Impaired B-cell development at the pre-BII-cell stage in galectin-1–deficient mice due to inefficient pre-BII/stromal cell interactions

Abstract

Activation of the pre-B-cell receptor (pre-BCR) in the bone marrow depends on both tonic and ligand-induced signaling and leads to pre-BII-cell proliferation and differentiation. Using normal mouse bone marrow pre-BII cells, we demonstrate that the ligand-induced pre-BCR activation depends on pre-BCR/galectin-1/integrin interactions leading to pre-BCR clustering at the pre-BII/stromal cell synapse. In contrast, heparan sulfates, shown to be pre-BCR ligands in mice, are not implicated in pre-BCR relocalization. Inhibition of pre-BCR/galectin-1/integrin interactions has functional consequences, since pre-BII-cell proliferation and differentiation are impaired in an in vitro B-cell differentiation assay, without affecting cellular apoptosis. Most strikingly, although galectin-1-deficient mice do not show an apparent B-cell phenotype, the kinetics of de novo B-cell reconstitution after hydroxyurea treatment indicates a specific delay in pre-BII-cell recovery due to a decrease in pre-BII-cell differentiation and proliferation. Thus, although it remains possible that the pre-BCR interacts with other ligands, these results highlight the role played by the stromal cell-derived galectin-1 for the efficient development of normal pre-BII cells and suggest the existence of pre-BII-specific stromal cell niches in normal bone marrow.

Pre-B cell receptor binding to galectin-1 modifies galectin-1/carbohydrate affinity to modulate specific galectin-1/glycan lattice interactions

“…We have shown previously that, similarly to normal pre-BII cells, the Nalm6 pre-B cell line expresses preBCRs and integrins required for the formation of the pre-B cell synapse and the induction of an efficient pre-BCR signal [18][19][20]26 . In addition, OP9 stromal cells were shown to strongly support normal pre-BII cell differentiation, due to the expression of GAL1 and integrin ligands required for the formation of the pre-B cell synapse 20 . Therefore, even though immortalized cells often show alterations of cell surface receptors, pre-BCR relocalization and signalling using Nalm6 and OP9 cells reflect what is observed in primary cells.…”

“…To establish the biological relevance of the differences observed on glycan array screenings, we performed glycomic analysis of Nalm6 pre-BII and OP9 stromal cell lines using lectin microarray experiments. These cell lines have been chosen since they have been used in many functional assays [18][19][20]26 to study the role of GAL1 and GAL1/pre-BCR interaction for pre-BCR relocalization and signalling. We have shown previously that, similarly to normal pre-BII cells, the Nalm6 pre-B cell line expresses preBCRs and integrins required for the formation of the pre-B cell synapse and the induction of an efficient pre-BCR signal [18][19][20]26 .…”

“…These cell lines have been chosen since they have been used in many functional assays [18][19][20]26 to study the role of GAL1 and GAL1/pre-BCR interaction for pre-BCR relocalization and signalling. We have shown previously that, similarly to normal pre-BII cells, the Nalm6 pre-B cell line expresses preBCRs and integrins required for the formation of the pre-B cell synapse and the induction of an efficient pre-BCR signal [18][19][20]26 . In addition, OP9 stromal cells were shown to strongly support normal pre-BII cell differentiation, due to the expression of GAL1 and integrin ligands required for the formation of the pre-B cell synapse 20 .…”

“…At the contact zone between pre-BII and stromal cells, GAL1, preBCRs and glycosylated integrins relocalize 18 . This relocalization is allowed by the dual interaction network of GAL1 with the pre-BCRs (protein-protein interactions) and with glycosylated counter receptors (protein-oligosaccharide interactions) at the cell surfaces [18][19][20] . To date, this GAL1/pre-BCR interaction is the first example of a GAL1/unglycosylated protein interaction in the extracellular compartment.…”

“…We previously evidenced a crucial role of GAL1 in B-cell development through the formation of a GAL1-dependent lattice between pre-BII and stromal cells [18][19][20][21] . B cells are generated from haematopoietic stem cells and develop in the bone marrow before they migrate into the blood to reach peripheral lymphoid organs.…”