hsp27, but not Hsp72, in a timeand concentration-dependent manner. Induction of Hsp27 by fMLP was specific since the fMLP-analogues MRP and MLP were not effective. Hsp27 induction by fMLP was blocked by the fMLP-receptor antagonist BOC-FLFLF and was blocked when the dipeptide transporter PepT1, an entry pathway for fMLP, was silenced. FMLP activated both the p38 and ERK1/2 MAP kinase pathways in Caco2bbe cells, but not the stressactivated protein kinase/c-Jun NH2-terminal kinase (JNK) pathway. The p38 inhibitor SB203580, but not the MEK-1 inhibitor PD98059, blocked Hsp27 induction by fMLP. FMLP treatment inhibited actin depolymerization and decreased transepithelial resistance (TER) caused by the oxidant monochloramine and this inhibition was reversed by silencing Hsp27 expression. FMLP pretreatment also inhibited activation of pro-inflammatory transcription factor NF-κB by TNF-α in Caco2bbe cells, reducing induction of NF-κB target genes by TNF-α both in human intestinal biopsies and Caco2bbe cells. In conclusion, fMLP may contribute to the maintenance of intestinal homeostasis by mediating physiological expression of Hsp27, enhancing cellular protection, and negatively regulating the inflammatory response. Page 3 of 34