Protease-Activated Receptor-2 in the Intestinal Epithelium & Differential Effects of Beta Arrestins on the Internalization, Desensitization & ERK 1/2 Activation Downstream of Protease-Activated Receptor-2
- Author(s): Lau, Chang Shun
- Advisor(s): DeFea, Kathryn A
- et al.
Research of G-protein coupled receptor signaling (GPCR) for therapeutic applications have historically been a hot topic of research. In the past, GPCR studies have been primarily focused on the molecular mechanism of its signaling pathway debunking the components of either traditional G-protein signaling or by other novel and more complex signaling pathways. However, recent GPCR studies have transitioned to examining distinct behaviors exhibited by and physiological responses that are triggered by cell- and localization-specific GPCRs. These responses include inflammatory, anti-inflammatory, cell migration and metastasis. Further, research of GPCR signaling have extended to the utilization of "biased agonists" where these modified agonists activates a specific GPCR and have the ability to trigger the activation of a specific pathway and inhibit other pathways that otherwise is propagated via activation by the non-modified agonist.
In the first study, we focus on the two distinct pools of protease-activated receptor-2 (PAR-2) present in intestinal epithelial cells: an apical pool facing the lumen, and a basolateral pool facing the bloodstream. Studies have demonstrated that introduction of PAR-2 agonists such as 2-furoyl-LIGRL-O-NH2 (2fAP) to the lumen can activate apical PAR-2 while it has been predicted mast cells and recruited leukocytes release proteases that can activate basolateral PAR-2. However, whether both pools of PAR-2 are equally capable of signaling, and the possible distinction between apical and basolateral PAR-2 induced responses have yet been addressed. Here we identified the expression of both apical and basolateral PAR-2 in cultured CACO2-BBe monolayers, and in mouse proximal jejunum. We reveal apical and basolateral PAR-2 in the intestinal epithelium are accessible by PAR-2 agonist 2fAP, and have both temporally and mechanistically signaling distinctions. Further, we demonstrate the apical and basolateral pools of PAR-2 can trigger distinct physiological responses as well.
Secondly, we illustrate that PAR-2 activation enhanced bacteria uptake in cultured colonocytes via a clathrin and phosphotidyl-inositol-3-kinase dependent manner. Moreover, we show that PAR-2 activation stimulated bacteria uptake in mice intestines. These results suggested that activation of the receptor plays a crucial role in gastrointestinal barrier dysfunction and is indeed a contributing factor to bacterial infection, further allowing for better understanding of PAR-2 and its physiological role in the gastrointestinal system.
On the whole these studies attempts to provide clarification for the characterization of PAR-2 in the gastrointestinal system that can be used further in the research for the usage of PAR-2 as a therapeutic target.
Lastly, findings for which I was a supporting author in a recent publication, we examined the differential effects of β-arrestins on internalization, desensitization and signaling of PAR-2. We demonstrate here that β-arrestin-1 and β-arrestins-2 have distinctive roles in PAR-2 signaling, including mechanistic and temporal distinctions in signaling, signal termination, cellular localization of signaling components and degradation.