Understanding the Molecular Mechanism of Gradient Sensing

Abstract

The G-protein coupled receptor CXCR4 plays a central role in stem cell homing, organogenesis, inflammation and tissue repair. It mediates cell migration towards increasing concentration of the chemokine ligand CXCL12 (chemotaxis). The expression of CXCR4 on malignant cells may influence the biology of cancer, in modulating tumor survival, growth and angiogenesis. CXCR4 also plays an important role in directing metastatic CXCR4-expressing tumor cells to organs that express CXCL12. The CXCR4/CXCL12 pathway mediating cell migration is well known and understood. On the other hand the mechanism of gradient sensing remains to be discovered.Here we use Ewing's sarcoma derived cells to unravel the processes that are involved in CXCR4 related metastasis formation. Cells are transfected with DNA encoding CXCR4-eYFP. using single-molecule imaging technique we measure the diffusion coefficient of the individual receptors in the membrane and analyse diffusion in terms of confinement. We observed a decrease in mobile receptor fraction under global stimulation with the ligand - CXCL12 - in a concentration-dependent manner. In an integral approach, these molecular insights are complemented by whole cell behavior characterization, like motility as obtained from single-cell migration assays. The results are compared with models established for non-cancer cell lines. Our findings highlight the molecular machinery of chemokine gradient recognition and its effect on cell motility in the context of cancer spreading.