Tohoku J. Exp. Med., 2022 July, 257(3)

Co-localization of Fibronectin Receptors LILRB4/gp49B and Integrin on Dendritic Cell Surface

Naoyuki Takahashi,¹ So Itoi,^1,2 Mei-Tzu Su,¹ Shota Endo¹ and Toshiyuki Takai¹

¹Department of Experimental Immunology, Institute of Development, Aging and Cancer, Tohoku University, Sendai, Miyagi, Japan
²Department of Hematology and Rheumatology, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan

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.

Keywords —— focal adhesion kinase; immunoreceptor tyrosine-based inhibitory motif; inflammatory signal; outside-in signal; spleen tyrosine kinase

© 2022 Tohoku University Medical Press

===============================

Tohoku J. Exp. Med 2022, 257, 171-180.

Correspondence: Toshiyuki Takai, Department of Experimental Immunology, Institute of Development, Aging and Cancer, Tohoku University, Sendai, Miyagi 980-8575, Japan.

e-mail: toshiyuki.takai.b8@tohoku.ac.jp