Cytoskeletal Control of CD36 Diffusion Promotes Its Receptor and Signaling Function

Abstract

Summary The mechanisms that govern receptor coalescence into functional clusters – often a critical step in their stimulation by ligand – are poorly understood. We used single-molecule tracking to investigate the dynamics of CD36, a clustering-responsive receptor that mediates oxidized LDL uptake by macrophages. We found that CD36 motion in the membrane was spatially structured by the cortical cytoskeleton. A subpopulation of receptors diffused within linear confinement regions that simultaneously facilitated freedom of movement along one axis while increasing the effective receptor density. Co-confinement within troughs enhanced the probability of collisions between unligated receptors and promoted their clustering. Cytoskeleton perturbations that inhibited diffusion in linear confinement regions reduced receptor clustering in the absence of ligand, and, following ligand addition, suppressed CD36-mediated signaling and internalization. These observations demonstrate a role for the cytoskeleton in controlling signal transduction by structuring receptor diffusion within membrane regions that increase their collision frequency.

The actin cytoskeleton modulates the activation of iNKT cells by segregating CD1d nanoclusters on antigen-presenting cells

“…These barriers locally confine membrane receptors, increasing their local concentration and promoting clustering (23). In the case of hCD1d molecules, we observed similar arrest on its mobility in actin-rich regions.…”

“…For instance, it has been shown that the actin cytoskeleton promotes the dimerization rate of EGF receptors and facilitates ligand binding and signaling activation (18,22). Confinement of CD36 has also been observed as a result of its diffusion along linear channels dependent on the integrity of the cortical cytoskeleton (23). This constrained diffusion promotes CD36 clustering, influencing CD36-mediated signaling and internalization.…”

“…Previous reports indicate that the actin cytoskeleton regulates the lateral organization and nanoclustering of receptors on the cell membrane (23). Given the marked effect of the actin cytoskeleton and the cytoplasmic tail of hCD1d on the lateral mobility of hCD1d molecules that traffic through endosomes, we thought to visualize the nanoscale organization of hCD1d on the surface of THP-1 cells using stimulated emission depletion (STED) nanoscopy (35).…”

Actomyosin dynamics drive local membrane component organization in an in vitro active composite layer

“…Although these models based on thermodynamic equilibrium principles have successfully explained the organization and dynamics of a range of membrane components and molecules, there is a growing class of phenomena that appears inconsistent with chemical and thermal equilibrium, which might warrant a different explanation. These include aspects of the organization and dynamics of outer leaflet glycosyl-phosphatidylinositol-anchored proteins (GPIanchored proteins) (10-13), inner leaflet Ras proteins (14), and actin-binding transmembrane proteins (13,15,16).Recent experimental and theoretical work has shown that these features can be explained by taking into account that many cortical and membrane proteins are driven by ATP-consuming processes that drive the system out of equilibrium (13,15,17). The membrane models mentioned above have by-and-large neglected this active nature of the actin cortex where actin filaments are being continuously polymerized and depolymerized (18-21), in addition to being persistently acted upon by a variety of myosin motors (22-24) that consume ATP and exert contractile stresses on cortical actin filaments, continually remodeling the architecture of the cortex (4, 21, 25).…”

“…Although these models based on thermodynamic equilibrium principles have successfully explained the organization and dynamics of a range of membrane components and molecules, there is a growing class of phenomena that appears inconsistent with chemical and thermal equilibrium, which might warrant a different explanation. These include aspects of the organization and dynamics of outer leaflet glycosyl-phosphatidylinositol-anchored proteins (GPIanchored proteins) (10-13), inner leaflet Ras proteins (14), and actin-binding transmembrane proteins (13,15,16).…”