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.

Chymase-mediated intestinal epithelial permeability is regulated by a protease-activating receptor/matrix metalloproteinase-2-dependent mechanism

“…PAR-2 expression was confirmed by RT-PCR analysis (results not shown), and previous studies demonstrated apical and basolateral expression of PAR-2 on Caco-2 BBe cells (32). The intramolecular activation of PAR-2 leads to G-coupled protein activation and subsequent activation of downstream MAPK pathways (55).…”

“…An alternative explanation is that PAR-2 activation promoted the redistribution of TJ proteins, leading to altered intestinal epithelial permeability. Consistent with this, basolateral PAR-2 activation of intestinal epithelial cells induced TJ protein redistribution (32). Western blot analysis of total protein from Caco-2 BBe cells revealed loss of claudin-5 protein, suggesting that the phenotype was related to proteolytic loss of claudin-5; however, we cannot rule out a role for PAR-2 signaling in the redistribution of intestinal epithelial TJ proteins and modification of paracellular permeability.…”

PAR2-dependent activation of GSK3β regulates the survival of colon stem/progenitor cells

“…Conversely, PAR 2 is mainly apical in surface cells of the crypt. Because it has been shown different signaling pathways depending on PAR 2 basolateral or apical localization (31), and particularly basolateral PAR 2 was critical for tight junctions regulation, it is tempting to speculate that, in intestinal stem/progenitor cells, PAR 2 activates GSK3␤ through a cross talk with ␤ 1 -integrin that can associate with E-cadherins (62). Our data showing that Rho kinase controls a switch between GSK3␤ activation in ␤-arrestin 2 complex and GSK3␤ inhibition in Akt complex downstream of PAR 2 activation are in favor of this hypothesis.…”

Reelin Is Involved in the Crypt-Villus Unit Homeostasis

“…In the small intestine, b1-arrestin activates the actin-depolymerizing factor/cofilin. 41 The absence of reelin may inactivate intestinal cofilin via downregulation of b1-arrestin and, hence, modify those cell processes that depend on the actin cytoskeleton. Although in the brain, reelin inactivates cofilin, 42 it is interesting to note that in both, brain and intestine, reelin initiates signaling cascades that affect the same cytosolic protein, cofilin, but we are far from knowing the cell signaling events triggered by reelin in the intestine.…”