Signal Sequence within FcγRIIA Controls Calcium Wave Propagation Patterns: Apparent Role in Phagolysosome Fusion

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 100; no. 8; pp. 4533 - 4538
• Main Authors: Worth, Randall G., Kim, Moo-Kyung, Kindzelskii, Andrei L., Petty, Howard R., Schreiber, Alan D.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 15.04.2003; National Acad Sciences; The National Academy of Sciences
• Subjects: Amino Acid Motifs; Amino Acid Sequence; Animals; Biological Sciences; Biophysical Phenomena; Biophysics; Calcium; Calcium Signaling; Cell membranes; Chelating Agents - pharmacology; CHO Cells; Cricetinae; Dextrans; Egtazic Acid - analogs & derivatives; Egtazic Acid - pharmacology; Fluorescence; Lysosomes - metabolism; Membrane Fusion - drug effects; Microscopy; Mutation; Neutrophils; Phagocytosis; Phagosomes; Phagosomes - metabolism; Protein Sorting Signals - genetics; Receptors, IgG - genetics; Receptors, IgG - metabolism; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; Wave propagation
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0836650100

Calcium oscillations and traveling calcium waves have been observed in living cells, although amino acid sequences regulating wave directionality and downstream cell functions have not been reported. In this study we identify an amino acid sequence within the cytoplasmic domain of the leukocyte IgG receptor FcγRIIA that affects the amplitude of calcium spikes and the spatiotemporal dynamics of calcium waves in the vicinity of phagosomes. By using high-speed microscopy to map calcium-signaling routes within cells, we have discovered that bound IgG-coated targets trigger two calcium waves traveling in opposite directions about the perimeter of cells expressing FcγRIIA. After phagocytosis, one calcium wave propagates around the plasma membrane to the site of phagocytosis where it splits into two calcium signals: one traveling to and encircling the phagosome once, and the second continuing around the plasma membrane to the point of origin. However, in a genetically engineered form of FcγRIIA containing a mutation in the cytoplasmic L-T-L motif, the calcium signal travels around the plasma membrane, but is not properly routed to the phagosome. Furthermore, these calcium pattern-deficient mutants were unable to support phagolysosome fusion, although recruitment of phagolysosome-associated proteins lysosome-associated protein 1, Rab5, and Rab7 were normal. Our findings suggest that: (i) calcium signaling is a late step in phagolysosome fusion, (ii) a line of communication exists between the plasma membrane and phagosome, and (iii) the L-T-L motif is a signal sequence for calcium signal routing to the phagosome.