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. 2010 Oct 29;33(4):583-96.
doi: 10.1016/j.immuni.2010.09.010. Epub 2010 Oct 7.

The Rab11a GTPase controls Toll-like receptor 4-induced activation of interferon regulatory factor-3 on phagosomes

Harald Husebye  1 , Marie Hjelmseth Aune, Jørgen Stenvik, Eivind Samstad, Frode Skjeldal, Oyvind Halaas, Nadra J Nilsen, Harald Stenmark, Eicke Latz, Egil Lien, Tom Eirik Mollnes, Oddmund Bakke, Terje Espevik
Affiliations

The Rab11a GTPase controls Toll-like receptor 4-induced activation of interferon regulatory factor-3 on phagosomes

Harald Husebye et al. Immunity. .

Abstract

Toll-like receptor 4 (TLR4) is indispensable for recognition of Gram-negative bacteria. We described a trafficking pathway for TLR4 from the endocytic recycling compartment (ERC) to E. coli phagosomes. We found a prominent colocalization between TLR4 and the small GTPase Rab11a in the ERC, and Rab11a was involved in the recruitment of TLR4 to phagosomes in a process requiring TLR4 signaling. Also, Toll-receptor-associated molecule (TRAM) and interferon regulatory factor-3 (IRF3) localized to E. coli phagosomes and internalization of E. coli was required for a robust interferon-β induction. Suppression of Rab11a reduced TLR4 in the ERC and on phagosomes leading to inhibition of the IRF3 signaling pathway induced by E. coli, whereas activation of the transcription factor NF-κB was unaffected. Moreover, Rab11a silencing reduced the amount of TRAM on phagosomes. Thus, Rab11a is an important regulator of TLR4 and TRAM transport to E. coli phagosomes thereby controlling IRF3 activation from this compartment.

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Figures

Figure 1.
Figure 1.. The Rab11a-Positive ERC Contains High Amounts of TLR4 in HEK293 TLR4YFP Cells
Orthographic and planar projection data were obtained via confocal microscopy on fixed cells. Overlapping regions appear as yellow in the overlay panels. (A) Orthographic projections of HEK293-TLR4YFP cells coexpressing the trans-medial Golgi marker β−1,4 galactosyl transferase linked to CFP (β−1,4 GTCFP). (B) Planar sections of HEK293-TLR4YFP cells stained for endogenous Rab11a via the Rab11a antibody (ab3612). (C) 3D modeling of the cis-Golgi (GM130), TLR4YFP, and Rab11aCFP in HEK293-TLR4YFP cells cotransfected with Rab11aCFP, MD-2, and CD14. (D and E) HEK-TLR4Cherry cells cotransfected with dominant-negative GDP-bound Rab11aSNGFP (D) or constitutive active GTP-bound Rab11aQLGFP (E) together with MD-2 and CD14. Scale bars represent 10 μm. Data are representative of four independent experiments. See also Figure S1.
Figure 2.
Figure 2.. The Rab11a-Positive ERC Contains High Amounts of TLR4 in Human Monocytes
Orthographic and planar projection data were obtained with confocal microscopy on fixed cells. Overlapping regions appear as yellow in the overlay panels. (A) Orthographic projections of a human monocyte costained for TLR4 and trans-medial Golgi (Golgin-97). (B) Human monocytes costained for TLR4 and Rab11a. Scale bars represent 10 μm. Data are representative of three independent experiments. See also Figure S2.
Figure 3.
Figure 3.. TLR4 and Rab11a Accumulate around Phagocytosed E. coli, but Not around S. aureus
Human monocytes were incubated with E. coli or S. aureus particles (5.0 × 106/ml) for 15 min and fixed and stained for TLR4 or Rab11a. Overlapping regions appear as yellow in the overlay panels. (A) TLR4 accumulates toward the E. coli phagosome. TLR4 (green), E. coli (red), and overlay (right). (B) TLR4 does not accumulate toward the S. aureus phagosome. TLR4 (green), S. aureus (red), and overlay (right). (C) Rab11a accumulates toward the E. coli phagosome. Rab11a (green), E. coli (red), and overlay (right). (D) Rab11a does not accumulate toward the S. aureus phagosome. Rab11a (green), S. aureus (red), and overlay (right). Scale bars represent 10 μm. Data are representative of three independent experiments. See also Figure S3.
Figure 4.
Figure 4.. Addition of E. coli to Human Monocytes Results in Intracellular Redistribution of TLR4 and Rab11a
Human monocytes were incubated with E. coli particels (2 × 106/ml), fixed, and immunostained for TLR4 or Rab11a. (A) TLR4 voxel intensity in the ERC in cells incubated with or without E. coli for 15 min was measured (p = 0.001). (B) Rab11a voxel intensity in the ERC in cells incubated with or without E. coli for 15 min (p < 0.0001). (C) TLR4 voxel intensity on E. coli phagosomes as a function of incubation time (p < 0.0001 for TLR4 from 15 min to 30+30 min). (D) Rab11a voxel intensity on E. coli phagosomes as a function of incubation time (p = 0.046 for Rab11a from 15 min to 30+30 min). Bars in plots represent the median. n = number of observations. Data are representative of three independent experiments. See also Figure S4 and Movie S1.
Figure 5.
Figure 5.. Recruitment of TLR4 to E. coli Phagosomes Requires TLR4 Signaling and Intact Actin Filaments, but Not Dynamin
Human monocytes incubated with bacterial particles, fixed, and immunostained for TLR4, TRAM, and MyD88; with normal rabbit IgG as control antibody. (A) TLR4 recruitment to the phagosome requires TLR4 signaling. Fold increase in phagosomal TLR4 voxel intensity in cells immunostained for TLR4 versus cells stained with control antibody. Cells were incubated 30 min with heat-killed Y. pestis (2 × 106/ml) cultured at 26°C or 37°C. (B) TRAM voxel intensity on E. coli phagosomes (p < 0.0001). (C) IRF3 voxel intensity on E. coli phagosomes. An increase in IRF3 was observed from 30 min to 30+30 min (p < 0.0028). (D) TLR4 recruitment to E. coli phagosomes requires intact actin filaments. Cells were pretreated with 2 μM cytochalasin D (cyto D) or vehicle (DMSO) for 30 min and incubated with E. coli for 30 min in the presence of inhibitor or vehicle (p < 0.0001). (E) TLR4 recruitment to E. coli phagosomes occurs independent of Golgi. The cells were pretreated with 5 μg/ml Brefeldin A or vehicle (DMSO) and incubated 30 min with E. coli in the presence of inhibitor or vehicle. (F) Inhibition of dynamin does not cause a reduction in phagosomal TLR4. Monocytes were incubated for 2 hr under serum-free conditions and treated for 30 min with opsonized E. coli. Subsequently the cells were washed two times and incubated for 30 min with 80 μM Dynasore or vehicle (DMSO) in serum-free medium (p = 0.0002 for DMSO and Dynasore treatments). Monocytes were incubated with E. coli particles (3.0–8.0 × 106/ml) (B–F). Bars in plots represent the median. n = number of observations. Data are representative of three independent experiments. See also Figure S5.
Figure 6.
Figure 6.. E. coli-Induced IFN-β Signaling Requires Phagocytosis, and TLR4 Recruitment to Phagosomes Is Rab11a Dependent
(A and B) Induction of IFN-β mRNA (A) and TNF mRNA (B) in monocytes stimulated for 60 min with different concentrations of E. coli particles or LPS. The amounts of IFN-β and TNF mRNAs were determined by QPCR and is presented as mean relative to nonstimulated monocytes and standard deviations. (C and D) Induction of IFN-β (C) and TNF mRNAs (D) in monocytes stimulated with E. coli particles (8.0 × 106/ml) or LPS (100 ng/ml) for 60 min. The impact of phagocytosis was examined by incubation with or without human A+ serum, with or without preopsonization as well as the phagocytosis inhibitor Cyto D or vehicle (DMSO). The amounts of IFN-β and TNF mRNAs were determined by QPCR and are presented as mean relative to nonstimulated monocytes and standard deviations. (E) HEK293-TLR4YFP cells or human monocytes were treated with nonsilencing RNA oligo (NS RNA) or Rab11a siRNA, cellular lysates were made, and immunoblotting performed with Rab11a antibody (ab3612) or Rab7a antibody. GAPDH was used for control of equal loading. (F) Confocal image of TLR4YFP (green) in HEK293-TLR4YFP cells coexpressing β−1,4 GTCFP (red) treated with NS RNA (left) or Rab11a siRNA (right). The arrow indicates the center of the Golgi ring. (G) TLR4 on E. coli phagosomes in monocytes treated with NS RNA or Rab11a siRNA and stimulated with E. coli particles (3 × 106/ml), p = 0.05 and p = 0.03 for TLR4 amounts in NS RNA compared to Rab11a siRNA-treated cells at 15 min and 30 min, respectively. (H) TRAM on E. coli phagosomes in monocytes treated with NS RNA or Rab11a siRNA stimulated with E. coli particles (3 × 106/ml), p = 0.02 for TRAM amounts in NS RNA-compared to siRNA-treated cells. Bars in plots represent the median. n = number observations. Data are representative of four independent experiments. Scale bars represent 5 μm. See also Figure S6.
Figure 7.
Figure 7.. Silencing of Rab11a Selectively Affects TLR4-Mediated IRF3 Activation and IFN-β Induction
(A and B) Human monocytes were treated with NS RNA or siRNA (48 hr) and stimulated with E. coli particles (A) or LPS (B) as indicated. Immunoblotting was performed with IRF3 antibodies recognizing phosphorylated-IRF3 (Ser 396) and total-IRF3. α-Tubulin was used as a control of equal loading. (C and D) IkB-α degradation in siRNA-treated monocytes (C) and HEK293TLR4YFP cells (D) stimulated with E. coli particles (1.0 × 107/ml) as indicated, with GAPDH as loading control. (E and F) HEK293 TLR4Cherry cells treated with siRNA or NS RNA for 72 hr, plated, and transfected with MD-2, CD14, and the Gal4-IRF3-luciferase reporter (E) or the NF-κB-luciferase reporter (F). The cells were incubated with E. coli or LPS for 9 hr. Gal4-IRF3 activation was normalized toward Renilla Luciferase. Activation is presented as mean relative luciferase units (RLU) to Gal4DBD signals and standard deviations. (G and H) Human monocytes treated with NS RNA or siRNA and stimulated with E. coli (3.0 × 106/ml) as indicated, fixed, and immunostained for total IRF3 (G) or total p65 (H). Quantification of nuclear IRF3 (G). Silencing of Rab11a resulted in decreased nuclear IRF3 translocation compared to NS RNA-treated cells (15 min; p = 0.0145, 30 min; p = 0.0009). Quantification of nuclear p65 (H). Silencing of Rab11a resulted in increased nuclear p65 translocation at 30 min (p = 0.0031). Bars represent the median. n = number of observations. Scale bars represent 10 μm. (I and J) Human monocytes treated with NS RNA or siRNA for 20 hr were stimulated with E. coli particles (3.0 × 106/ml) as indicated. Total RNA was isolated and the level of IFN-β and TNF mRNA quantified by QPCR shown as mean relative to reference sample (NS RNA, 0 min) and standard deviations. Data are representative of three independent experiments. See also Figure S7.
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