Extracellular nucleotides activate the p38-stress-activated protein kinasecascade in glomerular mesangial cells

1 Extracellular ATP and UTP have been reported to activate a nucleotide rec eptor (P2Y(2)-receptor) that mediates arachidonic acid release with subsequ ent prostaglandin formation, a reaction critically depending on the activit y of a cytosolic phospholipase AL In addition, extracellular nucleotides tr igger activation of the classical mitogen-activated protein kinase (MAPK) c ascade and cell proliferation as well as of the stress-activated protein ki nase (SAPK) cascade. 2 In this study. we report that ATP and UTP are also able to activate the p 38-MAPK pathway as measured by phosphorylation of the p38-MAPK and its upst ream activators MKK3/6, as well as phosphorylation of the transcription fac tor ATF(2) in a immunocomplex-kinase assay. 3 Time courses reveal that ATP and UTP induce a rapid and transient activat ion of the p38-MAPK activity with a maximal activation after 5 min of stimu lation which declined to control levels over the next 20 min. 4 A series of ATP and UPT analogues were tested for their ability to stimul ate p38-MAPK activity. UTP and ATP were very effective analogues to activat e p38-MAPK, whereas ADP and gamma-thio-ATP had only moderate activating eff ects. 2-Methyl-thio-ATP, beta gamma-imido-ATP, AMP, adenosine and UDP had n o 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. 5 In summary. these results demonstrate for the first time that extracellul ar nucleotides are able to activate the MKK3/6- p38-MAPK cascade most likel y ria the P2Y(2)-receptor, Moreover, this finding implies that all three MA PK subtypes are signalling candidates for extracellular nucleotide-stimulat ed cell responses.