Mechanisms of phospholipase C activation by the vasoactive intestinal polypeptide/pituitary adenylate cyclase-activating polypeptide type 2 receptor.
The vasoactive intestinal polypeptide/pituitary adenylate cyclase-activating polypeptide type 2 (VPAC(2)) receptor was shown to induce both [(3)H]inositol phosphate ([(3)H]InsP)and cAMP production in transfected COS7 cells and in GH(3) cells where it is natively expressed. Neither cholera toxin nor forskolin could elicit an equivalent [(3)H]InsP response, suggesting independent coupling of the two pathways. The VPAC(2) receptor-mediated [(3)H]InsP response was partially inhibited by pertussis toxin (Ptx) and by the G beta gamma-sequestering C-terminal fragment of GRK2 (GRK2-ct) in COS7 and GH(3) cells, whereas responses of control receptors were unaffected. Blockers of receptor-activated Ca(2+) influx pathways (Co(2+) and SKF 96365) also partially inhibited VPAC(2) receptor-mediated [(3)H]InsP responses. This inhibition was not present in the component of the response remaining after Ptx treatment. A range of blockers of voltage-sensitive Ca(2+) channels were ineffective, consistent with the reported lack of these channels in COS7 cells. The data suggest that the VPAC(2) receptor may couple to phospholipase C through both Ptx-insensitive and Ptx-sensitive G proteins (G(q/11) and G(i/o), respectively) to generate [(3)H]InsP. In addition to G beta gamma, G(i/o) activation appears to require receptor-activated Ca(2+) entry. This is consistent with the possibility that not only G alpha(q/11)-responsive and G beta gamma-responsive isoforms of phospholipase C but also Ca(2+)-responsive forms may contribute to the overall [(3)H]InsP response.
MacKenzie
C J
CJ
Medical Research Council Membrane and Adapter Proteins Co-operative Group, Membrane Biology Group, Department of Biomedical Sciences, University of Edinburgh, Edinburgh, United Kingdom EH8 9XD.
Lutz
E M
EM
Johnson
M S
MS
Robertson
D N
DN
Holland
P J
PJ
Mitchell
R
R
D037361:Adenylate Cyclase Toxin; D000818:Animals; D019556:COS Cells; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D004789:Enzyme Activation / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000502:physiology; D007295:Inositol Phosphates / Q000096:biosynthesis; D037342:Pertussis Toxin; D020033:Protein Isoforms / Q000502:physiology; D051236:Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide; D011979:Receptors, Pituitary Hormone / Q000502:physiology*; D018005:Receptors, Vasoactive Intestinal Peptide / Q000502:physiology*; D051239:Receptors, Vasoactive Intestinal Peptide, Type II; D015398:Signal Transduction; D010738:Type C Phospholipases / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D037361:Adenylate Cyclase Toxin; D007295:Inositol Phosphates; D020033:Protein Isoforms; D051236:Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide; D011979:Receptors, Pituitary Hormone; D018005:Receptors, Vasoactive Intestinal Peptide; D051239:Receptors, Vasoactive Intestinal Peptide, Type II; D010566:Virulence Factors, Bordetella; D037342:Pertussis Toxin; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D002118:Calcium