B‐CAM/LU expression and the role of B‐CAM/LU activation in binding of low‐ and high‐density red cells to laminin in sickle cell disease

Abstract

Red blood cells from patients with sickle cell disease (SS RBC) adhere to laminin and over-express the high-affinity laminin receptor basal cell adhesion molecule/Lutheran protein (B-CAM/LU). This receptor has recently been shown to undergo activation in vitro through a protein kinase A-dependent mechanism. Low-density SS RBC express twothirds more B-CAM/LU than high-density SS RBC. However, high-density SS RBC have been identified as most adherent to laminin under flow conditions. We investigated the ability of low-and high-density SS RBC to interact with laminin under various conditions and explored factors that might be responsible for the differences in B-CAM/LU-laminin interaction between high-and low-density SS RBC. We confirmed that high-density SS RBC adhere to laminin more strongly than low-density SS RBC under flow conditions. However, low-density SS RBC bind soluble laminin most strongly and are the most adherent to laminin under static conditions. Soluble recombinant Lutheran extracellular domain protein completely blocked SS RBC adhesion to laminin under both static and flow conditions. The protein kinase A inhibitor 14-22 amide inhibited adhesion to laminin during flow by high-density SS RBC from patients with strongly adherent cells but had no effect on adhesion observed after a static phase. Deletion of the cytoplasmic domain of B-CAM as well as mutation of the juxtamembranous tyrosine residue failed to reduce B-CAM-mediated adhesion to laminin by transfected MEL cells. These studies confirm that B-CAM/LU is the most critical receptor mediating adhesion to laminin under both static and flow conditions. Dense SS RBC are most adherent to laminin despite bearing fewer laminin receptors, apparently due to a reversible protein kinase A-dependent process that is unlikely to involve direct phosphorylation of B-CAM/LU. Our results also suggest that the nature of the interaction of B-CAM/LU with laminin may be different under static and flow conditions. Am.

Glycophorin-C sialylation regulates Lu/BCAM adhesive capacity during erythrocyte aging

“…The low-density sickle erythrocytes, containing young erythrocytes, were found to be more susceptible to epinephrine stimulation, whereas the old, highly dense erythrocytes, that contain fewer Lu/BCAM molecules, were found to be most adherent to laminin-a5. 5 Here we report a novel mechanism that drives Lu/BCAM activation on aging erythrocytes, which can account for abnormal erythrocyte adhesion in SCD and other pathological states such as sepsis. We identified a domain within Lu/BCAM that bears homology to the SIGLEC family of sialic acid-binding receptors.…”

“…3 Erythrocytes express 500 to 4000 Lu/BCAM molecules on their surface, a quantity that gradually decreases as erythrocytes shed membrane and become increasingly dense during their lifespan. 4,5 Lu/BCAM can interact with the extracellular matrix (ECM) component laminin-a5, allowing the capturing of erythrocytes through this interaction even under flow conditions. 6,7 As the ECM is normally not exposed to circulating erythrocytes, the function of Lu/BCAM on terminally differentiated erythrocytes is currently unclear.…”

Adhesion molecules and hydroxyurea in the pathophysiology of sickle cell disease

“…11,12 Zen et al confirmed that BCAM/Lu is the most important receptor mediating HbS erythrocyte adhesion to laminin under flow and static conditions. 13 The BCAM/Lu interaction with immobilized laminin under flow conditions appeared to be upregulated by protein kinase A (PKA), downstream of β2 adrenergic receptors. 13,14 While BCAM/Lu is found on both reticulocytes and mature erythrocytes, CD36 and VLA-4 expression, however, is limited to reticulocytes.…”

“…13 The BCAM/Lu interaction with immobilized laminin under flow conditions appeared to be upregulated by protein kinase A (PKA), downstream of β2 adrenergic receptors. 13,14 While BCAM/Lu is found on both reticulocytes and mature erythrocytes, CD36 and VLA-4 expression, however, is limited to reticulocytes. CD36 and VLA-4 are among the most extensively studied adhesion receptors.…”

Genética das doenças hematológicas: as hemoglobinopatias hereditárias

“…In common with the K-Cl system, when K + leaves the cell it is followed by efflux of water, cellular dehydration and increased internal concentration of Hb S. Endothelin (a vasoactive compound that is elevated in SCA patients), prostaglandin E2 and other cytochemokines alter Gardos channel kinetics, provoking dehydration and polymerization of Hb S. 41,42 Sickled can also significantly increase endothelial adhesion. 5,40,43 Everything points to endothelial cell inflammation and activation playing a central role in the vasoocclusion observed in SCD. Monocyte activation, with secretion of proinflammatory cytokines (IL-1 and TNF-α), leads the leukocytes, which are always present in large numbers, to adhere to the inflamed endothelium and interact with the sickled red blood cells.…”