Integrins are cell membrane adhesion receptors involved in morphogenesis, immunity, tissue healing, and metastasis. A central, yet unresolved question regarding the function of integrins is how these receptors regulate both their conformation and dynamic nanoscale organization on the membrane to generate adhesion-competent microclusters upon ligand binding.
In an article recently appeared in Proc Natl Acad Sci USA, Alessandra Cambi in collaboration with the BioNanophotonics group of the Insitute of Photonic Sciences (Barcelona, Spain) exploited the high spatial (nanometer) accuracy and temporal resolution of Single Dye Tracking (SDT) to dissect the relationship between conformational state, lateral mobility, and microclustering of the integrin receptor lymphocyte function-associated antigen 1 (LFA-1) expressed on immune cells.
Cambi and colleagues found that on monocytes, LFA-1 nanoclusters were primarily mobile on the cell surface with only a small subset of conformational active LFA-1 nanoclusters pre-anchored to the cytoskeleton. Lateral mobility within the plasma membrane resulted crucial for the formation of larger microclusters upon ligand binding and for stable adhesion under shear flow. Activation of high-affinity LFA-1 by extracellular Calcium resulted in an eight-fold increase on the percentage of immobile nanoclusters as result of cytoskeleton anchorage. Although having the capacity to bind to their ligands, these active nanoclusters failed to support firm adhesion in static and low shear-flow conditions because mobility and macroclustering capacity were highly compromised. This work demonstrates an intricate coupling between conformation and lateral diffusion of integrins and further underscores the crucial role of receptor mobility for the onset of leukocyte adhesion.
Gert Jan Bakker, Christina Eich, Juan Torreno-Pina, Ruth Diez-Ahedo, Gemma Perez-Samper, Thomas S. van Zanten, Carl G. Figdor, Alessandra Cambi, and Maria F. Garcia-Parajo "Lateral mobility of individual integrin nanoclusters orchestrates the onset for leukocyte adhesion." (2012) Proc Natl Acad Sci USA vol. 109 no. 13, 4869-4874.