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. 2008 Aug 8;134(3):485-95.
doi: 10.1016/j.cell.2008.05.050.

Phosphorylation of SNAP-23 by IkappaB Kinase 2 Regulates Mast Cell Degranulation

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Free PMC article

Phosphorylation of SNAP-23 by IkappaB Kinase 2 Regulates Mast Cell Degranulation

Kotaro Suzuki et al. Cell. .
Free PMC article

Abstract

Mast cells are known to play a pivotal role in allergic diseases. Cross-linking of the high-affinity receptor for IgE (FcepsilonRI) leads to degranulation and allergic inflammation; however, the regulatory mechanisms of IgE-dependent exocytosis remain unknown. We show here that IkappaB kinase (IKK) 2 in mast cells plays critical roles in IgE-mediated anaphylaxis in vivo, and IgE-mediated degranulation in vitro, in an NF-kB-independent manner. Upon FcvarepsilonRI stimulation, IKK2 phosphorylates SNAP-23, the target membrane soluble N-ethylmaleimide-sensitive fusion factor attachment protein receptor (SNARE), and ectopic expression of a phospho-mimetic mutant of SNAP-23 partially rescued the impaired IgE-mediated degranulation in IKK2-deficient mast cells. These results suggest that IKK2 phosphorylation of SNAP-23 leads to degranulation and anaphylactic reactions. While this reaction is NF-kB-independent, we additionally show that IKK2 also regulates late-phase allergic reactions promoted by the release of proinflammatory cytokines in an NF-kB-dependent manner. The findings suggest that IKK2 is a central player in allergic reactions.

Figures

Figure 1
Figure 1. Severe Impairment of Anaphylactic Responses in the Absence of IKK2
(A) PCA in WT or IKK2−/− mast cell-reconstituted W/Wv mice was performed as described in the Experimental Procedures. Ear swelling was quantified by three consecutive measurements of ear thickness with a caliper before (baseline) and 1, 2, 3, and 4 hr after antigen challenge. Data are means ± SD from eight independent experiments. Results show a severe impairment of anaphylactic shock; *p < 0.01. (B) Upon antigen challenge, leakage of injected Evans blue dye into the ear is severely decreased in IKK2−/− FLMC transplanted mice. Representative data from eight independent experiments are shown. (C) Vascular leakage assayed by EB extravasation into ear tissues. Inner ear rims were removed 90 min after i.v. challenge with antigen with EB, or EB only, and subsequently extracted in formamide. Plots show mean optical density at 620 nm ± SD; *p < 0.01. (D) PSA in WT or IKK2−/− mast cell-reconstituted W/Wv mice was performed as described in the Experimental Procedures and monitored by measuring rectal temperature several times following antigen challenge. Data are mean ± SD from eight independent experiments. Data shown in Figure 1D demonstrate decrease in systemic anaphylaxis in mice injected with IKK2−/− mast cells; *p < 0.01.
Figure 2
Figure 2. IKK2 Plays Critical Roles in Mast Cell Degranulation
(A) IgE-induced β-hexosaminidase release is impaired in IKK2−/− FLMCs. FLMCs were incubated with anti-TNP IgE for 2 hr and then surface IgE was cross-linked with (black columns) or without (white columns) TNP-BSA. After 30 min, the percentage of specific β-hexosaminidase release was determined as described in the Experimental Procedures. Data are means ± SD from five independent experiments. *Significantly different from the mean value of control group (WT), *p < 0.01. (B) IgE-induced histamine release is impaired in IKK2−/− FLMCs. FLMCs were incubated with anti-TNP IgE and cross-linked with (black columns) or without (white columns) TNP-BSA. After 30 min, supernatants and cell lysates were recovered. Histamine was measured by EIA. Data are means ± SD from five independent experiments. *Significantly different from the mean value of control group (WT), *p < 0.01. (C) A23187-induced β-hexosaminidase release is impaired in IKK2−/− FLMCs. FLMCs were stimulated with (black columns) or without (white columns) A23187 (500 ng/ml). After 30 min, the percentage of specific β-hexosaminidase release was determined as described in the Experimental Procedures. Data are means ± SD from five independent experiments. *Significantly different from the mean value of control group (WT), *p < 0.01. (D) IgE-induced annexin-V binding is decreased in IKK2−/− FLMCs. FLMCs were incubated with anti-TNP IgE and cross-linked with or without TNP-BSA. After 30 min, cells were stained with annexin-V and analyzed by flow cytometry. Representative FACS profiles from five independent experiments are shown. (E) Overexpression of IKK2 results in increase of FcεRI-stimulated β-hexosaminidase release. GFP-IKK2, GFP-IKK2KM, or GFP (as control) stably expressing RBL-2H3 cells were obtained as described in the Experimental Procedures. IgE-induced β-hexosaminidasereleasewasperformedasdescribedinFigure 2A. Data are means ± SD from five independent experiments. *Significantly different from the mean value of control group (mock), *p < 0.01. NS, not significant. (F) Western blots to assess expression of GFP, GFP-IKK2, or GFP-IKK2KM in zeocin-resistant RBL-2H3 cells (Figure 2G). Antitubulin blots were used as loading controls.
Figure 3
Figure 3. NF-κB Activation Is Not Essential for Mast Cell Degranulation
(A) IκBαM stably expressing RBL-2H3 cells were obtained as described in the Experimental Procedures. Cells were transfected with HIV-3x-κB luciferase and β-galactosidase plasmid by electroporation. After 24 hr, cells were stimulated with (black columns) or without (white columns) TNF-α (10 ng/ml); 6 hr later, luciferase activity was measured. Data are means ± SD from five independent experiments. *Significantly different from the mean value of control group (mock), *p < 0.01. (B) Zeocin-resistant cells were incubated with anti-TNP IgE for 2 hr and then surface IgE was cross-linked with (black columns) or without (white columns) TNP-BSA. After 30 min, the percentage of specific β-hexosaminidase release was determined as described in the Experimental Procedures. Data are means ± SD from five independent experiments. (C) Western blots to assess expression of GFP, or GFP-IkBαM in zeocin-resistant RBL-2H3 cells (Figures 3A and 3B). (D) IgE-induced β-hexosaminidase release from IKK2−/−, IKK1−/−IKK2−/−, or IKK1−/− FLMCs. IgE-induced β-hexosaminidase release was performed as described in Figure 2A. Data are means ± SD from five independent experiments; *p < 0.01. NS, not significant compared to WT.
Figure 4
Figure 4. IKK2 Is Recruited to the Lipid Raft Fractions upon FcεRI Stimulation and Associates with SNAP-23
(A) Localization of GM1 (CTx), IKK2, SNAP-23, syntaxin 4, and VAMP-2 in lipid raft fraction upon FcεRI stimulation. Cell lysates of unstimulated (only IgE) or stimulated (IgE + antigen) RBL-2H3 cells were fractionated by sucrose density gradient ultracentrifugation and blotted with each antibody. Representative data from five independent experiments are shown. (B) IKK2 associates with GFP-SNAP-23 when coexpressed in 293T cells by immunoprecipitation (IP) assay. Representative data from five independent experiments are shown. (C) IKK2 associates with SNAP-23 in the lipid raft fractions only after FcεRI stimulation. Fraction 5 was solubilized in 1% octylglucoside and subjected to IP with anti-SNAP-23 antibody. Immunoprecipitants were blotted with each antibody.
Figure 5
Figure 5. IKK2 Phosphorylates SNAP-23 on Ser120 and Ser95
(A) Equal amounts of purified WT and mutant GST-SNAP-23 proteins were incubated with [γ-32P]ATP and IKK2 as described in the Experimental Procedures and the reaction was analyzed by SDS-PAGE and PhosphorImager analysis. Representative data from five independent experiments are shown. (B) 0.5 μg of purified GST-fused WT or several mutants of SNAP-23 proteins were submitted to SDS-PAGE and detected with CBB. (C) IgE-induced phosphorylation of SNAP-23 on Ser120 and Ser95 is impaired in IKK2−/− FLMCs. FLMCs were incubated with anti-TNP IgE and cross-linked with or without TNP-BSA. Fifteen minutes later, cell lysates were recovered and analyzed by immunoblot analysis using phosphorylation site specific antibodies. Representative data from five independent experiments are shown. (D) FcεRI-induced formation of SNARE complex of SNAP-23/synatxin 4/VAMP-2 is impaired in IKK2−/− mast cells. Cell lysates of unstimulated (only IgE) or stimulated (IgE + antigen) FLMCs were fractionated by sucrose density gradient ultracentrifugation. Lipid raft fraction 5 was solubilized in 1% octylglucoside and subjected to IP with anti-SNAP-23 antibody. Immunoprecipitants were blotted with each antibody.
Figure 6
Figure 6. Phosphorylation of SNAP-23 on Ser120 and Ser95 Involved in IKK2-Mediated Degranulation
(A) Western blots to assess expression of SNAP-23 in puromycin-resistant RBL-2H3 cells. (B) IgE-induced β-hexosaminidase release is impaired in SNAP-23 shRNA-expressing mast cells. SNAP-23 shRNA stably expressing RBL-2H3 cells were obtained as described in the Experimental Procedures. IgE-induced β-hexosaminidase release was performed as described for Figure 2A. Data are means ± SD from five independent experiments; *p < 0.01; NS, not significant. (C) Overexpression of IKK2 does not enhance IgE-induced β-hexosaminidase release in SNAP-23 shRNA-expressing mast cells. SNAP-23 shRNA and/or GFP-IKK2 stably expressing RBL-2H3 cells were obtained as described in the Experimental Procedures. U6 or GFP indicate control. IgE-induced β-hexosaminidase release was performed as described in Figure 2A. Data are means ± SD from five independent experiments; *p < 0.01; NS, not significant. (D) Transduction of SNAP-23 shRNA-resistant SNAP-23 rescues IgE-induced β-hexosaminidase release in SNAP-23 shRNA-expressing mast cells. SNAP-23 shRNA, and FLAG-R-SNAP23 or FLAG-R-SNAP23AA, stably expressing RBL-2H3 cells were obtained as described in the Experimental Procedures. U6 or FLAG indicate control. IgE-induced β-hexosaminidase release was performed as described in Figure 2A. Data are means ± SD from five independent experiments *p < 0.01; NS, not significant. (E) Overexpression of IKK2 enhances IgE-induced β-hexosaminidase release in SNAP-23 shRNA and SNAP-23 shRNA-resistant WT SNAP-23, but not SNAP-23 shRNA and SNAP-23 shRNA-resistant SNAP-23AA-expressing mast cells. SNAP-23 shRNA, GFP-IKK2, and FLAG-R-SNAP23 or FLAG-R-SNAP23AA stably expressing RBL-2H3 cells were obtained as described in the Experimental Procedures. GFP indicates control. IgE-induced β-hexosaminidase release was performed as described in Figure 2A. Data are means ± SD from five independent experiments. (F) Expression of phosphomimetic mutant of SNAP-23 partially rescue the impairment of FcεRI-induced β-hexosaminidase release in IKK2−/− mast cells. FLMCs were infected with retroviruses of pMX-puro-FLAG-WT SANP-23, pMX-puro-FLAG-SNAP-23EE, or pMX-puro (mock). After selection with puromycin, IgE-induced β-hexosaminidase release was performed as described in Figure 2A. Data are means ± SD from five independent experiments; *p < 0.01; NS, not significant compared to mock-infected IKK2−/− FLMCs. (G) Mock vector transduced WT FLMCs, and mock vector, WT SNAP-23, or SNAP-23EE transduced IKK2−/− FLMCs were injected i.d. in the right ear of W/Wv mice. After 4 weeks, PCA was performed as described in the Experimental Procedures. Ear swelling was quantified by three consecutive measurements of ear thickness with a caliper before (baseline) and 1 hr after challenge. Data are means ± SD from six independent experiments; *p < 0.01; NS, not significant compared to mock-infected IKK2−/− FLMC-reconstituted mice.
Figure 7
Figure 7. Impairment of Late-Phase Allergic Reactions in the Absence of IKK2
(A) Late-phase PCA reactions in WT or IKK2−/− mast cell-reconstituted W/Wv mice were performed as described in the Experimental Procedures. Ear swelling was quantified by three consecutive measurements of ear thickness with calipers before (baseline) and indicated time after hapten challenge. Data are means ± SD from six independent experiments. Data demonstrate decrease in late-phase PCA reactions in mice injected with IKK2−/− mast cells. (B) IgE-induced TNF-α release is impaired in IKK2−/− FLMCs. FLMCs were incubated with anti-TNP IgE and cross-linked with (black columns) or without (white columns) TNP-BSA; 6 hr later, TNF-α in the supernatants was quantified by ELISA. Data are means ± SD from five independent experiments. *Significantly different from the mean value of control group (WT), *p < 0.01. (C) A23187-induced TNF-α release is impaired in IKK2−/− FLMCs. FLMCs were stimulated with (black columns) or without (white columns) A23187 (500 ng/ml); 6 hr later, TNF-α in the supernatants was quantified by ELISA. Data are means ± SD from five independent experiments. *Significantly different from the mean value of control group (WT), *p < 0.01. (D) GFP-IKK2, GFP-IkBαM, or GFP stably expressing RBL-2H3 cells were obtained as described in the Experimental Procedures. Cells were incubated with anti-TNP IgE, and cross-linked with (black columns) or without (white columns) TNP-BSA; 6 hr later, TNF-α in the supernatants was quantified by ELISA. Data are means ± SD from five independent experiments. *Significantly different from the mean value of control group (WT), *p < 0.01.

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