부산대학교 도서관

1 Extracellular nucleotides can activate a common purinoceptor mediating various cell responses. In this study we report that stimulation of rat mesangial cells with ATP and UTP leads to a rapid activation of the protein kinase B/Akt (PKB) pathway. Time-course studies reveal a rapid and transient phosphorylation of both Ser[sup 473]and Thr[sup308] of PKB with a maximal effect after 5 min of Stimulation. The response is concentration-dependent with a maximal effect at 30 μM of ATP and UTP. Western blot analysis of mesangial cells reveals the expression of the isoenzymes PKB-α and PKB-γ but not the PKB-β. 2 ATP and UTP also activate the upstream located PI 3-kinase-dependent kinase. Furthermore. the ATP- and UTP-induced PKB phosphorylation is abolished by two inhibitors of the PI 3-kinase. In addition, suramin, a putative P2Y[sub2] receptor antagonist, and pertussis toxin, an inhibitor of G[sub1]/G[sub0] activation, markedly block ATP- and UTP-induced PKB phosphorylation. 3 A series of ATP and UTP analogues were tested for their ability to stimulate PKB phosphorylation, UTP, ATP and γ-thio-ATP are the only compounds capable of activating PKB. 4 Stress-induced apoptosis of mesangial cells is reduced by the stable ATP analogue, γ-thio-ATP, and this inhibitory effect is reversed in the presence of LY 294002. 5 In summary, these results demonstrate that extracellular nucleotides are able to activate the PI 3-kinase/PDK/PKB cascade via the P2Y[sub2]-receptor and a pertussis toxin-sensitive G[sub1] protein. Moreover, in mesangial cells this cascade may have an important role in the antiapoptotic response but not in the mitogenic or inflammatory response produced by extracellular nucleotides. [ABSTRACT FROM AUTHOR]