Published March 27, 2015, doi:10.4049/jimmunol.1402459 The Journal of Immunology Microtubule Nucleation in Mouse Bone Marrow–Derived Mast Cells Is Regulated by the Concerted Action of GIT1/ bPIX Proteins and Calcium Vadym Sulimenko,* Zuzana Ha´jkova´,*,† Marke´ta Cernohorska ´,*,† Tetyana Sulimenko,* Vladimı´ra Sla´dkova´,* Lubica Dra´berova´,‡ Stanislav Vinopal,* Eduarda Dra´berova´,* and Pavel Dra´ber* Ag-mediated activation of mast cells initiates signaling events leading to Ca2+ response, release of allergic mediators from cytoplasmic granules, and synthesis of cytokines and chemokines. Although microtubule rearrangement during activation has been described, the molecular mechanisms that control their remodeling are largely unknown. Microtubule nucleation is mediated by complexes that are formed by g-tubulin and g-tubulin complex proteins. In this study, we report that, in bone marrow–derived mast cells (BMMCs), g-tubulin interacts with p21-activated kinase interacting exchange factor b (bPIX) and G protein–coupled receptor kinase-interacting protein (GIT)1. Microtubule regrowth experiments showed that the depletion of bPIX in BMMCs stimulated microtubule nucleation, whereas depletion of GIT1 led to the inhibition of nucleation compared with control cells. Phenotypic rescue experiments confirmed that bPIX and GIT1 represent negative and positive regulators of microtubule nucle- ation in BMMCs, respectively. Live-cell imaging disclosed that both proteins are associated with centrosomes. Immunoprecipi- tation and pull-down experiments revealed that an enhanced level of free cytosolic Ca2+ affects g-tubulin properties and stimulates the association of GIT1 and g-tubulin complex proteins with g-tubulin. Microtubule nucleation also was affected by Ca2+ level. Moreover, in activated BMMCs, g-tubulin formed complexes with tyrosine-phosphorylated GIT1. Further experiments showed that GIT1 and bPIX are involved in the regulation of such important physiological processes as Ag-induced chemotaxis and degranulation. Our study provides for the first time, to our knowledge, a possible mechanism for the concerted action of tyrosine kinases, GIT1/bPIX proteins, and Ca2+ in the propagation of signals leading to the regulation of microtubule nucleation in activated mast cells. The Journal of Immunology, 2015, 194: 000–000. ast cells play a crucial role in allergy, as well as in innate aggregation of which triggers mast cell activation, resulting in de- and adaptive immune responses. They express plasma granulation, the release of proinflammatory mediators, and the M membrane–associated high-affinity IgERs (FcεRIs), the production of various cytokines. The first step in FcεRI signaling is tyrosine phosphorylation of the FcεRI b- and g-subunits by the *Department of Biology of Cytoskeleton, Institute of Molecular Genetics, Academy Src family nonreceptor kinase Lyn. This is followed by enhanced of Sciences of the Czech Republic, CZ-142 20 Prague 4, Czech Republic; activity of tyrosine kinase Syk and the phosphorylation of trans- †Department of Cell Biology, Faculty of Science, Charles University Prague, CZ-128 ‡ membrane adaptors, which organize and coordinate further sig- 43 Prague 2, Czech Republic; and Department of Signal Transduction, Institute of 2+ Molecular Genetics, Academy of Sciences of the Czech Republic, CZ-142 20 Prague 4, nals, resulting in a Ca efflux from the endoplasmic reticulum Czech Republic (ER). Depletion of Ca2+ from the ER lumen induces Ca2+ influx Received for publication September 26, 2014. Accepted for publication February 27, across the plasma membrane, leading to enhancement of the free 2015. cytoplasmic Ca2+ concentration, a step that is important in further This work was supported in part by Grants P302/12/1673, P302/11/P709, P302/14/ signaling events (1). 09807S, and 15-22194S from the Grant Agency of the Czech Republic, Grants LD13015 and LH12050 from the Ministry of Education, Youth, and Sports of the Microtubules, built up from ab-tubulin heterodimers, are impor- Czech Republic, Grant NT14467 from Ministry of Health of the Czech Republic, tant for mast cell degranulation, because the movement of secretory Grant GAUK 796913 from the Grant Agency of Charles University, and by Institu- granules depends on intact microtubules (2, 3), and compounds tional Research Support (RVO 68378050). We also acknowledge support of the COST Action BM1007 Mast Cells and Basophils–Targets for Innovative Therapies. inhibiting tubulin polymerization suppress degranulation (4). It was ε Address correspondence and reprint requests to Dr. Pavel Dra´ber, Department of Biol- reported that Fc RI aggregation leads to reorganization of mi- 2+ ogy of Cytoskeleton, Institute of Molecular Genetics, Academy of Sciences of the crotubules (3, 5) and that the influx of Ca plays a decisive role in Czech Republic, Vı´denska ´ 1083, 142 20 Prague 4, Czech Republic. E-mail address: microtubule remodeling (6, 7). An important role in Ca2+ influx was [email protected] reported for stromal-interactingprotein1(STIM1),theCa2+ sensor The online version of this article contains supplemental material. in ER that associates with the end binding protein 1 located on the Abbreviations used in this article: BMMC, bone marrow–derived mast cell; tips of growing microtubules (8). Depletion of STIM1 resulted in the BMMCL, BMMC line; BMMCL-gTb, BMMCL stably expressing TagRFP-tagged mouse g-tubulin; ER, endoplasmic reticulum; GCP, g-tubulin complex protein; GIT, inhibition of microtubule reorganization in stimulated cells (6). Al- G protein–coupled receptor kinase-interacting protein; HEK, HEK 293-FT; hGIT1, though these data point to the necessity of the microtubule network human GIT1; hbPIX, human bPIX; mGIT1, mouse GIT1; mbPIX, mouse bPIX; MS, mass spectrometry; PAK, p21-activated kinase; bPIX, p21-activated kinase interact- for mast cell degranulation, the molecular mechanisms responsible ing exchange factor b; P-Tyr, phosphotyrosine; ROI, region of interest; shRNA, short for microtubule reorganization in activated mast cells are still largely hairpin RNA; STIM1, stromal-interacting protein 1; gTuRC, g-tubulin ring complex; unknown. The role of Ca2+ in this process is also unclear. tv, transcript variant. In cells, microtubules are dominantly nucleated from centro- Copyright Ó 2015 by The American Association of Immunologists, Inc. 0022-1767/15/$25.00 somes or the other microtubule-organizing centers. One of the key www.jimmunol.org/cgi/doi/10.4049/jimmunol.1402459 Downloaded by guest on October 1, 2021 2 GIT1/bPIX PROTEINS AND MICROTUBULE NUCLEATION IN MAST CELLS components for microtubule nucleation is g-tubulin (9), a highly Australia) (17). In this article, the cells are denoted as BMMC lines 2/2 2+ conserved member of the tubulin superfamily. In cytosol, g-tubulin (BMMCLs) or Lyn BMMCLs. Both the Ca response (18) and Ag- induced degranulation (L. Dra´berova´ and P. Dra´ber, unpublished observa- exists as a g-tubulin ring complex (gTuRC; with size ∼2.2 MDa) 2/2 ∼ tions) were decreased in Lyn BMMCLs compared with BMMCLs. Cells comprising g-tubulin small complexes ( 280 kDa), composed of were cultured in freshly prepared culture medium (RPMI 1640 supplemented two molecules of g-tubulin, one molecule of g-tubulin complex with 20 mM HEPES [pH 7.5], 100 U/ml penicillin, 100 mg/ml streptomycin, protein (GCP)2, one molecule of GCP3, and some other proteins 100 mM MEM nonessential amino acids, 1 mM sodium pyruvate, 10% FCS, (10). Cumulative data indicate that protein tyrosine kinases phos- and 10% WEHI-3 cell supernatant as a source of IL-3). In some cases, cells were cultivated for 30 min in serum-free and Ca2+-free medium to which phorylate g-tubulin or associated proteins and, in this way, modu- Ca2+ was freshly added to a final concentration of 1.8 mM. Alternatively, late g-tubulin functions (5, 11, 12). The significance of Src kinases cells were incubated with 1 mM ionomycin in the presence or absence of 2+ for microtubule nucleation from centrosomes was ascertained by Ca .Cellsweregrownat37˚Cin5%CO2 in air and passaged every 2 d. microtubule regrowth experiments (13). Identification of tyrosine HEK 293-FT (HEK) cells (Promega Biotech) were grown at 37˚C in 5% kinase substrates that regulate g-tubulin functions should help to CO2 in DMEM supplemented with 10% FCS and antibiotics. The cells used for lentivirus production were at passage 4–15. HEK cells were transfected elucidate the mechanisms involved in the regulation of microtubule with 17 mg DNA/9-cm tissue culture dish using 51 mg polyethylenimine nucleation. (Polysciences) and serum-free DMEM. After 24 h, the transfection mixture In this study, we examined the hypothesis that phosphotyrosine was replaced with fresh medium supplemented with serum, and cells were (P-Tyr) proteins associated with g-tubulin modulate microtubule incubated for an additional 24 h. nucleation in activated mast cells. We identified p21-activated Cell activation kinase (PAK) interacting exchange factor b (bPIX) and G pro- Cells were sensitized with DNP-specific IgE and activated with Ag (DNP- tein–coupled receptor kinase-interacting protein (GIT)1 as sig- BSA conjugate, 30–40 mol DNP/mol BSA), as described (6). Alternatively, naling proteins that interact with g-tubulin and associate with cells were activated by pervanadate. Pervanadate solution was freshly pre- centrosomes. GIT1 is phosphorylated on tyrosine in activated cells pared by mixing sodium orthovanadate solution with H2O2 to get a 10 mM and interacts with g-tubulin in a Ca2+-dependent