Synaptotagmin II could confer Ca(2+) sensitivity to phagocytosis in human neutrophils.
Phagolysosome fusion and granule exocytosis in neutrophils are calcium-dependent processes. The calcium requirements vary between granule types, suggesting the presence of different calcium sensors. The synaptotagmins, a family of calcium-binding proteins, previously shown to participate in vesicle fusion and vesicle recycling in excitable cells, are putative calcium-sensors of exocytosis in excitable cells. In this study, we show that synaptotagmin II is present in human neutrophils and may participate in phagocytic and in exocytotic processes. In protein extracts from human neutrophils, we identified synaptotagmin II by Western blot as an 80 kDa protein. Subcellular fractionation revealed that synaptotagmin II was associated with the specific granules. In fMLP-stimulated cells, synaptotagmin II translocated to the plasma membrane. This correlated with the upregulation of complement receptor 3 (CR 3), reflecting the translocation of specific granules to the cell surface. Synaptotagmin II also translocated to the phagosome after complement-mediated phagocytosis in the presence of calcium. LAMP-1 translocated in parallel but probably was located to another subcellular compartment than synaptotagmin II. Under calcium-reduced conditions, neither synaptotagmin II nor LAMP-1 translocated to the phagosome. We therefore suggest a role for synaptotagmin II as calcium-sensor during phagocytosis and secretion in neutrophils.
Lindmark
I Maria
IM
Division of Medical Microbiology IMK, Linköping University, SE-581 85, Linköping, Sweden. malin@ihm.liu.se
Karlsson
Anna
A
Serrander
Lena
L
Francois
Patrice
P
Lew
Daniel
D
Rasmusson
Birgitta
B
Stendahl
Olle
O
Nüsse
Oliver
O
D000818:Animals; D015703:Antigens, CD / Q000378:metabolism; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D005089:Exocytosis / Q000502:physiology; D006801:Humans; D066298:In Vitro Techniques; D051907:Lysosomal Membrane Proteins; D008561:Membrane Fusion / Q000502:physiology; D008562:Membrane Glycoproteins / Q000378:metabolism; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009419:Nerve Tissue Proteins / Q000502:physiology*; D009504:Neutrophils / Q000187:drug effects / Q000502:physiology*; D010587:Phagocytosis / Q000502:physiology*; D010588:Phagosomes / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013347:Subcellular Fractions / Q000378:metabolism; D050861:Synaptotagmin II
D015703:Antigens, CD; D051907:Lysosomal Membrane Proteins; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; C494262:SYT2 protein, human; D050861:Synaptotagmin II; C494264:Syt2 protein, rat; D009240:N-Formylmethionine Leucyl-Phenylalanine; D002118:Calcium