Desensitization of human CRF2(a) receptor signaling governed by agonist potency and βarrestin2 recruitment

Abstract

The primary goal was to determine agonist-specific regulation of CRF_2(a) receptor function. Exposure of human retinoblastoma Y79 cells to selective (UCN2, UCN3 or stresscopins) and non-selective (UCN1 or sauvagine) agonists prominently desensitized CRF_2(a) receptors in a rapid, concentration-dependent manner. A considerably slower rate and smaller magnitude of desensitization developed in response to the weak agonist CRF. CRF₁ receptor desensitization stimulated by CRF, cortagine or stressin1-A had no effect on CRF_2(a) receptor cyclic AMP signaling. Conversely, desensitization of CRF_2(a) receptors by UCN2 or UCN3 did not cross-desensitize Gs-coupled CRF₁ receptor signaling. In transfected HEK293 cells, activation of CRF_2(a) receptors by UCN2, UCN3 or CRF resulted in receptor phosphorylation and internalization proportional to agonist potency. Neither protein kinase A nor casein kinases mediated CRF_2(a) receptor phosphorylation or desensitization. Exposure of HEK293 or U2OS cells to UCN2 or UCN3 (100 nM) produced strong βarrestin2 translocation and colocalization with membrane CRF_2(a) receptors while CRF (1 μM) generated only weak βarrestin2 recruitment. βarrestin2 did not internalize with the receptor, however, indicating that transient CRF_2(a) receptor–arrestin complexes dissociate at or near the cell membrane. Since deletion of the βarrestin2 gene upregulated Gs-coupled CRF_2(a) receptor signaling in MEF cells, a βarrestin2 mechanism restrains Gs-coupled CRF_2(a) receptor signaling activated by urocortins. We further conclude that the rate and extent of homologous CRF_2(a) receptor desensitization are governed by agonist-specific mechanisms affecting GRK phosphorylation, βarrestin2 recruitment, and internalization thereby producing unique signal transduction profiles that differentially affect the stress response.