Endothelin-converting enzyme-1 actions determine differential trafficking and signaling of corticotropin-releasing factor receptor 1 at high agonist concentrations

CRF receptor 1 (CRF ₁), a key neuroendocrine mediator of the stress response, has two known agonists corticotropin-releasing factor (CRF) and urocortin 1 (Ucn1). Here we report that endothelin- converting enzyme-1 (ECE-1) differentially degrades CRF and Ucn1; ECE-1 cleaves Ucn1, but not CRF, at critical residue Arginine-34/35', which is essential for ligand-receptor binding. At near K _D agonist concentration (30 nM), both Ucn1- and CRF-mediated Ca ²⁺ mobilization are ECE-1 dependent. Interestingly, at high agonist concentration (100 nM), Ucn1-mediated Ca ²⁺ mobilization remains ECE-1 dependent, whereas CRF-mediated mobilization becomes independent of ECE-1 activity. At high agonist concentration, ECE-1 inhibition disrupted Ucn1-, but not CRFinduced CRF1 recycling and resensitization, but did not prolong the association of CRF ₁ with β-arrestins. RNA interference-mediated knockdown of Rab suggests that both Ucn1- and CRFinduced CRF ₁ resensitization is dependent on activity of Rab11, but not of Rab4. CRF ₁ behaves like a class A G protein-coupled receptor with respect to transient β-arrestins interaction. We propose that differential degradation by ECE-1 is a novel mechanism by which CRF ₁ receptor is protected from overactivation by physiologically relevant high concentrations of higher affinity ligand to mediate distinct resensitization and downstream signaling.