Stimulation by extracellular ATP and UTP of the stress-activated protein kinase cascade in rat renal mesangial cells

Abstract

1. Extracellular adenosine 5′-triphosphate (ATP) and uridine 5′-triphosphate (UTP) have been shown to activate a nucleotide receptor (P_2U receptor) in rat mesangial cells that mediates phosphoinositide and phosphatidylcholine hydrolysis by phospholipases C and D, respectively. This is followed by an increased activity of the mitogen-activated protein kinase cascade and cell proliferation. Here we show that ATP and UTP potently stimulate the stress-activated protein kinase pathway and phosphorylation of the transcription factor c-Jun.

2. Both nucleotides stimulated a rapid (within 5 min) and concentration-dependent activation of stress-activated protein kinases as measured by the phosphorylation of c-Jun in a solid phase kinase assay.

3. When added at 100 μM the rank order of potency of a series of nucleotide analogues for stimulation of c-Jun phosphorylation was UTP>ATP=UDP=ATPγS>2-methylthio-ATP>βγ-imido-ATP= ADP>AMP=UMP=adenosine=uridine. Activation of stress-activated protein kinase activity by ATP and UTP was dose-dependently attenuated by suramin.

4. Down-regulation of protein kinase C-α, -δ and -ε isoenzymes by 24 h treatment of the cells with 12-O-tetradecanoylphorbol 13-acetate did not inhibit ATP- and UTP-induced activation of c-Jun phosphorylation. Furthermore, the specific protein kinase C inhibitors, CGP 41251 and Ro 31-8220, did not inhibit nucleotide-stimulated c-Jun phosphorylation, suggesting that protein kinase C is not involved in ATP- and UTP-triggered stress-activated protein kinase activation.

5. Pretreatment of the cells with pertussis toxin or the tyrosine kinase inhibitor, genistein, strongly attenuated ATP- and UTP-induced c-Jun phosphorylation. Furthermore, N-acetyl-cysteine completely blocked the activation of stress-activated protein kinase in response to extracellular nucleotide stimulation.

6. In summary, these results suggest that ATP and UTP trigger the activation of the stress-activated protein kinase module in mesangial cells by a pathway independent of protein kinase C but requiring a pertussis toxin – sensitive G-protein and tyrosine kinase activation.

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