Thyrotropin-induced hydrogen peroxide production in FRTL-5 thyroid cells is mediated not by adenosine 3',5'-monophosphate, but by Ca2+ signaling followed by phospholipase-A2 activation and potentiated by an adenosine derivative.
The production of hydrogen peroxide (H2O2) as an essential process for iodide organification is a key reaction in TSH-induced thyroid hormone synthesis. Here we characterize the signal transduction pathway involved in TSH-induced H2O2 production in FRTL-5 thyroid cells. At higher than 1 nM TSH, N6-(L-2-phenylisopropyl)adenosine (PIA), an adenosine receptor agonist having, by itself, no influence on H2O2 generation, potentiated this TSH action, whereas the TSH increase and PIA addition reduced cAMP accumulation. RO 20-1724, a phosphodiesterase inhibitor, amplified the TSH-induced cAMP accumulation, but did not change H2O2 generation in the whole range of TSH used. Ca(2+)-mobilizing agonists, GTP and ATP, also induced H2O2 production without stimulating cAMP accumulation. Chelation of intracellular Ca2+ markedly inhibited the TSH action, but intracellular Ca2+ increases by either thapsigargin or ionomycin mimicking it. All of the findings show the participation of Ca2+, but not cAMP, in the action of TSH. Desensitization of protein kinase-C (PKC) did not influence the receptor-mediated H2O2 production, suggesting the reduced importance of PKC activation compared to Ca2+ signaling to the reaction. A rise in intracellular Ca2+ independent of receptor activation also induced H2O2 production as well as arachidonate release, and both were potentiated by PIA. In addition, inhibitors of phospholipase-A2 and the arachidonate metabolic pathway depressed H2O2 generation, suggesting the participation of an arachidonate cascade in the Ca(2+)-dependent H2O2 production. Lipoxygenase inhibitors depressed the Ca2+ action without influencing arachidonate release, suggesting the involvement of a lipoxygenase product(s) of arachidonate in the Ca(2+)-signaling mechanism. In conclusion, in FRTL-5 cells, TSH-induced H2O2 production is mediated not by cAMP, but by the phospholipase-C/Ca2+ cascade, possibly followed by the Ca(2+)-dependent phospholipase-A2/arachidonate cascade. PIA amplifies TSH-induced H2O2 production at the steps of phospholipase-C and phospholipase-A2 activation in a pertussis toxin-sensitive manner.
Kimura
T
T
Department of Physical Biochemistry, Gunma University, Maebashi, Japan.
Okajima
F
F
Sho
K
K
Kobayashi
I
I
Kondo
Y
Y
D000241:Adenosine / Q000031:analogs & derivatives*; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D000242:Cyclic AMP / Q000502:physiology; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000502:physiology; D006861:Hydrogen Peroxide / Q000378:metabolism*; D037342:Pertussis Toxin; D010660:Phenylisopropyladenosine / Q000494:pharmacology; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction; D013961:Thyroid Gland / Q000166:cytology / Q000378:metabolism*; D013972:Thyrotropin / Q000494:pharmacology*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D010566:Virulence Factors, Bordetella; D016718:Arachidonic Acid; D010660:Phenylisopropyladenosine; D013972:Thyrotropin; D006861:Hydrogen Peroxide; D000242:Cyclic AMP; D037342:Pertussis Toxin; D011493:Protein Kinase C; D010741:Phospholipases A; D054467:Phospholipases A2; D019204:GTP-Binding Proteins; D000241:Adenosine; D002118:Calcium