PT  - JOURNAL ARTICLE
AU  - Danijela Markovic
AU  - Nikolleta Papadopoulou
AU  - Thalia Teli
AU  - Harpal Randeva
AU  - Michael A. Levine
AU  - Edward W. Hillhouse
AU  - Dimitris K. Grammatopoulos
TI  - Differential Responses of Corticotropin-Releasing Hormone Receptor Type 1 Variants to Protein Kinase C Phosphorylation
AID  - 10.1124/jpet.106.107441
DP  - 2006 Dec 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 1032--1042
VI  - 319
IP  - 3
4099  - http://jpet.aspetjournals.org/content/319/3/1032.short
4100  - http://jpet.aspetjournals.org/content/319/3/1032.full
SO  - J Pharmacol Exp Ther2006 Dec 01; 319
AB  - Corticotropin-releasing hormone (CRH) regulates diverse biological functions in mammals, through activation of two types of specific G protein-coupled receptors that are expressed as multiple mRNA spliced variants. In most cells, the type 1α CRH receptor (CRH-R1α) preferentially activates the Gs-adenylyl cyclase signaling cascade. CRH-R1α-mediated signaling activity is impaired by insertion of 29 amino acids in the first intracellular loop, a sequence modification that is characteristic of the human-specific CRH-R1β variant. In various tissues, CRH signaling events are regulated by protein kinase C (PKC). The CRH receptors contain multiple putative PKC phosphorylation sites that represent potential targets. To investigate this, we expressed recombinant CRH-R1α or CRH-R1β in human embryonic kidney 293 cells and analyzed signaling events after PKC activation. Agonist (oxytocin) or phorbol 12-myristate 13-acetate-induced activation of PKC led to phosphorylation of both CRH-R1 variants. However, CRH-R1α and CRH-R1β exhibited different functional responses to PKC-induced phosphorylation, with only the CRH-R1β susceptible to cAMP signaling desensitization. This was associated with a significant decrease of accessible CRH-R1β receptors expressed on the cell surface. Both CRH-R1 variants were susceptible to homologous desensitization and internalization following treatment with CRH; however, PKC activation increased internalization of CRH-R1β but not CRH-R1α in a β-arrestin-independent manner. Our findings indicate that CRH-R1α and -R1β exhibit differential responses to PKC-induced phosphorylation, and this might represent an important mechanism for functional regulation of CRH signaling in target cells.