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The ADP ribosylation factor nucleotide exchange factor ARNO promotes beta-arrestin release necessary for luteinizing
S Mukherjee1, V V Gurevich, J C Jones
1Department of Cell and Molecular Biology, Northwestern University Medical School, 303 East Chicago Avenue, Chicago, IL 60611, USA.
Abstract:
Desensitization of guanine nucleotide binding protein-coupled receptors is a ubiquitous phenomenon characterized by declining effector activity upon persistent agonist stimulation. The luteinizing hormone/choriogonadotropin receptor (LH/CGR) in ovarian follicles exhibits desensitization of effector adenylyl cyclase activity in response to the mid-cycle surge of LH. We have previously shown that uncoupling of the agonist-activated LH/CGR from the stimulatory G protein (G(s)) is dependent on GTP and attributable to binding of beta-arrestin present in adenylyl cyclase-rich follicular membrane fraction to the third intracellular (3i) loop of the receptor. Here, we report that LH/CGR-dependent desensitization is mimicked by ADP ribosylation factor nucleotide-binding site opener, a guanine nucleotide exchange factor of the small G proteins ADP ribosylation factors (Arfs) 1 and 6, and blocked by synthetic N-terminal Arf6 peptide, suggesting that the GTP-dependent step of LH/CGR desensitization is receptor-dependent Arf6 activation. Arf activation by GTP and ADP ribosylation factor nucelotide-binding site opener promotes the release of docked beta-arrestin from the membrane, making beta-arrestin available for LH/CGR; Arf6 but not Arf1 peptides block beta-arrestin release from the membrane. Thus, LH/CGR appears to activate two membrane delimited signaling cascades via two types of G proteins: heterotrimeric G(s) and small G protein Arf6. Arf6 activation releases docked beta-arrestin necessary for receptor desensitization, providing a feedback mechanism for receptor self-regulation.
Insights
Receptor desensitization involves beta-arrestin binding to the luteinizing hormone/choriogonadotropin receptor (LH/CGR). Arf6 activation releases beta-arrestin, regulating LH/CGR signaling and desensitization.
Area of Science:
- Endocrinology
- Molecular Biology
- Cell Signaling
Background:
- G protein-coupled receptor (GPCR) desensitization is a key regulatory mechanism.
- The luteinizing hormone/choriogonadotropin receptor (LH/CGR) in ovarian follicles undergoes desensitization in response to luteinizing hormone (LH).
- Previous work implicated beta-arrestin binding to the LH/CGR's third intracellular loop in desensitization, dependent on GTP and G(s) protein uncoupling.
Purpose of the Study:
- To investigate the role of ADP ribosylation factors (Arfs) in LH/CGR desensitization.
- To elucidate the mechanism by which beta-arrestin is recruited and released during LH/CGR desensitization.
- To identify the specific Arf proteins involved in regulating LH/CGR signaling.
Main Methods:
- Utilized ADP ribosylation factor nucleotide-binding site opener to mimic LH/CGR desensitization.
- Employed synthetic N-terminal Arf6 peptides to block desensitization.
- Investigated the effect of Arf activation on beta-arrestin release from the membrane.
Main Results:
- LH/CGR desensitization was mimicked by an Arf nucleotide exchange factor, suggesting Arf6 activation.
- Synthetic Arf6 peptides blocked LH/CGR desensitization, while Arf1 peptides did not.
- Arf activation promotes beta-arrestin release from the membrane, making it available for LH/CGR.
Conclusions:
- LH/CGR desensitization involves a GTP-dependent step mediated by Arf6 activation.
- LH/CGR signaling utilizes both heterotrimeric G(s) and small G protein Arf6.
- Arf6 activation provides a feedback mechanism for LH/CGR self-regulation through beta-arrestin release.