Abstract
Studies suggest that there are two distinct pools of proteinase-activated receptor-2 (PAR&sub2;) 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 PAR&sub2; agonists such as 2-furoyl-LIGRL-O-NH&sub2; (2fAP) to the intestinal lumen can activate PAR&sub2;, the presence of accessible apical PAR&sub2; has not been definitively shown. Furthermore, some studies have suggested that basolateral PAR&sub2; responses in the intestinal epithelium are mediated indirectly by neuropeptides released from enteric nerve fibers, rather than by intestinal PAR&sub2; itself. Here we identified accessible pools of both apical and basolateral PAR&sub2; in cultured Caco2-BBe monolayers and in mouse ileum. Activation of basolateral PAR&sub2; 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 PAR&sub2; did not. In contrast, both pools of PAR&sub2; activated extracellular signal-regulated kinase 1/2 (ERK1/2) via temporally and mechanistically distinct pathways. Apical PAR&sub2; promoted a rapid, biphasic PLCβ/Ca²(+)/PKC-dependent ERK1/2 activation, resulting in nuclear localization, whereas basolateral PAR&sub2; 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 PAR&sub2; activation is dependent on the specific receptor pool that is activated, allowing for fine-tuning of the physiological responses to different agonists.