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SKAP2 acts downstream of CD11b/CD18 and regulates neutrophil effector function

ABSTRACT: Background: The importance of CD11b/CD18 expression in neutrophil effector functions is well known. Beyond KINDLIN3 and TALIN1, which are involved in the induction of the high-affinity binding CD11b/CD18 conformation, the signaling pathways that orchestrate this response remain incompletely understood. Method: We performed an unbiased screening method for protein selection by biotin identification (BioID) and investigated the KINDLIN3 interactome. We used liquid chromatography with tandem mass spectrometry as a powerful analytical tool. Generation of NB4 CD18, KINDLIN3 or SKAP2 knock out neutrophils was achieved using CRISPR-Cas9 technology and the cells were examined for their effector function using flow cytometry, live cell imaging, microscopy, adhesion or antibody-dependent cellular cytotoxicity (ADCC). Results: Among the 325 proteins significantly enriched, we identified Src Kinase-Associated Phosphoprotein2 (SKAP2), a protein involved in actin polymerization and integrin-mediated outside-in signaling. CD18 immunoprecipitation in primary or NB4 neutrophils demonstrated the presence of SKAP2 in the CD11b/CD18 complex at steady state. Under this condition, adhesion to plastic, ICAM-1 or fibronectin was observed in the absence of SKAP2, which could be abrogated by blocking the actin-rearrangements with latrunculin B. Upon stimulation of SKAP2-deficient neutrophils, adhesion to fibronectin was enhanced whereas CD18 clustering was strongly reduced. This response corresponded with significantly impaired CD11b/CD18-dependent NADPH oxidase activity, phagocytosis and cytotoxicity against tumor cells. Conclusion: Our results suggest that SKAP2 has a dual role. It may restrict CD11b/CD18-mediated adhesion only under resting conditions, but its major contribution lies in the regulation of dynamic CD11b/CD18-mediated actin-rearrangements and clustering as required for cellular effector functions of human neutrophils.

INSTRUMENT(S): Orbitrap Fusion

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Neutrophil, Blood

DISEASE(S): Disease Free

SUBMITTER: Floris van Alphen

LAB HEAD: Hanke L. Matlung

PROVIDER: PXD048758 | Pride | 2024-02-16

REPOSITORIES: Pride

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Project description:We recently revealed that myeloid master regulator PU.1 directly represses metallothionein (MT)-1G through its epigenetic activity, but the functions of MT-1G in myeloid differentiation remain unknown. To clarify this, we established MT-1G-overexpressing acute promyelocytic leukemia NB4 (NB4MTOE) cells, and investigated whether MT-1G functionally contributes to all-trans retinoic acid (ATRA)-induced NB4 cell differentiation. Real-time PCR analyses demonstrated that the inductions of CD11b and CD11c and reductions in myeloperoxidase and c-myc by ATRA were attenuated in NB4MTOE cells. Since G1 arrest is a hallmark of ATRA-induced NB4 cell differentiation, we observed a decrease in G1 accumulation, as well as decreases in p21WAF1/CIP1 and cyclin D1 inductions, by ATRA in NB4MTOE cells. Nitroblue tetrazolium (NBT) reduction assays revealed that the proportions of NBT-positive cells were decreased in NB4MTOE cells in the presence of ATRA. Microarray analyses showed that the changes in expression of several myeloid differentiation-related genes (GATA2, azurocidin 1, pyrroline-5-carboxylate reductase 1, defensin-4, C-X3-C motif receptor 3, matrix metallopeptidase -8, S100 calcium-binding protein A12, neutrophil cytosolic factor 2 and oncostatin M) induced by ATRA were disturbed in NB4MTOE cells. Collectively, overexpression of MT-1G disturbs the proper differentiation of myeloid cells. The present study provides evidence that expression analysis of MT-1G in acute promyelocytic leukemia patients may be a good prediction marker to estimate the efficacy of ATRA. Cell culture and generation of MT-1G-overexpressing cells: To generate MT-1G-overexpressing cells and their control cells, the MT-1G expression vector and its parental pcDNA 3.1/myc-His(-) version A vector (Invitrogen) were transfected using a CLB-Transfection device (Lonza, Basel, Switzerland). NB4 clones stably transfected with the vectors were isolated by limiting dilution and selection with 400 µg/ml of neomycin in RPMI (Gibco BRL, Rockville, MD) containing 10% heat-inactivated fetal bovine serum (HIFBS). Cells were cultured under 5% CO2 at 37°C in a humidified atmosphere. Microarray analyses: MT-1G-overexpressing (NB4MTOE) cells and their control cells were seeded at a density of 1×105 cells/ml and treated with 1 µM all-trans retinoic acid (ATRA). The cells were harvested after 72 h and total cellular RNA was isolated from control (NB4pcDNA4, 6, 7) cells and NB4MTOE (NB4MT22, 23, 25) cells using an RNA Mini Purification Kit (Qiagen, Miami, FL) according to the manufacturer’s protocol. Aliquots containing 10 µg of RNA from each sample of control cells were mixed and used as controls. Similarly, 10 µg of RNA from each sample of NB4MTOE cells were mixed and used as NB4MTOE cells. The samples were subjected to microarray analyses using a CodeLink Human 54K Whole Genome Bioarray (Filgen, Nagoya, Japan).

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SKAP2 acts downstream of CD11b/CD18 and regulates neutrophil effector function

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