A permissive role of pertussis toxin substrate G-protein in P2-purinergic stimulation of phosphoinositide turnover and arachidonate release in FRTL-5 thyroid cells. Cooperative mechanism of signal transduction systems.
Extracellular ATP and other purinergic agonists were found to inhibit cAMP accumulation by depressing adenylate cyclase as an "inhibitory action" and/or to stimulate arachidonate release in association with phospholipase C or A2 activation and Ca2+ mobilization as "stimulatory actions" in FRTL-5 cells. The stimulatory actions of a group of P2-agonists represented by ATP were partially inhibited by the pretreatment of the cells with islet-activating protein (IAP), pertussis toxin, even when an about 41-kDa membrane protein(s) was completely ADP-ribosylated. Only the IAP-sensitive part of the stimulatory actions was antagonized by 1,3-diethyl-8-phenylxanthine (DPX), an adenosine antagonist. GTP and 8-bromoadenosine 5'-triphosphate (Br-ATP) at two to three orders of higher concentrations than ATP also exerted the stimulatory actions, although they were entirely insensitive to both IAP and DPX. Ligand binding experiments with, [35S]ATP gamma S and [3H]DPX showed that ATP occupies both DPX-sensitive and insensitive receptor sites, whereas GTP does only ATP-displaceable DPX-insensitive sites. Thus, lack of sensitivity of GTP action to DPX was associated with its inability to occupy the DPX-sensitive sites. Adenosine 5'-O-(1-thiotriphosphate) (ATP alpha S), adenosine 5'-O-(2-thiodiphosphate) (ADP beta S) and P1-agonists such as AMP and N6-(L-2-phenylisopropyl-adenosine (PIA) did not show any stimulatory action. Nevertheless, the agonists remarkably enhanced the stimulatory actions of GTP or Br-ATP. Such permissive actions of PIA and others were sensitive to both IAP and DPX, as were shown for a part of the stimulatory actions of ATP as well as the "inhibitory actions" of both PIA and ATP. We conclude that an IAP substrate G-protein(s) which mediates the inhibitory action of purinergic agonists via a DPX-sensitive purinergic receptor(s) may not directly link to the phospholipase C or A2 system but enhance the system which links to a DPX-insensitive P2-receptor, in an indirect or permissive manner.
Okajima
F
F
Department of Physical Biochemistry, Gunma University, Maebashi, Japan.
Sato
K
K
Nazarea
M
M
Sho
K
K
Kondo
Y
Y
D000244:Adenosine Diphosphate / Q000378:metabolism / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D037361:Adenylate Cyclase Toxin; D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D000242:Cyclic AMP / Q000037:antagonists & inhibitors / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000502:physiology*; D006160:Guanosine Triphosphate / Q000494:pharmacology; D037342:Pertussis Toxin; D010660:Phenylisopropyladenosine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism*; D051381:Rats; D011983:Receptors, Purinergic / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects; D013961:Thyroid Gland / Q000378:metabolism* / Q000502:physiology; D013972:Thyrotropin / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000037:antagonists & inhibitors / Q000502:physiology*; D014970:Xanthines / Q000494:pharmacology
D037361:Adenylate Cyclase Toxin; D001095:Arachidonic Acids; D010716:Phosphatidylinositols; D011983:Receptors, Purinergic; D010566:Virulence Factors, Bordetella; D014970:Xanthines; D016718:Arachidonic Acid; D010660:Phenylisopropyladenosine; C027512:1,3-diethyl-8-phenylxanthine; D000244:Adenosine Diphosphate; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D013972:Thyrotropin; D000242:Cyclic AMP; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D002118:Calcium