RT Journal Article
SR Electronic
T1 Preactivation Permits Subsequent Stimulation of Phospholipase C by G<sub>i</sub>-Coupled Receptors
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 700
OP 708
DO 10.1124/mol.57.4.700
VO 57
IS 4
A1 Chan, Joy S. C.
A1 Lee, Jonathan W. M.
A1 Ho, Maurice K. C.
A1 Wong, Yung H.
YR 2000
UL http://molpharm.aspetjournals.org/content/57/4/700.abstract
AB In the complex signal transduction networks involving G protein-coupled receptors there are numerous examples where Gi -linked receptors augment Gq-dependent signals. The mechanistic basis of such occurrences is thought to entail signal convergence at phospholipase Cβ (PLCβ) via the G protein βγ-dimers. Herein, we explored the possibility that augmentation by βγ-dimers requires preactivation of PLCβ. COS-7 cells were transiently cotransfected with cDNAs encoding various combinations of receptors and G protein subunits. The Gi-coupled δ- and κ-opioid receptors could not stimulate PLCβ unless they were coexpressed with Gα16. The opioid-induced response was dose-dependent and partially inhibited by pertussis toxin or coexpression with transducin, indicating the involvement of βγ-subunits released from the Giproteins. When PLCβ was preactivated by constitutively active mutants of Gα16, Gαq, or Gα14, opioids enhanced the activity by 80 to 300% and such responses were mostly pertussis toxin-sensitive. The opioid-induced enhancement was dose-dependent and could not be blocked by staurosporin, a protein kinase C inhibitor. Other Gi-coupled receptors that were ineffective on their own also acquired the ability to stimulate PLCβ in the presence of a constitutively active mutant of Gαq. Coactivation of endogenous or exogenous Gq-coupled receptors with the δ-opioid receptor produced strong stimulations of PLCβ and such responses could be partially blocked by pertussis toxin. These results show that enhancement of Gq-dependent signals by Gi-coupled receptors requires activated PLCβ and is mediated via the βγ-dimer.