Article

Cluster size regulates protein sorting in the immunological synapse

Department of Chemistry, University of California, Berkeley, CA 94720, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.81). 08/2009; 106(31):12729-34. DOI: 10.1073/pnas.0902621106
Source: PubMed

ABSTRACT During antigen recognition by T cells, signaling molecules on the T cell engage ligands on the antigen-presenting cell and organize into spatially distinctive patterns. These are collectively known as the immunological synapse (IS). Causal relationships between large-scale spatial organization and signal transduction have previously been established. Although it is known that receptor transport during IS formation is driven by actin polymerization, the mechanisms by which different proteins become spatially sorted remain unclear. These sorting processes contribute a facet of signal regulation; thus their elucidation is important for ultimately understanding signal transduction through the T cell receptor. Here we investigate protein cluster size as a sorting mechanism using the hybrid live T cell-supported membrane system. The clustering state of the co-stimulatory molecule lymphocyte function-associated antigen-1 (LFA-1) is modulated, either by direct antibody crosslinking or by crosslinking its intercellular adhesion molecule-1 ligand on the supported bilayer. In a mature IS, native LFA-1 generally localizes into a peripheral ring surrounding a central T cell receptor cluster. Higher degrees of LFA-1 clustering, induced by either method, result in progressively more central localization, with the most clustered species fully relocated to the central zone. These results demonstrate that cluster size directly influences protein spatial positioning in the T cell IS. We discuss a sorting mechanism, based on frictional coupling to the actin cytoskeleton, that is consistent with these observations and is, in principle, extendable to all cell surface proteins in the synapse.

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    • "More importantly, ligands conjugated supported lipid bilayers (SLBs) were used as a biomimetic cellecell interaction platform [30e33], where fluidic nature of SLB has shown to manipulate the clustering state of the surface bound ligands with respect to the specific cell location. For example, Hartman et al. have shown that on a SLB surface, ligand accumulates beneath the cell corresponding to the ligandereceptor focal positions but rapidly diffuse to a homogeneous distribution when there is no cell contact [30]. We have further demonstrated extracellular protein conjugated SLBs as a cell culture platform; by employing various extracellular proteins conjugated SLB, the fibroblast 3T3 preferentially adheres on the fibronectin conjugated SLB surface by recognizing the RGD domain. "
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    • "The movement of MCs containing the tyrosine kinase ZAP70 toward the cSMAC also depends strongly on D. This likely reflects the direct association of ZAP70 with phosphorylated ITAM motifs within the TCR complex. Several factors such as cluster size [38], differential coupling to actin flow [33], and integrin engagement [34], [39] have been proposed to affect the movement of signaling MCs at the IS. Our data suggest that membrane fluidity should also be considered. "
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