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Co-localization of Fibronectin Receptors LILRB4/gp49B and Integrin on Dendritic Cell Surface
Naoyuki Takahashi1, So Itoi1,2, Mei-Tzu Su1
1Department of Experimental Immunology, Institute of Development, Aging and Cancer, Tohoku University.
Insights
Leukocyte immunoglobulin-like receptor B4 (LILR B4) on dendritic cells suppresses fibronectin-mediated signaling. This interaction between LILR B4 and integrins reveals a novel regulatory mechanism in immune responses, potentially impacting autoimmune diseases and cancer therapies.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Leukocyte immunoglobulin-like receptor B4 (LILR B4), also known as ILT3/CD85k or gp49B, is a myeloid immune checkpoint expressed on dendritic cells (DCs).
- The regulatory role of LILR B4 on DCs, its ligands, and counteracting receptors remain incompletely understood.
- Recent identification of fibronectin (FN) as a ligand for LILR B4 raises questions about its interaction with classical FN receptors like integrins on DCs.
Purpose of the Study:
- To investigate the relationship and signaling crosstalk between LILR B4 and integrins on dendritic cells in response to fibronectin.
- To elucidate the mechanism by which LILR B4 regulates DC activation pathways mediated by fibronectin.
Main Methods:
- Co-expression analysis of LILR B4 and integrin on bone marrow-derived cultured DCs (BMDCs) and splenic DCs.
- Confocal laser scanning microscopy to assess co-localization of LILR B4 and integrin β1.
- Analysis of tyrosine phosphorylation of focal adhesion kinase (FAK) and spleen tyrosine kinase (Syk) in BMDCs plated on immobilized FN, with and without LILR B4.
Main Results:
- Fibronectin is not constitutively present on DCs, despite co-expression of integrin and LILR B4/gp49B.
- Partial co-localization of LILR B4/gp49B and integrin β1 was observed on the DC surface.
- Plating DCs on FN induced FAK and Syk phosphorylation; LILR B4 deficiency augmented Syk phosphorylation, indicating LILR B4 suppresses the integrin-mediated inflammatory cascade.
- FN binding to DCs triggers a signaling crosstalk between LILR B4 and integrins.
Conclusions:
- LILR B4 engages in intracellular signaling crosstalk with integrins on dendritic cells upon fibronectin stimulation.
- LILR B4 acts as a negative regulator, suppressing the integrin-mediated pro-inflammatory signaling cascade initiated by fibronectin.
- These findings offer insights into the therapeutic potential of blocking LILR B4 in autoimmune diseases and cancer.
Abstract:
A myeloid immune checkpoint, leukocyte immunoglobulin-like receptor (LILR) B4 (B4, also known as ILT3/CD85k in humans and gp49B in mice) is expressed on dendritic cells (DCs). However, a mode of regulation of DCs by B4/gp49B is not identified yet in relation to the ligand(s) as well as to the counteracting, activation-type receptor. Our recent identification of the physiological/pathological ligand for B4/gp49B as the fibronectin (FN) N-terminal 30-kDa domain poses the question of the relationship between B4/gp49B and a classical FN receptor/cellular activator, integrin, on DCs. Here we showed that FN is not constitutively tethered on the surface of bone marrow-derived cultured DCs (BMDCs) or splenic DCs, even though the FN receptor integrin and gp49B are co-expressed on these cells. Confocal laser scanning microscopic analysis, however, revealed weak correlation of fluorescent signals between gp49B and integrin β1, suggesting their partial co-localization on the BMDC surface even in the absence of FN. We found that the plating of BMDCs onto immobilized FN induced tyrosine phosphorylation of focal adhesion kinase (FAK) and spleen tyrosine kinase (Syk). In the absence of gp49B, while the FAK phosphorylation level was virtually unchanged, that of phosphorylation of Syk was markedly augmented. These results suggested that the immobilized FN induced a crosstalk between gp49B and integrin in terms of the intracellular signaling of BMDCs, in which gp49B suppressed the integrin-mediated pro-inflammatory cascade. Our observations may provide a clue for elucidating the mechanism of the therapeutic efficacy of B4/gp49B blocking in autoimmune disease and cancer.
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