Leukotriene D4-induced mobilization of intracellular Ca2+ in epithelial cells is critically dependent on activation of the small GTP-binding protein Rho.
We have previously shown that the leukotriene D4 (LTD4)-induced mobilization of intracellular Ca2+ in epithelial cells is mediated by a G-protein that is distinctly different from the pertussis toxin-sensitive G-protein that regulates the subsequent influx of Ca2+. In the present study, we attempted to gain further knowledge about the mechanisms involved in the LTD4-induced mobilization of intracellular Ca2+ in epithelial cells by investigating the effects of compactin, an inhibitor of the isoprenylation pathway, on this signalling event. In cells preincubated with 10 microM compactin for 48 h, the LTD4-induced mobilization of intracellular Ca2+ was reduced by 75% in comparison with control cells. This reduction was reversed by co-administration of mevalonate (1 mM). The effect of compactin occurred regardless of whether or not Ca2+ was present in the extracellular medium, suggesting that isoprenylation must occur before Ca2+ is released from intracellular stores. In accordance with this, we also found that both the LTD4-induced formation of inositol 1,4,5-trisphosphate and the LTD4-induced phosphorylation of phospholipase C gamma 1 (PLC gamma 1) on tyrosine residues were significantly reduced in compactin-pretreated cells. These results open up the possibility that the activation of PLC gamma 1 is related to a molecule that is sensitive to impaired activity of the isoprenylation pathway, such as a small monomeric G-protein. This idea was supported by the observation that Clostridium botulinum C3 exoenzyme-induced inhibition of Rho proteins abolished the LTD4-induced intracellular mobilization of Ca2+. A regulatory role of Rho proteins in the LTD4-induced activation of PLC gamma 1 is unlikely to be indirectly mediated via an effect on the cytoskeleton, since cytochalasin D had no major effect on the LTD4-induced mobilization of Ca2+. Although the mechanism of interaction remains to be elucidated, the present findings indicate an important role of an isoprenylated protein such as Rho in the LTD4-induced Ca2+ signal.
Grönroos
E
E
Department of Cell Biology, Faculty of Health Sciences, Linköping University, Sweden.
Andersson
T
T
Schippert
A
A
Zheng
L
L
Sjölander
A
A
D036002:ADP Ribose Transferases / Q000494:pharmacology; D001905:Botulinum Toxins; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D015638:Cytochalasin D / Q000494:pharmacology; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D007422:Intestines; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D017998:Leukotriene D4 / Q000494:pharmacology*; D008148:Lovastatin / Q000031:analogs & derivatives* / Q000494:pharmacology; D008565:Membrane Proteins / Q000378:metabolism*; D008798:Mevalonic Acid / Q000494:pharmacology; D017368:Protein Prenylation; D015398:Signal Transduction / Q000187:drug effects*; D010738:Type C Phospholipases / Q000378:metabolism; D020743:rhoB GTP-Binding Protein
D004791:Enzyme Inhibitors; D007527:Isoenzymes; D008565:Membrane Proteins; C012258:mevastatin; D015638:Cytochalasin D; D017998:Leukotriene D4; D015544:Inositol 1,4,5-Trisphosphate; D008148:Lovastatin; D036002:ADP Ribose Transferases; C063007:exoenzyme C3, Clostridium botulinum; D010738:Type C Phospholipases; D001905:Botulinum Toxins; D019204:GTP-Binding Proteins; D020743:rhoB GTP-Binding Protein; D008798:Mevalonic Acid; D002118:Calcium