Extracellular nucleotides activate the p38‐stress‐activated protein kinase cascade in glomerular mesangial cells

Extracellular ATP and UTP have been reported to activate a nucleotide receptor (P2Y 2 ‐receptor) that mediates arachidonic acid release with subsequent prostaglandin formation, a reaction critically depending on the activity of a cytosolic phospholipase A 2 . In addition, extracellular nucleotides trigger activation of the classical mitogen‐activated protein kinase (MAPK) cascade and cell proliferation as well as of the stress‐activated protein kinase (SAPK) cascade. In this study, we report that ATP and UTP are also able to activate the p38‐MAPK pathway as measured by phosphorylation of the p38‐MAPK and its upstream activators MKK3/6, as well as phosphorylation of the transcription factor ATF 2 in a immunocomplex‐kinase assay. Time courses reveal that ATP and UTP induce a rapid and transient activation of the p38‐MAPK activity with a maximal activation after 5 min of stimulation which declined to control levels over the next 20 min. A series of ATP and UPT analogues were tested for their ability to stimulate p38‐MAPK activity. UTP and ATP were very effective analogues to activate p38‐MAPK, whereas ADP and γ‐thio‐ATP had only moderate activating effects. 2‐Methyl‐thio‐ATP, βγ‐imido‐ATP, AMP, adenosine and UDP had no significant effects of p38‐MAPK activity. In addition, the extracellular nucleotide‐mediated effect on p38‐MAPK was almost completely blocked by 1 m M of suramin, a putative P2‐purinoceptor antagonist. In summary, these results demonstrate for the first time that extracellular nucleotides are able to activate the MKK3/6‐ p38‐MAPK cascade most likely via the P2Y 2 ‐receptor. Moreover, this finding implies that all three MAPK subtypes are signalling candidates for extracellular nucleotide‐stimulated cell responses.British Journal of Pharmacology (2000) 129 , 612–618; doi: 10.1038/sj.bjp.0703077