Endothelin Converting Enzyme-2 Differentially Regulates Opioid Receptor Activity.

British journal of pharmacology

PubMedID: 24990314

Gupta A, Fujita W, Gomes I, Bobeck E, Devi LA. Endothelin Converting Enzyme-2 Differentially Regulates Opioid Receptor Activity. Br J Pharmacol. 2014;.
BACKGROUND AND PURPOSE
Opioid receptor function is modulated by post-activation events such as receptor endocytosis, recycling and/or degradation. While it is generally understood that the peptide ligand gets co-endocytosed with the receptor, relatively few studies have investigated the role of the endocytosed peptide and peptide processing enzymes in regulating receptor function. In this study we focused on ECE2, a member of the neprilysin family of metallopeptidases that exhibits an acidic pH optimum, localizes to an intracellular compartment and selectively processes neuropeptides including opioid peptides in vitro (reviewed in Devi and Miller (2013)), and examined its role in modulating µ receptor recycling and resensitization.

EXPERIMENTAL APPROACH
The effect of ECE2 inhibition on hydrolysis of the endocytosed peptide was examined using thin layer chromatography and on µ opioid receptor trafficking using either enzyme-linked immunosorbent assay or microscopy. The effect of ECE2 inhibition on receptor signaling was measured using a cAMP assay and on antinociception induced by intrathecally-administered opioids by the tail flick assay.

KEY RESULTS
We find that the highly selective ECE2 inhibitor, S136492, significantly impairs µ receptor recycling and signaling by only those ligands that are ECE2 substrates and this is seen both in heterologous cells and in cells endogenously co-expressing µ receptors with ECE2. We also find that ECE2 inhibition attenuates antinociception mediated only by opioid peptides that are ECE2 substrates.

CONCLUSIONS AND IMPLICATIONS
These results suggest that ECE2, by selectively processing endogenous opioid peptides in the endocytic compartment, plays a role in modulating opioid receptor activity.