F-actin dynamics control segregation of the TCR signaling cascade to clustered lipid rafts.
Following ligand binding the TCR segregates to plasma membrane microdomains, termed lipid rafts, characterized by a highly ordered lipid structure favoring partitioning of glycosyl phosphatidyl inositol-linked costimulatory receptors and acylated signaling molecules. Here we show that the inducible association of the TCR and key signaling proteins with lipid rafts is dependent on the actin cytoskeleton through a mechanism involving raft coalescence. Although lipid rafts are required for full activation of the TCR-dependent tyrosine phosphorylation cascade and sustained signaling, triggering of TCR-proximal events, including Fyn activation and a first wave of Vav phosphorylation, is independent of lipid rafts, while a second wave of raft-dependent Vav phosphorylation occurs after raft coalescence, as also supported by the finding that Vav is phosphorylated in response to lipid raft clustering by GM1 aggregation. The constitutive association found between Vav and the CD3zeta chain suggests a model whereby the TCR-associated signaling machinery initiates raft aggregation by promoting F-actin reorganization, which permits full activation of the tyrosine phosphorylation cascade, further reorganization of the actin cytoskeleton and sustained signaling, leading to cell activation.
Valensin
Silvia
S
Laboratory of Molecular Biology, Department of Evolutionary Biology, University of Siena, Siena, Italy.
Paccani
Silvia Rossi
SR
Ulivieri
Cristina
C
Mercati
David
D
Pacini
Sonia
S
Patrussi
Laura
L
Hirst
Tim
T
Lupetti
Pietro
P
Baldari
Cosima T
CT
D000199:Actins / Q000378:metabolism*; D018797:Cell Cycle Proteins; D003599:Cytoskeleton / Q000276:immunology / Q000378:metabolism; D006801:Humans; D019169:Jurkat Cells; D021962:Membrane Microdomains / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D008854:Microscopy, Electron; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051076:Proto-Oncogene Proteins c-fyn; D051567:Proto-Oncogene Proteins c-vav; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism; D051746:ZAP-70 Protein-Tyrosine Kinase
D000199:Actins; D018797:Cell Cycle Proteins; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D051567:Proto-Oncogene Proteins c-vav; D011948:Receptors, Antigen, T-Cell; D011993:Recombinant Fusion Proteins; C496618:VAV1 protein, human; C054979:antigen T cell receptor, zeta chain; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; C494957:FYN protein, human; D051076:Proto-Oncogene Proteins c-fyn; D051746:ZAP-70 Protein-Tyrosine Kinase; C497261:ZAP70 protein, human