Synaptotagmin-mediated vesicle fusion regulates cell migration

Richard A Colvin., et al. 2010. Nat Immunol. 11(6):495-502

Speaker: Chia-Yun Wu (吳佳芸)                               Time: 13:10~14:00, Oct. 20, 2010

Commentator: Dr. Yee-Shin Lin (林以行 博士)   Place: Room 611

Abstract:

Chemokines and chemoattrants direct cell migration which is essential for inflammatory and immune responses delivery and formation¹. Chemokines and chemoattrants bind to their receptors, a subfamily of G protein-coupled receptors on all leukocyte lineages, which activates the G protein and release the Gα and Gβγ subunits. In turn The Gβγ subunits active the phospholipase C, phosphatidylinositol-3-OH kinase, and Rho family signaling pathways to induce cell migration². However, there are many unknown gaps in how chemoattrants control the highly integrated process of cell migration. In the study, the authors used a lentivirus RNA-mediated interference (RNAi) based shRNA library and transwell assay to identify novel genes under CXCL12/CXCR4-mediated chemotaxis. And they found the genes which encode the synaptotagmin (SYT) family of calcium-dependent regulator of vesicle fusion could influence cell migration. SYT2 was a negative regulator, whereas SYTL5 and SYT7 were positive regulators of CXCL12/CXCR4-mediated chemotaxis. Meanwhile, they found that the small GTPases Rab27a and Rab3a, which regulate vesicle fusion and lysosome exocytosis with SYT, also participated in the situation. To explore the migration defect of lacking SYT, they showed that SYT7^-/- bone marrow derived cells had less migration distance, velocity, directionality and cell polarization than control cells. Using a murine gout inflammation model they also found that the percentage and number of bone marrow derived cells in SYT7^-/- mice were much lower than that in wild-type mice but not due to lost the expressions of chemokines. To interpret the mechanism of SYT that affect CXCL12/CXCR4-mediatedchemotaxis, they showed that knockdown of Rab and SYT did not affect the surface expression of CXCR4 receptor, the activation of the small GTPases Rho, Cdc42 and Rac for cell migration², the calcium influx and the F-actin polymerization for effective directional cell migration. SYT proteins have calcium-sensing domain that mediate vesicle fusion³. Using calcium chelator BAPTA to block the calcium influx after stimulation, the expression of lysosomal marker LAMP-1 on the cell surface and the migration percentage were much lower than control. Using time-lapse confocal microscopy, they showed that the migrating SYT^-/- cells had much more lysosomes accumulating in the distal ends of the uropods and had difficulty releasing uropods which resulted in impaired cell migration. In summary, after chemokines stimulation induced calcium influx, the SYT proteins that sense calcium to regulate lysosome exocytosis and uropod release to delivering factor to cell surface are essential for cell migration.

References:

1.      Viola, A. & Luster, A.D. Chemokines and their receptors: drug targets in immunity and inflammation. Annu. Rev. Pharmacol. Toxicol. 48, 171–197 (2008).

2.      Thelen, M. & Stein, J.V. How chemokines invite leukocytes to dance. Nat. Immunol. 9, 953–959 (2008).

3.      Martinez, I. et al. Synaptotagmin VII regulates Ca2+-dependent exocytosis of lysosomes in fibroblasts. J. Cell Biol. 148, 1141–1149 (2000).