Activation of PLC-delta1 by Gi/o-coupled receptor agonists.
The mechanism of phospholipase (PLC)-delta activation by G protein-coupled receptor agonists was examined in rabbit gastric smooth muscle. Ca(2+) stimulated an eightfold increase in PLC-delta1 activity in permeabilized muscle cells. Treatment of dispersed or cultured muscle cells with three G(i/o)-coupled receptor agonists (somatostatin, delta-opioid agonist [D-Pen(2),D-Pen(5)]enkephalin, and A(1) agonist cyclopentyl adenosine) caused delayed increase in phosphoinositide (PI) hydrolysis (8- to 10-fold) that was strongly inhibited by overexpression of dominant-negative PLC-delta1(E341R/D343R; 65-76%) or constitutively active RhoA(G14V). The response coincided with capacitative Ca(2+) influx and was not observed in the absence of extracellular Ca(2+), but was partly inhibited by nifedipine (16-30%) and strongly inhibited by SKF-96365, a blocker of store-operated Ca(2+) channels. Treatment of the cells with a G(q/13)-coupled receptor agonist, CCK-8, caused only transient, PLC-beta1-mediated PI hydrolysis. Unlike G(i/o)-coupled receptor agonists, CCK-8 activated RhoA and stimulated RhoA:PLC-delta1 association. Inhibition of RhoA activity with C3 exoenzyme or by overexpression of dominant-negative RhoA(T19N) or Galpha(13) minigene unmasked a delayed increase in PI hydrolysis that was strongly inhibited by coexpression of PLC-delta1(E341R/D343R) or by SKF-96365. Agonist-independent capacitative Ca(2+) influx induced by thapsigargin stimulated PI hydrolysis (8-fold), which was partly inhibited by nifedipine ( approximately 25%) and strongly inhibited by SKF-96365 ( approximately 75%) and in cells expressing PLC-delta1(E341R/D343R). Agonist-independent Ca(2+) release or Ca(2+) influx via voltage-gated Ca(2+) channels stimulated only moderate PI hydrolysis (2- to 3-fold), which was abolished by PLC-delta1 antibody or nifedipine. We conclude that PLC-delta1 is activated by G(i/o)-coupled receptor agonists that do not activate RhoA. The activation is preferentially mediated by Ca(2+) influx via store-operated Ca(2+) channels.
Murthy
Karnam S
KS
Department of Physiology, Medical College of Virginia Campus, Virginia Commonwealth University, Richmond, VA 23298, USA. skarnam@hsc.vcu.edu
Zhou
Huiping
H
Huang
Jiean
J
Pentyala
Srinivas N
SN
D000241:Adenosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000493:pharmacokinetics; D002478:Cells, Cultured; D020881:Enkephalin, D-Penicillamine (2,5)- / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000819:agonists / Q000378:metabolism*; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000378:metabolism; D007527:Isoenzymes / Q000378:metabolism*; D032389:Myocytes, Smooth Muscle / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D054799:Phospholipase C beta; D054803:Phospholipase C delta; D011817:Rabbits; D013004:Somatostatin / Q000494:pharmacology*; D013270:Stomach / Q000166:cytology; D010738:Type C Phospholipases / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
D000701:Analgesics, Opioid; D007527:Isoenzymes; C048599:N(6)-cyclopentyladenosine; D013004:Somatostatin; D020881:Enkephalin, D-Penicillamine (2,5)-; D010738:Type C Phospholipases; D054799:Phospholipase C beta; D054803:Phospholipase C delta; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D020742:rhoA GTP-Binding Protein; D000241:Adenosine; D002118:Calcium