Extracellular ATP counteracts the ERK1/2-mediated death-promoting signaling cascades in astrocytes

Oxidative stress is the main cause of neuronal death in pathological conditions. Hydrogen peroxide (H₂O₂), one of the reactive oxygen species, activates many intracellular signaling cascades including src family and mitogen-activated protein kinases (MAPKs), some of which are critically involved in the induction of cellular damage. We previously showed that H₂O₂-induced cell death in astrocytes and adenosine 5′-triphosphate (ATP), acting on P2Y₁ receptors, had a protective effect. Here, we examined the H₂O2-induced changes in intracellular signaling cascades that promote cell death in astrocytes, showing the molecular mechanisms by which the activation of P2Y₁ receptors counteracts such signals. Although H₂O₂ activated three MAPKs including ERK1/2, p38, and JNK, only the activation of ERK1/2 participated in the H₂O₂-evoked cell death. H₂O₂ induced a sustained activation of ERK1/2 mainly in the nucleus region, which was well in accordance with the H₂O₂-induced cell death. H₂O₂ also activated the src tyrosine kinase family, which was an upstream signal for ERK1/2. Activation of P2Y₁ receptors by 2methylthio-ADP (2MeSADP) inhibited the H₂O₂-evoked activation of src tyrosine kinase, resulting in the inhibition of the phosphorylated-ERK1/2 accumulation in the nucleus. 2MeSADP enhanced the gene expression and activity of protein tyrosine phosphatase (PTP), which was responsible for the inhibition of src tyrosine kinase. Thioredoxin reductase, another cytoprotective gene we previously showed to be upregulated by 2MeSADP, also controlled the activity of PTP. Taken together, ATP, acting on P2Y ₁ receptors, upregulates the PTP expression and its activity, which counteracts the H₂O₂-promoted death signaling cascades including ERK1/2 and its upstream signal src tyrosine kinase in astrocytes.