Calcium requirement for efficient phagocytosis by Dictyostelium discoideum.
Extracellular EDTA suppressed in a dose-dependent manner the phagocytosis of yeast particles by Dictyostelium discoideum cells. Activity was restored fully by the addition of Ca(2+), and partially by the addition of Mn(2+)or Zn(2+), but Mg(2+)was ineffective. The pH-sensitive, Ca(2+)-specific chelator EGTA also inhibited phagocytosis at pH 7.5, but not at pH 5, and Ca(2+)restored the inhibited phagocytosis. In contrast, pinocytosis was unaffected by EDTA. Consistent with the idea that Ca(2+)was required for phagocytosis, D. discoideum growth on bacteria was inhibited by EDTA, which was then restored by the addition of Ca(2+). It is concluded that Ca(2+)was needed for efficient phagocytosis by D. discoideum amoebae. A search for Ca(2+)-dependent membrane proteins enriched in phagosomes revealed the presence of p24, a Ca(2+)-dependent cell-cell adhesion molecule-1 (DdCAD-1) that could be the target of the observed EDTA and EGTA inhibition. DdCAD-1-minus cells, however, had normal phagocytic activity. Furthermore, phagocytosis was inhibited by EDTA and rescued by Ca(2+)in the mutant just as in wild type. Thus, DdCAD-1 was not responsible for the observed Ca(2+)-dependence of phagocytosis, indicating that one or more different Ca(2+)-dependent molecule(s) was involved in the process.
Yuan
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A
School of Biological Sciences, University of Nebraska-Lincoln, Lincoln, NE 68588-0118, USA. dyuan@unlserve.unl.edu
Siu
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CH
Chia
C P
CP
D000818:Animals; D002118:Calcium / Q000737:chemistry* / Q000378:metabolism*; D004023:Dictyostelium / Q000378:metabolism*; D004492:Edetic Acid / Q000737:chemistry; D004533:Egtazic Acid / Q000737:chemistry; D008345:Manganese / Q000737:chemistry / Q000378:metabolism; D010587:Phagocytosis / Q000502:physiology*; D010588:Phagosomes / Q000378:metabolism / Q000648:ultrastructure; D010873:Pinocytosis / Q000502:physiology; D015003:Yeasts; D015032:Zinc / Q000737:chemistry / Q000378:metabolism
D008345:Manganese; D004533:Egtazic Acid; D004492:Edetic Acid; D015032:Zinc; D002118:Calcium