Proteasome inhibitors exacerbate interleukin-8 production induced by protease-activated receptor 2 in intestinal epithelial cells

• PAR2 activation induced bidirectional interleukin-8 production in intestinal epithelial cells.
• PAR2 activation increased proteasome activity when combined with IL-1β stimulation.
• Proteasome inhibition exacerbated interleukin-8 release induced by PAR2 activation.

Protease activated receptors (PARs) and the ubiquitin-proteasome system (UPS) regulate inflammatory response in intestinal cells. We aimed to elucidate putative connections between PARs and UPS pathways in intestinal epithelial cells. Caco-2 cells were treated by agonist peptides of PARs and/or IL-1β and/or proteasome inhibitors, bortezomib or MG132. Inflammatory response was evaluated by measuring IL-8 production. Proteasome activities were also evaluated. We showed that PAR-1 and -2 activation increased release of IL-8 compared with vehicle and independently of IL-1β. In contrast, PAR-4 agonist peptide had no effect. Caspase-like and chymotrypsin-like proteasomal activities were increased by PAR-2 activation only in the presence of IL-1β. Interestingly, in polarized Caco-2 cells, the release of IL-8 was predominantly upregulated in the side where PAR-2 agonist peptide was added, apical or basalolateral. In contrast, proteasome activities were only affected when PAR-2 agonist peptide was added in the apical side. Proteasome inhibitors, bortezomib and MG132, enhanced IL-8 production in both sides, apical and basolateral. In conclusion, PAR-2 activation alone did not affect proteasome but needed inflammatory stimulus IL-1β to synergistically increase chymotrypsin-like activity in intestinal epithelial cells. However, proteasome inhibition led to exacerbate inflammatory response induced by PAR-2 activation.