Cell Biology

STIM1-ulating Phagocytosis

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Science  30 Nov 2012:
Vol. 338, Issue 6111, pp. 1128
DOI: 10.1126/science.338.6111.1128-b
CREDIT: P. NUNES ET AL., CURRENT BIOLOGY 22 (6 NOVEMBER 2012) © 2012 ELSEVIER LTD

Whether the endoplasmic reticulum (ER) fuses with phagosomes has been hotly debated. What is not in dispute is the juxtaposition of these organelles within cells. However, the mechanism and functional significance of this juxtaposition remain unclear. Nunes et al. found that ER membranes do not fuse with phagosomes but are recruited for signaling purposes by STIM1, which regulates the store-operated calcium entry pathway. A combination of fluorescence and electron microscopy in neutrophils from STIM1-deficient mice and in phagocytic fibroblasts lacking STIM1 revealed that STIM1 recruitment to phagosomes is required for efficient phagocytosis. STIM1 also increased the juxtaposition of thin ER cisternae with phagosomes, promoted the shedding of periphagosomal actin rings, and promoted localized calcium elevations. Furthermore, the effects of STIM1 on phagocytosis, actin shedding, and periphagosomal calcium elevations, but not on ER recruitment, required STIM1 to activate its target channels on phagosomes. Thus, STIM1-mediated ER recruitment to phagosomes, rather than initiating fusion, appears to open phagosomal calcium channels to generate localized calcium elevations that promote phagocytosis.

Curr. Biol. 22, 1990 (2012).

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