Send to

Choose Destination
Pharmacol Rep. 2014 Dec;66(6):1011-21. doi: 10.1016/j.pharep.2014.06.006. Epub 2014 Jun 26.

Ligand-directed trafficking of receptor stimulus.

Author information

National Medicines Institute, Warszawa, Poland. Electronic address:
Institute of Pharmacology, Polish Academy of Sciences, Kraków, Poland.
Medical Pharmacology and Toxicology, Department of Medical Biology, Faculty of Health Sciences, University of Tromsø - The Arctic University of Norway, Tromsø, Norway.


GPCRs are seven transmembrane-spanning receptors that convey specific extracellular stimuli to intracellular signalling. They represent the largest family of cell surface proteins that are therapeutically targeted. According to the traditional two-state model of receptor theory, GPCRs were considered as operating in equilibrium between two functional conformations, an active (R*) and inactive (R) state. Thus, it was assumed that a GPCR can exist either in an "off" or "on" conformation causing either no activation or equal activation of all its signalling pathways. Over the past several years it has become evident that this model is too simple and that GPCR signalling is far more complex. Different studies have presented a multistate model of receptor activation in which ligand-specific receptor conformations are able to differentiate between distinct signalling partners. Recent data show that beside G proteins numerous other proteins, such as β-arrestins and kinases, may interact with GPCRs and activate intracellular signalling pathways. GPCR activation may therefore involve receptor desensitization, coupling to multiple G proteins, Gα or Gβγ signalling, and pathway activation that is independent of G proteins. This latter effect leads to agonist "functional selectivity" (also called ligand-directed receptor trafficking, stimulus trafficking, biased agonism, biased signalling), and agonist intervention with functional selectivity may improve the therapy. Many commercially available drugs with beneficial efficacy also show various undesirable side effects. Further studies of biased signalling might facilitate our understanding of the side effects of current drugs and take us to new avenues to efficiently design pathway-specific medications.


Biased agonism; Biased signalling; Ligand-directed receptor trafficking; Stimulus trafficking

[Indexed for MEDLINE]

Supplemental Content

Full text links

Icon for Elsevier Science
Loading ...
Support Center