The GTPase Rab39a promotes phagosome maturation into MHC-I antigen-presenting compartments (2019)
Figure 6

Figure 6. Effect of Rab39a on intraphagosomal protein degradation

(A) DC3.2-Rab39a-H2-Ld cells (Rab39a KO with dox-inducible Rab39a) were incubated with 1 µg/ml dox overnight to induce Rab39a expression. 1x106 cells were fed at 4 beads/cell of biotinylated-Ova-magnetic-beads for 4 hours with the indicated inhibitors. Magnetic-bead phagosomes were isolated using the listed protocol. Phagosomes were washed, fixed, permeabilized and stained for Open and Closed (30-5-7s) forms of H2-Ld. Representative histograms of two independent experiments shown.

(B) Cells as in (A) were incubated with or without 1 µg/ml dox overnight to induce Rab39a expression. 1x106 cells were fed at 4 beads/cell of biotinylated-Ova-magnetic-beads for 4 hours. Phagosomes were isolated and stained for Ova and Open H2-Ld. Representative of 3 independent experiments.

(C, D) Quantification of Ova remaining in bead-phagosomes (C) and Nox2 staining (D). Representative Histogram shown. For analysis, the background fluorescence of unstained beads was subtracted from the resulting phagosome gMFI and the fold change of target protein (dox/no dox) was calculated. Three independent experiments were combined. P<0.05 using two-tailed ratio-paired Student's t-test. Error bars show SD between experiments.

(E) Cells as in (A) were incubated with or without 1 µg/ml dox overnight to induce Rab39a expression. 1x106 cells were incubated on ice with 4 beads/cell of biotinylated-Ova-beads for bead attachment. Cells were then transferred into 37oC media containing 5 µM CellROX Deep Red. After 4 hours of incubation, unfixed phagosomes were extracted and analyzed via flow cytometry for CellROX fluorescence. For analysis, the background fluorescence of unstained beads was subtracted from the resulting phagosome gMFI and the fold change (dox/no dox) was calculated. Three independent experiments were combined. P<0.05 using two-tailed ratio-paired Student's t-test. Error bars show SD between experiments.

(F) Same as in C with Sec22b staining. Three independent experiments were combined. P<0.05 using two-tailed ratio-paired Student's t-test. Error bars show SD between experiments.

(G) Cells as in (A) were fed at 1 bead per cell with pHrodo conjugated beads that increase fluorescence at low pH. After 4 hours of incubation, whole cells were harvested and run through flow cytometry to measure fluorescence of eaten beads. For analysis, the background fluorescence of uneaten beads was subtracted from the resulting gMFI and the fold change of dox/no dox was calculated. Three independent experiments were combined. p<0.05 using two-tailed ratio-paired Student's t-test. Error bars show SD between experiments. Also shown are histograms of whole cells compared to background fluorescence of pH beads.

(H) DC3.2R cells were treated with the indicated siRNA. 48 hours after transfection, cells were fed with Ova-Fe (2 µg Ova) with or without 100 µM leupeptin. RF33.70-Luc reporter T cells were added. After overnight incubation, T cell luciferase was measured. Representative plot of two independent experiments. Error bars show SD between 3 replicate wells. p values were calculated using 2-way ANOVA.

(I) 5x104 DC3.2-Rab39a-H2-Ld cells were fed with Ova-Fe (1µg Ova) with or without 1 µg dox and/or 100 µM leupeptin. RF33.70-Luc reporter T cells were added. After overnight incubation, T cell luciferase was measured. Representative plot of two independent experiments. Error bars show SD between 3 replicate wells. p values were calculated using 2-way ANOVA.