Alpha 4 beta 1 and alpha 5 beta 1 are differentially expressed during myelopoiesis and mediate the adherence of human CD34+ cells to fibronectin in an activation-dependent way

Abstract

To study the receptors involved in the interaction between extracellular matrix proteins and hematopoietic progenitor cells, we analyzed the expression of beta 1 integrins on CD34+ bone marrow cells by means of immunoflowcytometry. Alpha 4 beta 1 and alpha 5 beta 1 were expressed, whereas alpha 1 beta 1, alpha 2 beta 1, alpha 3 beta 1, alpha 6 beta 1, and alpha v beta 1 were virtually absent. Furthermore, we assessed the alpha 4 and alpha 5 expression on committed myeloid progenitor cells. These colony-forming cells were detected in the alpha 4 dull fraction and the alpha 5 dull fraction. During myeloid differentiation, both in vivo and in vitro, a differential expression of alpha 4 beta 1 and alpha 5 beta 1 was observed. alpha 5 beta 1 was found to be lost at the myelocytic-metamyelocytic stage, before the loss of alpha 4 beta 1, at the band stage. Functional studies showed no binding of erythroid progenitor-depleted, CD34+ bone marrow cells to fibronectin. However, protein kinase C activation strongly induced fibronectin binding (68% of the cells). Inhibition experiments with specific antibodies and peptides showed the binding to be mediated by both alpha 4 beta 1 and alpha 5 beta 1. Also, colony-forming cells of granulocytes and macrophages were demonstrated to adhere to fibronectin in an activation-dependent way. During granulocyte colony-stimulating factor-induced in vitro maturation, the activation-dependent fibronectin binding capacity is gradually lost. We conclude that: (1) CD34+ bone marrow cells express alpha 4 beta 1 and alpha 5 beta 1; (2) the expression of alpha 4 beta 1 and alpha 5 beta 1 is differentially expressed during myeloid differentiation; and (3) binding of CD34+ bone marrow cells to fibronectin is activation dependent.

The role of CS1 moiety of fibronectin in VLA4‐mediated haemopoietic progenitor trafficking

“…However, the concentration of CS1 peptides required to block the VLA4/VCAM-1 interaction are considerably higher than those required to block binding to fibronectin (Makarem et al, 1994). This disparity in VLA4's affinity for its two ligands may also explain the observation that, whereas unmanipulated CD34 þ cells bind to VCAM-1, they require prior activation to bind to intact fibronectin in significant numbers (Kerst et al, 1993). These observations emphasize the difference between in vitro and in vivo observations and caution against the extrapolation of in vitro data on the role of other cytoadhesion molecules in in vivo progenitor homing.…”

“…It is speculated that this is followed by a series of secondary anchoring events which firmly tether the progenitor to the bone marrow stroma and extracellular matrix, and that each of these steps is mediated by the interaction of cytoadhesion molecules expressed on the surface of the progenitor with their respective cognate ligands on the vascular endothelium or on the bone marrow microenvironment (Gordon & Greaves, 1989;Long, 1992). Although a number of different cytoadhesion molecules including integrins, selectins and CD44 have been shown to mediate the adhesion of progenitors to constituents of the bone marrow microenvironment in vitro (Kerst et al, 1993;Miyake et al, 1990;Simmons et al, 1992;Williams et al, 1991;Zannettino et al, 1995), the molecular pathways mediating the in vivo homing of progenitors are largely unexplored. The role of adhesion molecules in the initial stage of in vivo homing has been studied by determining the effect of antibodies to candidate adhesion molecules on progenitor lodgement in the first few hours after transplantation.…”

The Role of Osteoblasts in the Hematopoietic Microenvironment

“…Membrane-bound growth factor/cytokines include: IL-1α, M-CSF, c-kit ligand [83][84][85], and ECM-bound factors; IL-3, GM-CSF, and TGF-β1 [86][87][88], which themselves may serve as CAMs. Thus, while the population of CD34 + cells in the marrow is limited, based upon CD34 and CAM receptor density and/or affinity, many options exist to localize CD34 + cells to a particular microenvironment [73,[89][90][91][92][93][94]. In this regard, marked heterogeneity in the adherence of CD34 + cells has been observed in patients with myeloproliferative disorders [81,[95][96][97].…”

Biology of IL‐8‐Induced Stem Cell Mobilization

“…For instance, CD34 + cells in steady state bone marrow have been reported to express β1-integrins VLA-4 and VLA-5 in an inactive state. 25 Following treatment with mobilization-inducing cytokines (SCF, M-CSF), a dose-dependent increase in ligand binding properties was observed. Expression of c-kit, the ligand for stem cell factor, appears to be downregulated following mobilization induced by IL-3, GM-CSF and SCF, suggesting that hematopoietic cell mobilization is mediated via a common cytokine network that ultimately results in altered c-kit expression.…”