Surface LAT Signals

Science Signaling  26 Mar 2013:
Vol. 6, Issue 268, pp. ec72
DOI: 10.1126/scisignal.2004172

Engagement of the T cell receptor (TCR) complex by antigen leads to the activation of T cells. One of the early events in TCR signaling is the phosphorylation and recruitment of the adaptor protein LAT (linker for activation of T cells) into microclusters (signaling complexes) at the cell surface. LAT is a transmembrane protein that is found at the plasma membrane and in intracellular vesicles; however, whether a combination of cell-surface and vesicular LAT is required for T cell activation or whether vesicular LAT alone is sufficient is controversial. Balagopalan et al. fused the extracellular domain of the receptor CD4 to LAT, which enabled monitoring of plasma membrane–localized CD4-LAT with an antibody specific for CD4. Imaging of CD4-LAT–expressing cells that were incubated with the CD4-specific antibody on ice before being exposed to coverslips coated with an antibody that activated the TCR at 37°C showed that plasma membrane–localized CD4-LAT was recruited into microclusters in cells fixed 2 minutes after activation. In addition, live-cell imaging showed the recruitment of CD4-LAT into microclusters within seconds of TCR activation. Western blotting analysis of CD4-LAT–expressing cells that were labeled with a membrane-impermeable biotinylation reagent, incubated on activating coverslips, and then subjected to avidin-based purification showed that plasma membrane–localized CD4-LAT was phosphorylated within 2 minutes after TCR stimulation. Further analysis suggested that 90% of phosphorylated LAT in these cells was derived from the cell surface. Together, these data indicate that at early times after T cell activation, plasma membrane–localized LAT is efficiently phosphorylated and recruited into microclusters, suggesting that vesicular LAT may be recruited at later time points.

L. Balagopalan, V. A. Barr, R. L. Kortum, A. K. Park, L. E. Samelson, Cutting edge: Cell surface linker for activation of T cells is recruited to microclusters and is active in signaling. J. Immunol. Published online before print 13 March 2013, doi:10.4049/jimmunol.1202760 [Online Journal]