Development and Characterization of Pepducins as Gs-biased Allosteric Agonists [Cell Biology]

November 13th, 2014 by Carr, R., Du, Y., Quoyer, J., Panettieri, R. A., Janz, J. M., Bouvier, M., Kobilka, B. K., Benovic, J. L.

The β2-adrenergic receptor (β2AR) is a prototypical G protein-coupled receptor (GPCR) that mediates many hormonal responses including cardiovascular and pulmonary function. β-agonists used to combat hypercontractility in airway smooth muscle stimulate β2AR-dependent cAMP production that ultimately promotes airway relaxation. Chronic stimulation of the β2AR by long acting β-agonists used in the treatment of asthma can promote attenuated responsiveness to agonist and an increased frequency of fatal asthmatic attacks. β2AR desensitization to β-agonists is primarily mediated by GPCR kinases (GRKs) and β-arrestins that attenuate receptor-Gs coupling and promote β2AR internalization and degradation. A biased agonist that can selectively stimulate Gs signaling without promoting receptor interaction with GRKs and β-arrestins should serve as an advantageous asthma therapeutic. To identify such molecules, we screened ~50 lipidated peptides derived from the intracellular loops of the β2AR, known as pepducins. This screen revealed two classes of Gs-biased pepducins, receptor-independent and receptor-dependent, as well as several β-arrestin-biased pepducins. The receptor-independent Gs-biased pepducins operate by directly stimulating G protein activation. In contrast, receptor-dependent Gs-biased pepducins appear to stabilize a Gs-biased conformation of the β2AR that couples to Gs but does not undergo GRK-mediated phosphorylation or β-arrestin-mediated internalization. Functional studies in primary human airway smooth muscle cells demonstrate that Gs-biased pepducins are not subject to conventional desensitization and, thus, may be good candidates for the development of next generation asthma therapeutics. Our study reports the first Gs-biased activator for the β2AR and provides valuable tools for the study of β2AR function.