Jean-Pierre Levesque

A Novel Monoclonal Antibody Recognizing a Cation-Dependent Epitope within the Regulatory Loop of Human β1 Integrin (CD29)

Cell adhesion receptors of the integrin superfamily can be expressed in different affinity states towards their ligands. It has been previously demonstrated that beta(1) integrins alpha4beta(1) and alpha5beta(1) are expressed in a nonligand binding form by human hemopoietic progenitor cells but can be activated into a ligand binding form by a variety of stimuli including intracellular stimuli generated by cytokine receptors and extracellular stimuli generated by function-activating anti-beta(1) integrin monoclonal antibodies (MAbs). In both instances, the activation of beta(1) integrins is believed to be the result of conformational changes propagating along the beta(1) integrin chain which in turn increase accessibility to the ligand. A cluster of either function-activating or function-inhibiting anti-beta(1) integrin MAbs have been shown to bind within a 12 amino acid long regulatory loop between residues 207 and 218 of the human beta(1) integrin chain. We describe in this report the first MAb (96.9H9) specific for this regulatory loop whose binding is cation-dependent and requires either Ca(2+) or Mn(2+) but not Mg(2+). In addition, the activation of alpha4beta(1) and alpha5beta(1) integrins by 96.9H9 is a two-step process with distinct cation requirements. Whereas Ca(2+) is sufficient to promote binding of the antibody to the beta(1) integrin chain, Mg(2+) is necessary for activating function following 96.9H9 binding. Our data therefore suggest that the regulatory epitope of the human beta(1) integrin chain is flexible with multiple conformations according to the cationic environment.

The Interaction of Cytokines with Stem Cell and Stromal Cell Physiology

It is now well established that cellular interactions between primitive haemopoietic progenitor cells (HPC) and the stromal tissue of the bone marrow (BM) play a central role in regulating haemopoiesis. Despite considerable research efforts, the precise molecular mechanisms responsible for this control remain to be fully defined. Nevertheless, from these studies has emerged the general consensus that at least two classes of molecules including haemopoietic growth factors (HGF) and members of several cell adhesion molecule (CAM) superfamilies contribute to the regulation of haemopoiesis although the exact contribution made by each class of molecule remains to be determined. There are abundant data derived from studies performed in vitro and in vivo demonstrating HGF as potent regulators of HPC survival, growth and differentiation. The exact contribution made by CAMs is less well understood but emerging evidence derived from studies performed both in the haemopoietic and other systems clearly demonstrate that in addition to their well documented pro-adhesive functions, CAMs, like cytokine receptors, are also signalling molecules. Such observations therefore support the notion that in addition to their well documented role in initiating and maintaining contact between HPC and stromal cells, CAMs may also participate more directly in the growth and development of primitive HPC. In support of this proposal are recent data which demonstrate the considerable functional overlap and interdependence between the HGF and CAM families as demonstrated, for example, by the capacity of HGF to regulate the functional properties of CAMs on primitive HPC.