After removal of cell surface CD4 and LAG-3 with pronase treatment, cells were incubated with colchicine (tubulin polymerization inhibitor) or cytochalasine D (actin polymerization inhibitor) for 3 h and the restoration of cell surface CD4 and LAG-3 was measured. Brefeldin A, which was shown above to block the restoration MG-132 datasheet of LAG-3/CD4 expression, was included as a positive control. Surprisingly, actin and tubulin depolymerization did not affect restoration of cell surface CD4 and LAG-3 (Fig.
4). To confirm disruption of actin and tubulin after inhibitor treatment, we stained actin and tubulin in inhibitor-treated cells and verified disruption of actin and tubulin by confocal microscopy (data not shown). We then incubated pronase-treated T cells with different vesicular acidification/function inhibitors (NH4Cl, chloroquine, concanamycin A). Interestingly, all three inhibitors decreased CD4 and LAG-3 cell surface restoration in
T cells (Fig. 4), suggesting that vesicular acidification/function was required for the restoration of both molecules. To assess the subcellular location of LAG-3 and CD4, we treated activated T cells with pronase, and then RAD001 permeabilized and stained with anti-CD4 or anti-LAG-3 in conjunction with Ab against different subcellular markers for analysis by confocal microscopy. A significant proportion of LAG-3 appeared to colocalize with the microtubule organizing center (MTOC), using γ-tubulin as a marker (Fig. 5A). While the colocalization of γ-tubulin with LAG-3 was statistically greater than with CD4, as determined using Pearson coefficient analysis (Fig. 5C), some CD4/γ-tubulin colocalization was still evident. A significant proportion of both intracellular CD4 and LAG-3 appeared to colocalize with the early and recycling endosome marker, early endosomal antigen 1 (EEA1), which likely represents newly synthesized protein that is on route to the cell surface and/or Sunitinib molecular weight in the process of recycling (Fig. 5B and D). To further investigate subcellular location and possible intracellular trafficking pathway of CD4 and LAG-3, we used Rab11b, which is a marker of the endosomal recycling compartment, and Rab27a, which plays a critical role
in secretory lysosome-dependent exocytosis. In the staining of both markers, a significantly higher proportion of LAG-3 appeared to colocalize with Rab11b and Rab27a than CD4, although this was most evident with Rab11b:LAG-3 colocalization (Fig. 6). These observations suggest that CD4 and LAG-3 have partially overlapping but distinct patterns of intracellular location and trafficking mechanisms that might play an important role in regulating LAG-3 membrane expression in activated T cells. Finally, we asked which domains of CD4 and LAG-3 are important for their differential intracellular retention. We generated a panel of LAG-3/CD4 chimeric constructs that were transduced into a LAG-3−/CD4− 3A9 T-cell hybridoma (Supporting Information Fig. 1A).