Figure 1.
Ubiquitinated aggregates accumulate near SCVs in HeLa cells.
(A) Single confocal sections of HeLa cells infected with GFP-expressing S. Typhimurium strains (blue) for 10 h, fixed and immunolabelled for LAMP1 (green) and ubiquitin (Ub, red) (false coloured, scale bars, 5 µm). The far right panels show merged images of LAMP1, ubiquitin and Salmonella. Arrows indicate SCV-associated ubiquitinated aggregates. (B) Quantification of the percentage of infected cells containing SCV-associated ubiquitinated aggregates. Cells were processed as in (A) and analysed by fluorescence microscopy. (C) Kinetics of the formation of SCV-associated ubiquitinated aggregates. Cells were infected with GFP-expressing S. Typhimurium strains for the indicated amount of time, and processed as in (A). (D) Quantification of the percentage of infected cells with SCV-associated ubiquitinated aggregates in HeLa cells infected with S. Typhimurium strains for 14 h. Cells were processed as in (A) and analysed by fluorescence microscopy. For all quantifications, a minimum of 50 infected cells were counted per experiment and values are the mean ± SEM from at least 3 independent experiments. * p<0.05; ** p<0.01; *** p<0.001.
Figure 2.
Ubiquitin accumulates in dense cytosolic aggregates and forms K63-linked chains.
(A) Immunoelectron microscopy of HeLa cells infected with S. Typhimurium strains for 12 h (ubiquitin - 10 nm gold particles; scale bars, 0.5 µm). Arrows indicate ubiquitin accumulations near bacteria within vacuoles. (B) Single confocal sections of HeLa cells infected with GFP-expressing ΔsseL mutant bacteria (blue) for 10 h and immunolabelled for ubiquitin (all chain types - Ub, red) and lysine-48-linked (K48-Ub, green) or lysine-63-linked (K63-Ub, green) ubiquitin chains (false coloured, scale bars, 5 µm). Arrows indicate SCV-associated ubiquitin and K63-Ub labelling.
Figure 3.
SseL DUB activity reduces the recruitment of ubiquitin and autophagic markers to Salmonella microcolonies.
Single confocal sections of HeLa cells infected with GFP-expressing ΔsseL mutant bacteria (blue) for 12 h and immunolabelled for ubiquitin (Ub, red) and (A) p62 (green) or (B) LC3 (green) (false coloured, scale bars, 5 µm). The far right panels show merged images of p62 or LC3, ubiquitin and Salmonella. Arrows indicate SCV-associated ubiquitin labelling with p62 or LC3. (C–E). Quantification of the relative fluorescence intensity of (C) ubiquitin, (D) p62 and (E) LC3 per microcolony (see Materials and Methods). Cells were processed as in (A) and a minimum of 30 microcolonies analysed for each bacterial infection per experiment. Results from representative experiments showing the relative mean fluorescence intensity ± SEM are shown. Similar results were obtained in at least 3 independent experiments. * p<0.05; ** p<0.01; *** p<0.001.
Figure 4.
SCV-associated ubiquitinated aggregates are autophagy substrates.
(A) Quantification of the percentage of infected cells with SCV-associated ubiquitinated aggregates. HeLa cells were infected with ΔsseL mutant bacteria for 12 h. At 8 h post-infection, cells were subjected to the indicated treatments for 4 h before fixation and immunolabelling. A minimum of 50 cells were counted per condition in each experiment and values are the mean ± SEM of at least 3 independent experiments. p values are relative to the mean value of mock-treated cells. * p<0.05; ** p<0.01; *** p<0.001. (B) Single confocal sections of HeLa cells infected with GFP-expressing ΔsseL mutant bacteria (blue), treated and processed as in (A) and analysed by fluorescence microscopy for ubiquitin (Ub, red) and LC3 (green) (scale bars, 5 µm). The far right panels show merged images of LC3, ubiquitin and Salmonella.
Figure 5.
SseL reduces the accumulation of ubiquitinated aggregates and ALIS in macrophages.
(A) Single confocal sections of RAW264.7 macrophages infected with GFP-expressing strains of S. Typhimurium (green) for 10 h and immunolabelled for ubiquitin (Ub, red) (scale bars, 5 µm). (B) Quantification of infected macrophages containing ubiquitinated aggregates 10 h after bacterial uptake. Cells were processed as in (A) and analysed by fluorescence microscopy. A minimum of 50 cells were counted for each bacterial infection per experiment and values are the mean ± SEM of at least 3 independent experiments. * p<0.05; *** p<0.001. Uninfected cells (uninf) were from the same wells as infected and therefore were exposed to extracellular bacteria. (C) Immunoelectron microscopy of RAW264.7 macrophages infected with the ΔsseL mutant bacteria for 12 h. Arrows and arrowheads indicate ubiquitin (15 nm gold particles) and p62 (10 nm gold particles), respectively (scale bar, 0.5 µm). (D and E) Single confocal sections of RAW264.7 macrophages infected with GFP-expressing strains of S. Typhimurium (blue) and immunolabelled for ubiquitin (Ub, red) and (D) p62 (green) or (E) LC3 (green). The far right panels show merged images of p62 or LC3, ubiquitin and Salmonella. Arrows indicate Arrows indicate SCV-associated ubiquitin labelling with p62 or LC3 (scale bars, 5 µm). Cell outlines and nuclei are delineated by white lines.
Figure 6.
SseL deubiquitinates Salmonella- and puromycin-induced ALIS.
(A) Quantification of large (>2 µm), ubiquitinated aggresome-like induced structures (ALIS) in macrophages. Primary bone marrow-derived macrophages (BMM) were infected with the indicated GFP-expressing S. Typhimurium strains for 10 h, immunolabelled for ubiquitin and analysed by confocal microscopy. A minimum of 50 cells were counted for each bacterial infection per experiment and values are the mean ± SEM of 3 independent experiments. Uninfected cells (uninf) were from the same wells as infected and therefore were exposed to extracellular bacteria. * p<0.05; ** p<0.01. (B) Quantification of the number of puromycin-induced ubiquitin inclusions in cells. HeLa cells were transfected with a vector expressing myc-SseL or myc-SseLC/A for 16 h followed by treatment with puromycin (5 µg/ml) for 4 h and immunolabelled with anti-myc, anti-p62 and anti-ubiquitin. 50 individual cells were counted per condition in each experiment. Values are the means ± SEM of at least 3 independent experiments. ** p<0.01. (C) Single confocal sections of HeLa cells transfected with a vector expressing myc-SseL for 16 h followed by treatment with puromycin (5 µg/ml) for 4 h and immunolabelled with anti-myc (blue), anti-p62 (green) and anti-ubiquitin (Ub, red) (scale bars, 5 µm). The lower panels show a merged image of p62, ubiquitin and myc-SseL. Arrows indicate ubiquitin and p62 aggregates present in untransfected cells and arrowheads indicate cells expressing myc-SseL.
Figure 7.
SseL interacts with p62 and autophagic substrates.
(A and B) Co-immunoprecipitation from RAW264.7 macrophages infected with ΔsseL mutant bacteria expressing SseL-HA or SseLC/A-HA for 10 h. (A) Infectedcell lysates and immunoprecipated fractions were probed with anti-HA, anti-ubiquitin and anti-p62 antibodies. (B) At 7 h post-infection, infected cells were subjected to mock, 3-MA or starvation (Stv) treatments for 3 h before harvesting and processing as described in (A). Cell lysates and immunoprecipiations were probed with anti-HA and anti-ubiquitin antibodies.
Figure 8.
SseL reduces autophagic flux and can promote bacterial replication in macrophages.
(A) Lipidated LC3B (LC3-II) levels in RAW264.7 macrophages infected with the indicated strains of S. Typhimurium for 12 h. Cells were left untreated (−) or subjected to 10 mM NH4Cl treatment (+) for 2 h before harvesting. (B) Quantification of relative LC3 II levels in infected cells. Denistometry of bands was analysed using Image J software. The ratio of LC3-II/tubulin signal intensity was normalized to 1 for wild-type untreated infections. The graph shows the mean relative LC3 II/tubulin ratios ± SEM for 3 independent experiments. (C) RAW264.7 or (D) murine bone marrow-derived primary macrophages were infected with the indicated strains of S. Typhimurium for (C) 10 h or (D) 16 h and bacterial replication was monitored using flow cytometry. Results are represented as fold replication normalized to wt; values are the means ± SEM of at least 3 independent experiments. * p<0.05; ** p<0.01.