Leukotriene D4 induces a rapid increase in cAMP in the human epithelial cell line, Int 407: a potential role for this signal in the regulation of calcium influx through the plasma membrane.
Although the LTD4-induced Ca2+ influx in human epithelial cells has been shown to be regulated by a pertussis toxin-sensitive heterotrimeric G-protein, most likely a G alpha i3 protein [Adolfsson J.L.P., Ohd J.F., Sjölander A. Leukotriene D4-induced activation and translocation of the G-protein alpha i3-subunit in human epithelial cells. Biochem Biophys Res Commun 1996; 226: 413-419], the signalling pathway further downstream is still unclear. In the present study, we investigated the possible involvement of cAMP and protein kinase A activity in the LTD4-induced Ca2+ influx in the epithelial cell line Int 407. Stimulation with LTD4, but not with the calcium ionophore ionomycin, triggered a rapid increase (peak at 7 s) in the cellular cAMP level, an effect that was totally abolished by pertussis toxin. Furthermore, the LTD4-induced Ca2+ signal was reduced by 60% when cells that had been pre-incubated with the protein kinase A inhibitor Rp-cAMPS (50 microM for 30 min) were stimulated in a calcium containing medium. In contrast, Rp-cAMPS had no apparent effect on the LTD4-induced Ca2+ signal when the cells were stimulated in a calcium-depleted medium. The immediate LTD4-induced protein tyrosine phosphorylation (15 s), previously shown to be necessary for the subsequent Ca2+ influx, was abolished not only by pretreatment with pertussis toxin but also by exposure to Rp-cAMPS. Furthermore, direct activation of the cellular adenylyl cyclase activity by treatment with forskolin alone induced a prompt Ca2+ signal in the presence, but not in the absence, of extracellular Ca2+, identical results were obtained with the cell permeable cAMP analogue 8-bromo-cAMP. In addition, forskolin induced protein tyrosine phosphorylation similar to that seen with LTD4. These results suggest that protein kinase A activity participates in the regulation of the LTD4-induced Ca2+ influx at a site that is downstream of the activation of the pertussis toxin-sensitive G-protein but upstream of a LTD4-stimulated tyrosine kinase(s).
Grönroos
E
E
Department of Laboratory Medicine, Lund University, Malmö, Sweden.
Thodeti
C K
CK
Sjölander
A
A
D000262:Adenylyl Cyclases / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells; D019204:GTP-Binding Proteins / Q000378:metabolism; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D017998:Leukotriene D4 / Q000502:physiology*; D010766:Phosphorylation; D013873:Thionucleotides / Q000494:pharmacology; D014443:Tyrosine / Q000378:metabolism
D004791:Enzyme Inhibitors; D007527:Isoenzymes; D013873:Thionucleotides; D005576:Colforsin; C016957:adenosine-3',5'-cyclic phosphorothioate; D014443:Tyrosine; D017998:Leukotriene D4; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D002118:Calcium