Apical and basolateral pools of proteinase-activated receptor-2 direct distinct signaling events in the intestinal epithelium

Abstract

Studies suggest that there are two distinct pools of proteinase-activated receptor-2 (PAR2) present in intestinal epithelial cells: an apical pool accessible from the lumen, and a basolateral pool accessible from the interstitial space and blood. Although introduction of PAR2 agonists such as 2-furoyl-LIGRL-O-NH2 (2fAP) to the intestinal lumen can activate PAR2, the presence of accessible apical PAR2 has not been definitively shown. Furthermore, some studies have suggested that basolateral PAR2 responses in the intestinal epithelium are mediated indirectly by neuropeptides released from enteric nerve fibers, rather than by intestinal PAR2 itself. Here we identified accessible pools of both apical and basolateral PAR2 in cultured Caco2-BBe monolayers and in mouse ileum. Activation of basolateral PAR2 transiently increased short-circuit current by activating electrogenic Cl− secretion, promoted dephosphorylation of the actin filament-severing protein, cofilin, and activated the transcription factor, AP-1, whereas apical PAR2 did not. In contrast, both pools of PAR2 activated extracellular signal-regulated kinase 1/2 (ERK1/2) via temporally and mechanistically distinct pathways. Apical PAR2 promoted a rapid, biphasic PLCβ/Ca2+/PKC-dependent ERK1/2 activation, resulting in nuclear localization, whereas basolateral PAR2 promoted delayed ERK1/2 activation which was predominantly restricted to the cytosol, involving both PLCβ/Ca2+ and β-arrestin-dependent pathways. These results suggest that the outcome of PAR2 activation is dependent on the specific receptor pool that is activated, allowing for fine-tuning of the physiological responses to different agonists.