Extracellular ATP-mediated phospholipase a2 activation in rat thyroid FRTL-5 cells: Regulation by a Gi/Go protein, Ca2+, and mitogen-activated protein kinase
✍ Scribed by Elina Ekokoski; Benoit Dugué; Minna Vainio; Petri J. Vainio; Kid Törnquist
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- English
- Weight
- 234 KB
- Volume
- 183
- Category
- Article
- ISSN
- 0021-9541
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✦ Synopsis
We investigated the mechanism of phospholipase A 2 (PLA 2 ) activation in response to the P2 receptor agonist ATP in rat thyroid FRTL-5 cells. The PLA 2 activity was determined by measuring the release of [ 3 H]-arachidonic acid (AA) from prelabeled cells. ATP evoked a dose-and time-dependent AA release. This release was totally inhibited by pertussis toxin (PTX) treatment, indicating the involvement of a G i /G o protein. The AA release was also diminished by chelating extracellular Ca 2ϩ with EGTA or by inhibiting influx of Ca 2ϩ using Ni 2ϩ . Although the activation of protein kinase C (PKC) by 12-phorbol 13-myristate acetate (PMA) alone did not induce any AA release, the ATP-evoked AA release was significantly reduced when PKC was inhibited by GF109203X or by a long incubation with PMA to downregulate PKC. Both the ATP-evoked AA release and the mitogen-activated protein kinase (MAP kinase) phosphorylation were decreased by the MAP kinase kinase (MEK) inhibitor PD98059. Furthermore, the ATP-evoked MAP kinase phosphorylation was also inhibited by GF109203X and by downregulation of PKC, suggesting a PKC-mediated activation of MAP kinase. Inhibiting Src-like kinases by PP1 attenuated both the MAP kinase phosphorylation and the AA release. These results suggest that these kinases are involved in the regulation of MAP kinase and PLA 2 activation. Elevation of intracellular cAMP by TSH or by dBucAMP did not induce a phosphorylation of MAP kinase. Furthermore, neither the ATP-evoked AA release nor the MAP kinase phosphorylation were attenuated by TSH or dBucAMP. Taken together, our results suggest that ATP regulates the activation of PLA 2 by a G i /G o protein-dependent mechanism. Moreover, Ca 2ϩ , PKC, MAP kinase, and Src-like kinases are also involved in this regulatory process.