L-selectin, also known as CD62L, is a type I transmembrane glycoprotein that is primarily expressed on leukocytes and has a role in cell adhesion and migration (1,2). L-selectin is closely related to the other family members E- and P-selectin (1,2). Human L-selectin protein is encoded by SELL and is 372 amino acids (aa) in length with a predicted molecular weight (MW) of ~30 kDa (1,2). However, due to glycosylation the observed MW ranges between 65-100 kDa and glycosylation is cell-type dependent (1,2). The L-selectin protein contains an N-terminal C-type lectin domain (CTLD), an epidermal growth factor (EGF)-like domain, two sequence consensus repeat (CSR) domains, a cleavage site, a transmembrane (TM) domain, and a short cytoplasmic tail (1,2).
L-selectin expressed on leukocytes binds to ligands expressed by endothelial cells where it plays a role in lymphocyte homing to secondary lymphoid organs (2-5). L-selectin specifically recognizes and binds to sulfated sialyl-Lewis epitopes of O-linked glycans (2-4). Ligands for L-selectin include glycosylation-dependent cell adhesion molecule-1 (GlyCAM-1), CD34, mucosal vascular addressin cell adhesion molecule-1 (MAdCAM-1), and P-selectin glycoprotein ligand-1 (PSGL-1) (2,4). Elevated levels of selectin ligands on tumor cells are associated with cancer progression and metastasis (3). High levels of L-selectin and soluble L-selectin (sL-selectin) has been implicated in a number of pathologies from viral infection and allergies, to sepsis and multiple sclerosis (2,4,5). For example, L-selectin has been shown to play a role in human immunodeficiency virus (HIV) infection. HIV envelope glycans, such as gp120, binds to L-selectin/CD62L on CD4+ T cells, facilitating viral adhesion (2,5). A disintegrin and metalloproteinase (ADAM)17 is the primary enzyme responsible for L-selectin shedding in leukocytes, which is triggered in response to inflammatory signals (1,2,5). AMAD17 inhibitors block L-selectin shedding and reduce viral release (2,5). Given their role in cancer and other diseases, selectins and their ligands are potential targets for therapeutic intervention (3,5). For instance, murine models have shown that anti-L-selectin antibodies can delay onset of graft versus host disease (5).
References
1. Ivetic A. (2018). A head-to-tail view of L-selectin and its impact on neutrophil behaviour. Cell and Tissue Research, 371(3), 437-453. https://doi.org/10.1007/s00441-017-2774-x
2. Ivetic, A., Hoskins Green, H. L., & Hart, S. J. (2019). L-selectin: a major regulator of leukocyte adhesion, migration and signaling. Frontiers in Immunology, 10, 1068. https://doi.org/10.3389/fimmu.2019.01068
3. Borsig L. (2018). Selectins in cancer immunity. Glycobiology, 28(9), 648-655. https://doi.org/10.1093/glycob/cwx105
4. Kneuer, C., Ehrhardt, C., Radomski, M. W., & Bakowsky, U. (2006). Selectins-potential pharmacological targets?. Drug Discovery Today, 11(21-22), 1034-1040. https://doi.org/10.1016/j.drudis.2006.09.004
5. Segura, J., He, B., Ireland, J., Zou, Z., Shen, T., Roth, G., & Sun, P. D. (2021). The role of L-Selectin in HIV infection. Frontiers in Microbiology, 12, 725741. https://doi.org/10.3389/fmicb.2021.725741