Sustained Activation of Cell Adhesion Is a Differentially Regulated Process in B Lymphopoiesis

It is largely unknown how hematopoietic progenitors are positioned within specialized niches of the bone marrow microenvironment during development. Chemokines such as CXCL12, previously called stromal cell–derived factor 1, are known to activate cell integrins of circulating leukocytes resulting in transient adhesion before extravasation into tissues. However, this short-term effect does not explain the mechanism by which progenitor cells are retained for prolonged periods in the bone marrow. Here we show that in human bone marrow CXCL12 triggers a sustained adhesion response specifically in progenitor (pro- and pre-) B cells. This sustained adhesion diminishes during B cell maturation in the bone marrow and, strikingly, is absent in circulating mature B cells, which exhibit only transient CXCL12-induced adhesion. The duration of adhesion is tightly correlated with CXCL12-induced activation of focal adhesion kinase (FAK), a known molecule involved in integrin-mediated signaling. Sustained adhesion of progenitor B cells is associated with prolonged FAK activation, whereas transient adhesion in circulating B cells is associated with short-lived FAK activation. Moreover, sustained and transient adhesion responses are differentially affected by pharmacological inhibitors of protein kinase C and phosphatidylinositol 3-kinase. These results provide a developmental cell stage–specific mechanism by which chemokines orchestrate hematopoiesis through sustained rather than transient activation of adhesion and cell survival pathways

Focal Adhesion Kinase (FAK) Is Required for CXCL12-Induced Dhemotaxis and Adhesion to VCAM-1 in B Lymphocytes and Hematopoietic Stem/Progenitor Cells

Abstract The chemokine CXCL12 (SDF-1) and its receptor CXCR4 play a critical role in hematopoietic progenitor cell migration and positioning within the bone marrow (BM). However, CXCL12/CXCR4-induced signaling pathways in blood cell migration are poorly characterized. Based on previous studies of BM progenitor B cells indicating a strong correlation between FAK signaling and CXCL12 induced adhesion to VCAM-1, we speculated that FAK might be an important signaling component in CXCL12-induced chemotaxis and integrin-mediated adhesion. Here, we used two approaches to reduce FAK expression in (human and mouse) progenitor B cells and mouse Sca-1+, Kit+, Lin− stem/progenitor cells. FAK specific siRNAs reduced FAK expression by 80% and abolished both CXCL12-induced chemotaxis and adhesion to VCAM-1 in the pro-B cell line, REH. FAK knock-down did not change expression levels of CXCR4 and VLA-4 integrin. FAK expression was rescued by transfection with wild type, chicken FAK, which also restored both CXCL12-induced chemotaxis and adhesion. Furthermore, we found that in FAK deficient cells CXCL12-induced activation of the GTP-ase Rap1 was reduced, suggesting the importance of FAK in CXCL12-mediated inside-out integrin activation. CXCL12-mediated chemotaxis was also impaired in primary progenitor B cells and hematopoietic stem/progenitor cells (HSC/P) isolated from FAK floxed mice, in which FAK was deleted by Cre-mediated excision of FAK floxed alleles. Cre-mediated FAK deletion did not affect cell viability or induce apoptosis. These studies suggest that FAK may function as a key intermediary in signaling pathways controlling hematopoietic cell migration and lineage development

An efficient 3D cell culture method on biomimetic nanostructured grids.

Current techniques of in vitro cell cultures are able to mimic the in vivo environment only to a limited extent, as they enable cells to grow only in two dimensions. Therefore cell culture approaches should rely on scaffolds that provide support comparable to the extracellular matrix. Here we demonstrate the advantages of novel nanostructured three-dimensional grids fabricated using electro-spinning technique, as scaffolds for cultures of neoplastic cells. The results of the study show that the fibers allow for a dynamic growth of HeLa cells, which form multi-layer structures of symmetrical and spherical character. This indicates that the applied scaffolds are nontoxic and allow proper flow of oxygen, nutrients, and growth factors. In addition, grids have been proven to be useful in in situ examination of cells ultrastructure

HeLa cells stained with Hoechst 33342 and propidium iodide after 24 (A), 48 (B) and 72 (C) hours of 3D culture on the nanostructure grids.

<p>Original magnification x200. A fragment of the spherical 3D structure of cell growing on nanostructured grids visualized after 48 hours. Original magnification x400 (D).</p

Light microscopy image of nanostructured grid.

<p>Original magnification x200 (A). Scanning electron microscopy image of nanostructured microfiber. Original magnification x500 (B).</p

Cells growing on the scaffold visualized using light microscopy after 48 hours of incubation.

<p>Original magnification x200 (A). Scanning electron microscopy image of HeLa cells on the nanostructured grid fibers after 48 hours of incubation. Original magnification x100 (B).</p