Cancer and the chemokine network

Granulocyte colony-stimulating factor (G-CSF) induced hematopoietic stem cell mobilization is widely used for clinical transplantation; however, the mechanism is poorly understood. We report here that G-CSF induced a reduction of the chemokine stromal cell derived factor 1 (SDF-1) and an increase in its receptor CXCR4 in the bone marrow (BM), whereas their protein expression in the blood was less affected. The gradual decrease of BM SDF-1, due mostly to its degradation by neutrophil elastase, correlated with stem cell mobilization. Elastase inhibition reduced both activities. Human and murine stem cell mobilization was inhibited by neutralizing CXCR4 or SDF-1 antibodies, demonstrating SDF-1 CXCR4 signaling in cell egress. We suggest that manipulation of SDF-1 CXCR4 interactions may be a means with which to control the navigation of progenitors between the BM and blood to improve the outcome of clinical stem cell transplantation.

Vascularization of organs generally occurs by remodelling of the preexisting vascular system during their differentiation and growth to enable them to perform their specific functions during development. The molecules required by early vascular systems, many of which are receptor tyrosine kinases and their ligands, have been defined by analysis of mutant mice. As most of these mice die during early gestation before many of their organs have developed, the molecules responsible for vascularization during organogenesis have not been identified. The cell-surface receptor CXCR4 is a seven-transmembrane-spanning, G-protein-coupled receptor for the CXC chemokine PBSF/SDF-1 (for pre-B-cell growth-stimulating factor/stromal-cell-derived factor), which is responsible for B-cell lymphopoiesis, bone-marrow myelopoiesis and cardiac ventricular septum formation. CXCR4 also functions as a co-receptor for T-cell-line tropic human immunodeficiency virus HIV-1. Here we report that CXCR4 is expressed in developing vascular endothelial cells, and that mice lacking CXCR4 or PBSF/SDF-1 have defective formation of the large vessels supplying the gastrointestinal tract. In addition, mice lacking CXCR4 die in utero and are defective in vascular development, haematopoiesis and cardiogenesis, like mice lacking PBSF/SDF-1, indicating that CXCR4 is a primary physiological receptor for PBSF/SDF-1. We conclude that PBSF/SDF-1 and CXCR4 define a new signalling system for organ vascularization.

Cell adaptation to hypoxia (Hyp) requires activation of transcriptional programs that coordinate expression of genes involved in oxygen delivery (via angiogenesis) and metabolic adaptation (via glycolysis). Here, we describe that oxygen availability is a determinant parameter in the setting of chemotactic responsiveness to stromal-derived factor 1 (CXCL12). Low oxygen concentration induces high expression of the CXCL12 receptor, CXC receptor 4 (CXCR4), in different cell types (monocytes, monocyte-derived macrophages, tumor-associated macrophages, endothelial cells, and cancer cells), which is paralleled by increased chemotactic responsiveness to its specific ligand. CXCR4 induction by Hyp is dependent on both activation of the Hyp-inducible factor 1 α and transcript stabilization. In a relay multistep navigation process, the Hyp–Hyp-inducible factor 1 α–CXCR4 pathway may regulate trafficking in and out of hypoxic tissue microenvironments.