Characterization of CB1 Cannabinoid Receptors Using Receptor Peptide Fragments and Site-Directed Antibodies
- Department of Pharmacological and Physiological Science, Saint Louis University School of Medicine, St. Louis, Missouri 63104
Abstract
The mechanism by which CB1 cannabinoid receptors are coupled to the Gi/Go class of G proteins was studied. A peptide representing the juxtamembrane carboxyl terminus robustly stimulated guanosine-5′-O-(3-thio)triphosphate binding. Peptides simulating subdomains of the third intracellular loop (IL3) activated minimally when present alone but produced additive effects when present in combination. Peptides representing the amino-side IL3 and the juxtamembrane carboxyl terminus autonomously inhibited adenylate cyclase, and this response was not significantly augmented or inhibited by peptides representing other intracellular domains. Site-directed antipeptide antibodies developed against the domains of the amino terminus, first extracellular loop, amino-side IL3, and juxtamembrane carboxyl terminus of CB1 receptors failed to influence binding of [3H]CP-55940. However, IgG raised against the amino-side IL3 diminished the agonist-dependent inhibition of adenylate cyclase. These experiments suggest that the juxtamembrane carboxyl terminus is critical for G protein activation by CB1 cannabinoid receptors and that the amino-side IL3 also may interact with Gi proteins leading to inhibition of adenylate cyclase.
Footnotes
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Send reprint requests to: Dr. Allyn C. Howlett, Department of Pharmacological and Physiological Science, 1402 South Grand Boulevard, St. Louis, MO 63104. E-mail:howletta{at}slu.edu
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↵1 Current affiliation: Department of Surgery, Beth Israel Deaconess Hospital, Harvard Medical School, Boston, MA 02115.
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This work was supported National Institute on Drug Abuse Grants R01-DA03690, R01-DA06312, and K05-DA00182.
- Abbreviations:
- IL3
- third intracellular loop of the G protein-coupled receptor
- BSA
- bovine serum albumin
- CHAPS
- 3-[(3-cholamidopropyl)dimethylammonio]propanesulfonate
- DALN
- desacetyllevonantradol
- EL1
- first extracellular loop of the G protein-coupled receptor
- ELISA
- enzyme-linked immunosorbent assay
- GTPγS
- guanosine-5′-O-(3-thio)triphosphate
- KLH
- keyhole limpet hemocyanin
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- Received August 4, 1997.
- Accepted November 13, 1997.
- The American Society for Pharmacology and Experimental Therapeutics
