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Characterization of G Protein-coupled Receptors by a Fluorescence-based Calcium Mobilization Assay
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Signal transduction during cannibalistic sexual phagocytosis: calcium is not the trigger but GTP-binding protein

K E Lewis1, D D Browning, D H O'Day

  • 1Department of Zoology, Erindale College, University of Toronto, Mississauga, Ontario, Canada.

Cellular Signalling
|February 1, 1994
PubMed

Insights

Calcium does not trigger cannibalistic phagocytosis in Dictyostelium discoideum. Instead, GTP-binding proteins in cell membranes are crucial for this engulfment process during sexual reproduction.

Area of Science:

  • Cell Biology
  • Developmental Biology
  • Biochemistry

Background:

  • Dictyostelium discoideum undergoes sexual reproduction, forming a zygote giant cell.
  • This zygote engulfs hundreds of surrounding amoebae through a process termed sexual phagocytosis.
  • The molecular mechanisms triggering this phagocytosis are not fully understood.

Purpose of the Study:

  • To investigate the role of intracellular calcium and GTP-binding proteins in Dictyostelium discoideum sexual phagocytosis.
  • To identify potential molecular triggers and signaling pathways involved in zygote engulfment.

Main Methods:

  • Pharmacological inhibition of calcium signaling pathways and downstream effectors.
  • Treatment with nucleotide analogues (GTPγS, GDPβS) to assess GTP-binding protein involvement.
  • Cellular sub-fractionation, SDS-PAGE, western blotting, and immunolocalization to identify specific proteins.

Main Results:

  • Pharmacological agents affecting intracellular calcium levels, except A23187, did not inhibit sexual phagocytosis.
  • Inhibitors of calmodulin and protein kinase C also failed to alter the phagocytic process.
  • GTPγS and GDPβS significantly inhibited sexual phagocytosis, implicating GTP-binding proteins.
  • GTP-binding proteins were identified in both cell membrane and intracellular membrane fractions of phagocytic cells.

Conclusions:

  • Intracellular calcium is unlikely to be the primary trigger for sexual phagocytosis in Dictyostelium discoideum.
  • GTP-binding protein activity is essential for sexual phagocytosis.
  • Specific GTP-binding proteins located in cell membranes may play a key role in mediating this engulfment process.

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