Expression of the mammalian calcium signaling response to Trypanosoma cruzi in Xenopus laevis oocytes.
Infective stages of the protozoan parasite Trypanosoma cruzi contain a soluble factor that induces elevation in the intracellular free Ca2+ concentration ([Ca2+]i) of mammalian cells. The process is pertussis toxin (PTx)-sensitive, and involves phospholipase C (PLC) activation, inositol 1,4,5-trisphosphate (IP3) formation and Ca2+ release from intracellular stores (Tardieux I, et al. J Exp Med 1994;179:1017-1022; Rodriguez A, et al. J Cell Biol 1995;129:1263-1273). We now report that a molecule exposed on the surface of the target cells is required to trigger the signaling cascade, and that a response with identical characteristics can be induced in Xenopus laevis oocytes injected with mRNA from normal rat kidney (NRK) fibroblasts. Xenopus oocytes do not show an endogenous response to the trypomastigote Ca2+ signaling factor, but a vigorous response in the form of a propagating Ca2+ wave is expressed after injection of NRK cell mRNA. As previously demonstrated for mammalian cells, the response is inhibited when injected oocytes are pretreated with PTx, implicating Galphai or Galphao trimeric G-proteins, and with thapsigargin, which depletes intracellular Ca2+ stores. Moreover, the [Ca2+]i transients triggered by the T. cruzi soluble factor in mRNA-injected oocytes are blocked by the same inhibitors of the parasite oligopeptidase B that abolish the [Ca2+]i response in NRK cells (Burleigh B, Andrews NW. J Biol Chem 1995;270:5172-5180; Burleigh BA et al. J Cell Biol 1997;136:609-620). The NRK mRNA fraction that induces expression of the [Ca2+]i response to the T. cruzi signaling factor contains messages from 1.5 to 2.0 kb, a size range consistent with the family of seven-transmembrane G-protein-coupled receptors.
Leite
M F
MF
Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA.
Moyer
M S
MS
Andrews
N W
NW
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002457:Cell Extracts / Q000494:pharmacology*; D005260:Female; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D015870:Gene Expression; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D009865:Oocytes; D037342:Pertussis Toxin; D011480:Protease Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000494:pharmacology; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D019284:Thapsigargin / Q000494:pharmacology; D014349:Trypanosoma cruzi; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D014982:Xenopus laevis
D002457:Cell Extracts; D011480:Protease Inhibitors; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D010566:Virulence Factors, Bordetella; D019284:Thapsigargin; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D002118:Calcium