G protein Coupled Receptors (GPCRs) transduce information from chemical or hormonal stimuli across the cell membrane to activate heterotrimeric G proteins and thereby elicit physiological/cellular responses. Adhesion G Protein Coupled Receptors (aGPCRs) comprise a 33-member sub-family of GPCRs that have become subjects of intense investigation due to an expanding understanding of the roles these receptors have in developmental disorders and adult cancers. Despite the intense study, direct measurements of heterotrimeric G protein activation by any aGPCR family member had never been made until our very recent work. We leveraged a new technology that we developed to purify large quantities of all classes of heterotrimeric G protein ? subunits and successfully reconstituted G protein activation mediated by two adhesion GPCRs (GPR56 and GPR110). We determined the G protein subtypes that GPR56 and GPR110 activate and found that the extracellular fragments of both receptors inhibit the G protein activating activity of the receptor portion that is intercalated in the membrane (TM or Trans-membrane domain). Receptor activation occurs when the inhibitory extracellular fragment is dissociated from the TM domain, perhaps by the action of protein ligands in the extracellular space that bind to it. This act unmasks a short portion of the TM domain that acts upon itself in positive regulatory fashion (a tethered agonist). These preliminary data lead us to propose that the entire adhesion GPCR class shares a common mechanism of action in being regulated by tethered agonists. We seek to verify the mechanism for GPR56, GPR114, and the Group VI adhesion GPCRs and perform detailed studies to define the exact composition of the tethered agonist and the way that it engages the TM domain. We will conduct studies to investigate the way that natural ligands of the receptors act to reveal the tethered agonist while we molecularly identify authentic receptor ligands. Screens of small molecule chemical libraries will be conducted to identify synthetic adhesion GPCR modulators. These compounds will greatly aid our mechanistic studies as research tools and may find use as leads to block the pathophysiologic actions of adhesion GPCRs in disease contexts. Understanding the mechanism of action of adhesion GPCRs is a pre- requisite to the development of therapies for the increasing number of diseases ascribed to this GPCR-class. Our work strives to elucidate the mechanism of adhesion GPCR action.

Public Health Relevance

Adhesion G protein Coupled Receptors (GPCRs) link cell adhesion to intracellular signaling events. Adhesion GPCR function or expression aberrancies are linked to autism, developmental disorders and cancers. We provide the first direct measurements of adhesion GPCR coupling to heterotrimeric G proteins. The molecular mechanisms by which adhesion GPCRs regulate G proteins will be investigated and means of inhibiting adhesion GPCRs in pathophysiological states will be explored.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM120110-03
Application #
9532246
Study Section
Molecular and Integrative Signal Transduction Study Section (MIST)
Program Officer
Dunsmore, Sarah
Project Start
2016-09-15
Project End
2019-07-31
Budget Start
2018-08-01
Budget End
2019-07-31
Support Year
3
Fiscal Year
2018
Total Cost
Indirect Cost
Name
University of Michigan Ann Arbor
Department
Pharmacology
Type
Schools of Medicine
DUNS #
073133571
City
Ann Arbor
State
MI
Country
United States
Zip Code
48109
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Giera, Stefanie; Luo, Rong; Ying, Yanqin et al. (2018) Microglial transglutaminase-2 drives myelination and myelin repair via GPR56/ADGRG1 in oligodendrocyte precursor cells. Elife 7:
Stoveken, Hannah M; Larsen, Scott D; Smrcka, Alan V et al. (2018) Gedunin- and Khivorin-Derivatives Are Small-Molecule Partial Agonists for Adhesion G Protein-Coupled Receptors GPR56/ADGRG1 and GPR114/ADGRG5. Mol Pharmacol 93:477-488
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Stoveken, Hannah M; Bahr, Laura L; Anders, M W et al. (2016) Dihydromunduletone Is a Small-Molecule Selective Adhesion G Protein-Coupled Receptor Antagonist. Mol Pharmacol 90:214-24